SYSTEM
DESCRIPTION
LIBERTY POWER COMPLEX
1 ´ 225 MW
Combined Cycle Power Plant
Goth Illahi Bukhsh, District Ghotki
Sindh, Pakistan
Gas Turbine Generator
LP-SD-401
TNB Generation Pakistan, Operator
TABLE OF CONTENTS
1.0 PURPOSE AND SCOPE................................................................................................ 5
2.0 SYSTEM OVERVIEW................................................................................................... 5
3.0 SUBSYSTEM AND
MAJOR COMPONENTS................................................................... 8
3.1 Gas Turbine General Outline................................................................................. 8
3.2 Starting System.................................................................................................. 9
3.3 Air Inlet System................................................................................................. 11
3.4 Rotor................................................................................................................ 19
3.5 Compressor...................................................................................................... 20
3.6 Combustion System.......................................................................................... 26
3.7 Turbine.............................................................................................................. 32
3.8 Exhaust System................................................................................................ 36
3.9 Cooling and Sealing Air System......................................................................... 37
3.10 Gas Turbine Bearings......................................................................................... 38
3.11 Shaft Glands..................................................................................................... 41
3.12 Lubricating Oil System....................................................................................... 43
3.13 Control Oil System............................................................................................ 50
3.14 Trip Oil System.................................................................................................. 52
3.15 Gas Fuel System............................................................................................... 54
3.16 Light Fuel Oil System......................................................................................... 60
3.17 Control System................................................................................................. 70
3.18 Safety and Protective Systems.......................................................................... 76
3.19 Gas Turbine Instrumentation............................................................................... 77
3.20 GT Generator Outline......................................................................................... 79
3.21 GT Generator Cooling System............................................................................ 80
3.22 Generator Stator................................................................................................ 82
3.23 Generator Stator Winding................................................................................... 82
3.24 Generator Rotor................................................................................................. 83
3.25 GT Generator Bearings....................................................................................... 85
3.26 GT Generator Bearing Insulation......................................................................... 85
3.27 GT Generator Rotor Grounding........................................................................... 85
3.28 Static Excitation System.................................................................................... 85
3.29 GT Generator Sound-proof enclosure................................................................. 86
3.30 Generator Instrumentation.................................................................................. 87
3.31 GT Generator Protection System........................................................................ 87
4.0 SYSTEM AUTOMATION.............................................................................................. 93
5.0 REFERENCES............................................................................................................ 93
6.0 ATTACHMENTS.......................................................................................................... 94
6.1 Major Assemblies of Gas Turbine Unit................................................................ 97
6.2 Sectional and Cut-away Views of Gas
Turbine..................................................... 98
6.3 Principles of Rectifier Drive and Starting
System Control Block Diagram.............. 99
6.4 Air Inlet Assemblies......................................................................................... 100
6.5 Air Inlet Damper Motor..................................................................................... 101
6.6 PID - Air Intake System.................................................................................... 102
6.7 Gas Turbine Rotor and Hirth Couplings............................................................. 103
6.8 Compressor Intake Casing............................................................................... 104
6.9 Compressor Variable Inlet Guide Vane.............................................................. 105
6.10 Compressor Stator Blade Carrier...................................................................... 106
6.11 Compressor Rotor and Stator Blade................................................................. 107
6.12 Compressor Exhaust Diffuser:......................................................................... 108
6.13 Intermediate Shaft............................................................................................ 109
6.14 Gas Turbine Support System............................................................................ 110
6.15 Compressor Blow-Off System Schematic......................................................... 111
6.16 Sectional View of Combustion Chamber........................................................... 112
6.17 Combustion Chamber Internals......................................................................... 113
6.18 Secondary Air Ring Mechanism........................................................................ 114
6.19 Fuel Burner Assembly:..................................................................................... 115
6.20 Light Fuel Oil Burner (detail).............................................................................. 116
6.21 Ignition Gas System:........................................................................................ 117
6.22 Ignition Gas Cylinder Room.............................................................................. 118
6.23 Turbine Stator.................................................................................................. 119
6.24 Turbine Rotor and Stator Blade......................................................................... 120
6.25 Turbine Inner Casing......................................................................................... 121
6.27 Center Casing.................................................................................................. 122
6.27 Hydraulic and Manual Turning Gear................................................................... 123
6.28 Exhaust Casing............................................................................................... 124
6.29 Exhaust Diffuser.............................................................................................. 125
6.30 Exhaust Ducting.............................................................................................. 126
6.31 Cooling and Sealing Air System....................................................................... 127
6.32 Compressor Bearing........................................................................................ 128
6.33 Turbine Bearing................................................................................................ 129
6.34 Shaft Glands Types......................................................................................... 130
6.35 Lube Oil System.............................................................................................. 131
6.36 Main/Auxiliary and Emergency Lube Oil Pumps................................................. 132
6.37 Shaft Lift Oil Pump Assembly.......................................................................... 133
6.38 Gas Turbine Generator Lube Oil Cooling
System............................................... 134
6.39 Lube Oil Filters................................................................................................ 135
6.40 Oil Vapor Extractor and Thermostatic Valve
Details........................................... 136
6.41 Control Oil System Schematic Diagram............................................................. 137
6.42 Control Oil Supply Simplified Diagram.............................................................. 138
6.43 Electrohydraulic Converter and Control Oil
Pump............................................... 139
6.44 Fuel Gas Schematic Diagram and Fuel Gas
Filter.............................................. 140
6.45 Fuel Gas Emergency Stop Valve and Fuel Gas
Control Valve............................ 141
6.46 Differential Pressure Indicator........................................................................... 142
6.47 Light Fuel Oil System (Simplified)..................................................................... 143
6.48 Fuel Oil Emergency Stop Valve and Fuel Oil
Ball Valve Assembly...................... 144
6.49 Fuel Oil Shut-Off Valve and Fuel Oil Control
Valve Assembly............................. 145
6.50 Electrohydraulic Converter Sectional View......................................................... 146
6.51 GT Generator Cooling System.......................................................................... 147
6.52 GT Generator Water – Air Coolers..................................................................... 148
6.53 GT Generator Stator Winding............................................................................ 149
6.54 GT Generator Rotor (Sheet 1 and 2).................................................................. 150
6.55 Static Excitation System.................................................................................. 151
1.1
This document provides the description of the
Gas Turbine Generator of the LIBERTY POWER COMPLEX.
1.2
The complex comprises of 1 X 145 MW gas turbine,
(SIEMENS V 94.2), one dual pressure heat recovery boilers and one steam
turbine. The gas turbine is fueled with a mixture of natural gas with light
fuel oil being provided as a back-up fuel.
1.3
It is also possible to use the gas turbine
without the steam cycle by mean of the gas bypass stack (Diverter valve).
2.1
The gas turbine installed at Liberty Power
Complex is an Ansaldo Energia Spa gas turbine. It is a single shaft, single
casing heavy duty gas turbine driving a 50 Hertz air cooled synchronous
generator and auxiliary equipment.
2.2
It operates either in the open (simple) cycle
mode or combined cycle mode. It comprises the following major assemblies (as
shown in Attachment 6.1):
2.2.1
Air intake section
2.2.2
Compressor section
2.2.3
Combustion section
2.2.4
Turbine section
2.2.5
Exhaust section
2.2.6
GT Generator
2.3
Attachment 6.2 shows the sectional views of the
gas turbine and a cut away view of the gas turbine illustrating the above major
assemblies. The gas turbine is operated with the support of the following
auxiliary systems:
2.3.1
Starting System
2.3.2
Air Intake System
2.3.3
Combustion System
2.3.4
Cooling and Sealing Air System
2.3.5
Lubricating and Control Oil System
2.3.6
Gas Fuel System ( see System Description
LP-SD-EK*)
2.3.7
Light Fuel System (see System Description
LP-SD-EG*)
2.3.8
Control System
2.3.9
Safety and Protective Systems
2.3.10
GT Generator
2.4
The gas turbine is started using a static
frequency converter which is fed from the station 6 kV system. The gas turbine
generator is used as a motor to turn the shaft. The frequency converter provides
a varying alternating current to the generator stator thus generating a
magnetic field.
2.5
Excitation current flowing through the generator
rotor at the same time generates a torque on the shaft causing it to turn and
accelerate. The frequency converter switches off at 2100 rpm after combustion
is achieved. Combustion gases expanding through the turbine section then
sustain acceleration of the gas turbine.
2.6
When the gas turbine start-up frequency
converter begins to turn the shaft, ambient air is drawn into the intake casing
through an inlet filter and silencers and passes to a 16-stage axial flow
compressor.
2.7
The compressor increases the pressure of air
delivered to the combustion chambers. To prevent surging, the compressor is
provided with a blow-off system with air bleed-off points fitted with
pneumatically operated valves that operate during gas turbine startup and
shutdown.
2.8
The gas turbine has dual fuel capability; it
operates on natural gas fuel, light fuel oil or a combination of both fuels
with automatic changeover under some operating conditions. The gas turbine has
sixteen dual fuel nozzles arranged in two combustion chambers.
2.9
Mechanical handling and electrical control
components deliver gas fuel and/or light fuel oil to these sixteen fuel
nozzles. The light fuel oil is pressure atomized and does not require atomizing
air for combustion assistance.
2.10
The fuel of choice is gas fuel. Combustion is
started by pilot flame. Combustion of gas fuel and or light fuel oil in the
combustion chambers increases the energy level of the compressed air.
2.11
The high temperature, high velocity combustion
gases expand in a 4-stage turbine causing the turbine to rotate. The turbine
couples directly to a generator. The rotation of the generator rotor in the
presence of a magnetic field results in the generation of electricity; three
phase, 50 Hertz electricity is generated at a voltage of 15 kV at the
generation terminals.
2.12
The hot gases discharge from the turbine through
the exhaust hood and into an exhaust diffuser. The exhaust diffuse connects to
the exhaust ducting through expansion joints. The exhaust ducting is also
insulated thermally and acoustically.
2.13
The gases discharge to an exhaust duct housing
the diverter valve that directs the exhaust gases to atmosphere either through
a blast stack (chimney) or through a waste heat recovery boiler. The diverter
valve is described in System Description LP-SD-HA*.
2.14
Air extraction from the compressor discharge air
to the combustion chambers and the 10th stage of the axial flow compressor
supplies cooling and sealing air to seal the gas turbine bearings and cool the
internal gas turbine parts subjected to high temperature.
2.15
Air passages are drilled in the turbine casing,
turbine nozzle and rotating wheels. These passages direct the flow of cooling
and sealing air from the compressor discharge to hot parts of the turbine.
2.16
A forced feed lubrication system supplies
lubrication oil to the gas turbine bearings and other rotating components. The
lubrication system provides filtered lubricant at the proper temperature and
pressure to the compressor, turbine and generator bearings and the control oil
system.
2.17
Pressurized lube oil also drives the rotor shaft
turning gear. A forced draft air-coolers removes heat from the lubrication
system. The cooling system comprises an off-base mounted air-cooler with the
requisite piping and associated flow-regulating valves and manual isolating
valves.
2.18
Regulated and filtered lube oil from the lube
oil supply header feeds the suction of the control oil booster pump, which
delivers high pressure fluid to the control oil system. The control oil system
provides pressurized hydraulic fluid to operate the control and protection
components of the gas turbine like gas and light fuel oil control valves, the
gas and light fuel oil emergency shut-off valves and the electro-hydraulic
converter.
2.19
The trip oil system is the primary protection
interface between the turbine control system and the components on the turbine
which admit or shut off fuel to the turbine. Control oil from the booster pump
discharge header supplies pressurized oil to the trip oil system to perform the
trip functions; abnormal and emergency shutdown of the turbine.
2.20
The gas turbine system interfaces with the gas
fuel and light fuel oil supply forwarding systems. Gas fuel is piped from the
nearby Quadirpur Gas Field to a gas fuel forwarding skid. The gas supply and
forwarding system is described in the System Description LP-SD-EK*.
2.21
Light fuel oil is supplied by SHELL, stored in
holding tanks and delivered by transfer pumps to the light fuel oil injection
skid where the injection pumps supply the light fuel oil to the combustion
chambers. The light fuel oil supply and forwarding system is described in the
System Description LP-SD-EG*.
2.22
The Liberty Power Complex is provided with black
start facilities that energize electrical boards from which the main
lubricating oil pumps take supply. Operation of the main oil pumps during
blackout conditions ensures that the turbine can be placed on turning gear.
2.23
The gas turbine has control systems, which
regulate speed, load/frequency and turbine inlet temperature. Each of the above
parameters is controlled through regulation of fuel control valve opening.
2.24
Each control system produces a final control
signal, which either increases or decreases the fuel control valve opening to
regulate flow into the combustion chambers to increase or decrease the value of
the controlled parameter.
2.25
The gas turbine has two distinct control
systems; the electrohydraulic control system and the hydraulic control system.
The motive force for the fuel control valves is secondary oil pressure
generated by the hydraulic and electrohydraulic systems.
2.26
The electrohydraulic control system is normally
in service to control gas turbine speed, load and turbine inlet temperature.
The hydraulic control system is a back-up system used to control gas turbine
speed and load; it has no facility for controlling turbine inlet temperature.
2.27
Sequential startup, shutdown and protective
control functions for the gas turbine are provided by a microprocessor based
control system, termed INFI 90. This control system provides for a
single-command, automatic startup and shutdown of the unit.
2.28
The control system directs subsystem via
sub-loop control (SLC) programs that in turn supervise the startup and shutdown
of these subsystems. The control system runs up the unit to speed, synchronizes
it to the grid, controls the loading pattern of the unit to preset limits,
enables on-load fuel change-over, automatically unloads the unit, takes it
off-bars and shuts it down to turning gear operation. The gas turbine INFI
90-control system is described in the System Description LP-SD-302.
2.29
The gas turbine is provided with safety and
protective systems to trip or shutdown the gas turbine on occurrence of a fault
or abnormal condition and to protect the gas turbine from transient conditions
during startup and shutdown. The main components of the safety and protective
systems are the components of the trip oil system and over-speed trip device.
The gas turbine is provided with a fire protection system, which is described
separately in System Description LP-SD-SG*.
2.30
When operating in the open cycle mode, the gas
turbine exhaust gases are directed to atmosphere. When operating in the
combined cycle mode, the gases exhaust to a waste heat recovery boiler.
Operation in the combined cycle mode is much efficient than operation in the
open cycle mode. In the combined cycle mode, a substantial amount of energy in
the gas turbine exhaust gases is recovered to raise HP and LP steam to drive a
steam turbine generator.
2.31
The gas turbine when burning gas fuel is rated
at ** [as1]MW base
load and **[as2] MW
peak load in the open cycle mode and **[as3] MW
base load and ** [as4]MW peak
load in the combined cycle mode. These ratings are associated with an ambient
temperature of ** oC and a barometric pressure of 1.013 barg.
2.32
When burning light fuel oil, the gas turbine is
rated at ** [as5]MW base
load and **[as6] MW
peak load in the combined cycle mode under the same ambient conditions. The net
output of the gas turbine is the difference between the power produced in the
turbine and that absorbed by the compressor. Typically about two-thirds of the
turbine power is used to drive the compressor.
The gas
turbine consists of the following subsystems and major components:
3.1.1
Starting system
3.1.2
Air inlet system
3.1.3
Compressor
3.1.4
Combustion System
3.1.5
Turbine
3.1.6
Exhaust system
3.1.7
Cooling and sealing air system
3.1.8
Bearings
3.1.9
Gland seals
3.1.10
Lubricating oil system
3.1.11
Gas fuel system
3.1.12
Light fuel system
3.1.13
Control system
3.1.14
Safety and protective system
3.1.15
Instrumentation
3.1.16
GT Generator
3.2.1
The gas turbine requires to be rotated from
standstill to a minimum speed for combustion and subsequent fired acceleration.
The functions of the starting system are to:
3.2.1.1
crank the gas turbine unit from standstill
3.2.1.2
accelerate the gas turbine to a speed where it
can be fired
3.2.1.3
after the gas turbine is fired, further
accelerate it to a self sustaining speed.
3.2.2
The starting system comprises a static frequency
converter connected to the gas turbine generator. Together with the excitation
unit, the static frequency converter energizes the stator and rotor windings of
the generator utilizing it as a motor to accelerate the gas turbine to firing
speed.
3.2.3
Gas turbine cannot start themselves because they
only develop sufficient fired acceleration momentum above a certain minimum speed.
Each gas turbine is provided with its own starting system.
3.2.4
The basic function of the static frequency
converter can best be explained by comparing it with a rectifier-supplied speed
controlled synchronous motor. The principal design features of a rectifier
drive are shown in Attachment 6.3.
3.2.5
The converter comprises two three-phase AC
bridge circuits. The AC inputs of the bridge circuits are connected to the
mains while the outputs are connected to the stator of the synchronous machine
being fed.
3.2.6
The frequency circuits of the bridge circuits
are connected through an intermediate smoothing circuit reactor. The table
shows the thyristor ignition sequence with numbers used on the line side and
letters on the machine side.
3.2.7
With thyristors ‘1’ and ‘2’ firing on the line
side and thyristors ‘a’ and ‘b’ firing on the machine side a current will flow
from the line phase ‘R’ through thyristors ‘1’ along the intermediate circuit
reactor, through thyristor ‘a’ and generator stator phases ‘U’ and ‘W’ to
thyristors ‘b’ and ‘2’ and returns to line phase ‘T’.
3.2.8
The principle of electromagnetism states that an
electric current passing through a conductor produces an asociated magnetic
field around that conductor. The magnetic field, say f1,
is thus created in the generator stator winding. If we assume that an
excitation current is flowing at the same time in the generator rotor winding,
a magnetic field fF, will be
building up in the rotor.
3.2.9
The position of this field will be determined by
the position of the axis of the rotor excitation winding. The theory of
electromagnetic induction states that when two conductors having magnetic
fields around them are placed together, an electromotive force proportional to
the angular difference between the magnetic fields is generated.
3.2.10
In our present example, the elctromotive force
proportional to the angular difference between f1
and fF, causes the generator rotor to turn.
The rotor would stop turning when the angular differences between f1
and fF, is zero. To prevent this a changeover
of the thyristors in the machine bridge-circuit occurs; thyristor ‘c’ will be
fired and thyristor ‘a’ will be blocked. Current will now flow through
generator stator phases ‘W’ and ‘V’.
3.2.11
The resulting stator field us shifted to the
position of vector f2.
A further electromotive force is generated and the rotor goes on turning.
Successive thyristor switchover will thus sustain the acceleration of the
generator rotor. The two forced air rectifier bridge circuits are mounted in
control cubicles located in the gas turbine local control room. The operating
temperature of the rectifiers cannot be allowed to exceed 40oC**.
3.2.12
Attachment 6.3 is the control block diagram of
the static frequency converter. The starting system comprises the following two
main subsystems:
3.2.12.1
Power Unit
3.2.12.2
Control and Regulation Unit
3.2.13
The components that regulate and supervise the
frequency converter have been designed on plug-in cards located in cubicles in
the Local Control Room adjacent to the Gas Turbine Hall.
3.2.14
The power unit comprises the frequency
transformer ‘TR’, the line-coomutated converter ‘LCC’, the smoothing reactor
‘L’ and the machine-commutated converter. The static frequency converter has
been designed for an external source start, where the converter directs the
full rated current to the gas turbine generator and switches off at 2100 rpm.
3.2.15
When the gas turbine-generator is being
accelerated, the line-commutated converter (LCC) works in rectifier operation
while the machine-commutated converter works in inverter operation.
3.2.16
The average DC voltage difference between the
LCC and the MCC induces a DC current flow in the intermediate circuit. The
intermediate circuit, or ‘smoothing’ reactor absorbs the varying instantaneous
voltage differences between the LCC and the MCC. The smoothing reactor is
located in the Local Control Room.
3.2.17
The build-up of generator terminal voltage
curtails the current output from the MCC. However, between standstill and a
minimum speed of 48 rpm**, the synchronous generator cannot build up the
voltage required to control the current. Within this range, current commutation
is achieved by intermittently switching the LCC from rectifier to inverter
operation.
3.2.18
During these periods, the current in the
intermediate circuit and the circuit branches of the MCC drop to zero and the
output of MCC is blocked. Ignition of the follow-up thyristor in both the LCC
and MCC causes a current switchover to the next stator phase of the generator.
When the gas turbine is started from the turning gear operation (120 rpm)**,
this operation is not required.
3.2.19
The gas turbine-generator is initially driven by
a constant torque and at almost constant acceleration up to speed during, which
the generator terminal voltage increases continuously to rated voltage. After
combustion is achieved, further acceleration of the gas turbine occurs under
constant terminal voltage and current.
3.2.20
The block diagram in Attachment 6.3 details the
starting converter regulator circuits. The regulator comprises a speed
controller ‘1’ with a subordinate current controller ‘3’. The speed controller
compares the speed control value xn to the fixed reference value wn.
3.2.21
The speed control value is derived by converting
the frequency of the digital signal from the generator voltage detector ‘9’,
‘10’ and ‘11’ into an analog value in the frequency-voltage converter ‘8’. The
speed controller output is the reference value for the current controller.
Because the starting converter operates at full load to reach the required
speed in the shortest possible time, the speed controller is overdriven and the
drive runs at its current limit.
3.2.22
Specification
3.2.22.1
General
3.2.22.1.1
Supplier :
3.2.22.1.2
Type :
Static
3.2.22.1.3
Max. Temperature :
40°C
3.2.22.1.4
Control Voltage :
380 VAC
3.2.22.1.5
Rated Voltage :
6.3 kV
3.2.22.1.6
Max. Rating :
2.9 MW
3.2.22.1.7
Normal Voltage Deviation : + 10%
3.2.22.1.8
Normal freq. Deviation : + 5%
3.2.22.2
Transformer
3.2.22.2.1
Supplier :
3.2.22.2.2
Type :
Resin encapsulated
3.2.22.2.3
Rated Voltage :
6 kV
3.2.22.3
Thyristors
3.2.22.3.1
Supplier :
3.2.22.3.2
Type :
3.2.22.3.3
Rated Voltage :
3.2.22.4
Reactor
3.2.22.4.1
Supplier :
3.2.22.4.2
Type :
3.2.22.4.3
Rated Voltage :
3.2.22.5
Thyristors Cooling Fans
3.2.22.5.1
Supplier :
3.2.22.5.2
Type :
Axial flow
3.2.22.5.3
Rated Voltage :
380 VAC
3.2.22.5.4
Min. Air flow :
3000 m3/hr
3.3.1
The air inlet system provides filtered air to
the gas turbine compressor. Silencers in the air inlet system reduce the noise
created by the suction of inlet air into the intake duct. The intake duct is
the suction point of the compressor and it reduces air pressure variations and
turbulence at the compressor inlet.
3.3.2
The net output of the gas turbine is the
difference between the power produced in the turbine and that absorbed by the
compressor. Typically about 2/3 of the turbine power is used to drive the
compressor. Performance of the gas turbine is very sensitive to the efficiency
of the air inlet components.
3.3.3
For example a loss of 5% in compressor
efficiency will result in over 10% reduction in power output. Inlet air filters
are used to protect the blading of the gas turbine from dust, fumes, pollen and
aerosols from the atmosphere air that could erode, corrode or form deposits on
the compressor and turbine blading and reduce their efficiency. Combustion air
drawn in by the compressor is cleaned in a combination of filters.
3.3.4
The air inlet system consists of two subsystem:
3.3.4.1
Air Intake Filter
3.3.4.1.1
The air intake filter provides filtered air to
the gas turbine compressor. The intake filter is a stage filter. The filter
house consists of 6 modules. The single modules are welded structures of
beveled sheet metal sectional frames.
3.3.4.1.2
The modules are screwed among each other by
means of flanged connections. The arrangement is 3 main modules in
U-configuration with each main module consists of two sub-modules.
3.3.4.1.3
The modules are designed to horizontally
accessible by gratings between the filter stages. KAEFER’s filter house
standard door constitutes the lockable access opening for each filter module
cell.
3.3.4.1.4
The entire filter house is placed on a steel
structure. The steel structure consists of sectional steels, which are bolted
together. An access ladder ensures the access to the single filter house
modules.
3.3.4.1.5
The transition piece that is connected to the
filter house connects the clean air plenum with the silencer and the by-pass
dampers (implosion doors) are integrated with the transition piece. The
transition piece consists of a supporting structure of hollow sections to be
cladded with beveled sheet plate.
3.3.4.1.6
The single filter stages are:
·
Weather Hoods
·
Vertical Rain Louver
·
Coalescer
·
Pre-Filter
·
Main Filter
3.3.4.1.7
These filter stages are formed by frame
structures. These frames are firmly connected to the respective filter module
by means of flanged connections.
3.3.4.1.8
The rain louver and the coalescer stage are not
to be considered as filter stages, but as protection against free moisture in
the intake air. The secondary pre-filter and main filter stage are filtering
the intake air according to the separation classifications EU3 and EU8.
3.3.4.1.9
The grade of the contamination will be
determined by permanent pressure differential control. The pressure
differential measurement is to be carried out once for each filter stage in the
front module.
3.3.4.1.10
Each of the measured negative pressures of the
single filter stages is indicated by a measuring device at the filter house
control box and transmitted to the main control room as a 4-20 mA signal.
3.3.4.1.11
Specification
·
Maximum length :
approx. 12,700 mm
·
Maximum width :
approx. 19,000 mm
·
Maximum height :
approx 7,500 mm
3.3.4.2
Intake Duct
3.3.4.2.1
To guide the intake air from the transition
piece filter house to the intake flange of the gas turbine.
3.3.4.2.2
The intake duct attenuates the intake noise of
the gas turbine to a permissible limiting value. The intake duct is designed in
modules and connects the filter house with the gas turbine.
3.3.4.2.3
The intake duct is a welded structure. It
consists of 6 mm thick steel sheet plates which are forming 6 duct sections
with stiffening welded.
3.3.4.2.4
The air intake duct is composed of the following
main components:
·
intake house of lower and upper part, intake
cone and different attaching parts
·
one intermediate piece
·
one fitting piece
·
air intake damper
·
intake elbow
·
intake silencer with baffles in one-stage
design.
3.3.4.2.5
In the area beneath the fitting piece, a cloth
compensator is applied for structure-borne noise insulation and compensation of
unavoidable assembly tolerances. As for additional sound insulation the
compensator is covered by the elements applied from outside.
3.3.4.2.6
The shut off damper is placed beneath the compensator
and followed by the intake house upper part, intake house lower part and intake
cone. The intake cone and intake guide pieces are screwed to the turbine
respectively by means of tensioning elements.
3.3.4.2.7
The plenum area in front of the compressor inlet
is accessible through a sound insulated door lockable by means of a heavy duty
closer. The door lock is provided with a lock cylinder to be unlocked from
inside for emergency opening. At the outside the intake duct there are openings
and for measuring as well as the ventilation openings for connections of the
dryer.
3.3.4.2.8
Specification
·
Maximum length :
approx. 6,000 mm
·
Maximum length :
approx. 13,700 mm
·
Maximum hight :
approx. 17,000 mm
Note: See Attachment 6.4
for detailed layout.
3.3.5
The following are the main components arranged
sequentially along the air flow path from atmosphere to the compressor intake:
3.3.5.1
Weather Hoods
3.3.5.1.1
All rainfall will be restrained from the intake
opening of the filter house by the weather hoods.
3.3.5.1.2
Hollow sections are forming the welded
supporting structure. The roof consists of trapezoidal sheet metal sections.
3.3.5.1.3
The entire structural component is designed as a
flange construction and is mounted in front of the intake opening of the filter
house.
3.3.5.2
Weather Louver (Vertical Rain Louver)
3.3.5.2.1
A vertical rain louver is installed in the frame
of the intake opening of every filter house module. The purpose of the rain
louver is to collect rain drops of a permissible size.
3.3.5.2.2
The arrangement of the vertical rain louver in
the filter house is in flow direction directly in front of the air inlet
opening.
3.3.5.2.3
The constructional design of each frame consists
of a beveled sheet metal frame and the rain louver sections placed between. The
single sections is fixed in the frame by two horizontal threaded rods provide
for the respective vertical distance of the sections among each other.
3.3.5.2.4
The bolted connections are additionally secured
by welding. The entire frame structure consists of stainless steel. The frame
of the vertical rain louver is inserted into the intake opening of the filter
house module and fastened by means of bolted connections according to the
flange drillings. A flexible sealing of all joints and flanges provides for a
faultless function of the filter stage.
3.3.5.2.5
Specification
·
Intake air volume : 415 m3/s
·
Louver type :
Low velocity standard
3.3.5.3
Coalescer Pad
3.3.5.3.1
Always one filter wall per filter house module
directly behind the weather louver forms the coalescer stage. Here the smaller
rain drops are collected which could reach the inside of the filter house
through the weather louver.
3.3.5.3.2
The arrangement of the coalescer stage in the
filter house is in flow direction directly behind the vertical rain louver. A
frame structure of altogether 210 pieces filter frame/module forms the
coalesces filter stage.
3.3.5.3.3
The constructional design of the frame consists
of stainless steel frames, which are installed, in a frame consisting of
beveled profiles. This filter wall is inserted completely into the filter house
module and fastened by means of riveted connections.
3.3.5.3.4
Drain pipes in flow direction behind each filter
row will lead the separated water into the lateral beveling of the filter house
module. From here the water will be drained out of the filter house via the
drainage system through the single filter house modules in vertical direction.
3.3.5.3.5
The holding frames of the coalescer consist of
stainless steel. The connections between the coalescer frames are executed with
stainless steel rivets. A flexible sealing of all joints and flanges provides
for a faultless function of the filter stage.
3.3.5.3.6
The coalescer mats are fastened to the frame by
means of a holding grid. At the sides this holding grid is held by means of 4
holding bars. At the upper and lower edge of the holding frame 4 holding hooks
of the holding grid are keeping the supporting grid in position. Coalescer mats
can be changed or replaced without any tools.
3.3.5.3.7
The coalescer comprises of
M-81Demister-Coalescing highly efficient Mist Eliminator pad that are
configured to operates at a low pressure drop. The unique construction of these
pads provide excellent free moisture removal at velocities up to 4.3 m/s.
3.3.5.3.8
The pads are made with an exclusive two stage
density, consisting of an open weave fiber pattern on the air entering side and
a tighter weave on the air leaving side with the permits to use full depth of
the pad, thus increasing the amount of water each pad can hold.
3.3.5.3.9
Specification
·
Filter Type :
AMER-kleen M81
·
Thickness :
75 mm
·
Intake air volume : 415 m3/s
·
No. of pads :
210 pcs.
3.3.5.4
Pre Filter
3.3.5.4.1
Always one filter wall per filter house module
placed in front of the main filter stage forms the pre-filter stage. Here the
contaminant particles of the intake air will be filtered, which the filter
class EU3 is able to separate according to DIN 24185.
3.3.5.4.2
The arrangement of the pre-filter stage in the
filter house is in flow direction directly in front of the main filter. A frame
structure of altogether 407 pieces filter frames forms the pre-filter stage.
3.3.5.4.3
The constructional design of the frame consists
of a stainless steel frame, which is installed in front of the main filter
frame by means of bolted connections.
3.3.5.4.4
The entire pre-filter frame consists of material
1.4301 stainless steel. A flexible sealing of all joints and flanges provides
for a faultless function of the filter stage.
3.3.5.4.5
The filter elements are hold in place by a
clamping device in the filter-supporting frame. By a simple release of the
clamping the filter elements are removable. Tools are not necessary for
replacement of the filter.
3.3.5.4.6
The pre-filter comprises of AMER-Kleen M-80
disposable adhesive-impregnated glassfibre pad held in a permanent, galvanized
retaining frame. The density of each pad increases towards the clean airside so
that the entire thickness of the pad is utilized for dust entrapment. When the
pressure drop across the filter rises to 250 Pa, the filters need to be
replaced.
3.3.5.4.7
Specification
·
Filter type :
AMER-kleen M80
·
Rated face velocity : 2.5 m/s
·
Initial resistance : 75 Pa
·
Recommended final resistance : 200 Pa
·
Average Arrestance : 89%
·
Thickness :
95 mm
·
Filter class :
EU3, DIN 24185
·
Intake air volume : 415 m3/s
·
No. of pads :
407 pcs.
3.3.5.5
Main Filter (Fine Filter)
3.3.5.5.1
The main filter is the final filter and has a
filtering efficiency of 90%. Always one filter wall per filter house module
forms the filter frame. The main filter elements are pushed into the filter
frame and fixed with the respective fastening angles.
3.3.5.5.2
The pre-filter frame is placed directly on the
frames of the main filter. Here the contamination particles of the intake air
will be filtered, which the filter class EU8 is able to separate according to
DIN 24185.
3.3.5.5.3
The arrangement of the main filter stage in the
filter house is in flow direction directly behind the pre-filter. A frame
structure of one filters frame per filter house module with altogether 407
pieces filter frames forms the main filter stage.
3.3.5.5.4
The bolted connections are additionally secured
by welding. A flexible sealing of all joints and flanges provides for a
faultless function of the filter stage. The filter elements are hold in place
by bolted connections. By a simple release of the bolted connections the filter
elements are removable.
3.3.5.5.5
The main or fine filter comprises TMP filters of
glass fiber paper with mini-pleated into mats. It is maintenance free and
easily replaced after use. When the pressure drop across the filter rises to
6.5 mbar (2.5” w.g), the filters need to be replaced.
3.3.5.5.6
Specification
·
Filter type :
TMP 95
·
Recommended final resistance : 6.5 mbar
·
Burst pressure :
50 mbar (20” w.g)
·
Filter class :
EU8, DIN24185
·
Intake air volume : 415 m3/s
·
No. of pads :
407 pcs
3.3.5.6
By Pass Door (Implosion Door)
3.3.5.6.1
Six counter-weighted implosion door will open
incase of extreme increase of the pressure loss and provide for a pressure
release in the intake area.
3.3.5.6.2
The implosion doors consist of a weighted damper
blade. The 6 pieces of by-pass dampers are situated in the wall of the
transition piece and weather protection weather hoods are provided outside the
transition piece.
3.3.5.6.3
The implosion doors are set to open when the
pressure drop across the filter combination increases to 12 mbar. The position
of the damper is inquired via limit switches and wired onto the terminal as
potential free signal that are forwarded to the DCS system.
3.3.5.7
Silencer
3.3.5.7.1
The absorption silencer is located in the upper
area of the intake duct.
3.3.5.7.2
It consists of aluminum baffles which, are
filled with mineral wool. The mineral wool is protected from the airflow by
means of protected sheet plates and trickling protection material.
3.3.5.8
Air Intake Shut-Off Damper (Air Flap)
3.3.5.8.1
The shut-off damper is placed beneath the
compensator. It will interrupt the airflow through the turbine during
standstill.
3.3.5.8.2
The shut-off device consists of one blade
segment, which arranged in the direction to the axis of the turbine in the
airflow. In the position “open” the blade is standing vertically.
3.3.5.8.3
The drive of these blades is effected via an
electric motor with worm gear drive. The torque will be forwarded through a
multi-plate-slipping clutch to the damper plate.
3.3.5.8.4
The drive system with the integrated multi plate
slipping clutch serves as a safety function when the damper is closed. In case
of a pressure differential of 5 mbar over closed damper the clutch will open
3.3.5.8.5
This guarantees a protection of the intake duct
against too high-pressure differentials during non-orderly start of the
turbine. In the “open” position, a release of this connection, e.g. by power
failure, will not be possible.
3.3.5.8.6
The position “closed” will be reported to the
control system via a mechanic switch, which the shut-off of the motor is
controlled by the limit switch.
3.3.5.8.7
Specification (Damper Motor)
·
Supplier :
auma norm
·
Model :
SA 07.1-SA 16.1
Note: See Attachment 6.8.
3.3.5.9
Air Intake Duct
The component parts of the intake duct are extensively
maintenance free. However, the individual component parts should be subjected
to a visual inspection at regular time intervals.
3.3.6
Air Filters Pressure Monitoring System
3.3.6.1
An air filter monitoring system is provided to
monitor the differential pressure drops across each air filter plane, across
the filter combination and the pressure at the filter outlet.
3.3.6.2
Attachment 6.6 shows the PID diagram of the
arrangement of the air filters differential pressure monitoring system. The
differential pressure gauges are located in a single housing adjacent to air
filter intake.
3.4.1
The compressor and turbine, the two principal
components of the gas turbine, have a common rotor. The rotor combines the
compressor and turbine sections on a single shaft, which is supported on
bearings at both ends.
3.4.2
The compressor blades converting mechanical work
to kinetic energy of the combustion air and the turbine blades converting
kinetic energy of the hot gas to mechanical work. The mechanical work is partly
used for driving the compressor, and the remaining part is transferred from the
rotor via the intermediate shaft to the generator.
3.4.3
Attachment 6.7 shows a sectional view of the
rotor. The rotor is built-up of compressor and turbine blade discs and a front,
central and rear hollow shaft. The hollow shaft sections and disc are clamped
together by a central tie-rod and located in position ”Hirth” couplings, which
transmit the torque and allow free thermal expansion and contraction.
3.4.4
This rotor construction results in a
self-supporting drum of great stiffness and a low mass thus featuring a high
critical speed. The tie-rod is braced against the discs by different rings
provided at several points. (See Attachment 6.7 for Hirth-Coupling)
3.4.5
O-ring seals at the central compressor stages
prevent the compressed air from re-circulating from the high-pressure stages
back to the low-pressure stages through the Hirth couplings and the interior of
the rotor.
3.4.6
Damper rings (damping cone) prevent excitation
of bending vibration of the tie-rod due to friction at the contacting surfaces
of the damper rings and the tie-rod. For rotor balancing, six planes are
available, with three planes being accessible without opening the turbine and
compressor unit.
3.4.7
All rotor blades may be mounted and dismounted
without disassembling rotor. The turbine section of the rotor is internally and
externally cooled. A small portion of the compressed air is bled off from the
main flow at the end of the compressor and admitted to the interior of the
rotor through holes in the center hollow shaft.
3.4.8
The air is distributed between the turbine discs
and directed to the blade roots and active blade sections of the first rotor
blade ring. The cooling air then discharges into the hot gas stream, with the
blade root cooling air providing a cooling film over the hub.
3.5.1
The gas turbine compressor increases the
pressure and flow of atmospheric air to the combustion chambers. At atmospheric
pressure, the combustion of a fuel does not produce sufficient energy to
deliver useful work from the expanding combustion gases.
3.5.2
The increased pressure and flow of air through
compression increases the amount of energy that can be obtained by the
combustion fuel. The compressor section describes the following main
components:
3.5.2.1
Compressor intake casing
3.5.2.2
Variable inlet guide vane
3.5.2.3
Compressor stator blade carriers
3.5.2.4
Compressor blading
3.5.2.5
Compressor exhaust diffuser
3.5.2.6
Intermediate shaft
3.5.2.7
Compressor/turbine support systems
3.5.2.8
Anti-condensation Heating System
3.5.2.9
Compressor blow-off system
3.5.3
Compressor intake casing
3.5.3.1
The intake casing directs air from the intake
duct to the compressor inlet. Attachment 6.8 shows a sectional view of the
intake casing. For general arrangement views of the intake casing see
Attachment 6.1 and Attachment 6.2.
3.5.3.2
The conical intake, which forms the inner
passage of the intake casing, is bolted to the compressor bearing housing
through a flange.
3.5.4
Variable Inlet Guide Vane
3.5.4.1
Variable inlet guide vane control loop is
applied in order to achieve a constant gas temperature at the gas turbine
exhaust, which is necessary for the heat recovery steam generator. During the
part load operation, the NOx-emission rate is positively influenced since the
guide vane adjustment is used for controlling the excess air ratio in the flame
zone in combination with the secondary air control at the combustion chamber.
3.5.4.2
The fixed guide vane position the turbine
exhaust temperature is dependent only on the fuel flow, which in turn depends
on the required gas turbine output. In the range of low loads the exhaust
temperature is low, and at higher loads the temperature increases.
3.5.4.3
This dependence is charged by varying the
compressor air flow by means of adjusting the inlet guide vanes. Depending on
load changes, that means fuel mass flow changes, the inlet guide vane
staggering angle is changed such, that the air mass flow is changed than amount
required for keeping the exhaust temperature at a steady value.
3.5.4.4
For example when the turbine output is reduced,
the automatic control:
3.5.4.4.1
decreases the fuel flow
3.5.4.4.2
thus the exhaust temperature decreases also
3.5.4.4.3
the inlet guide vanes are closed as far as
necessary
3.5.4.4.4
thus the air mass flow decreases
3.5.4.4.5
the exhaust temperature is kept steady by these
procedures
3.5.4.5
The following components are installed on the
variable inlet guide vane system to allow adjustment of the exhaust temperature
and air mass flow:
3.5.4.5.1
Actuator for guide vane adjustment
[MBA11-AS001-M01]
3.5.4.5.2
Limit switch “open” – position [MBA11-AS001-S11]
3.5.4.5.3
Torque switch direction “open” [MBA11-AS001-S13]
3.5.4.5.4
Limit switch “closed” – position
[MBA11-AS001-S21]
3.5.4.5.5
Torque switch direction “open” - [MBA11-AS001-S23]
3.5.4.5.6
Transmitter for guide vane position –
[MBA11-CG001]
3.5.4.5.7
Control panel Instrumentation
3.5.4.6
The Inlet Guide Vane Control is totally
independent from Electro Hydraulic Turbine Control, which acts on the fuel
control valves. The separate drive controller [MBA11-AS001] uses as its input
the corrected is adjusted in the relevant software during pre-commissioning to
a value which, is 15oC lower than base load outlet temperature.
3.5.4.7
During normal base load outlet temperature =
540oC the temperature set point for the inlet guide vane controller would be
525oC. The inlet guide vane controller would keep a constant exhaust
temperature of 525oC in the load range between 70% and 100% load.
3.5.4.8
Unfortunately the range of inlet guide vane
adjustment does not allow to keep the exhaust temperature constant over the
whole load range. At load 70% the inlet guide vanes are in maximum closed
position and thus the exhaust temperature will decrease as the load does. The
setting time of the actuator is relatively short, so that the control movements
are done in a stepping mode in order to avoid large temperature transients.
3.5.4.9
Operation and indication of the variable inlet
guide vane is done at the gas turbine control panel. Manual operation is only
possible when the automatic inlet guide vane control is switched off. This is
not allowed during start-up, otherwise the start-up program could be disturbed.
Generally manual operation is only used during commissioning if required, and
during compressor washing to improve the cleaning effect.
Note: refer to Attachment 6.9
3.5.5
Compressor Stator Blade Carriers
3.5.5.1
The compressor stator secures blade rings with
mounted stator blades and transmits the reaction forces set-up by the
compressor airflow and pressure to the outer casing.
3.5.5.2
The compressor stator consists of three stator
blade carriers. Stator blade carrier no.1 is located between the compressor
bearing housing and the center casing and forms part of the outer casing.
Stator blade carriers nos.2 and 3 are suspended in the center casing thus
allowing for thermal expansion.
3.5.5.3
To allow for vertical alignment relative to the
rotor, the stator is provided with four support brackets with adjustable shims.
Mating support brackets with shims take up the torque while horizontal
alignment and location is achieved by centering pins with eccentric bushes in
the upper and lower parts. Adjustable shims located between the mating support
brackets and the center casing provide axial location and transmission of
thrust forces to the casing.
3.5.5.4
Between the stator blade carriers, annular gaps
are provided for bleeding air into the spaces between the stator blade carriers
and the outer casing. During start-up and shutdown, air is bled through the
annular gaps between the stator blade carriers and center casing when the
rotational speed does not match to the possible pressure increase in the
compressor stages.
Note: refer to Attachment 6.10
3.5.5.5
The horizontally split stator blade support
rings are inserted into circumferential grooves machined in the stator blade
carriers. Compressor rotor blade clearances can be measured at several
clearance measurement holes provided at the front and rear end of each stator
blade carrier and in the center casing.
3.5.5.6
The angular position of the compressor inlet
guide vanes can be changed so that both the turbine outlet temperature and the
excess air ratio in the combustion chamber can be optimized according to the
needs at partial load operation.
3.5.6
Compressor Blading
3.5.6.1
Compressor Rotor Blades
3.5.6.1.1
The compressor rotor blades convert the
rotational mechanical energy of the compressor into kinetic and potential
energy of the combustion air and together with the stator blades pressurize the
air. One compressor stage consists of one row of rotating blades, which is
followed by one row of stator blades.
3.5.6.1.2
Attachment 6.14 shows a general arrangement view
of a compressor rotor blade. Each blade is of single piece construction with
its airfoil shaped to ensure optimum flow characteristics and strength
properties.
3.5.6.1.3
The blade root consists of a dovetail with a
short parallel guide. The blades are inserted into corresponding grooves in the
rotor blade wheels at the required angle. To fix the blade axially, the end
faces of the blade roots are caulked in recesses provided in the disc groove.
3.5.6.1.4
The blades are manufactured out of stainless
steel and the first few stages (0 to 5th stage) are coated for
corrosion protection. The blades can be assembled and removed without
disassembling the rotor.
3.5.6.2
Compressor Stator Blades
3.5.6.2.1
The compressor stator blades deflect the
accelerated air stream passing through the blade passages in a direction
opposite to the direction of the rotation of the rotor. The resulting
deceleration of the airflow is accompanied by a pressure rise.
3.5.6.2.2
At the compressor inlet, there is one row of
inlet guide vane that can be adjusted to vary the air mass flow to ensure
partial load efficiency of the combined cycle plant is improved. The adjustable
guide vanes are supported at both ends with pins and bushes.
3.5.6.2.3
Attachment 6.11 shows general arrangement and
sectional view of a compressor stator blade. Each blade is of single piece
construction with its airfoil shaped to ensure optimum flow characteristic and
strength. The blade comprises of a dovetail with short parallel guide.
3.5.6.2.4
The blades are assembled in split rings
comprising an outer ring and an inner ring. The blade roots are inserted
corresponding grooves in the outer rings. The outer rings are in turn assembled
in grooves in the stator blade carriers and fixed in the axial direction.
3.5.6.2.5
The inner rings join the blades along the inner
diameter and form a sealing line (gland). The inner rings are of two-part
screwed construction with a double hook and nose arrangement for blade
attachment. The blades are made of stainless steel material. The blades of the
first few stages are coated to prevent corrosion.
3.5.6.3
Compressor Exhaust Diffuser
3.5.6.3.1
The compressor exhaust diffuser with the best
possible efficiency converts the kinetic energy of the compressed air into
pressure.
3.5.6.3.2
The diffuser comprises of horizontally split
outer and inner walls that are connected through the guide vanes and the last
stage compressor stator blade ring.
3.5.6.3.3
The outer wall is flanged to the compressor
stator blade carrier no. 3 while the inner wall mounts a support ring for the
radiation liner. The guide vanes ensure turbulent flow of compressed air into
the combustion chambers.
3.5.6.3.4
Attachment 6.12 shows a sectional view of the
compressor exhaust diffuser.
3.5.6.4
Intermediate Shaft
3.5.6.4.1
The intermediate shaft connects the gas turbine
to the generator at the compressor end and transmits the useful power to it.
Attachment 6.13 shows a sectional view of the intermediate shaft.
3.5.6.4.2
A long intermediate shaft for direct coupling of
the gas turbine and generator consists of a hollow shaft with integrally forged
coupling flanges.
3.5.6.4.3
The turbine and generator shafts are connected
to the intermediate shaft via coupling bolts. Shaft torque is transmitted
through reamed bolts.
3.5.6.5
Gas Turbine Support System
3.5.6.5.1
The gas turbine support system comprises of
compressor supports, turbine supports and a center guide fixed at the turbine
exhaust casing.
3.5.6.5.2
The gas turbine is supported on the support
brackets at the front bearing pedestal and these supports form the fixed point
of the gas turbine.
3.5.6.5.3
Integrally cast brackets of the compressor
casing rest on bolts grouted into concrete foundation. For alignment purposes,
the brackets and bolts are separately adjustable in height, in longitudinal and
transverse direction (adjustable in all three coordinates).
3.5.6.5.4
The turbine bearing housing rests on supporting
bars at both sides that compensate for the thermal expansion in the horizontal
plane of the unit. The bars are connected to an anchor plate at the bottom and
to the lower half casing flange at the top. The anchor plates are welded to
soleplates.
3.5.6.5.5
The center guide at the turbine exhaust casing
maintains the gas turbine in its center line position on the foundation. The
center guide comprises a support bracket and guide bracket that permits the key
on the exhaust casing to move in longitudinal direction.
Note: Refer to Attachment 6.14.
3.5.6.6
Anti-condensation Heating System
3.5.6.6.1
To prevent corrosion due to excessive relative
humidity during outages, a heating system is provided before the compressor
inlet. This anti-condensation heating system heats air in the inlet duct to a
temperature at which no corrosion can occur in the gas turbine.
3.5.6.6.2
The heating system comprises of two portable
electrical hot-air blower units. Each anti-condensation unit comprises a
blower, a heater and a nozzle with an attached flexible hose. The blower has
two speeds. The hot air is introduced to the compressor through flexible metal
hoses connected to wall fittings provided in the intake duct.
3.5.6.7
Compressor Blow-Off System
3.5.6.7.1
The compressor is designed for a speed of 3000
rpm. At speeds of less than 3000 rpm, excessive throttling occurs in the intake
end blading that causes airflow separation; his phenomena is called compressor
surge.
3.5.6.7.2
Flow separation causes air delivery to become
unstable. Rapid fluctuations in compressor discharge pressure, heavy vibration
and surge noise in rhythm with pressure fluctuations characterize surging.
3.5.6.7.3
During surging, the compressor blades are
subject to high bending stresses and temperatures. Bleeding part of the intake
air at a suitable stage of the compressor prevents compressor surge. At low
speeds, the compressor surge limit is thus shifted towards the high-pressure
end.
3.5.6.7.4
The compressor is provided with two extraction
points behind stages 5 and 10. Solenoid operated valves control the air
blow-off at these points. Operation of the solenoid valves is controlled by the
gas turbine sequence signal.
3.5.6.7.5
Attachment 6.15 is a schematic diagram of the
compressor blow-off system. The blow-off system comprises of:
·
Three pneumatically operated blow-off valves
[1MBA41-AA011, 1MBA41-AA012 and 1MBA42-AA011].
·
Three blow-off lines connecting the blow-off
valves to the exhaust diffuser
·
Four solenoid actuated valve that controls the
opening and closing of the pneumatically operated blow-off valves
[1MBA41-AA010A, 1MBA41-AA010B, IMBA42-AA011A and 1MBA42-AA011B]
·
Air receiver [1MBA40-BB001]
·
Rack mounted blow-off control system.
3.5.6.7.6
Air is blown off through valves [1MBA41-AA011]
and [1MBA41-AA012] after compressor wheel no. 5; these two valves and the
blow-off lines comprises Blow-off System 1.
3.5.6.7.7
Air is blown off through valve [1MBA42-AA001]
after compressor wheel no. 10; this valve and blow-off line comprises Blow-off
System 2.
3.5.6.7.8
The bled air is discharged to the exhaust
diffuser via the blow-off lines. A pneumatic actuator controls each blow-off
valve. Compressor speed determines the operation of these actuators. Motive air
for the actuators is tapped from a point downstream of the last compressor
stage.
3.5.7
Compressor Specification
3.5.7.1
Supplier :
Ansaldo Energia s.p.s
3.5.7.2
Type :
Axial flow, heavy duty
3.5.7.3
No. of stages :
16
3.5.7.4
Speed :
3000 rpm
3.5.7.5
Casing :
Horizontal split, flanged
3.6.1
Fuel gas, light fuel oil or mixture of both
fuels is burnt in the combustion chamber using the combustion air delivered by
the compressor thus discharging the hot gas to the turbine inlet.
3.6.2
Therefore the function of the combustion system
are to:
3.6.2.1
direct compressed air to the combustion chambers
3.6.2.2
disperse and mix fuel with proper amount of
combustion air
3.6.2.3
ignite the fuel/air mixture to form heated
combustion gases
3.6.2.4
direct the hot combustion gases to the turbine.
3.6.3
The air is delivered by the compressor burns in
the combustion chambers with fuel gas, fuel oil, or a combination of both
fuels, to reach turbine inlet temperature. The gas turbine is also sometimes
called a combustion turbine to distinguish it from ‘non-combustion’ turbines
like steam and hydro turbines.
3.6.4
The combustion system comprises of the following
major components:
3.6.4.1
Pressure jacket
3.6.4.2
Internals: flame tube plate, flame tube and
mixing chamber
3.6.4.3
Air adjusting ring
3.6.4.4
Burner assembly
3.6.4.5
Ignition gas system
3.6.5
There are two combustion chambers arranged as
shown in Attachment 6.2. The two combustion chambers are flanged to opposite
sides of the turbine casing. The combustion chambers are identified as the
right (CCR) and left (CCL) combustion chambers when viewed facing the direction
of gas flow.
3.6.6
Attachment 6.16 shows a sectional view of the
combustion chamber illustrating structural details and the air and gas flow
paths. Air from the compressor enters the combustion chambers through the
annular space between pressure jacket and inner liner and flows to the
dual-fuel hybrid burners (burner assemblies) as primary air.
3.6.7
At the lower part of the flame tube compressed
air passes the inner wall as secondary air. This flow is increased at
decreasing load by means of openings, which are more or less covered by the
electricity actuated air-adjusting ring.
3.6.8
The combustion chambers are suitable for use
with burner assemblies for single fuel or dual fuel operation (light fuel oil
and fuel gas). When the fuel gas is admitted into the burner assembly for fuel
gas firing, the fuel oil nozzle of the burner assembly is provided with cooling
air. Pilot flames start combustion. Each burner assembly has one permanently
installed gas-electric igniter for igniting the flame.
3.6.9
A diagonal swirler ensures better mixing of air
and fuel. Depending on the adjustment of the pressure drop in the combustion
chamber a separate flow path is branched off further upstream. This air is
admitted into the mixing chamber via openings (not shown in the drawing) to mix
with the combustion gas. The hot gas leaves the combustion chamber and flows to
the turbine.
3.6.10
A manhole is provided for easy access to the
combustion chamber for inspections of internals and the turbine inlet section.
Two light receivers located on the pressure are provided for flame monitoring.
In the event of a flame failure in the combustion chamber, the light receivers
initiate tripping/closing of the fuel emergency stop valve immediately
3.6.11
The combustion flames can be inspected through
an inspection tube in the manhole cover. A platform with railing is arranged
around the combustion chamber. The fuel, cooling air and ignition gas lines and
the electricity supply leads to the burner assemblies are installed on the top
dome.
3.6.12
Pressure Jacket
3.6.12.1
The pressure jacket forms the outer enclosure of
the combustion chamber and contains the pressure forces generated by compressor
discharge air and the combustion process.
3.6.12.2
The pressure jacket comprises a combustion
chamber jacket and top dome. A combustion liner is provided where the air inlet
opens into the mixing chamber. The lower end of each combustion chamber is
flanged to the turbine casing.
3.6.13
Internals
3.6.13.1
The internal parts of the combustion chamber
enclose the space where the combustion is generated, mixed and channeled to the
turbine. The hot gas leaves at ‘A’, while fuel and primary air are supplied
through ‘B’. Attachment 6.17 shows a sectional view of the combustion chamber
internals.
3.6.13.2
The internals comprises a flame tube plate,
flame tube and mixing chamber. The flame plate consists of a framework and a
segmented double plate. The framework is welded to the flame tube.
3.6.13.3
The flame tube comprises a cylindrical outer
shell with refractory lining. Bricks of the refractory lining are vertically
supported on a cooled brick support ring and horizontally located in position
by sprung brick holders.
3.6.13.4
The inner surface of the flame tube is cladded
with ceramic tiles, which are fixed with clamps to the sheet metal liner.
Compressed air penetrates the liner through a lot of bores to the rear side of
the tiles so that the liner and the fixings are protected against overheating.
During an internal inspection of the combustion chamber the tiles can be easily
be exchanged if there is a damaged
3.6.13.5
Ribs suspend and center the flame tube in the pressure
jacket. A tapping line is provided to measure the pressure in the combustion
interior. The mixing chamber comprises a conical section and is carried on two
trunnions to ensure free movement and is centered with two guide members.
3.6.14
Air Adjusting Ring
3.6.14.1
In the lower part of the combustion chamber
flame tube the variable secondary air openings are provided. These are opened
during idling operation and closed at base load by means of an adjusting ring.
3.6.14.2
Attachment 6.18 shows the overview of the
secondary air ring mechanism. The lever (3) is moved between maximum and
minimum positions by means of an electric motor provided with a gear system (4)
which is attached to the pressure jacket of the combustion chamber.
3.6.14.3
This movement is transferred to the adjusting ring
(1) and the roller carts (2) carrying the ring by a double-joint rod (5). Each
air mixture opening is covered to some extent by part of the roller cart.
3.6.14.4
The air mixture adjustment done by these
secondary air openings separates and distributes the airflow that enters the
combustion chamber in two flow paths. The primary air flows to burners for fuel
combustion. The secondary air that does not take part in the combustion process
flows into the combustion chambers via the variable secondary openings.
3.6.15
Hybrid Burner Assembly
3.6.15.1
The burner assembly is used to distribute the
fuel into a flow of fine particles so that it is easily mixed with the
combustion air. Therefore the following fuel nozzle are provided:
3.6.15.1.1
Fuel oil burner
3.6.15.1.2
Diffusion gas burner
3.6.15.1.3
Pilot gas burner
3.6.15.1.4
Premix gas burner
3.6.15.1.5
Ignition gas supply and spark plug
3.6.15.1.6
Water distribution nozzles.
Note: Refer to Attachment
6.19 for burner assembly sectional view.
3.6.15.2
The burner is mounted on a burner support. The
air baffle components form an integral part of the flame tube plate. The major
portion of the primary air is required for combustion enters at the main air
inlet via a diagonal swirler.
3.6.15.3
The air then flows through an annular duct into
the combustion zone. The remaining primary air or the inner flow path is
admitted via an axial swirler and mixed with fuel upstream of the swirler and
with light fuel oil downstream of the swirler.
3.6.15.4
The fuel oil burner, the pilot burner, the
diffusion gas burner, the spark plug and the water distribution are connected
to the flange. The axial swirler is part of the diffusion gas burner, whereas
the diagonal swirler attached to the flame tube top is part of the premix gas
burner.
3.6.15.5
Water distribution nozzles are used to reduce
detrimental emission in the flue gas in order to reduce the flame temperature.
The water flows into the annular space, is injected, and is mixed with the
smaller part of the primary air in the axial swirler.
3.6.15.6
Gas fuel Burner
3.6.15.6.1
The pilot and diffusion gas burners and the
spark plug are connected to the flange. The axial swirler is part of the
diffusion gas burner, whereas the diagonal swirler is attached to the flame
tube top.
3.6.15.6.2
The premix gas burner consists of a row of tubes
loosely fixed on the top of the diagonal swirler. The double bent premix gas
distributor pipes locate the loose tubes.
3.6.15.6.3
The larger part of the primary combustion air
passes the diagonal swirler and flows as a vortex into the flame tube. The
smaller part of the combustion air flows through the axial swirler and is mixed
with the diffusion gas.
3.6.15.6.4
During the fuel gas operation higher load range,
the fuel gas flows through the premix burner nozzles is intensively mixed with
the airflow and passes through the diagonal swirler into the flame tube.
3.6.15.6.5
During premix operation, a certain amount of gas
is burnt in a diffusion flame in order to achieve flame stability. This is done
via the pilot burner tubes, to which the gas is fed and mixed with the smaller
part of the primary air in the axial swirler.
3.6.15.6.6
At lower load, the fuel gas is fed to the
diffusion burner nozzles and is mixed with the primary air in the axial swirler
before burnt in the flame tube. The ignition flame used to fire/ignite the main
flame is fed by a separate gas flow and ignited by means of a spark plug.
Note: Refer to Attachment 6.19.
3.6.15.7
Light Fuel Oil Burner
3.6.15.7.1
The light fuel oil burner atomizes the liquid
fuel under all operating conditions ensuring flame stability and completes fuel
combustion. Attachment 6.20 shows a sectional view of the light fuel oil
burner.
3.6.15.7.2
Each mechanical atomizer burner uses a single
swirl chamber, the fuel flow rate being controlled by return flow. The light
fuel oil system is described in detail in section 3.14.
3.6.15.7.3
Light fuel oil enters the annular duct ‘a’ of
the burner via the distillate fuel inlet. A high vortex action is imparted to
the distillate fuel while flowing through tangential slots ‘b’ in the swirl
chamber ‘c’. The vortex action ensures sufficient atomization when the fuel
enters the combustion zone through nozzle ‘4’.
3.6.15.7.4
Depending on the control port opening in the
light fuel oil return line, fuel oil supply to the burners is partly injected
and partly returned to the light fuel oil storage tank. A needle in the return
flow tube ensures flow stabilization. Maximum fuel flow is injected into the
burning when the return line is fully closed.
3.6.15.7.5
When tangential slots ‘b’ are clogged, the check
valve prevents light fuel oil from flowing back into the combustion chamber
from the common return line of the burners. After the unit shutdown, any
excessive pressure built up in the fuel oil system is relieved through a duct
in the check valve disc. During fuel gas operation the check valve prevents any
transverse flow of the hot combustion chamber gas.
3.6.15.7.6
Depending on the fuel selected for operation, a
double ball valve assembly admits either distillate fuel or cooling air to the
distillate burner. Operation of the double ball valve is described in detail in
section 3.14 ‘Light Fuel Oil System’
3.6.16
Ignition gas system
3.6.16.1
The primary purpose of the ignition gas system
is to supply the two main combustion chambers with ignition gas to produce a
flame for ignition of the primary fuel in a specific speed range and for a
fixed period of time during the gas turbine power plant start-up.
3.6.16.2
The igniter lights on the fuel in the dual fuel
burners. It produces a pilot flame that lights the fuel as soon as it leaves
the burner. Attachment 6.21 shows a sectional view of an igniter and a
schematic diagram of the ignition system.
3.6.16.3
The ignition gas enters the igniter at the gas
inlet and flows into the mixing tube via a nozzle. At the end of the mixing
tube, the ignition spark ignites the gas. The ignition spark is produced
between the ignition electrode and the end of the mixing tube acting as the
ground electrode.
3.6.16.4
Ignition transformers, one for each combustion
chamber, are located on the top domes. The short-circuit-proof ignition
transformers supply the ignition voltage to the igniters via high-voltage
cables.
3.6.16.5
Ignition voltage, 5000 V, is switched on and
maintained during the entire ignition period. To obtain an optimum flame, the
specific distance between the ignition electrode and the ground electrode is
set. Combustion air is fed to the ignition flame via an air inlet duct. The
ignition flame leaves the igniter at the end of the air inlet duct.
3.6.16.6
The ignition system consists of two [as7]gas
cylinders, lines, valves and fittings, ignition transformers and igniters. The
ignition gas valve rack houses a pressure reducer, relief valve, two solenoid
valves, two pressure switches and the wiring terminal box. Either natural gas
fuel or bottle gas (propane or butane) is used as ignition fuel.
3.6.16.7
The ignition gas cylinders are located outside
the gas turbine building i.e. at the east of the gas turbine building.
Attachment 6.22 shows the schematic diagram of the ignition cylinder arrangement.
A manual isolating valve can separately isolate each ignition gas cylinder.
3.6.16.8
The permissible minimum cylinder gas pressure
upstream of pressure reducer is 1.9 barg[as8]. When
the ignition gas cylinder pressure falls below this minimum value, an alarm annunciates
at the DCS control panel in central control room / GT local control room.
3.6.16.9
A minimum ignition gas pressure of 1 barg is
required upstream igniters. This pressure is set at the pressure reducer,
allowing for the pressure drop in the ignition line. A three-way valve serves
as main shutoff valve. The ignition gas flows to igniters in the combustion
chambers via this solenoid valve and swing-check valves.
3.6.16.10 Prior
to start-up, solenoid valve [1MBQ11-AA021] is opened and pressure switch
[1MBQ11-CP001] transmits an ignition release signal when the specified ignition
gas pressure is reached. When the gas turbine reaches ignition speed 450 to 550 [as9]rpm,
solenoid valve [1MBQ11-AA022] is opened through a contactor, which at the same
time release the ignition voltage.
3.6.16.11 This
ensures that solenoid valve [1MBQ11-AA022] closes on loss of the ignition
voltage. Pressure switch [1MBQ11-CP001] transmits a release signal for opening
of the emergency stop valve. The main flame is started 10 seconds later when
the emergency stop valves opens and a minimum fuel flow is admitted into the
combustion chamber.
3.6.16.12 The
ignition voltage is switched off by the contactor and solenoid valves
[1MBQ11-AA021] and [1MBQ11-AA022] are closed prior to expiry of the 10 seconds
time delay allowed for safe ignition. The section between the two solenoid
valves and the three-way valve is vented via the 3rd way of solenoid
valve [1MBQ11-AA021], with any leakage gas being vented to atmosphere. The open
out door end of the vent pipe points downward and is protected against
contamination by screen.
3.6.16.13 The
ignition gas cylinder bay has 4 propane gas cylinders with a weighing device
for each cylinder. When the cylinder weight decreases below 15%[as10]
of a predetermined cylinder weight, an alarm annunciates at the DCS pane and GT
local panel. The ignition gas bay is vented by natural draught and secured
against unauthorized access. Open flame lamps and electric lamps without
explosion protection are not allowed.
3.6.17
Specifications
3.6.17.1
Dual fuel burners
·
Type :
Hybrid pressure atomization
·
Quantity :
16 nos.
3.6.17.2
Spark plugs
·
Quantity :
16 nos.
·
Voltage :
5000 V
3.6.17.3
Flame detectors
·
Supplier :
Iris
·
Type :
Infra-red
·
Quantity :
4 nos
·
Supply Voltage :
220 V AC
3.7.1
The turbine converts the high pressure and temperature
gases produced by the combustion of gas fuel or light fuel oil into mechanical
energy. The turbine drives the compressor and the gas turbine generator.
3.7.2
This section describes the following main
turbine components:
3.7.2.1
Turbine stator
3.7.2.2
Turbine blading
3.7.2.3
Turbine casing
3.7.2.4
Hydraulic turning gear
3.7.2.5
Hand barring gear
3.7.3
Turbine Stator
3.7.3.1
The turbine stator secures the stator blade
rings with the stator blades in position and transmits the reaction forces
set-up by the combustion gas flow and pressure to the outer casing.
3.7.3.2
Attachment 6.23 shows the sectional view through
the turbine stator. The turbine stator comprises one stator blade carrier that
supports the stator blade rings and the stator blades of stages nos. 1 to 4.
The turbine stator blade carrier is suspended in the center casing to allow for
thermal expansion.
3.7.3.3
Two eccentric-centering pins in the upper part,
next to the horizontal split are provided for vertical adjustment of the stator
relative to the rotor and for taking the torque. The lateral adjustment of the
stator is made by means of eccentric-pins opposite to each other in the upper
and lower parts respectively.
3.7.3.4
The axial forces are transmitted to the outer
casing by a collar that fits to a circumferential groove at the turbine outer
casing. Shims are provided to fix the turbine stator in the axial direction.
Stator blades of stages 1 to 3 are inserted in circumferential grooves in both
the stator blade carrier and the shrouds of the adjacent blade and secured in
position by pins with clearance provided to accommodate expansion.
3.7.3.5
At the inner diameter of the stator, the 2nd
and 3rd stage stator blades are supported by segmented seal rings.
The 4th stage stator blades are welded at their outer diameter to
the segmented ring, which is inserted into circumferential grooves in the
stator blade carrier. The 4th stage blade seal ring fits into
shrouds welded to the inner diameter of the blades.
3.7.3.6
Cooling air flows through the hollow spaces
between the stator blade carrier and the stationary shrouds of the stator
blades and through the hollow stator blades of the 1st , 2nd
and 3rd stages. In the 2nd stage, part of the cooling air
is diverted through the seal rings as seal rings as seal air. The cooling and
sealing air systems are described in section 3.9.
3.7.4
Turbine Blading
3.7.4.1
Turbine Rotor Blades
3.7.4.1.1
The turbine rotor blades convert the thermal
energy of the combustion gases (hot gases) into mechanical energy that needed
to drive the compressor and the generator. Attachment 6.24 shows the overview
of the turbine rotor blades.
3.7.4.1.2
Each rotor blade consists of the airfoil, the
blade root with the platform plate. The blade root comprises of a fir-tree
dovetail with long shank and two or three serrations.
3.7.4.1.3
The blade platform confines the hot gas path and
protects the blade fixing roots against the high temperature. The blades are
inserted in corresponding grooves of the rotor discs. The blades are locked in
axial direction by keys on the 1st and 2nd stages and by
a pin inserted at the mid-span between the blade platform and the disc rim on
the 3rd and 4th stages.
3.7.4.1.4
Because of the high mechanical and thermal
stress all rotor blades are made of high-temperature alloys. The first two
stage rotor blades are internally cooled with air. The first blade row consists
of castings with internal channels allowing cooling air to enter the root
radially and discharged through holes on the trailing edge. (See Attachment
6.24)
3.7.4.1.5
The second stage blades are castings with a
couple of radial bores. The cooling air enters these blades radially at the
root and leaves them at the tips. The third and fourth stage rotor blades are
solid and cooling air that passes the spaces at the fixings cools their roots.
3.7.4.2
Turbine Stator Blades
3.7.4.2.1
The turbine stator blades together with rotor
blades convert the thermal energy of combustion gases (hot gas) into mechanical
energy available in the rotor. Attachment 6.24 shows the sectional views of the
turbine stator blades, stage 1 to 4.
3.7.4.2.2
The stator blades consist of outer shroud,
airfoil section and inner shroud. The outer shrouds are used to fix them in the
stator blade carrier and form the outer boundary of the hot gas path. The inner
shrouds confine the hot gas path against the rotor.
3.7.4.2.3
The airfoils of the 1st, 2nd
and 3rd stages are hollow and are air cooled while the airfoils of
the 1st and 2nd stages have partitions with holes for
improved cooling. In each case, cooling air is discharged through holes in the
trailing edges of the airfoils.
3.7.4.2.4
At 2nd stage blade row a part of the
cooling air flows into the sealing ring through a set of bores and is passed
through the sealing labyrinths. Due to the high stress at elevated temperature,
the stator blades are made of high temperature alloy castings. The first and
second stages are coated with VPS (Vacuum Plasma Spray) and chroming for
improving the high-temperature corrosion resistance coats the third stage.
3.7.5
Turbine casing
3.7.5.1
Inner casing
3.7.5.1.1
The inner casing directs the hot gas from the
two combustion chambers to the turbine blades. Attachment 6.25 shows the
general arrangement and sectional views of the inner casing.
3.7.5.1.2
The inner casing is a welded construction of
heat resistant and non scaling sheet metal. Together with an unsplit protective
liner, it forms a structural unit that envelops the rotor in a concentric
arrangement relative to the central hollow shaft. These items are unsplit so
that the thermal expansion does not affect the tightness and they can only be
assembled and disassembled together with rotor.
3.7.5.1.3
The compressor discharge air passes over the
outer surface of the inner casing on its way to the combustion chambers. To
ensure uniform cooling by the compressor air, the inner casing is provided with
a radiation liner at its front end and an air baffle at its rear end.
3.7.5.1.4
The inner casing is supported and adjusted in
its vertical position with four brackets and shims. Centering pins and
excentric bushes in the upper and lower part of the center casing allow for
lateral adjustment.
3.7.5.1.5
The cylindrical protective liner is supported by
a ring/circumferential grooves arrangement at the hub of the inner casing and at
its compressor end by the ring at the inner wall of the diffuser.
3.7.5.1.6
At the turbine end side of the inner
casing/protective liner arrangement, seal strips are inserted between the first
stage rotor blade row and the radiation liner. A split seal ring is provided
for connection and sealing between the inner casing and the stator blade
carrier.
3.7.5.2
Center casing
3.7.5.2.1
The center casing connects the turbine stator
blade carrier1 to the exhaust casing and contains the internal pressure of
compressed air and combustion gases. The center casing accommodates the
compressor and turbine internals and serves as a connection for the combustion
chambers.
3.7.5.2.2
Attachment 6.26 shows the general arrangement
and sectional views of the center casing that comprises of a cylindrical outer
shell with a horizontal joint and lateral branches. Flanges are provided for
connection to the compressor stator blade carrier 1, exhaust casing and
combustion chambers.
3.7.5.2.3
Partitions subdivide the cylindrical into
several compartments required for different pressures. Centering devices and
supports are provided for guidance and support of compressor stator blade
carriers 2 and 3 and the turbine stator blade carrier. Pipe branches connect to
the compressor anti-surge blow-off lines.
3.7.6
Hydraulic turning gear
3.7.6.1
The hydraulic turning gear keeps the rotor
turning after the gas turbine has been shut down. Continuous rotation of the
shaft ensures uniform cooling down and prevents radial shaft distortions
(bending). Furthermore, during standstill program, the shaft is turned from
time to time so that seizing of the metal surfaces is avoided. Attachment 6.27
shows the cross section view of the hydraulic turning gear.
3.7.6.2
A minimum rotational speed is required to form a
load-carrying oil wedge in the journal bearings and to avoid semi-fluid
friction. The hydraulic turning gear is located at the generator side of the
compressor bearing housing.
3.7.6.3
Pressurized lube oil that is supplied by the
main oil pumps through solenoid valves [1MBV41-AA001] drives an pelton-type
turbine wheel so that the turbine rotates at about 120 rpm.
3.7.6.4
Although this speed is sufficient for
lubricating the bearings, the shaft lift oil pump is also in operation during
turning gear mode for safety reasons. Since the oil flow required relatively
large amount, both main oil pumps are in operation.
3.7.7
Hand barring gear
3.7.7.1
The hand barring gear enables the shaft to be
turned by hand to any desired position and serves as a final back-up for shaft
rotation in case of failure of the hydraulic turning gear.
3.7.7.2
The hand barring gear is used for turning the
gas turbine rotor during maintenance and absolutely necessary that the shaft
lift oil pump is in service at barring operation otherwise the shaft could only
be turned by applying excessive force that would cause damages to the bearings.
3.7.7.3
The barring gear is located on the enclosure of
the intermediate shaft near the generator end coupling flange. To operate the
barring gear the lever moves the pawl in the direction of rotation so that it
engages the toothed rim on the coupling flange and rotates the shaft. (see
Attachment 6.27)
3.8.1
The exhaust system conveys hot exhaust gas from
the gas turbine either to the atmosphere or to the waste heat recovery boiler.
The exhaust system is designed to achieve maximum possible energy recovery from
the hot turbine exhaust gas. Therefore the exhaust gas must be channeled
through a relatively unobstructed and heat insulated path to the waste heat
recovery boiler. The exhaust gas system provides such path.
3.8.2
The exhaust system consists of the following
major components that are arranged sequentially after the turbine section:
3.8.2.1
Exhaust casing
3.8.2.2
Exhaust diffuser
3.8.2.3
Exhaust ducting and silencer
3.8.3
Exhaust Casing
3.8.3.1
The exhaust casing is bolted to the center
casing at the downstream end of the turbine and provides a flow path for the
exhaust gas. The exhaust casing also supports the turbine bearing.
3.8.3.2
Attachment 6.28 shows sectional views of the
exhaust casing. It is of welded construction and horizontally split; it
comprises an outer and inner cylinder that are connected through oval tubes and
struts. Flanges are provided at the two ends for connection to center casing
and the exhaust diffuser.
3.8.3.3
The inner cylinder of the exhaust casing
accommodates the turbine bearing housing with oil supply and return lines
passing through the oval tubes. A liner with lagging protects the supporting
walls and struts against the hot exhaust gas.
3.8.4
Exhaust diffuser
3.8.4.1
The turbine exhaust gases pass from the turbine
to the exhaust ducting through the exhaust diffuser. Attachment 6.29 shows a
schematic view of the exhaust diffuser.
3.8.4.2
The exhaust diffuser comprises of a tapered duct
with a welded expansion joint at each end; the diffuser takes up expansion and
contractions resulting from gas turbine startup, shutdown and normal operation.
3.8.5
Exhaust ducting
3.8.5.1
The exhaust gases discharge from the exhaust
diffuser into the exhaust ducting is shown in Attachment 6.30. The exhaust
ducting routes the exhaust gas either to the bypass stack (chimney) or through
the waste heat recovery boiler that connected to the gas turbine.
3.8.5.2
The Wahlco Diverter damper of two fully
insulated blade located just before the branch to the chimney controls the flow
of gas, diverting it to the chimney during open-cycle operation and through the
waste heat boiler during combined cycle operation. The Wahlco diverter damper
and ducting downstream of it is described in the document LP-SD-HA*.
3.9.1
The inner casing, the turbine stator and the
turbine blading are exposed to the hot gas flow and therefore made of high
temperature alloys. Since the temperatures are far beyond the tolerable
material temperature, these components have to be effectively cooled. (See
Attachment 6.31)
3.9.2
Cooling improves the service reliability of the
items in the hot gas path by significantly increasing their resistance to high
temperature corrosion. At several points in the hot turbine region sealing air
and seal air located so that the hot gas is blocked from escaping into
neighboring spaces. These will protect other components especially the rotor
drum against overheating.
3.9.3
The cooling and seal air of stages 1 and 2 of
the turbine stator is taken from the compressor discharge air flowing to the combustion
chamber and for stages 3 and 4 from the compartment of compressor Blow-Off
System 2 after the 10th compressor stage. Following components are
provided with cooling air:
3.9.3.1
Turbine inner casing
The outer surface is cooled with compressor discharge air.
Portions where the flow velocity would be too low and for ensuring sufficient
cooling are provided with cooling air baffles to obtain a defined passage for
directing the air flow over the inner casing.
3.9.3.2
Surfaces facing the hot gas
3.9.3.2.1
These surfaces defined are the outer shrouds of
the turbine stator blades and the turbine rotor hub section.
3.9.3.2.2
These surfaces are wrapped in a layer of cooling
air that is used for cooling the turbine inner casing and enters the hot gas
path through the circumferential slots between the inner casing and both the
outer and inner shrouds of the first stator blades.
3.9.3.2.3
A second cooling air flow for the hub section
enters the hot gas path between first stage stator and rotor blades. It is used
as sealing air between the compressor exhaust diffuser and the rotor and flows
through the annular space between the protective liner and rotor.
3.9.3.3
Turbine stator blades
3.9.3.3.1
The cooling air for stator blade rows no.1 and 2
is ducted from the compressor via the spaces between stator blade carrier and
the outer shrouds into the hollow airfoil sections.
3.9.3.3.2
The cooling air leaves the blades through bores
at the trailing edges of the stator blades and is mixed with the hot gas. At
stator blades row no.2, a portion of the airflow to the U-ring, which is part
of the hub section and is used as seal air.
3.9.3.3.3
At stator blade rows no.3 and 4, the cooling air
from the compressor air bleed at stage no.10 flows into the relevant spaces
between the stator blade carrier and the outer shrouds of the stator blades.
Thus, the outer confinement of the hot gas path is cooled. At blade row no.3
the cooling air flows to the U-ring and is also used as seal air at the rotor
seals.
3.9.3.4
Turbine rotor blades
3.9.3.4.1
The cooling air for the rotor blade rows nos.1
and 2 passes radial bores at the central hollow shaft and is conveyed to the
hub bores of the turbine rotor discs and enters the blades through openings at
the bottom of the root fixings.
3.9.3.4.2
In the rotor blades of stage no.1, the cooling
air passes through an internal duct that is twisted in the radial plane and
leaves the blade through a lot of small bores at the trailing edge of the
airfoil section (see Attachment 6.24).
3.9.3.4.3
At stage no.2 the internal ducts consists of
radial bores so that the cooling air leaves the blades at the tip seal.
Note: See Attachment 6.31.
3.9.3.5
Rotor blade root fixings
A fraction
of the rotor cooling air passes the axial slots at the root fixings so that the
rotor discs are protected. This air is mixed to the hot gases at rear ends of
the blade platform.
3.9.3.6
Turbine bearing
A small
portion of the air flows through a pipe from Blow-Off System 1 downstream of
the fifth-stage rotor compressor blades into the hollow support strut to the
turbine bearing casing thus protecting the rotor and bearing region from the
hot turbine exhaust gases.
3.10.1
There are two types of bearings used in the gas
turbine unit; journal and thrust bearings. Journal bearings support the
compressor-turbine rotor assembly and ensure the rotor on radial position.
Thrust bearings absorb axial thrust generated by the gas turbine unit and
position the rotors axially.
3.10.2
Two main journal bearings, the compressor and
turbine bearings support the gas turbine unit. The compressor bearing also
contains the thrust bearing. The two bearing assemblies are located in their
respective housing; the compressor bearing housing at the compressor intake
duct and the turbine bearing housing at the exhaust casing, respectively.
3.10.3
All bearings are lubricated by oil supplied from
the main lubricating oil system. Branch lines from the lube oil header feeds
oil to each bearing housing. The lubricating Oil System is described in Section
3.12
3.10.3.1
Compressor Bearing (Combined Journal and Thrust
Bearing)
3.10.3.1.1
Attachment 6.32 shows the compressor bearing
housing located in the compressor inlet casing assembly and the cross section
of the compressor bearing.
3.10.3.1.2
The bearing housing contains the combined
journal and thrust bearing and supports the rotor and the turbine/compressor
unit. It forms part of the outer casing and connects stator blade carrier 1 to
the compressor intake casing.
3.10.3.1.3
The housing comprises an outer and inner shell
which form the compressor intake duct. The outer and inner shells are connected
through struts. The inner cylindrical space of the housing accommodates the
bearing and associated pipework and measuring instruments. Bearing seal rings
seal the shaft at the front and rear ends. The hydraulic turning gear is
installed on the rotor at the front end of the compressor bearing housing.
3.10.3.1.4
The journal bearing is made up of two half
bearing sleeves. The active surfaces are lined with white metal (babbitt) and
shaped so that supporting oil wedges are produced between the bearing and the
shaft journal during operation.
3.10.3.1.5
The bearings are of the oil cooled type, with
pressurized oil supply from the lubricating oil header. Oil is fed from one
side of the horizontal joint formed by two bearing sleeves; as the rotor turns,
it produces a pumping action that builds up pressure and a film of oil between
the journal surface and the babbitt so that in normal operation, the surfaces
never touch.
3.10.3.1.6
Lubricating oil is fed to the bearing oil
pockets through ducts in an adjusting ring, annular groove and a groove in the
upper half bearing sleeve. For startup and shutdown, high pressure shaft lift
oil is admitted via ducts to maintain fluid friction. This oil film protects
the white metal surface from damage and provides for easy turning of the shaft.
The temperature of the white metal is monitored with a thermocouple screwed
into the lower half bearing sleeve at the point of maximum load.
3.10.3.1.7
The thrust forces of the axial flow compressor
are partially compensated by reversed thrust forces of the turbine. The
resultant thrust load tends to move the rotor assembly in a direction opposite
to that of the airflow through the compressor. During normal operation of a gas
turbine, the thrust load of the unit acts in one direction i.e. against the
direction of air flow.
3.10.3.1.8
However, during startup and shutdown of the
unit, the direction of the thrust load will generally reverse. Thus the need
for two thrust bearing surfaces, one on either side of the rotating thrust
collar. The bearing that takes the thrust load during normal operation is
called the ‘active’ or ‘loaded’ thrust bearing and that takes the thrust load
during startup and shutdown of the unit is called the ‘inactive’ or ‘unloaded’
thrust bearing.
3.10.3.1.9
Thus the ‘loaded’ bearing is at the forward end
and the ‘unloaded’ bearing is at the aft end of the thrust collar. The thrust
bearing consists of individual thrust pad whose active surfaces are lined with
white metal.
3.10.3.1.10
The thrust pads are secured in a bearing sleeve,
located with cylindrical pins and supported on shims for uniform load
distribution. Tilting edges at the bearing faces provide for self-alignment of
the pads and thus for the formation of the oil wedges. The axial forces are
transmitted to the bearing housing through the bearing sleeve and replaceable
shims.
3.10.3.1.11
Lubricating oil is admitted from the laterally
open oil pockets of the journal bearing. Seal strips throttle the flow of drain
oil. Baffles contain an annular space where the side leakage oil is collected
from being drained via slots.
3.10.3.1.12
The temperature of the white metal is monitored
through thermocouples installed in the upper and lower half bearing sleeves at
both ends of the bearing. The spherical seating of the bearing sleeve is held
in an adjusting ring that is supported on the bearing housing with locators
providing for horizontal and vertical alignment.
3.10.3.1.13
Replaceable shims under the locators permit the
radial position of the rotor to be changed. A retaining pin prevents the
bearing and the adjusting ring from turning in the bearing housing.
3.10.3.2
Turbine Bearing (Journal Bearing)
3.10.3.2.1
Attachment 6.33 shows the turbine bearing housing
located in exhaust casing and the sectional views of the journal bearing. The
bearing housing supports the rotor in the exhaust casing. The bearing housing
that is located in the inner cylinder of the exhaust casing to allow for
thermal expansions, is supported on brackets below the horizontal shaft center
line and on a centering device, which determine the height and lateral location
of the bearing.
3.10.3.2.2
The bearing housing accommodates a journal
bearing with adjusting ring. The oil space is closed off by an adjustable
bearing seal ring at the inboard end and by a cover at the outboard end. The
lubricating oil is admitted to the bearing via the supply tubes shown and
drained through the hollow ribs in the exhaust casing. The bearing cover is
provided with insulation to protect against heat.
3.10.3.2.3
The turbine journal bearing supports the rotor
in the bearing housing at the turbine end. The active surfaces of the bearing
are lined with white metal and shaped so that supporting oil wedges are
produced between the bearing and the shaft journal during operation.
Pressurized lubricating oil is fed to an oil pocket via ducts in an adjusting
ring, annular groove and duct in the lower bearing sleeve and then passed to an
oil pocket via groove in the upper half bearing sleeve.
3.10.3.2.4
For startup and shutdown, high-pressure shaft
lift oil is admitted in order to maintain fluid friction. This oil film
protects the white metal surface from damage and provides for easy turning of
the shaft. Baffles contain one annular space each where the side leakage oil is
collected before being drained through drain holes. The temperature of the
white metal is monitored with a thermocouple screwed into lower half bearing
sleeve at the point of maximum load.
3.10.3.2.5
The spherical seating of the journal bearing is
held in an adjusting ring. The upper half adjusting ring is designed as a
bearing saddle and bolted to the bearing housing. The lower half adjusting ring
is supported on the bearing housing, with locators provided for horizontal and
vertical alignment. Replaceable shims under the locators permit the radial
position of the rotor to be changed. A retaining pin prevents the bearing and
the adjusting ring from turning in the bearing housing
3.11.1
Shaft glands are used to minimize leakage
between spaces with different pressures at places where rotating parts meet
stationary parts. The reliability and the efficiency of the unit depends
essentially on an optimum shaft gland design: The gland clearance has to be
large enough so that touching is avoided at all operating conditions and it
must be close enough to avoid excessive losses of compressed air or hot gas.
3.11.2
In the case of hot gas glands, it is necessary
to avoid hot gases blowing through the narrow gaps, because the surfaces would
be overheated due to the very efficient heat transfer at high flow velocity.
Thus bleed air is conveyed from the compressor to those glands so that
relatively cold air pushes the hot gases back. At the hot turbine parts, this
seal air was used first as cooling air.
3.11.3
The gas turbine rotor penetrates the compressor
and turbine stators at each end of the compressor and turbine respectively. The
internal pressure at these shaft penetrations are appreciably higher than
atmospheric pressure. In the absence of shaft glands the following would occur:
3.11.3.1
at the inlet end of the compressor, oil laden
air from the compressor bearing housing would be drawn into the compressor
3.11.3.2
at the discharge end of the compressor,
compressed air would flow directly to the turbine section along the cooling
ducts, bypassing the combustion chambers
3.11.3.3
at the outlet end of turbine, hot combustion gas
would leak into the turbine bearing housing.
3.11.4
The compressor and turbine inter-stage seals
prevent cross-leakage of compressed air/combustion gas from one stage to next.
The turbine/compressor shaft glands are of a non-contacting labyrinth type. The
word ‘labyrinth’ means ‘a difficult or complex path to follow’. Labyrinth seals
are provided both on the rotating and stationary components.
3.11.5
Attachment 6.34 shows sectional view of the two
types of shaft glands provided. The major part of the labyrinths on the
stationary components are designed as seal strips that are secured in grooves
by caulking (design A). In the high temperature region, integrally machined
teeth (design B) are provided. If the teeth are damaged, caulked seal strips
may be subsequently inserted.
3.11.6
The labyrinths on the stationary part are more
closely spaced and consist of single-thread spirals with a pitch opposing the
direction of leakage air flow. As compressed air or combustion gas leaks past
the narrow spaces between the seal strips/teeth and stationary parts, its
pressure drops. The pressure of the compressed air/combustion gas is greatly
reduced by the time it travels from one end of the seal to the other.
3.11.7
Compressor Shaft Glands
3.11.7.1
Attachment 6.34 shows the sectional views of the
compressor shaft glands. In the region of the compressor inlet, i.e. at the
front hollow shaft, the shaft glands have to avoid sucking of oil vapor from
the compressor bearing housing into the flow path.
3.11.7.2
To this purpose atmospheric air enters the space
at the rear side of the bearing housing. Due to the slight vacuum provided by
the oil vapor extractor that seal air is sucked into the lube oil tank.
3.11.7.3
A second seal air flow consists of atmospheric
air that is sucked through the gland into the space downstream the inlet guide
vane due to the pressure losses in the air path from ambient conditions.
Between the inner rings of the compressor stator blades and the rotor discs,
labyrinth seals are provided to minimize back-flow of compressed air.
3.11.8
Center Hollow Shaft Glands
3.11.8.1
Attachment 6.34 shows the sectional views of the
center hollow shaft glands. A gland is arranged between the center hollow shaft
and the compressor exhaust diffuser conveying air that is tapped downstream the
last compressor rotor stage.
3.11.8.2
The major part of this air flows through radial
bores and the interior of the rotor to the turbine rotor discs and is used for
cooling the turbine rotor blades and the root fixings.
3.11.8.3
The remaining part of the seal air flows after
having passed the gland to the front face of the turbine first stage rotating
disc and enters the hot gas path through the gap between the inner shrouds of
the first stage stator respectively rotor blades.
3.11.9
Turbine Glands
3.11.9.1
Attachment 6.34 shows the sectional views of the
turbine glands. Pressurized air is bled from different stages at the compressor
and conveyed to the spaces between the turbine stator blade carrier and the
outer shrouds of the turbine stator blade.
3.11.9.2
It flows through the hollow stator blades to the
inner U-rings and enters through a set of bores the space between the
proceeding rotating blade and the actual stator blade.
3.11.9.3
A part of the air is mixed directly to the hot
gas at the stator blade inner shroud, whereas the other part flows first
through the labyrinth seal and is mixed to the hot gas at the rear side. This
applies for stator blades of the stages 2 and 3.
3.11.10
Rear Hollow Shaft Glands
3.11.10.1 Attachment
6.34 shows the sectional views of the rear hollow shaft glands. The hot gas
flow exerts at the shaft a certain force in axial direction (thrust) towards
the turbine end. This force is compensated by the thrust bearing at the
compressor end.
3.11.10.2 To
relief the thrust bearing, the pressure at compressor blow off system 1 is
admitted to the space at the rear side of the rear hollow shaft via external
pipe work.
3.11.10.3 The
seal air flows partly through the seal to the rear end of the turbine rotor
blades of stage no. 4 and the other part to the turbine bearing housing. Thus
both the hot gases of the turbine exhaust and the oil vapor of the turbine
bearing housing are separated from each other and pollution by lube oil around
the bearing is largely avoided.
3.12.1
The lube oil system supplies oil to the bearings
of the gas turbine and generator, the turning gear and the control oil system.
The lube oil pumps convey the oil from the tank via the cooler, the temperature
control valve and the filter to the bearing oil forward line. From here the oil
flows through restrictors to the individual consuming units and finally flows
into the tank without being subject to pressure.
3.12.2
The main bearings are in addition supplied with
lift oil that is pumped by the lift oil pump through throttle valves to the
bearings. Turbine lube oil is a mineral oil with additives that protect
corrosion, oxidation, foaming, emulsification and wear in relative to the
solidification point, thus the oil viscosity are adjusted.
3.12.3
The most important properties of oil are as
follows:
3.12.3.1
Viscosity
The
viscosity is the measure for the resistance of a fluid against shifting of
neighboring layers by inner friction. This property is important for forming a
lubrication film in the bearings. It is a function of the oil temperature.
3.12.3.2
Air Release Ability
During the
lube oil circulation, the lube oil absorbs air in the clearance at the bearings
and in the hydraulic turning gear. Together with the returning lube oil the air
is collected in the lube oil tank, where the air is separated more or less
quickly. Too much air in the lube oil causes problems in the lube oil pumps and
aging of the oil due to oxidation. The air release ability is defined as the
time that is necessary to release the air content down to 0.2% by volume. This
period of time is a function of the temperature. At 50oC air release
takes 5 minutes and at 25oC it takes 15 minutes.
3.12.4
The functions of the lubricating oil system are
to:
3.12.4.1
to lubricate the turbine and generator bearings
under all operating conditions of the gas turbine generator set even in the
case of AC power failure
3.12.4.2
to cool the turbine and generator bearings
3.12.4.3
to drive the hydraulic turning gear
3.12.4.4
to lift the shaft at low speed
3.12.4.5
to supply oil at proper pressure to the control
oil system
3.12.4.6
to supply oil at proper pressure to the trip oil
system
3.12.4.7
to condition the lube oil, i.e. cool the oil to
a constant inlet temperature at the bearings, to filter the lube oil and to
extract oil vapor.
3.12.5
The lube oil is stored in the lube oil tank. It
contains the oil required for lubrication, cooling and control of the turbine
generator. The lube oil is filled into the tank via an oil strainer. Air and
gases that are entrained into the lube oil are collected at the top of the tank
and removed by the oil vapor extracting system.
3.12.6
The two main lube oil pumps are submerged into
the oil tank. Their task is to supply all users with sufficient oil. One DC
driven lube oil pump cools and lubricates the bearings in the event of main
lube oil pump failure and consequent coasting down of the turbine generator
set. This pump supplies the oil directly into the lube oil supply header, i.e.
the cooler and the lube oil filter are bypassed in this operation mode, thus DC
energy is saved.
3.12.7
Downstream the main lube oil pump, the heat of
the oil is dissipated through the air-blast oil cooler. The lube oil flow that
bypasses the oil cooler is controlled so that a constant inlet temperature at
the bearings are achieved. Downstream the cooler, the duplex lube oil filter is
located, which remove the foreign matter. Only one of the filter is in
operation whereas the other one is in standby.
3.12.8
In front of each bearing an orifice is installed
in its oil supply line that allows for adjusting lube oil pressure and flow.
The oil for the turning gear is tapped downstream the main lube oil pumps and
to the oil turbine nozzle via a ball valve.
3.12.9
In the shaft lift oil system, a high pressure
pump supplies the lube oil from the lube oil tank through a filter and a
separate distribution header to the oil pockets at the bottom of every bearing
in order to avoid metal to metal contact at the bearings during low speed.
3.12.10
The lube oil tank is located inside the turbine
building between the gas turbine air intake casing and the generator. All lube
oil supply components are installed on top of the tank except the rotary vane
pump located on the concrete foundation adjacent to the tank and the oil/air
heat exchangers are located outside the building next to the gas turbine
exhaust duct. The respective components of the control oil system is also
located on top of the tank.
3.12.11
The lubricating oil system comprises of the
following main components:
3.12.11.1 Lube
Oil Tank [1MBV10-BB001]
3.12.11.2 AC
Main Oil Pump 1 [1MBV21-AP011]
3.12.11.3 AC
Main Oil Pump 2 [1MBV21-AP012]
3.12.11.4 DC
Emergency Lube Oil Pump [1MBV21-AP021]
3.12.11.5 AC
Shaft Lift Oil Pump [1MBV31-AP011]
3.12.11.6 AC
Rotary Vane Pump [1MBV30-AP011]
3.12.11.7 Oil
Tank Vapor Extractor Fan [1MBV50-AN011]
3.12.11.8 Oil
Temperature Control Valve [1MBV24-AA001]
3.12.11.9 Pressure
Limiting Valves [1MBV31-AA031 and MBV30-AA031]
3.12.11.10 Turning
Gear Solenoid Valve [1MBV41-AA001]
Note: Refer to Attachment
6.35 for detail Lube Oil System.
3.12.12
Lube Oil Tank
3.12.12.1 The
lube oil tank stores all lubrication and control oil which is used at the gas
turbine generator set. The oil tank also serves as a mounting platform for the
oil pumps, filters, and control oil components, the fuel gas emergency stop
valve and the fuel control valve.
3.12.12.2 The
total tank capacity amounts to **[as11]
m3 and when all pipes and components of the system are filled the
tank contains **[as12]
m3 which represents the normal oil level.
3.12.12.3 The
tank is sized thus the complete oil volume is circulated at a rate of 8 m3
per hour. Thus the residence time of the oil between admission to the tank and
discharge from the pumps is approximately 7 to 8 minutes. This allows for
releasing entrained air and settling of impurities.
3.12.12.4 The
oil returning from the system reaches the riser of the tank, where a first
degasification takes place. From there the oil flows through strainers into the
neighboring chamber. At the end of this chamber, i.e. at the end of the
separator wall, the oil flow makes an U-turn into the suction chamber of the
pumps thus ensuring the residence time is as long as possible.
3.12.12.5 The
strainers are of the screen basket type with mesh width of approximately 0.3 mm. They can be
changed or cleaned after opening the man hole on the tank top. The bottom of
the tank is slopped so that the tank cam be drained at its lowest point via the
drain valve [1MBV10-AA201].
3.12.12.6 The
tank is air-tight. Air and gases are removed by the oil vapor extractor
[1mbv50-an011]. The extractor consists of an impeller that maintains a sub
atmospheric pressure of 2 mbar, which is also transmitted to all bearing
casings via the large oil back-flow pipes and preventing the oil contamination
in the vicinity of the shaft glands.
3.12.12.7 Oil
droplets that are extracted together with the gases are collected in the
separator [1MBV50-AT001] downstream the vapor extractor and return back to the
tank. The oil level in the tank is measured locally by level gauge [1MBV10-CL501]
and remotely by electric level transmitter [1MBV10-CL011[as13]].
(Note:
See Attachment 6.35 Lube Oil Tank Layout)
3.12.13
Main Lube Oil Pumps
3.12.13.1 The
main lube oil pumps draw oil from the oil tank and supply the lubricating oil
to the generator, compressor and turbine bearings via a strainer and oil
cooler. Oil discharge from the bearings drain back to the oil tank. Either main
oil pump 1 or 2 is sufficient to maintain the required lubricating oil supply
pressure and flow. Orifice plates control the oil pressure to the various
components in the oil circuit.
3.12.13.2 One
of the two main lube oil pumps (2 x 100%) discharge the oil to the lube oil and
the control oil systems at a pressure of approximately 5 bars. Normally only
one of the pump is in service during nearly the entire operating time of the
gas turbine so that in case of a pump failure the other pump is available.
3.12.13.3 The
main lube oil pumps are driven by AC motors. In the case of unit power supply
failure the unit is tripped and during coasting down the DC driven emergency
lube oil pump protects the bearings from damage.
3.12.13.4 The
main lube oil pumps are of the single-stage, centrifugal type with vertical
shaft. The pump is driven by the electric motor through a flexible coupling.
The pump is submerged into the oil. The suction mouth is approximately 700 mm
below the normal operation oil level whereas the lube oil level low alarm point
is set at 445mm.
3.12.13.5 The
pump discharge penetrates the cover plate of the tank. The pump shaft is
supported at the impeller end by a journal bearing and at the motor by a
deep-groove ball bearing. The bearings are lubricated with oil obtained from
the pump discharge, the journal bearing via a bore in the volute, and the
deep-groove ball bearing via a lubricating oil line.
3.12.13.6 Labyrinth
rings in the volute casing and suction nozzle mate with seal faces on the pump
impeller to seal the pump discharge from the pump suction. The oil flows
through the suction nozzles to the impeller in the volute casing, is
pressurized and delivered to the oil system through pump discharge nozzle. The
pump discharge pressure is approximately 5 barg.
Note: See Attachment 6.36.
3.12.14
Emergency Lube Oil Pump
3.12.14.1 The
emergency lube oil pump supplies the bearing with lube oil for the following
reasons:
·
in the event of unit power supply failure
·
the lube oil pressure decreases below a certain
value (< 1 barg) and the unit is
tripped.
3.12.14.2 The
emergency lube oil supply is not in service during normal operation. It feeds
directly into the bearing lube oil supply header bypassing the oil coolers and
filter so that, due to the smaller discharge pressure, the DC power source is
saved.
3.12.14.3 The
DC pump drive is arranged on top of the main oil tank whereas the pump is
submerged into the oil tank suction chamber. The suction mouth is approximately
700 mm below the normal operative oil level. The pump discharge penetrates the
cover plate of the tank. The pump shaft is supported at the impeller end by a
journal bearing and at the motor end by a ball bearing.
Note: See Attachment 6.36.
3.12.15
Shaft Lift Oil Pump
3.12.15.1 This
pump supplies oil at high pressure at the bottom of the bearings so that an oil
wedge in cases of low rotational speed carries the turbine shaft.
3.12.15.2 As
the gas turbine shaft coasts to rest, mixed friction occurs in journal bearings
at shaft speeds less than 200 rpm. At low speeds of the turbine during startup
and shutdown, the hydraulic shaft lift oil system is required to build up and
maintain an oil film between the shaft and the bearings and to provide almost
hydrodynamic lubrication.
3.12.15.3 When
the unit is started, the shaft is lifted to reduce the torque needed to be
developed by the turning gear. A motor driven shaft lift oil gear pump supplies
high pressure oil that is admitted below the individual shaft journals. The
high pressure oil lifts the shaft by building up required oil film between the
bearing sleeve and the shaft.
3.12.15.4 The
lift oil pump is of the rotating displacement type. Two eccentrically machined
double-cam rotors with 90 degree phase angle mounted on the pump shaft rotate
in two ring-shaped stators. Each stator has two integrally machined inlet ducts
and outlet ducts on opposite sides. Radially movable blades as separators
between the suction (inlet) and discharge (outlet) spaces located in two slots
on the rotor.
3.12.15.5 The
stators, the rotors and the blades form four rotating spaces in which at all
times the pressure in the opposing spaces is equal. Thus, no free torque has to
be compensated. Due to rotor shape, uniform oil flow is achieved because the
total sum of both the suction and discharge flow is constant during one
revolution.
Note: See Attachment 6.37.
3.12.16
Rotary Vane Pump
3.12.16.1 This
pump supplies oil at high pressure at the bottom of the generator bearings so
that an oil wedge in cases of low rotational speed carries the generator shaft.
3.12.16.2 To
reduce the generator bearing friction during low speeds, the generator bearings
are supplied with lifting oil or jacking oil by the rotary vane pump. Oil flows
via check valve [1MBV30-AA051] to the rotary vane pump that supplies the
generator bearings with the lifting oil.
3.12.16.3 Then
the oil flows via filter [1MBV30-AT001] for cleaning. The safety valve
[1MBV30-AA031] limits the pressure in the event of high pressure.
3.12.17
Lube Oil Coolers
3.12.17.1 The
function of the lube oil coolers is to keep the bearing oil temperature at 50
to 55oC by dissipating the heat which is transferred to the oil at the bearings
and in the pumps. This temperature is achieved by means of the three-way valve
(Thermostatic Valve) downstream the air-cooled lube oil cooler that controls
the lube oil cooler bypass.
3.12.17.2 Forced
draft type fin fan air coolers consist of 3 X 50% Fan Cooler Cell of the
required capacity are provided to cool the lube oil. Each unit cooler fan is
driven by direct-coupled 2 x 50% 380 VAC 50 Hz electrical motor. Manual
operated valves are provided upstream (inlet valve provided with locking device
and position indicator) and downstream (outlet) for each fan cooler cells to
allow for easy maintenance.
3.12.17.3 Each
fan cooler cell is equipped with priming and drain valves used to prime the
lines and coolers tubes to ensure no air blocks or air bubbles in the system.
The inlet and outlet lines are connected to their inlet and outlet common
headers respectively. Each fan cooler unit is equipped with pressure indicator
in the inlet [KKS] and outlet line to monitor the pressure drop across the
cooler and a local temperature indicator [KKS] in the outlet line to regularly
monitor the outlet lube oil temperature.
3.12.17.4 The
air-cooled coolers common inlet and outlet header is equipped with local
pressure and temperature indicators as well as remote high temperature switch
connected to the DCS system.
3.12.17.5 The
cooler comprises of bundles of finned tubes in a staggered arrangement across
the airflow direction. Lubricating oil arrives at the inlet header and
distributed to the 2 x 50% in-service fan coolers and the discharge pipes from
the cooler sections connect to a return header, which channels the cooled
lubricating oil to the gas turbine/generator bearings.
3.12.17.6 The
cooler is fitted with a three-way temperature controlled bypass valve, which controls
the flow of oil through the cooler to maintain the oil temperature downstream
of the three-way valve to between 40oC and 52.5oC.
3.12.17.7 Until
the lubricating oil reaches a temperature of 40oC, all oil flow is
through the bypass line. When the lubricating oil reaches a temperature of >
52.5oC, all oil flow is through the cooler. A first stage alarm
annunciates when the lubricating oil temperatures reaches 56oC. A
second stage alarm annunciates when the lubricating oil temperature reaches 100oC.
The gas turbine has an high lubricating oil temperature trip protection trip
interlock set at 120oC. The bypass line is fitted with an orifice
plate to compensate for the pressure drop across the cooler.
Note: See Attachment 6.38.
3.12.18
Oil Filters
3.12.18.1 The
lube oil passes strainers and filters for protecting the bearings, seals and
the control system components. Coarse particles are collected in the basket
strainers in the main oil tank. The total oil flows passes these strainers
prior to being pumped forward. The lubricating oil is filtered in a double
(duplex) filter. The duplex filter comprises of two filter housings, which are
interconnected by a changeover valve assembly. Only one filter is used during
normal operation and the other one is in standby.
3.12.18.2 Each
filter housing contains a screen-type filter element whose individual
double-shell strainers are concentrically arranged. To protect the wire mesh,
the outer strainers are surrounded by a wide-mesh protective screen. The cover
flange has a vent fitted with a manual valve. The oil can drain via drain plugs
at the bottom of the filter housing. The change-over valve assembly comprising
two valve discs, permits a smooth changeover. Pressure equalizing and a filter
line facilitates changeover at high operating pressures and is used for filling
the empty filter housing. The filter chambers should be regularly vented.
3.12.18.3 To
effect a filter change-over the operator has to manually opens vents on the
both filter housing with the change over valve in its center position, i.e.
when both filter pots are in service. When oil starts to emerge after the air
has been displaced the vents are closed. The operator has to manually switch
over to the standby filter by actuating the changeover valve assembly.
3.12.18.4 The
operator has to take care that the clogged filter is cleaned, reassembled,
filled with oil and carefully vented so that during operation there is always
at least one clean filter available. Both the filters are never left in service
simultaneously as a filter changeover will then no longer be possible when both
filters are contaminated. A shutdown of the unit for filter cleaning would then
be required.
3.12.18.5 The
duplex strainer is fitted with a differential pressure assembly which measures
and displays the differential pressure across the filter. The differential
pressure switch has two electrical contacts which make at two limits of an
adjustable pressure difference. The service filter element should be cleaned
when the pressure drop across the filter reaches the 0.8 bar[as14].
This pressure drop can be read at differential pressure indicator
[1MBV25-CP011].
Note: See Attachment 6.39.
3.12.18.6 In
the shaft lift oil pump suction line a magnetic strainer type filter is
installed which traps magnetic and non-magnetic particles. An indicator issues
a locally visible signal if this filter is clogged.
3.12.18.7 The
magnetic filter and the contamination indicator form one unit, which is
enclosed in a housing. The filter inlet and outlet are located at diametrically
opposite points. The filter housing contains a filter element consisting of a
magnet assembly and a double-shell strainer cage.
3.12.18.8 Ferrous
particles are retained on the outer circumference of the magnet assembly.
Coarse non-magnetic particles are arrested on the inner cylinder of the
strainer cage and fine particles on the outer cylinder. The inner cylinder has
several openings, which minimize the pressure drop and ensure continuous
flushing of the outer cylinder. Uniform clogging of the outer strainer is thus
prevented.
Note: See Attachment 6.39.
3.12.19
Oil Vapor Extractor
3.12.19.1 The
oil vapor extractor produces a slight vacuum in the oil tank and in the bearing
housings to prevent oil from escaping between the shaft and the housing. The
oil tank is bolted airtight and the oil pipes connecting it to the oil tank are
properly sealed; an uncontrolled ingress of air into the oil tank would impair
the effective performance of the oil vapor extractor. The oil vapor extractor
is mounted directly on oil tank and comprises of a fan and a three-phase AC
driven motor.
3.12.19.2 The
motor driven fan draws air from the oil tank and discharges it to the
atmosphere via a pipe connected to the lower part of the fan. The oil droplets
entrained in the air are thrown out by the centrifugal force. An oil drain cock
is provided at the lowest point of the discharge pipe. To ensure unobstructed
venting of the air to the atmosphere, the oil collecting in the pipe should be
drained at regular intervals and at least once per month. The oil vapor
extractor stops when all lubricating oil pumps are shutdown.
Note: See Attachment 6.40.
3.12.20
Oil Temperature Control Valve
3.12.20.1 The
oil temperature control valve (Thermostatic Valve) is designed to maintain the
bearing inlet oil temperature at 50 to 55oC. The thermostatic valve
is a 3-way valve, which is self-controlled by a temperature detector.
3.12.20.2 During
startup of the gas turbine and when the lube oil is cold the valve prevents the
oil flow to enter the lube oil cooler and leads the oil flow directly to the
bearings.
3.12.20.3 When
the lube oil temperature has reached the preset value the valve adjusts the oil
flow which bypasses the lube oil cooler. The 3-way action of the Thermostatic
Valve allows a constant flow rate of lube oil through the main lube oil pumps
at all times with no pump restriction even when the gas turbine generator is
still cold.
Note: See Attachment 6.40.
3.12.21
Pressure Limiting Valves
The pressure limiting valve keeps the pressure in the lift oil
pressure header constant. If the pressure rises above the set point of its
spring (about 120 bar for turbine and **
bar[as15]
for generator) the excess oil is fed back to the oil tank. The actual pressure
at the bearings is individually adjusted by throttles.
3.13.1
The control oil system is directly connected to
and supplied from the lube oil system. The control oil also connected to the
trip oil system as secondary oil system. The control oil system is used to
supply oil of about 9 bar to control the fuel flow to the gas turbine. The
secondary oil controls the hydraulic setpoint for the required fuel control
valve position. Since these oil system perform several hydraulic functions the
medium is sometimes referred to as “hydraulic oil”.
3.13.2
The control oil system serves the purpose of
positioning the valve cone of the fuel gas fuel oil control valves in such a
way that the quantity of fuel required by the control system is adjusted
correspondingly. The control oil system provides the working fluid for the
hydraulically actuated control valves and for the trip oil system at the
required pressure and quantity.
Note: See Attachment 6.41 for Control Oil System
Schematic Diagram
3.13.3
Control Oil Supply System.
Note: See Attachment 6.42.
3.13.3.1
Control oil serves as the hydraulic fluid used
at the various valve actuators and at the pilot valves. A predetermined oil
flow is taken from the lubricating oil circuit through a branch line and fed to
the control pump [1MBX21-AP001]. It is filtered [1MBX20-AT001] and is brought
to a pressure of about 8 to 9 bar by the control oil pump.
3.13.3.2
If the control oil pump fails during operation, the
lubrication oil remains available at a pressure of about 4 to 5 bar via the
check valve [1MBX21-AA051]. Operation continues to be possible at this
pressure, but a start-up of the unit is not possible with this low control oil
pressure.
3.13.3.3
In the event of a sudden pressure drop, the
control oil pressure is maintained by hydraulic accumulator [1MBX21-BB001]. The
accumulator serves to ensure that sufficient control oil is available in the
event of control operations. It is charged with nitrogen at about 4 to 5 bar
via the check valve [1MBX21-AA052] by means of a charging device forming part
of the tool kit. To this end cock [1MBX21-AA101] is closed and cock
[1MBX21-AA201] is opened. After the charging operation is over, the above
mentioned cocks are returned to their normal position.
Note: Nitrogen charging of the accumulators takes
place when there are no demands on the control oil system, i.e. when the gas
turbine is at standstill or during turning gear operation of the gas turbine.
3.13.4
Secondary Oil System
3.13.4.1
Part of the control oil is fed to the trip oil
circuit via changeover valve [1MBX22-AA001] and remote trip-out solenoid valve
[1MBX41-AA001].
3.13.4.2
The secondary oil pressure is the hydraulic
setpoint value for the position of the relevant fuel control valve. At a secondary
oil pressure of approximately 1.5 bar, the fuel control valve is the zero load
position. At approximately 3.3 bar, it is in the full load position.
3.13.4.3
The secondary oil system is supplied with oil
via throttle at a supply pressure of about 8 to 9 from the trip oil system.
Thus in the event of an emergency shut-off, the control valves are at zero load
position immediately after the trip release.
3.13.5
The following are the devices used in the
control oil system:
3.13.5.1
Electro Hydraulic Converter for fuel gas and light
fuel oil [1MBX52-BY021 and 1MBX52-BY011] (see Attachment 6.43 for the sectional
view of EHC) The electro-hydraulic converter is the link between the electrical
and hydraulic parts of the control system. It converts the signal received from
the electric controller into hydraulic signals and amplifies them before they
ere transmitted to the control valve.
3.13.5.2
Fuel Gas Control Actuator
The
actuator of the fuel gas control valve adjusts the required valve travel
according to the secondary oil pressure so that the combustion chambers are
supplied with a fuel gas flow corresponding to the set point.
3.13.5.3
Fuel Oil Control Actuator
The
actuator of the light fuel oil control valve adjusts the required valve travel
according to the secondary oil pressure so that the combustion chambers are
supplied with a light fuel oil flow corresponding to the set point.
3.13.5.4
Control Oil (Booster) Pump
3.13.5.4.1
The control oil booster pump raises the pressure
of the lube oil to 9 bar required for control oil functions. Attachment 6.43
shows a sectional view of the booster pump.
3.13.5.4.2
The booster pump is a vertical-shaft, single
stage centrifugal pump with radial-flow impeller (10) and pump casing (9). The
pump is driven by electric motor (1) through pump shaft (5). Electric motor (1)
is bolted to pump casing (9) over bearing pedestal (2) and casing cover (6).
Pump shaft (5) is guided in a bush (12). The pump casing is sealed with a flat
gasket (7) and pump shaft (5) with a sliding-ring gland.
3.13.5.4.3
Oil tapped from the lube oil circuit flows
through the suction nozzle (8) to the impeller (10) in pump casing (9), where
the control oil pressure is established, and is then delivered to the control
oil circuit through discharge nozzle (11).
3.14.1
In case of a gas turbine trip the trip oil
system reduces the normal operational system pressure abruptly to zero, thus
closing the fuel emergency shut-off valves.
3.14.2
The task of the trip oil system is to open or to
close the emergency stop valves of the fuel systems [MBN13-AA001 for the fuel
oil system and MBP13-AA001 for the fuel gas system], when the gas turbine unit
is started or shutdown or when the fuel is changed.
3.14.3
The fuel oil system also serves to close the
emergency stop valves in case of faults which demands immediate shut-down of
the gas turbine. This shut-off is
performed by undelayed trip oil pressure releases to nearly atmospheric
condition, thus causing the emergency stop valves to close by their compression
spring.
3.14.4
The trip oil system in addition supplies the
secondary oil circuits with oil as working fluid.
3.14.5
The trip oil system is supplied with control oil
at approximately 8 to 9 bar via connection “C”.
This oil proceeds to the hydraulic cylinder of the emergency stop valve
via several valves:
3.14.5.1
trip solenoid valve [1MBX41-AA001] – open 1-2;3
closed
3.14.5.2
solenoid valve for fuel oil stop valve
[1MBN13AA001A] – open 3-2;1 closed.
3.14.5.3
solenoid valve for fuel gas stop valve
[1MBP13AA001A] – open 3-2;1 closed.
3.14.6
When these solenoid valves are in the above
described position an oil pressure of 8 to 9 bar is established at the fuel
emergency stop valves and the quoted valves are open and if the valve
[MBN41-AA001] closes (2-3; 1 closed), the trip oil pressure collapses or dumps
to zero and both fuel emergency stop valves close.
3.14.7
When the solenoid valve [MBN13-AA001A] closes
(2-1; 3 closed), only the trip oil pressure to the fuel oil emergency stop
valve collapses dump to zero and closes it, whereas the fuel gas emergency stop
valves remains open.
3.14.8
When the solenoid valve [MBN13-AA001A] closes (2-1;
3 closed) , the trip oil pressure to the fuel gas emergency stop valve
collapses dump to zero and closes it whereas the fuel oil emergency stop valve
remains open.
3.14.9
With the exception of the slight leakages, no
oil flows in the trip oil system. Neither the does the oil from the hydraulic
cylinder of the fuel emergency stop valves flow back via the solenoid valves
[MBN13-AA001A] or [MBP13-AA001A] if they are closed but it is drained directly
at the fuel emergency stop valves to the main lube oil tank.
Note: See Attachment 6.42
3.14.10
The mode of trip oil system operation is
explained on the basis of the gas turbine start with fuel gas, and fuel oil is
to be cut in during operation.
3.14.11
Initial situation with the gas turbine at the
standstill is
3.14.11.1 trip
solenoid valve [MBN41-AA001] – 2-3;1closed.
3.14.11.2 solenoid
valve for fuel gas stop valve [MBP13-AA001A] – 2-3;1closed.
3.14.11.3 solenoid
valve for fuel oil stop valve [MBN13-AA001A] – 2-1;3 closed.
3.14.11.4 control
oil pressure at connection “C” approximately 0 bar.
3.14.12
After start of the lube oil pump [MBV21-AP011]
and start of the control oil pump [MBX21-AP011] the trip solenoid valve
[MBN13-AA001] is opened as a result which the trip oil pressure is then
available at ports 3 of the solenoid valves [MBN13-AA001A] and [MBP13-AA001A]. The trip solenoid valve [MBN41-AA001] is
opened is the same step of the gas turbine start program as the ignition is
initiated (at approximately 576 RPM).
3.14.13
After the certain speed has been reached the
solenoid valve [MBP13-AA001A] is opened (3-2;1 closed) as a result of which the
fuel gas emergency stop valve [MBP13-AA001] is opened. At gas turbine shutdown
the fuel gas emergency stop valve is closed simultaneously with the solenoid
valve.
3.14.14
When the gas turbine has reached rated speed and
the gas turbine is to be operated additionally on fuel oil, the solenoid valve
[MBN12-AA001A] is opened (3-2;1 closed) as the result of which the fuel oil
emergency stop valve is opened. The pressure switch [MBX41-CP001] causes alarm
if the trip oil pressure drops below a certain value.
3.14.15
At gas turbine shut-down the trip solenoid valve
[MBX41-AA001] is closed at the same step in the shut-off program where the fuel
emergency stop valve is closed. During distributed operation there several
signals which trip the gas turbine. Any
emergency gas turbine stop, which automatically or manually released activates
the trip solenoid valve [MBX41-AA001] and starts the automatic shut-down
procedure.
3.14.16
The following are the components of the trip oil
system:
3.14.16.1 Fuel
Gas Emergency Stop Valve (ESV)
The fuel
gas emergency stop valve serves for reliable and quick isolation for opening of
gas supply. The emergency stop valve has no control function. Drive of the fuel
gas emergency stop valve is the ESV actuator.
3.14.16.2 Fuel
oil emergency stop valve (ESV)
The fuel
oil emergency stop valves serves for reliable and quick isolation or opening of
the fuel oil supply. The (ESV) actuator drives the fuel oil emergency stop
valve.
3.14.16.3 Emergency
stop valve (ESV) actuator
The ESV
actuator for fuel gas respectively fuel oil emergency stop valves which are
nearly identical is described on the basis of the fuel gas ESV actuator
hereafter. The ESV actuator is a hydraulic device using control oil
respectively trip oil of 9 bar as working fluid for the different valve
functions.
3.15.1
The fuel gas system supplies gas to combustion
chamber burners and controls the rate at which the fuel flows into the
combustion chambers to accommodate the requirements of start-up, normal
operation and shutdown. Under certain
fault conditions, the fuel gas systems also stops flow of fuel gas to the gas
turbine.
3.15.2
The fuel gas system supplies the burners with
fuel gas and controls the amount, which flows into the combustion chamber
corresponding the demands on start-up, on operation, and on shutdown.
3.15.3
The fuel gas system also includes all elements,
which allow to operate the gas turbine unit.
Every gas turbine unit is supplied by an own individual fuel gas system,
all installed fuel gas system are identically build up. The fuel gas system
allows different modes of firing, i.e. premix and diffusion mode.
3.15.4
The gas turbine is designed to operate with gas
fuel, light fuel oil and a combination of both fuels. A fuel selector switch enables manual
selection either of gas, light fuel oil or mixed fuel operation. This section
describes the gas fuel system. The light
fuel oil system is described in section 3.16 since gas fuel appreciably cheaper
and cleaner than distillate fuel, gas
fuel is the preferred fuel and is normally used. Light fuel oil is used only as a backup fuel
upon loss of gas pressure or when gas fuel is not available.
3.15.5
Dry, clean fuel gas must be supplied to the gas
turbine to prevent corrosion, erosion and the formation of the deposits in the
gas the combustion flow paths. The fuel
gas system provides a route for the gas from the point of the bulk supply to
the burners. Gas is supplied to the
station from the Quadirpur gas field bulk supply pipeline; the gas passes
through the gas skid on its way to the gas turbine. The section of the fuel gas system from the
point of the entry to the station of the fuel gas skid is descried in the
system description (LP-OP-EG*). The
section of the fuel gas system after the gas skid to the burners is described
in this section.
3.15.6
The fuel gas system consists of the several
elements, which are described hereafter in terms of a short description of the
operational function of the elements, and how they operate together. The major
components of the fuel gas systems are:
3.15.6.1
Coarse filter [1MBP12-AT001]
3.15.6.2
Emergency stop valve [1MBN13-AA001]
3.15.6.3
Fuel gas control valve [1MBP13-AA002]
3.15.6.4
Start-up flow restrictor throttle [1MBP13-BP001]
3.15.6.5
Fuel gas burners [1MBN31-AV001 to AV008 and
1MBN32-AV001 to 008]
3.15.6.6
Fuel gas vent valve [1MBN14-AA001]
3.15.6.7
Fuel gas diffusion valve [1MBP21/22-AA001]
3.15.6.8
Fuel gas premix valves [1MBP21/22-AA002]
3.15.6.9
Fuel gas pilot valves [1MBP21/22-AA003]
3.15.6.10 Pilot
fuel gas control valve [1MBP15-AA002]
3.15.7
Attachment 6.44 shows a schematic diagram of the
gas fuel system. The fuel gas
system. The fuel gas system components
are described in the sections below in the order in which the fuel gas passes
through them.
3.15.8
Coarse filter.
3.15.8.1
The coarse filter [1MBP12-AT001] protects the
downstream components the fuel gas systems from large particles, which may be,
present the gas fuel supply piping.
Pressure loss across the coarse filter is monitored by differential
pressure switch [1MBP12-CP001]. An alarm
annunciates at the DCS control desk when the pressure difference across the
filter exceeds **[as16]
bar fuel gas pressure is monitored by pressure switches [1MBP11-CP001] and
[1MBP13-CP403].
3.15.8.2
In normal cases, hardly any loss in pressure
will be detected in this filter since the fuel gas enters in an already
filtered state. Any indicated pressure
loss signalizes that the fine filter system requires maintaining. In this case, in addition to cleaning of the
filter recommended here, the fine filter should also be inspected and put in
order. In addition, the piping system
should be cleaned and the components of the fuel gas system should be checked
to detect wear and tear and deposits of dirt.
3.15.9
Simplex Filter
3.15.9.1
This filter serves to remove particles 0.78 mm
and larger in the fuel gas in order to protect the emergency stop valve and the
control valve from damage.
3.15.9.2
The filter consists of a filter housing with a
strainer basket, which is a screen cylinder.
A vent is located on the cover flange and is drain plug is arranged at
the bottom of the filter housing.
Supports brackets are bolted to the lower part of the filter housing.
3.15.9.3
When installing the filter in the fuel gas line,
care is taken to avoid distortion of the filter housing. A differential pressure indicator with
contact displays the pressure drops across the filter. When the maximum permissible pressure drop
has been reached, the strainer basket must be cleaned. Otherwise, the filter may be damaged,
resulting in serious consequential damage to equipment downstream of the filer.
3.15.9.4
To clean the fouled filter, the housing cover is
removed and the strainer basket is taken out.
The filtering space must be depressurized prior to removing the
cover. The strainer basket is rinsed in
a suitable cleaning fluid and the brush for removal of solid particles is
recommended. The strainer basket should
then be blown out with compressed air from outside. The dirt collected on the filter-housing
bottom must be removed by flushing via the drain plug.
Note: See Attachment 6.44
3.15.10
Emergency stop valve
3.15.10.1 Emergency
stop valve [1MBN13-AA001] isolates or admits fuel gas into the combustion chamber
an start-up and shutdown of the gas turbine, as well as when changing over from
fuel gas to distillate, or vice versa.
It also closes on accurance of faults requiring immediate shutdown of
the gas turbine.
3.15.10.2 It
is opened hydraulically through solenoid valve [1MBN13-AA001A] and closed by
spring force in less than 0.5 second.
Pressure gauge [1MBP13-CP003] displays the fuel gas pressure upstream of
the emergency stop valve.
3.15.10.3 Attachments
6.45 shows a sectional view of the gas fuel emergency stop valve. The fuel gas
emergency stop valve serves the reliable and quick isolation or opening of the
fuel supply.
3.15.10.4 Construction
The fuel
gas emergency stop valve consists essentially of the hydraulic part and the
valve part. Both are connected together
by an intermediate element. Sealing in
the valve part is by metal to metal contact.
In addition an O-ring (9) provides a flexible seal. Actuating disc (5) is connected to a valve
cone (8) by a valve stem (11). A
diaphragm stem seal (10) prevents escape of gas into the turbine house.
3.15.10.5 Mode
of operation
3.15.10.5.1
To close the valve, space (b), which is
connected to the trip oil system via connection “E”, is depressurized.
3.15.10.5.2
Due to the release of pressure, the holding
force of actuating disc (5) is abolished and springs (2,3) force actuating disc
(5) and thus valve cone (8) into the close position with auxiliary position
(12) initially remaining in the upper position.
Push rod (13) follows valve stem (11).
3.15.10.5.3
The oil from space (b) flows around actuating
disc (5) offering only slight resistance to the closing action. The valve thus closed at high speed. A hydraulic damping device cushions the
impact. Limit switch (7) repairs the
closed positions to control room.
3.15.10.5.4
When the valve is closed a procedure is
initiated immediately to reactivate the valve for opening. Springs (15 and 16, detail X) press pilot
valve (14) with its stop against the pilot bush, control oil then flows through
the ducts (g, h) which are connected together, into space (f) and presses
auxiliary piston (12) downward against the force of the spring (2, 3) and thus
against actuating disc (5). Joined, the auxiliary piston (12) and the actuating disc (5) from an oil
tight unit again. Pilot valve (14) which
operates together with the springs (15, 16) as a pressure retaining valve
maintains an oil pressure in space (f) which lies slightly above the force of
springs (2, 3). The fuel gas emergency
stop valve is now ready again for opening.
3.15.10.5.5
To open the fuel gas emergency stop valve trip
oil is released by a three way solenoid valve to space (b) via connection
(e). The actuating disc and the
auxiliary piston are forced back by the trip oil entering at a higher pressure
than the pressure prevailing in space (f) and thus the valve opens. Due to the opening procedure the pressure in
space (f) rises and forces the pilot valve (14) so far the backspace (f) is
connected via ducts (k) with the return line (a) by means of the push rod (13)
operated by the valve stem, the pilot valve is kept in the position shown when
the emergency stop valve is open and thus disconnects the control oil inflow
duct (h) to space (f) as the consequence the pressure in space (f) decreases
due to the leakage.
3.15.10.5.6
With the fuel gas emergency stop valve in the
open position, space (b) continue to
communicate with the trip oil. Limit
switch (6) signalizes the open position to the control room.
3.15.10.6 The
1.5 bar value is equivalent to low fuel gas flow, and the 3.3 bar pressure is
equivalent to full load fuel gas flow.
An attachment shows a sectional view of gas fuel control valve.
3.15.11
Fuel gas control valve
3.15.11.1 Fuel
gas control valve [1MBP13-AA002] controls the flow of the fuel gas to the
combustion chambers. The fuel gas
control valve is hydraulically actuated.
The secondary oil pressure generated by a control oil system (see
section 3.13) determines value lift. At
secondary oil pressure of about 1.5 bar, the valve is fully closed, and at
about 3.3 bar it is fully open. The fuel gas control valve serves to supply the
amount of fuel corresponding to the preset set-point to the combustion chamber
without delay.
3.15.11.2 Construction
The fuel
gas control valve is operated by an actuator, which forms a single unit
together with the control valve. A
diaphragm seal prevents the escape of the gas into the turbine house. A
protection bush at double seat valve cone and a bush at the valve body prevent
the sliding surface of the valve stem from collecting any solids in the gas
space.
Note: See Attachment 6.45
3.15.11.3 Mode
of operation
3.15.11.3.1
The fuel gas control valve serves to adjust the
fuel gas flow. The fuel gas from the
emergency stop valve flows through two annular chambers to the outlet and then
passes to the combustion chambers.
3.15.11.3.2
Any change in the position of the double seat
valve cone results in a change in a cross sectional areas and thus in a change
of the fuel gas flow. The hydraulic operating force produced in the actuator of
the fuel gas control valve is transmitted to the valve stem via rod, lever, and
link.
3.15.11.3.3
The valve position is indicated by a mechanical
pointer on a scale. Electrical remote transmission
of the valve position is done by means of a differential transformer. The
differential transformer converts the position of double seat valve cone into
an analogue voltage signal, which is a measure of the travel.
3.15.11.4 Start-up
flow restrictor/ throttle
Flow
restrictor [1MBP13-BP001] located on a bypass line across the fuel gas control
valve, controls the flow of fuel on star-up and shutdown of the gas turbine
when the fuel gas control valve is still fully closed.
3.15.11.5 Ball
valve
3.15.11.5.1
Motorized ball valves [1MBP21-AA001to 003] and
[1MBP22-AA001 to 003] are arranged on each combustion chamber by means of which
the fuel gas flow to the combustion chambers can be shutoff additionally to the
fuel gas emergency stop valve.
3.15.11.5.2
Furthermore [1MBP21-AA001] and [1MBP22-AA001]
and [1MBP22-AA002] are used to change over between the operation modes
“diffusion burner” and “premix burner”.
[1MBP21-AA003] and [1MBP22-AA003] cut the gas supply to the pilot
burner.
3.15.11.6 Pilot
fuel gas control valve
3.15.11.6.1
During premix burner operation, pilot fuel gas
control valve [1MBP15-AA002] determines part of the fuel gas flow admitted into
the combustion chamber via the pilot burners.
The pilot fuel gas flow is constant above a compressor inlet temperature
of 20ºC.
3.15.11.6.2
With decreasing compressor inlet temperature,
the pilot gas flow shows a linear increase upto the compressor inlet
temperature of -20ºC. Below this
temperature, the pilot gas flow remains constant. An electric actuator operates
the pilot fuel gas control valve.
3.15.11.6.3
During diffusion burner operation, the pilot
fuel gas control valve is never fully closed.
This ensures that the lines between ball valves [1MBP21-AA003] and
[1MBP22-AA003] and the emergency stop valve will be depressurized after closing
of the emergency stop valve and opening of the vent valve [1MBP14-AA001].
3.15.11.7 Load
rejection valve [1MBP15-AA001]
In the
event of the load rejection, during premix burner operation, the load rejection
valve is opened immediately so that another part of the pilot fuel gas flow is
admitted into the combustion chamber.
The additional fuel gas flow is determined by throttle [1MBP15-BP002].
3.15.11.8 Fuel
gas vent valve
During gas
fuel operation, the fuel gas vent valve [1MBN14-AA001] is closed. When the gas turbine is taken off fuel gas,
the vent valve opens after the emergency stop valve and the shutoff valves on
the combustion chambers have closed.
Opening of the vent valves relieves pressure in the piping between the
emergency stop valve and the shutoff valves.
In the event of downstream valves passing, such leakages are released
into the atmosphere through the vent valve.
The fuel gas vent valve together with the emergency stop valve and
shutoff valves from a gas lock.
3.15.11.9 Fuel
gas burners
3.15.11.9.1
The fuel gas burners are designed in detail in
section 3.6 ‘combustion system’. The
sixteen fuel gas burners [1MBN31-AV001to 008] and [1MBN32-AV001 to 008] ensure
that the fuel gas flowing into the combustion chambers mixes thoroughly with
the compressor air which enters simultaneously forming a fuel air mixture that
burns completely. The fuel gas burners
are identical to ensure uniform distribution of the fuel gas to each burner,
which has a large number of gas outlet bores.
3.15.11.9.2
The flow of the fuel gas emerging from the
burner is dependent on the cross section of these bores and on the differential
pressure between the fuel gas upstream of the burner and the combustion
chamber. Gas turbine speed and the
turbine inlet temperature together determine the pressure in the combustion
chamber. At constant supply gas
pressure, the pressure in the fuel gas line to the burner is dependent on the
position of the fuel gas control valve.
3.15.11.9.3
The larger the controls valve opening, the
higher the fuel gas pressure upstream of the burner. These causes the differential pressure to the
combustion chambers to increase, thereby increasing the fuel gas flow. These
so-called hybrid burners consist of a diffusion burner, a premix burner and a
pilot burner. Generally only the
diffusion burner or the premix burner with pilot burner support is in operation
except for the short time period during change-over from one operation mode to
another. When the premix burner is in operation the pilot burners serve to
stabilize the flame. The fuel gas
burners can be operated in premix respectively in diffusion mode in order to
minimize the content of detrimental gases in the flue gas at any operation
condition.
3.15.11.10 Differential
pressure indicator.
3.15.11.10.1 The
device measures and displays a variable pressure difference and activates an
electrical signal at two limit values. A bellows sealed piston separates the
interior into two compartments. At zero
differential pressure, the spring-loaded piston in its zero position.
3.15.11.10.2 With
rising differential pressure (p > 0) the piston is moved against the action
of the spring. This causes the movement
of an indicator dial by magnetic means i.e. with low friction, and activates
two dry reed contacts. As the piston moves, the larger portion of the indicator
dial appears red within a range from 20 to 100% pressure differences. An electrical contact (warning) is actuated
at 75% pressure difference.
Note: See Attachment 6.46
3.16.1
The light fuel oil system delivers and evenly
distributes distillate fuel from an external fuel storage and forwarding
system, to the sixteen fuel nozzle of the combustion system. The system also
controls the volume of the fuel injected into the combustion chambers to meet
the requirements of the gas turbine during start-up, normal operation and
shutdown.
3.16.2
The gas turbine is designed to operate with gas
fuel, light fuel oil and the combination of both fuels. A fuel selector switch enables manual
selection of gas, distillate or mixed fuel operation.
3.16.3
Since gas fuel is appreciably cheaper and
cleaner than light fuel oil, gas fuel is preferred fuel and is normally used.
Light fuel oil is used is only as back up fuel upon loss of gas pressure or
when gas fuel is not available.
Attachment 6.47 shows a schematic diagram of the gas turbine light fuel
oil system. Many of the light fuel oil system system are skids mounted.
3.16.4
The system supplies the burners with the fuel
oil. The fuel oil is connected to the
fuel oil storage and supply system EG.
The delivered fuel oil has to meets the limits as outlined in the fuel
oil specifications published in the operation manual. Otherwise, damages at the GT components will
be encountered. The fuel oil specifications covers e.g. viscosity and
temperature limits, allowable particle sizes and contents of the contaminants.
3.16.5
The major components of the light fuel oil
system are:
3.16.5.1
Injection pumps [1MBN12-AP001].
3.16.5.2
Light fuel oil emergency stop valve
[1MBN13-AA001]
3.16.5.3
Start-up pressure relief valves [1MBN12-AA011
and 1MBN12-AA012]
3.16.5.4
Light fuel oil ball (combination globe) valves
[1MBN21-AA001 and 1MBN22-AA001].
3.16.5.5
Light fuel oil control valve [1MBN53-AA001].
3.16.5.6
Return fuel oil shut-off valve [1MBN51-AA001].
3.16.5.7
Safety valve [1MBN12-AA036].
3.16.5.8
Double flow restrictor [1MBN13-BP001].
3.16.5.9
Distillate fuel burners [1MBN31-AV001 to 008 and
1MBN32-AV001 to 008].
3.16.5.10 Leakage
oil tank [1MBN60-BB001].
3.16.6
The task of the fuel oil system MBN is to supply
the burners with fuel. Two major sections of system are:
3.16.6.1
Injection pump skid.
3.16.6.2
Fuel oil control system.
3.16.7
From the tank, the forwarding pump supply fuel
oil to the injection pump skid. The injection pump boosts the fuel oil pressure
to the values required by the burners.
The fuel oil system controls the amount of fuel which is injected into
the combustion chamber corresponding to the commands during start-up, load
operation and shutdown as well as the fuel oil system is able to shut-off the
connections between the burners and the fuel oil supply.
3.16.8
The fuel oil system is designed to supply the
burners with the fuel quantity depending on the actual performance (load) of
the gas turbine. For base load a fuel
oil mass flow rate of approximately 30-40 t/h is required.
For controlling the gas turbine load the fuel oil pressure to the
burners must be varied according to the load in a range between 10 bar and 52 bar.
3.16.9
The injection pump is designed for 75 bar at a flow rate of 16.5 dm3/s. The inlet pressure to the fuel oil injection
pump has to be in range of 2.5
to 10 bars. The fuel oil
viscosity is required according to the gas turbine specification between 1.9 to 28 c St. Fuel oil
temperature limits are established to ensure that the viscosity limits,
especially the lower viscosity values corresponding to high fuel temperature
are not exceeded.
3.16.10
Injection pump skid.
The fuel
oil system (MBN) gets the fuel from the fuel oil storage and supply system (EG)
via the duplex filters [1MBN11-AT001/011] and injection pump
[1MBN12-AP011]. These components are
installed on the fuel oil leakage tank [1MBN60-BB001] and are part of the
injection pump skid [MBN11].
The most important function is:
3.16.10.1 Degassifier
(fuel oil venting vessel) [1MBN11-AM001] where gases are removed which are
dragged along with the fuel oil. This is
necessary to achieve pure liquid flow at the
3.16.10.2 Injection
pump [1MBN12-AP001] this is a rotary displacement pump of the three screw
spindle type. When the pump starts the
3.16.10.3 Start-up
pressure relief valve [1MBN12-AA001] is open so that the pressure increase is
low. Closing the valve increases the
pressure in the fuel oil forwarding system.
3.16.10.4 The
adjustable throttles [1MBN13-BP001/003] are used during commissioning to adapt
the injection pump (which is standard pump] to the actual flow requirements.
3.16.10.5 Fuel
oil leakage tanks [1MBN60-BB001] where all rains and vents of the fuel oil
system are collected. When the level
reaches a certain value, the
3.16.10.6 Fuel
oil leakage pump [1MBN60-AP001] feeds the fuel oil back to the storage system.
3.16.11
Fuel oil controls systems.
The fuel
oil control system is provided for
3.16.11.1 Splitting
the forward fuel flow into a flow, which is injected and atomized in the
combustion chambers and that flow which is returned to the fuel system
3.16.11.2 Separate
the fuel oil supply system from the
combustion chambers and to
3.16.11.3 Keep
clean the burner nozzles in the case that the gas turbine remains in operation
on fuel gas.
3.16.11.4 The
fuel flow coming from the fuel oil pump skid can be isolated with the fuel oil
stop valve [1MBN13-AA001].
3.16.11.5 With
the flow meter [1MBN13-CF001] the fuel oil forwarding flow is measured. After that, the flow is split upto the two
combustion chambers.
3.16.11.6 The
ball valves assemblies [1MBN21/22-AA001] which can cut the connections to the
combustion chambers for both the forwarding and the return system and switch
over to the compressor air of the gas turbine for cleaning and cooling the
burner nozzles during fuel gas operation.
3.16.11.7 From
the forwarding part of the ball valve assembly a common header supplies the
burners [1MBN31/32-AV001/1/3/4/5/6/7/8] with the fuel oil. Dependent on the backpressure prevailing in
the return system, more or less fuel oil is injected through the burner
nozzles. The fuel oil that is not
injected is collected in the return header and passes the return part of the
ball valve assemblies.
3.16.11.8 The
returning amount is measured with the flowmeter [1MBN53-CF001]. The difference
between the forwarding and the return flow is the calculated injected flow, a
value that is used as the basis for the fuel consumption calculation.
3.16.11.9 Thereafter
the returning oil passes the return shut off valve [1MBN51-AA001], which is
second shut off valve in the return system.
3.16.11.10 The
backpressure in the return system is adjusted with the fuel oil control valve
[1MBN53-AA001]. During operation
absolutely no flow restriction (closed valve, rising fluid column etc) is
allowed downstream this valve, since this would influence the backpressure in
the return system and thus the injected fuel flow.
3.16.12
Connections to the other systems
3.16.12.1 EG
storage systems.
3.16.12.1.1
Supply to fuel oil pump via fuel oil filter
station.
3.16.12.1.2
Fuel oil return from the fuel oil burners.
3.16.12.1.3
Fuel oil return from the leakage oil tank.
3.16.12.2 MBA compressor air
Compressor outlet air is tapped off at the pressure jacket of
the combustion chambers for cooling and purging the fuel oil burners.
3.16.12.3 MBM
combustion chambers
The burner
assemblies, i.e. the fuel oil burners, are flanged to the combustion chambers.
3.16.12.4 MBX
control system
Supplies
the valve actuators with control oil and herewith sets the stroke of the
3.16.12.4.1
Fuel oil stop valve.
3.16.12.4.2
Fuel oil return shut off valve.
3.16.12.4.3
Fuel oil control valve.
3.16.13
Physical arrangement.
3.16.13.1 The
injection pump skid with leakage tank, filters, Degassifier, pump and start-up
relief valve is located in the fuel pump compartment.
3.16.13.2 The
fuel oil valves (stop valves and control valve) are installed on the top of the
lube oil tank.
3.16.13.3 The
fuel piping of the forwarding and the return flow between the lube oil tank and
combustion chamber penetrate the air intake duct of the GT and are installed to
the GT housing. Nearby the combustion
chambers the pipes are splitted and are connected with the assemblies on top of
the combustion chambers.
3.16.13.4 On
top of the combustion chambers are arranged the
3.16.13.4.1
Burner assemblies, the.
3.16.13.4.2
Ball valves assembles and the,
3.16.13.4.3
Fuel oil distribution headers for the forwarding
and the return lines.
3.16.14
Duplex filters [MBN11-AT001/011]
3.16.14.1 During
normal operation, only one of the filters is operating whereas the other one is
in standby. The fuel oil entering the
assembly at the upper flange which is connected to the outer shell. It passes the filter screen from outside to
inside and leaves the filter at the lower flange.
3.16.14.2 The
filter screen consists of a fine wire mesh, which is supported by an inner cage
(mesh width nom. 10µm). The filter can be switched over during
operation if required. A pressure
equalizing line maintains the system pressure in both compartments during
switch over.
3.16.15
Fuel oil injection pump [MBN12-AP011]
3.16.15.1 The
injection pump is a positive displacement pump of the three-screw spindle
type. For lubrication of the spindles,
this pump requires a certain viscosity of the fluids, which is pumped.
3.16.15.2 Thus,
the viscosity of the fuel oil has to be checked and, since the viscosity drops
with rising temperature, the maximum temperature, which is specified, must not
be exceeded.
3.16.15.2.1
Range of fuel oil viscosity: 1.9-28 c St.
3.16.15.2.2
Pump discharge pressure: 75 bar.
3.16.15.2.3
Flow rate: 16.5 dm3/s.
3.16.15.2.4
Power consumption: 150/200kW at 3 AC 3.3kV.
3.16.15.3 Injection
pump is used to boost the light fuel supply pressure to that required for
atomization in the burners. One
injection screw pump [1MBN12-AP011] is provided. If pressure upstream of the
in-service injection pump monitored by pressure switch [1MBN11-CP011] decrease
below 1.5 barg or distillate temperature, monitored by temperature switch
[1MBN11-CT002] increase above 145ºC , an interlock prevents the pump from being
switched on.
3.16.15.4 If
the above parameters limits are exceeded during operation, the service
injection pump trips and the gas turbine is automatically shutdown. Low suction pressure could result in pump
cavitatin damage. High fuel temperature
causes the viscosity of the fuel to decrease leading insufficient lubrication
of the pump screw spindles.
3.16.15.5 The
light fuel oil supply pressure up stream of the injection pumps can be read
from off from pressure gauge [1MBN11-CP501].
The injection pump has start-up pressure relief valve [1MBN12-AA501].
Two-nitrogen charged accumulators [1MBN13-BB001] and [1MBN13-BB002] are
provided to prevent the light fuel oil supply pressure from decreasing too much
during pump changeover.
3.16.16
Start-up pressure relief valve [1MBN12-AA001]
3.16.16.1 During
gas turbine start-up the injection pump is switched on the emergency stop valve
is opened. The fuel flow is then
diverted via the start-up pressure relief valve [1MBN12-AA001] into the return
line.
3.16.16.2 This
valve is operated by solenoid pilot valve [1MBN12-AA001A] so that the pump does
not have to start-up against high pressure.
A few seconds after the pump has been switched on, the solenoid valve is
again deenergised, and high pressure is established down stream of the pump.
3.16.17
Light fuel oil ball valve assembly
[1MBN21/22-AA001].
3.16.17.1 The
ball valve assembly [1MBN21-AA001 and 1MBN22-AA001] is arranged on each
combustion chamber. This consists of a
three-way ball valve and a shut off ball valves, which are linked together and
are operated jointly by a motor.
3.16.17.2 The
feed flow of the light fuel oil to the combustion chamber is blocked or opened
by means of the 3-way ball valve and shut-off ball valve which is in the return
piping.
3.16.17.3 When
the 3-way ball valve stops the feed flow of the fuel oil, the fuel oil piping
to the burners is connected to the outlet of the gas turbine compressor. Compressed air flows through the fuel oil
burners into the combustion chambers and prevents entering of hot gas from the
combustion chambers to the fuel oil system and is cooling the burner nozzles.
3.16.17.4 The
distillate fuel emergency stop valve [1MBN13-AA001] admits or isolates
distillate fuel flow into the combustion chambers during start-up and shutdown,
and when changing over from distillate fuel to fuel gas and vice versa. It also closes in the events of the faults
that require immediate shutdown of the gas turbine.
3.16.17.5 The
emergency stop valve hydraulically opened by oil admitted to the valve actuator
through solenoid valve [1MBN13-AA001A] spring loading ensures valve closure in
less than one second.
3.16.17.6 Attachment
6.48 shows a view of the light fuel oil emergency stop valve. The emergency
stop valve comprises an hydraulic actuator and the valve assembly which are
coupled together through an intermediate element. Sealing in the valve assembly is by metal to
metal contact. An actuating disc is
connected to a double seat valve cone through the valve stem. Oil leakages are drained via leakage oil
outlets ‘m’ and ‘p’.
3.16.17.7 To
close the valve, space ‘b’ is depressurized.
In the absence of the hydraulic pressure acting on the actuating disc,
the double valve closing springs force the actuating disc and thus the
double-seat valve cone into the closed positions. The auxiliary piston remains open at
first. The hydraulic oil flows around
the actuating disc, thus offering only minimal resistance to the closing
action. The valve is closed at high
speed. A hydraulic damping device
cushions the impact on the valve cone on the valve seat. A limit switch signals the valve-closed
positions to the control room.
3.16.17.8 On
valve closure, the valve is reactivated to prepare it for opening. A pilot
valve, which held in the extreme position by the valve stem when the valve is
open, is forced inward by auxiliary spring (see detail X) hydraulic oil
admitted via a flange then communicates between ducts ‘g’, ‘h’ and into space
‘e’, forcing the auxiliary piston against the actuating disc joined tightly, the auxiliary piston and the
actuating disc from a single unit, and the valve is again ready for
opening to open the emergency stop
valve, the pressure oil passes through a 3-way solenoid valve to enter space
‘b’, the solenoid valve is reactivated only when the tripping oil pressure has
been built up.
3.16.17.9 The
actuating disc and auxiliary piston are forced back and open the valve. The oil space ‘e’, ahead of auxiliary piston
is forced back into a return line via control port ’k’ by moving a pilot valve
which operates as a constant pressure valve in conjunction with the auxiliary
springs. The springs are adjusted so
that the oil pressure available for opening in space ‘b’, but high enough to
prevent the actuating disc from being separated from the auxiliary piston by
the main springs. The moving pilot valve
also closes pressure oil inlet duct ‘g’ to space ‘e’, thus depressurizing
space ‘e’ when actuating disc ‘5’ and
auxiliary piston ‘12’ have reached the stop at cylinder ‘I’. With the valve in the open position, space
‘b’ continues to communicate with the pressure oil circuit. Limit switch ‘6’signals the valve open
position to the control room.
3.16.18
Light fuel Oil Ball Valve Assembly.
3.16.18.1 The
ball valve (combination globe) valve assembly, fitted on each combustion
chamber, regulates flow on the distillate fuel feed and return lines and
cooling air supply to the distillated fuel burners. Attachment 6.48 shows a sectional view of the
distillate fuel combination globe valve assembly.
3.16.18.2 The
globe valve assembly comprises 3-way ball valve ‘14’ in the feed line,
throughway ball valve ‘11’ in the reverse flow line and motor actuator ‘9’ the
ball valves and the motor actuator are arranged in one line and interconnected
by means of links ‘10’ and ‘13’ balls ‘12’ and ‘15’ are sealed with soft
packings. Spring loaded gland packing
rings prevent the fuel oil from leaking out.
3.16.18.3 Prior
to opening of the light fuel oil emergency stop valve [1MBN13-AA001] , the ball
valve assembly is moved to a position in which the fuel and reverse flow lines
are open (positions 1-2 and 4-5 open) and cooling air inlet ‘6’ is closed. After closing the light fuel oil emergency
stop valve the ball valve assembly is changed ver so that the feed and return
flow lines are closed (positions 1-2 isolated) and cooling air from the
compressor is admitted to purge and cool the distillate feed lines (position
6-5 open). Limit switches on the actuator indicate valve positioning the
control room.
3.16.18.4 To
prevent any leakage oil accumulating at the 3-way valve from entering the gas
turbine compressor through the air line, the ball valve casing is provided with
a leakage oil line which leads to pressures leakage oil tank [1MBN60-BB001].
When the three way valves are changed over, the body is briefly connected for a
short time to a air line from the compressor outlets. During this time, the leakage oil line is
closed off by solenoid valve [1MBN20-AA002] and thus prevents too much hot air
from the compressor from flowing into the leakage oil tank. The solenoid valve is reopened after the ball
valves reached the desired position.
3.16.19
Fuel oil burners [1MBN31/32-AV001…008]
3.16.19.1 The
total of 16 fuel burners [1MBN31-AV001/2/3/4/5/6/7/8 and
1MBN32-AV001/2/3/4/5/6/7/8] atomize the fuel oil so that it is able to be burned
completely in the combustion chamber. All 16 burners are completely identical
so that the fuel oil quantity is distributed uniformly amongst all of the
burners.
3.16.19.2 All
the fuel oil conveyed enters the ignition chambers of the fuel oil burners and
is split there into one part which is injected into the combustion chamber and
one part which is flows to the fuel oil return system. The proportions are dependent on the opposing
pressure in the fuel oil return. In the
event of a low return pressure a large amount flows into the return system and
a small quantity is injected. In the
event of a high return pressure a small amount flows into the return and a
correspondingly large amount is injected.
3.16.19.3 The
magnitude of the return pressure is determined by the setting of the fuel oil
control valve [1MBN53-AA001] which is installed in the return line. The more the valve tends towards a closed
state a higher the return pressure and thus the greater the amount of the fuel
oil injected. The more the fuel oil
control valve tends towards the open state, the lower the return pressure and
thus the less the amount of the fuel injected.
3.16.19.4 The
burner nozzles diagram shows typical values of the injected fuel flows versus
the difference between fuel oil supply – and combustion chamber pressure and
how the control valve regulates the injected fuel oil flow by throttling the
return line.
3.16.20
Return shut-off valve [1MBN51-AA001]
3.16.20.1 The
light fuel oil shutoff valve [1MBN51-AA001] admits or isolates fuel flow in the
light fuel oil return line to the light fuel oil storage tank. The light fuel
oil shutoff valve:
3.16.20.1.1
Prevents the hot combustion chamber gas from
entering the fuel oil tank via the fuel oil return line during fuel gas
operation.
3.16.20.1.2
Prevents light fuel oil from the storage tank,
lacated at higher level, from flowing back into the combustion chambers during
standstill of the gas turbine.
3.16.20.1.3
If the return line is connected at a line system
in which there is over pressure and
3.16.20.1.4
Prevents gas from flowing into the fuel oil
system from the combustion chambers during operation with fuel gas.
3.16.20.2 This
valve is closes by a spring-loaded arrangement and is opened hydraulically if
fuel oil will be used from the feed. The
valve closes rapidly if during mixed operation (joint combustion of fuel oil
and fuel gas) the fuel is to be cut off.
This is brought about switch over of the solenoid valve [1MBN51-AA001A].
3.16.20.3 Attachment
6.49 shows a sectional view of a light fuel oil shutoff valve, which comprises
a valve assembly and hydraulic actuator, combined to form a unit. The motive fluid for valve actuation is
distillate tapped-off from the supply line after the emergency stop valve. The valve disc is provided with a metallic
seal and O-ring packing ‘6’ the actuator piston ‘5’ is connected to a valve
disc ‘7’ through valve stem ‘3’ with plastic ring provided for sealing and
guidance. A diaphragm stem seal ‘4’
prevents the leakage of distillate.
3.16.20.4 The
valve opens automatically as soon as pressure in the distillate supply line
exceeds the combustion chamber pressure i.e. immediately after opening of the
distillate emergency stop valve. The
distillate acts on the piston via check valve ‘8’ and opens the valve against
the combustion chamber pressure and the closing spring forces.
3.16.20.5 When
the distillate emergency stop valve closes on gas turbine shutdown, the
pressure in the distillate supply and return line equalizes with the combustion
chamber pressure. Springs ‘1’ and ‘2’
force the fuel oil from space ‘e’ via throttling bore ‘d’ into return flow
compartment ‘c’, resulting in delayed closing of the valve.
3.16.20.6 After
the distillate emergency stop valve closes, the combustion chamber pressure
forces any residual distillate into return line precluding the risk of
distillate dripping from distillate burners into the combustion chambers. Limit switches ‘9’ and’10’ signal the final
valve position to the control room.
3.16.20.7 The
distillate used to actuate the return flow shutoff valve is controlled by
solenoid valve [1MBN51-AA011A] during dual fuel operation, if the distillate
supply is suddenly shut-off, this valve must done quickly. By changing over
solenoid valve [1MBN51-AA001A] from supply to drain, the actuator of the return
flow shutoff valve is relieved of pressure and valve closes very quickly.
3.16.20.8 Check
valve [1MBN51-AA051] located upstream of solenoid valve [1MBN51-AA001A], is
provided with a small bore. This check valve permits the return flow shutoff
valve to close slowly when the gas turbine has to be shutdown during fuel oil
operation as described above. A small
bore opening above the drive piston of the return flow shutoff valve permits
slow.
3.16.20.9 Depressurization
of the valve hydraulic pressure.
Solenoid valve [1MBN51-AA001A] is not changed over on shutdown during
exclusive distillate operation. The bore
in the check valve prevents any pressure buildup between solenoid valve
[1MBN51-AA001A] and the check valve.
3.16.21
Fuel oil control valve [1MBN53-AA001]
3.16.21.1 The
light fuel oil control valve [1MBN53-AA001] regulates the distillate return
flow and thus the pressure and amount of fuel injected into the combustion
chambers. Attachments 6.49 shows a
sectional view of the distillate fuel control valve. The valve is operated hydraulically by a lift
type actuator. The secondary oil
pressure generated by a control oil system determines the position of this
valve. The control oil system is
described in section 3.13 of this document. At secondary oil pressure of
approximately 1.5 bar the valve is fully open and at 3.3 bar it is fully
closed.
3.16.21.2 The
control valve and is actuator from a single unit. The hydraulic actuator ‘9’ is connected to a
control valve stem ‘6’ via linkage ‘12’, lever ‘13’ and link ‘1’. The valve stem is guided in a guide member
‘5’. The valve member has a trapped
shape at throttle ring ‘7’ spring ‘8’ acting on a valve stem in the opening
direction eliminates any looseness in the linkage elements. Pointer ‘4 ‘an dial ‘11’ indicates the valve
position. The valve position is
electrically transmitted through LVDT (linear variable differential transducer)
‘10’ into mounted on a bracket. The
differential transducer converts the position of the valve stem into an
analogue voltage, which is proportional to the travel.
3.16.21.3 The
control valve is used to regulate the distillate return flow. The fuel admitted to space ‘b’ via connection
‘a’ flows into space ‘c’ via throttle ring ‘7’ and then is passed into the
reverse flow line. Depending the
position of the valve stem ‘6’, the tapered portion of the valve stem increase
or decrease the fuel oil flow through throttle ring ‘7’. By varying the return flow, the valve thus
adjusts the fuel flow injected into the combustion chambers; maximum opening of
the control valve corresponding to maximum fuel flow supplied to the combustion
chambers.
3.16.22
Safety valve
If the start-up pressure relief valve, [1MBN12-AA011] fails to
open for any reason when the injection pump is switched on, the safety valve
[1MBN12-AA032] which has a higher set pressure the start-up pressure relief
valves, will open.
3.16.23
Double flow restrictors.
Since the injection pumps are standards models from the
manufacturer’s range, the delivery rate is higher than that required by the gas
turbine. The surplus flow is diverted
into the return line by double flow restrictors [1MBN13-BP001].
3.16.24
Leakage oil tank.
3.16.24.1 Leakage
oil tank [1MBN60-BB001] collects leakage distillate from the vent tank and from
the ball valve assemblies. Drain lines
from the drain tank, accumulators and from the injection pump casing are also
routed oil tank. One leakage oil pump
[1MBN60-AP001] pump leakage light fuel oil from the leakage oil tank to the
light fuel oil tank to the light fuel oil main storage tank.
3.16.24.2 The
pumps are automatically switched on and off by level monitor [1MBN60-CL001] the
pump [1MBN60-AP001] starts at level 240mm and stops at level 130mm. Level switch [1MBN60-CL501] annunciates a
high level alarm at DCS when the leakage oil tank level increase above 130mm
from the top of the tank.
3.16.25
Flow meters.
The fuel oil volumetric flowmeters is measured by flowmeter
[1MBN13-CF001] in the supply line and the flowmeter [1MBN53-CF001] in the
return line. The difference between
these two readings is the fuel injection flow rate.
3.17.1
The control system will consist of the following
major input loops:
3.17.1.1
Speed control.
3.17.1.2
Turbine exhaust temperature control.
3.17.1.3
Start-up control.
3.17.1.4
Load control.
3.17.1.5
Normal shutdown.
3.17.2
The gas turbine control system ensures the
following functions:
3.17.2.1
Runs up the gas turbine to speed
3.17.2.2
Synchronises the gas turbine and maintains
constant speed within a predetermined range
3.17.2.3
Loads and unloads the gas turbine to maintain a
constant load at a preset reference value
3.17.2.4
Limit the turbine outlet temperature at a
pre-set value
3.17.2.5
Enables the unit to be fired on distillate fuel,
gas fuel and combination of both fuels
3.17.2.6
Enables on load fuel change-overs
3.17.2.7
Protects the gas turbine unnecessary trip-outs
by detecting the actual values of speed, load and temperature and matching them
to preset values and
3.17.2.8
Enables operation of the gas turbine under
frequency control mode with the droop compensator switched on.
3.17.3
The gas turbine has control systems which
regulate the following parameters:
3.17.3.1
Speed
3.17.3.2
Load/frequency
3.17.3.3
Turbine inlet temperature
3.17.4
Each of the above parameters is controlled
through variations in fuel control valve opening. Each control system produces a final control
signal which either increases or decreases the control valve opening to
regulate fuel flow into the combustion chambers. The gas turbine control system
consists of the electrohydraulic converter that converts signals received from
the electric controller into hydraulic signals.
3.17.5
The fuel control valve actuated by secondary oil
pressure generated by electrohydarulic control systems. The electrohydraulic control system is
normally in service to control gas turbine speed, load and turbine inlet
temperature. The output signals from the speed, load and temperature control
circuit of the electrohydraulic control system are channeled through a minimum
value gate which selects the control variable requiring the smallest control
valve opening. Depending on the fuel selected, the output signal from the
minimum value gate is routed to the gas fuel or the light fuel oil control oil
lift controller, through a fuel proportioner.
3.17.6
The fuel proportioner is activated only during
mixed-fuel operation. The output from the valve lift controller is the input
signal to the gas fuel or light fuel oil electrohydraulic convertor, again
depending on the fuel selected. The electrohydraulic convertor converts control
oil pressure into a secondary oil pressure proportional to the input signal
from the valve lift controller. The fuel
control valve uses this secondary oil pressure as its motive fluid. The
major components of the gas turbine
controls systems are:
3.17.6.1
Electrohydraulic control system comprising :
3.17.6.1.1
Electric speed transmitter
3.17.6.1.2
Electric controller including valve lift
controller
3.17.6.1.3
Electrohydraulic converters (gas fuel and
distillate fuel)
3.17.6.2
Gas fuel control valve
3.17.6.3
Light fuel oil control valve.
3.17.7
Electrohydraulic control system
3.17.7.1
Electric speed transmitter
3.17.7.1.1
Six digital magnetic sensors mounted on the free
shaft end of the generator measure gas turbine speed. The sensors scan the teeth of the toothed
shaft mounted gear wheel, which moves closely past the sensors. When a tooth cuts the magnetic field of the
permanent magnet in the sensor core, a voltage proportional to the shaft speed
is induced in the coil around the magnet.
3.17.7.1.2
The electronic circuit incorporated in the
sensor amplifies this voltage and converts it into a frequency independent
squarewave output signal. The signals
are then fed to a digital pulse convertor for signal multiplication and
processing (processor modules MFP) the output is the actual speed signal for
the electrohydraulic control system and the speed reference limiter. One output signal each is also transmitted to
a digital speed indicator on the gas turbine local control panel and the DCS
control desk.
3.17.7.2
Electrohydraulic converter
3.17.7.2.1
The electrohydraulic converter is the link
between the electrical and hydraulic parts of the control system. It converts signals received from the
electrohydraulic control system into hydraulic signals and amplifies them to
actuate the fuel control valve.
3.17.7.2.2
Attachment 6.50 shows sectional views of the
electrohydraulic converter. The
converter comprises plunger coil system ‘12’ with control sleeve ‘10’, pilot
valve ‘8’, follow-up piston ‘17’ and electrical feed back system ‘1’. The control signals from the electric
controller act a control sleeve ‘10’ via control plunger system ‘12’. The control sleeve slides on the upper part
of pilot valve ‘8’ and determines its position as a follow up piston.
3.17.7.2.3
The pilot valve and control sleeve is provided
with control ports; depending on the opening of the control ports more or less
control oil is drained. Under steady
state conditions, the main pilot valve is held in its center position by the
pressure in the control oil circuit against the force of compression
spring. To obtain high sensitivity and
unobstructed movement of the pilot valve, an integrally machined collar with
tangential holes for exit of the control oil causes a rotary motion of pilot
valve ‘8’.
3.17.7.2.4
When the pilot valve leaves its center position,
control oil entering at ‘a’ admitted to the space above or below amplifier
piston ‘5’ while the apposite piston face is connected to drain ‘c’; the
resulting movement of piston ‘5’ is transmitted to sleeve ‘16’ slides on follow
up piston ‘17’ the secondary oil pressure circuit from the hydraulic governor
is connected to the converter at ‘b’ the secondary oil pressure depends on the
tension of spring ‘18’ which holds follow up piston ‘17’ in position against
the force of this spring. Follow up
piston ‘17’ and sleeve ‘16’ are provided with control ports.
3.17.7.2.5
Depending of the openings of the control ports
more or secondary oil is drained. Changing
the throttling cross section by moving control sleeve ‘16’ causes a change in
the pressure in the follow up piston, causing it to follow the movement. The initial tension of spring ’18’ is changed
to restore equilibrium between the spring force and the new secondary oil
pressure. Each position of piston ‘5’
corresponds to a particular position of sleeve ‘16’ and thus also of follow up
piston ‘17’. The piston of the follow up piston thus determines the secondary oil
pressure at ‘b’ the initial tension of the follow up piston spring can be
changed by means of adjusting screw ‘19’.
3.17.7.3
Control sequence with electrohydarulic converter
3.17.7.3.1
If the electric controller transmits the command
for an increase in fuel flow, plunger coil system ‘12’ moves control sleeve ‘10’
upwards, causing the drain cross section to be reduced. The reduced drain cross section increases the
force exerted on the lower face of pilot valve ‘8’. The pilot valve moves upward and the control
oil entering at ‘a’ is supplied to the lower face of piston ‘5’.
3.17.7.3.2
The resulting movement of piston ‘5’ lowers
sleeve ‘16’ through levers ‘14’ and ‘15’, reducing the drain cross section
between the sleeve and the follow-up piston; this increases the pressure in the
follow-up piston and thus in the secondary oil circuit. The control valve is actuated in the more
fuel direction. The movement of piston ‘5’ causes pilot valve ‘8’ to return its
center position via differential transformer ‘1’.
3.17.7.3.3
Sleeve
‘1’ is returned to a position where pilot valve ‘8’ is in its center
position; this restores the equilibrium between the force exerted on the lower
face of the pilot valve and the force of spring ‘3’. If a command for a decrease in fuel flow is
given, the above control actions occur in reverse order.
3.17.7.4
Electrohydraulic speed control
3.17.7.4.1
Two types of speed control are required; one to
accelerate the turbine to related speed during start-up and the other to
maintain rated speed for generator synchronization.
3.17.7.4.2
The gas turbine generator is started by the
start-up frequency converter (see section 3.2 ‘starting system’). On opening of the fuel emergency stop valve
(ESV), fuel is admitted to the combustion chamber at minimum flow rate (see
section 3.15 ‘gas fuel system’ and section 3.16 ‘ light fuel oil system’).
3.17.7.4.3
The run up sequence control system then opens
the fuel control system then opens the fuel control valve according to a time
dependent setpoint function. The
frequency converter cuts out at approximately 2100 RPM (70% rated speed) and
the run up sequence control system runs the turbine generator set up to nominal
speed.
3.17.7.4.4
The following fuel control valve opening
setpoints are generated for run–up to speed to regulate control valve opening:
·
The controlled opening of the control valve h =
f(t) and
·
Speed control limitation of the control valve
lift h = f(n).
3.17.7.4.5
Both are applied to a minimum value gate and the
lower value is effective for run-up.
Because control valve opening h = f(t) is time controlled, the gas turbine generator run up to rated
speed under the normal start-up procedure without under stressing. In the event of the run up fault or reduced
start-up power, e.g. black start, the speed dependant lift limiter h = f(n)
intervenes and prevents overheating despite the slow rate of acceleration.
3.17.7.4.6
The electrohydraulic speed controller takes over
speed control when the gas turbine approaches rated speed and is effective
during generator synchronization. The
speed control circuit is a single loop controller; the controller compares the input
signal (actual turbine speed ) with a set point
(speed reference of 3000 RPM) and
produces and output signal that is proportional the difference or ‘error’
between the two inputs.
3.17.7.4.7
During the start-up sequence the speed
controller set point is 3000 RPM (50.00s-1). After synchronization and during load
operation, the load controller controls the gas turbine. During this time the speed control system
setpoints remains at 3000 RPM, ensuring that any speed increase during grid
disturbances (e.g. full load rejection) is kept below the setting of the
mechanical overspeeed trip setting.
3.17.8
Start-up control
3.17.8.1
The gas turbine unit will have an automatic
starting and loading system with all necessary facilities to permit for
independent operation in the open cycle mode, as well as combined cycle mode. This
initial run up, synchronization and loading to a demanded load level will be
fully automated and started from the single button initiation and minimum
operator supervision.
3.17.8.2
The automatic start-up sequence will be fully
supported by stage initiations, subject to all necessary interlocks at the
functional group, subgroup and remote manual control levels, where appropriate,
to permit operator intervention under abnormal start-up or fault conditions.
The start-up control is an open loop with inputs from the sequencer to
determine fire, warm-up acceleration an the signal required to position the
fuel valve (s). Each of the preset
values are established as a function of speed or time and are in place to avoid
flame-out, over temperature or improper warm-up or acceleration.
3.17.8.3
Start-up control provides input to the minimum
value gate circuits, like the other parameters of speed and exhaust
temperature, any of which can limit fuel and protect the turbine. Upon start-up
the static frequency converter sarting device, bring the turbine approximately
20 percent rated speed. At this time the unit is purged of any residual fuel,
and then fuel and spark or introduced. When flame is detected, the fuel flow is
set to the warm up value.
3.17.8.4
After warm-up the starting device contributes
maximum power, and the acceleration is increased exponentially, as in the
temperature control, so as not to allow the exhaust temperature to rise at rate
of more than 5ºC per second and the speed of 1% per second normally and 2% per
second for the fast rate. As the turbine speed rises exhaust temperature will
stop rising and start to decrease.
3.17.8.5
At approximately 70% speed the starting is cut
off and the speed controller takes command at nominal speed, completing the
start-up sequence and preparing the turbine for synchronization and
loading. Auto synchronization will be
performed by the DCS through dedicated circuits.
3.17.8.6
The speed sequencing and time setting will be
programmed and produced within the redundant MFPs. As one of the features
provided with the Infi 90 system, the plant personnel will have the capability
to completely tune the control system to take advantage of changing site
conditions.
3.17.9
Load control
3.17.9.1
The load controller is used primarily for
control in operation. It is also used
for the controlled loading and unloading of the turbine generator set along the
loading characteristics PS =
f(t) generated by the load set point controller, both during start-up shutdown
and normal operation. The actual load is sensed at the generator terminals and
fed to the load controller. After set
point / actual value comparison, the load controller acts on the valve lift
controller and on the fuel control valve via the respective Electro-hydraulic
converters.
3.17.9.2
The load control combines the speed error signal
with the load reference signal limit and biases to determined desired fuel flow
rate. The fuel control system is a closed loop configuration, which includes
the number of supplemental, mechanical devices when fired on oil, gas or
mixing. When multiple fuel are used, the system provides to proportion fuels
along with the basic requirements of speed, exhaust temperature and start-up
limiting. The fuel control loops are position control loops with fuel control
stroke position on the gas control valve.
3.17.10
Turbine inlet temperature control.
3.17.10.1 The
temperature controller operates as a standby limiter to protect the turbine
against high inlet gas temperature during start-up and load operation. The unit
may, however also be operated under the exclusive control of this controller. The turbine outlet temperature is measured by
six double element thermocouples. The
average value derived from these measurements is corrected for the compressor
inlet temperature, measured by means of two double element resistance
temperature detectors.
3.17.10.2 The
corrective compensates for the effect of fluctuations in the compressor inlet
temperature. The ratio of the corrected
exhaust gas temperature of the turbine inlet temperature is constant at nominal
speed. The corrected turbine outlet
temperature is fed to the temperature controller as an actual value signal. In
the event of failure of one or more of the exhaust gas thermocouples an alarm
annunciates at the DCC control desk. The
mean values that continues to be generated by the remaining functioning
thermocouples.
3.17.10.3 The
DCS system provides the capability to monitor / trend the temperature signal
ensuring increased life of the turbine combustion and hot gases path
components; thereby increasing turbine life and running time between maintenance
outages. A minimum value selector bring in the temperature limit controller
when the corrected exhaust gas temperature exceeds the permanently set limit
for base or peak load operation. An
indication “TEMP- LIMIT CONTR.” At the DCS control desk indicates when the
temperature controller is activated.
3.17.10.4 The
temperature limit controller goes back into standby operation when the load set
point is lowered and the corrected exhaust gas temperature drops back below the
selected limit value. The temperature controller is used to set the gas turbine
exhaust temperature that required for combined cycle operation. A temperature set point of between 200ºC and
600ºC can be set at the “TEMPERATURE SET POINT” panel control module [1MBY10-DE010]
3.17.11
Normal shutdown
3.17.11.1 The
control system is designed to automatically shutdown the gas turboset from full
load following the proper sequence of operations initiated by the operator. The
control systems will first transfer from temperature control from load control
providing the unit is base or peak loaded.
3.17.11.2 Once
the unit has reached 40% load, automatic transfer of the unit from premix to
diffusion burner will begin. Once the
unit has transferred to the diffusion burners, the unit will be further loaded
until ultimately opening the generator breaker.
As the unit coasts down in speed the turning gear and lift oil pump will
be engaged. The sequence will be completed stopping the turning gear and lift
oil pump after a proper cooling cycle in function of GT thermal conditions.
3.17.12
Control cabinet
Most of the
control system components described above are housed in the gas turbine local
control cabinet located next to the main lubricating oil tank (see figure
1.3.3). Figure 2.13.8 shows arrangement
and facia drawings of the control cabinet and identifies the locations of the
main components.
3.18.1
The safety and protective devices provide a
means of tripping the gas turbine both during normal shutdown and during fault
conditions. The gas turbine is a prime mover operating at 3000 RPM using high
pressure gas at temperature exceeding 1000ºC.
Under such severe operating conditions, it is imperative that is
effective means be provided for an immediate shutdown of the gas turbine when
fault conditions develop.
3.18.2
The gas turbine is ‘tripped’ by shutting off
fuel supply; the fuel emergency shut-off valve (ESV) is closed by spring
force. On interruption f fuel supply and
thus combustion flame, the motive power of the gas turbine is lost and it
coasts down to turning gear operation.
Operation of the fuel gas (ESV) is described in section 3.15 and the
light fuel oil (ESV) in section 3.16.
The (ESV) is held open by hydraulic oil pressure supplied from the
control oil system see section 3.13. All
tripping and protective devices drain the (ESV) supply oil and spring comprise
the following main components:
3.18.2.1
Trip oil system (see section 3.14)
3.18.2.2
Trip solenoid valve
3.18.2.3
Protective instrumentation.
3.18.2.4
Over speed protective devices – protech 203
Woodward.
3.18.3
The trip oil system that supply the control oil
at approximately 8 to 9 bar proceeds to the hydraulic cylinders of the stop
valves via solenoid several valves as mentioned below:
3.18.3.1
Trip solenoid valve [1MBX41-AA001].
3.18.3.2
Solenoid valve for fuel oil stop valve
[1MBV13-AA001A].
3.18.3.3
Solenoid valve for fuel gas stop valve
[1MBP13-AA001A].
3.18.4
When the trip solenoid valve closed the trip oil
pressure dumps to zero and both the fuel stop valves close thus tripping and
stopping the gas turbine. The protection function of the system protects the
turbine and parts of the installation associated with it form operating
conditions are not permissible.
3.18.5
The structure of the system guarantees that the
installation will, in case of malfunction, be brought into the safe condition
with no danger to human life or the machine.
Supervision instrumentation for critical process are installed and
incorporated with trip / protections system of the gas turbine. The following
typical trip functions provided for gas turbine unit:
3.18.5.1
Rotor vibration very high (with start-up
override).
3.18.5.2
Bearing temperature very high.
3.18.5.3
Exhaust temperature very high.
3.18.5.4
Exhaust differential temperature very high.
3.18.5.5
Flame failure.
3.18.5.6
Lube oil temperature very high.
3.18.5.7
Lube oil pressure very low.
3.18.5.8
Turbine over-speeds.
3.18.5.9
Trouble in control power supply.
3.18.5.10 Fuel
pressure very high.
3.18.5.11 Fuel
pressure very low.
3.18.5.12 Generator
tripped.
3.18.5.13 Fire.
3.18.5.14 Others
if required.
3.18.6
The safety signals are sent directly to the trip
circuits, without being interlocked to one another. All trip signals formed and
processed electronically are integrated into the protection system. In
particular, hardware and software configuration of modules will allow the
acquisition of trip signals in 1 out of 1, 2 out of 2 and 3 out of 3 logic. The
electrical protection system operates on two solenoid valves connected in
parallel in a normally open circuit. The protection system will display the
first trip cause to allow the operator the analysis of the emergency shutdown.
3.19.1
The gas turbine instrumentation is designed to
provide continuous monitors of the process flow parameters. Critical process flow parameters stringently
monitored and transmitted to the gas turbine local control panel and DCS
control desk.
3.19.2
Instrument monitoring safety signals are sent
directly to the trip circuits without being interlocked to one another where as
all trip signals from the instrument are formed and processed electronically
and integrated into the protection system.
3.19.3
Following are the types of measuring points and
applications of signals.
3.19.3.1
Speed signals.
3.19.3.2
Vibration measurement.
3.19.3.3
Temperature measurement.
3.19.3.4
Level measurements.
3.19.3.5
Pressure measurements.
3.19.3.6
Flow measurements.
3.19.3.7
Flame intensity measurement.
3.19.3.8
Limit signals (open \ close) and etc.
3.19.4
The gas turbine instrumentation, with the
exception of instrumentation belonging to the auxiliary systems, is indicated
in the PID. The auxiliaries instrumentation is illustrated in the separate PID
diagram relating to the various auxiliary systems, the list of measuring
instruments also shows the setting for switching type instruments. Following
are the critical field instrumentation used in the gas turbine:
3.19.4.1
Speed measurement.
The speed
of the turbine generator set is measured by means of two 3-channel–type redundant
systems featuring speed transmitters [1MBA10-CS001/2/3/4/5/6]. The speed data
are used for the electrical speed controller, the speed dependant switching
operations, the electrical over-speed trip device and speed indicators.
3.19.4.2
Vibration measurement.
Vibration
transmitters [1MBD11-CY021] and [1MBD12-CY021] measures casing vibrations near
the turbine bearing and the compressor bearing.
The vibrations are displayed and/or recorded. A bearing vibration high alarm is issued if
an initial limit value is exceeded, and if a higher limit is exceeded, turbine
trip is initiated by emergency solenoid valve [1MBX41-AA001].
3.19.4.3
Bearing temperature measurement.
The metal
temperature of the turbine bearing, the compressor bearing and the thrust
bearing for both directions are measured with thermocouples [1MBD11-CT011,
1MBD12-CT011 and 1MBD12-CT031 through …034].
The temperatures are displayed.
If the T. LARGER.M limit value is exceeded (e.g. 100ºC), a bearing
temperature high alarm is issued, and if the higher limit T.LARGER.S is
exceeded (e.g. 120ºC), turbine trip is initiated by [1MBX41-AA001].
3.19.4.4
Air temperature upstream of compressor.
Resistance
thermometers [1MBA11-CT011/12/13]
measures the compressor intake temperature which is required for calculating
the corrected exhaust gas temperature (ATK) for temperature limit control and
for turbine temperature protection. The
measurement is also used to determine the compressor mass flow value.
3.19.4.5
Pressure upstream of compressor
Pressure
transducer [1MBA11-CP004] measures the sub-atmospheric pressure in the
compressor intake duct. It must be
ensured that isolation valve [1MBA11-AA302] is always open in order to prevent
measuring error. This pressure measurement
in combination with the air temperature measurement upstream of the compressor
is used to determine the compressor mass flow.
3.19.4.6
Compressor surge detection
The
pressure drop between the intake duct and the compressor inlet (at the inlet
guide vane row) is measured by differential pressure switch
[1MBA11-CP001]. If, at a turbine speed
above S.TURB.15 (2520 RPM) the differential pressure falls below a certain
value something which occurs if the compressor surges turbine trip is initiated
by solenoid valve [1MBX41-AS301]. Once
the gas turbine is standstill drain valves [1MBA11-AA201and …AA211] must be
opened for a short period in order to drain the pressure sensing lines. The isolation valves ahead of the measuring
instruments must always be open in order to prevent measuring error.
3.19.4.7
Compressor discharge temperature and pressure.
Pressure
transducer [1MBA12-CP001] and thermocouples [1MBA12-CT001] measures the
compressor discharge pressure and temperature for local display at the turbine
generator set control console and where appropriate for data acquisition. Following turbine standstill drain valve
[1MBA12-AA201] must be opened for a short period of time in order to drain the
pressure sensing line.
3.19.4.8
Turbine cooling air temperature.
Differential
pressure indicator [1MBA21-CP501] measures the pressure drop between the
compressor outlet and the cooling air chambers in the turbine stage 1. Any change in the pressure differential for a
given set of operating condition indicates that there may be a malfunction in
the turbine cooling system. Once the
turbine has come to a standstill, opening drain valves [1MBA12-AA201] and
[1MBA21-AA201] must drain the pressure sensing line. It is imperative that these valves be
immediately closed again once the draining operation has been completed.
3.19.4.9
Turbine exhaust temperature.
The
temperature of the turbine exhaust gas is measured by 3 double thermocouples
[1MBA22-CT012/13/14 and 1MBA22-CT016/17/18] assigned to each combustion
chamber. One signal for each double
thermocouple is used to form the mean combustion chamber temperature
value. This in turn is used in
conjunction with the air temperature measurement upstream of the compressor to
from the corrected exhaust gas temperature ATK.
The ATK signal constitutes the actual value for the temperature limiter
controller, and is indicated and/or recorded at the local control console.
The generator is of a conventional design, water/air-cooled,
2-pole machine with cylindrical rotor, ventilated in closed circuit employing
air-to-water heat exchangers located in the lower part of the stator frame. It
consists of the following subsystem and major components:
3.20.1
GT Generator Cooling System
3.20.2
GT Generator Cooling Air Path in Stator
3.20.3
GT Generator Cooling Air Path in the Rotor
Conductors
3.20.4
GT Generator Make-up Filter
3.20.5
GT Generator Coolers
3.20.6
GT Generator Stator
3.20.7
GT Generator Stator Winding
3.20.8
GT Generator Rotor
3.20.9
GT Generator Bearings
3.20.10
GT Generator Bearing Insulation
3.20.11
GT Generator Rotor Grounding
3.20.12
Static Excitation System
3.20.13
Voltage Regulator
3.20.14
Excitation Slip-rings and Brush-holders
3.20.15
Sound-proof enclosure
3.20.16
Generator Instrumentation
Two axial
fans supply the self-ventilated generator with cooling air. There are two parallel cooling air circuits,
each fed by one of the axial fans, these cooling circuits are symmetrical to
the mid-plane of the generator as shown in Attachment 6.51.
3.21.1
GT Generator Cooling Air Path in Stator
3.21.1.1
The stator is subdivided to give four
ventilation chambers for each half of the generator. One portion of the cooling air is sent
directly into the air gap; there it joins the cooling air coming from the rotor
end winding.
3.21.1.2
Together they leave the air gap through radial
passages in the laminated core and enter the first chamber of the housing. From that point the warmed air flows to the
coolers and returns to the fan through the small pin in the foundation.
3.21.1.3
The other portion flows outward through the
stator ends winding, and passing through axial channels, enters the second
chamber of the housing. From that point,
it flows inward through the radial passages in the laminated core. It enters the air gap and splits up, one
portion passes outward through the radial passages and enters housing chamber
1, another portion flows to the center of the machine where it joins the rotor
cooling air.
3.21.1.4
One portion of the air from the second housing
chamber is then directed through axial channels to the fourth housing chamber,
from that point onwards it flow in a radial direction to the air gap where it
mixes with the rotor cooling air. The cooling air flows from housing chambers 2
and 4 and the rotor cooling air comes out through radial passages into housing
chamber 3. From that point, the warmed
air flows back through the coolers and then returns to the fan. See Attachment 6.52 Figure 2.
3.21.2
Generator Cooling Air Path in the Rotor
Conductors
3.21.2.1
The rotor generates its own flow of cooling air
by virtue of its rotation. The air
outlet is on a larger radius than the air inlet, this generates the necessary
pressure head required to produce the air flow.
3.21.2.2
The cooling air enters the rotor between the
centering ring and the shaft and flows into the end-winding chamber. At the inlet to the slots, the air enters
into the follow conductors. There it
splits up into two portions.
3.21.2.3
One portion flows through the hollow conductors
in the slots and reaches the center of the rotor, where it comes out into the
air gap through radial holes milled in the hollow conductors and in the slot
wedges.
3.21.2.4
A second portion flows through the hollow
conductors in the end winding. It reaches the polar axis where it leaves the
hollow conductors, emerging into the air gap through short slots in the end of
the rotor body.
3.21.3
Generator Make-up Filter
3.21.3.1
A self-ventilated closed cooling air circuit is
never completely free of leaks. In the
end zones where over pressure prevails (those on the pressure side of the fan)
air can therefore escape to the outside.
In the zones where a vacuum prevails (those on the suction side of the
fan) air can be drawn in from the outside.
However, this replacement air should not be allowed to enter freely into
the generator through cracks and seals.
Its entry should be controlled, through openings specially provided for
that purpose. These openings have been
made in that zone where static pressure has a minimum, i.e. immediately
upstream of the fan.
3.21.3.2
In order to prevent contamination from entering
the generator along with the replacement air, the replacement air openings have
been equipped with filters attached to the outer face covers (see Attachment
6.52 Figure 3). The filter medium is
made of fiber with a duct-retaining bonding.
The single-stage filter provides effective filtration for air that is
relatively cleans and contains no chemical pollutants and no conducting
particles. The filters are to cleaned or
taken out and replaced in conjunction with the periodic maintenance
inspections.
3.21.4
Generator Coolers
3.21.4.1
The coolers are surface type heat exchangers
used to cool the air (primary coolant) in the generator back down after it has
been warmed. The secondary coolant is
water.
3.21.4.2
The coolers consist of four elements arranged
horizontally in the lower part of the stator housing. They are hydraulically connected in parallel
both on water and airsides. Each element
consists of a fairly large number of straight tubes. In order to increase their surface area, they
have been provided with fins on the outside.
The cooling water flows within the tubes and the generator cooling air
is cooled off along the outside surface.
3.21.4.3
Both ends of the tubes are rolled into tube
plates, to which the water chambers are bolted.
The water chambers have been subdivided in such a way that the water
flows back and forth. This takes place
in a direction counter to that of the air (cross counter flow cooling). See Attachment 6.52 Figure 4.
3.22.1
The main parts of the stator are:
3.22.1.1
Housing
3.22.1.2
Laminated core, including winding
3.22.1.3
Flexible coupling of the stator core in the
housing.
3.22.2
The housing is a steel fabrication split
horizontally into top and bottom halves. The laminated cores are first wound
and then pun into the bottom half of the housing. The top half is then bolted on. The housing both transmits forces to the
foundation and guides the flow of the cooling air. The covers at the ends also serve this latter
purpose. The outer cover separates the
cooling circuit of the generator from the surrounding, the inner cover separates
the chambers before (suction) and after (pressure) the fan.
3.22.3
The laminated core consists of a fairly large
number of relatively narrow lamination packets separated by radial ventilation
passages. I-section spacers, mounted on
a support plate, define the width of these passages. The individual laminations consist of
low-loss, non-grain-oriented, segments made of silicon-alloyed
electroplate. The segments are stamped
from rolls of sheet steel. They are then
deburred and coated on both sides with a special heat-resistant insulating
varnish made of synthetic resin with inorganic pigments. This results in a high insulation resistance
between the segments with outstanding resistance to aging.
3.22.4
The self-supporting core is stacked outside the
housing and the segments are overlapped from one layer to the next. Tie bars on the back of the core serve two
purposes; they provide exact location of the individual laminations and a solid
connection to the press plates attached on both ends. These plates are made of quenched and
tempered cast aluminum alloy and by producing a good shield between the end
laminations and the end region stray field, they keep end region losses low.
These press plates have a slightly dished form, and effectively act as large
‘belleville’ washers. Press fingers
located between the press plate and the end plate transmit the pressure exerted
by the press plate to the core, and particularly to its teeth.
3.22.5
Flexible Coupling of the Laminated Core – The
laminated core is spring-mounted in the housing, in such a way that the
majority of the core vibrations are not transmitted to the foundation. This is accomplished by using a horizontal
two-point suspension. This arrangement
also takes up differences in thermal expansion between the housing and the
core.
3.23.1
The stator winding is a three-phase, double
layer, indirectly cooled Roebel bar winding.
Each bar consists of rectangular copper strands insulated by
fiberglass. These strands are transposed
in the Roebel configuration as shown in Attachment 6.53 Figure 5. This keeps the circulating current losses to
a minimum.
3.23.2
The slot portion of the bar, impregnated with
resin that consolidates the fiberglass surrounding the strands, is cured in a
heated press. The end-winding portion of
each bar is formed so that the entire end winding is cone shaped with its axis
coincident with the machine axis. Once
the bars have been so shaped, the main insulation is applied. This consists of a continuous length of
fiberglass fabric mica tape wound over the whole length of the bar. After this the corona protection is provided
by applying conducting tapes to the slot portion and one of semi-conductive
paint to the end winding to grade the potential over the bar surface.
3.23.3
The bars are built into the slots with liners at
the slot bottom, spacers between the bars and fillers under the wedges (see
Attachment 6.53 Figure 6). Absorbent
fiberglass cords woven amongst the bars are used to brace the cone-shaped end
winding and to ensure correct spacing between the bars.
3.23.4
The entire end winding is supported on
trapezoidal brackets of insulating materials that are bolted to the press
plates. The bars are tied tightly to
these supports by fiberglass ropes.
Brazing to form the coils joins the ends of the top and bottom
bars. At the collector rings side, the
support brackets are also used to carry the phase connectors and the
connections to the phase and neutral terminals.
3.23.5
The whole stator wound core is then totally
impregnated in a tank with solvent-free epoxy/polyester-based synthetic resin.
This is done in a vacuum-pressure impregnating process. After the impregnation, the whole stator
wound core is cured in hot air.
3.23.6
Alternatively, the single bars impregnation
process can be applied. In such a case,
after wrapping on the bars the ground insulation and applying the corona
protection on the slot portion and at the ends, the bars undergo to an
impregnating process similar to that described for the whole stator but applied
only to the bars.
3.23.7
The bars are then assembled in to the core slots
inserting conducting filling strips between the bars and the slot wall and the
top ripple spring between the top bar and the slot wedge (see Attachment 6.53
Figure 6b), in order to avoid loosening during operation due to thermal
effects. The end windings are braced to
the insulating brackets similarly to that described in case of total
impregnation as well for the other assembly phases.
3.23.8
The terminals are of rectangular copper bars
with holes drilled for bolting of the leads.
The insulating system gives the stator winding outstanding dielectric
properties and excellent thermal behavior.
These features guarantee a long life service for the winding. All insulating materials used in the stator
are of Insulation Class F. They are
flame-retardant and self-extinguishing.
The main parts of the rotor are:
3.24.1.1
Rotor body
3.24.1.2
Rotor winding
3.24.1.3
Damper winding
3.24.1.4
Retaining rings
3.24.1.5
Fans
3.24.1.6
The rotor body is a single-piece forging of
high-quality alloy steel. Extensive
checks both at the forge and at ANSALDO works allow to ascertain that the
required mechanical, chemical, and magnetic properties of this important part
of the machine are met. The coupling
with the turbine is made by means of an integral forged flange at the driving
end of the shaft. In the winding zone,
rectangular slots are milled into the rotor body to accommodate the
windings. The non-driving end of the
shaft has a concentric axial bore which extends as far as the rotor body and
accommodates the two semi-circular-section copper leads for the excitation
current (see Attachment 6.54 Figure 8 Sheet 1/2).
3.24.1.7
The rotor winding has direct axial cooling. It consists of hard-drawn rectangular hollow
conductors made of copper alloyed with 0.1% silver to increase its heat
strength. Heating up during operation
causes the rotor winding to expand symmetrically outward from the middle toward
both ends. The axial cooling ensures
minimal differences in temperature rise in radial direction within a coil. For this reason, no relative conductor
movement takes place under either transient or steady state conditions.
3.24.1.8
The whole structure (copper plus insulation) is
designed so that the entire slot fill expands as one unit and slides against
the wedge. This sliding takes place at a
low friction coefficient. This results
in vibration-free running under all load conditions. A U-shaped channel made of polyamide paper is
used as the slot insulation and the winding insulation in the end winding is of
the same material. In the slot,
fiberglass cloth impregnated with epoxy resin is used. In the end windings spacer pieces of
fiberglass cloth impregnated with epoxy resin are used to position the coils
exactly with respect to each other and to define the path of the cooling
air. All insulating materials used in
the rotor are on Insulation Class F, flame-retardant and
self-extinguishing. Dovetail-shaped
wedges made of a high-conductivity copper-nickel alloy are used to seal off the
slots. These are also a part of the
damper winding described further below.
See Attachment 6.54 Figure 9 Sheet 2/2.
3.24.1.9
The function of the damper winding is to provide
a low resistance path for the currents caused by fields rotating relative to
the rotor, thereby keeping that energy from causing damage. The damper winding is formed by the winding
slot wedges, made of a copper-nickel alloy with a good conductivity. Each of a single piece without interruptions
along the length of the rotor.
Centrifugal force binds them together in the area of the retaining ring
seat to form a complete damper cage.
This damper winding in sufficient to sustain inverse fields expressed,
in accordance with standards, as I2, or an equivalent unbalanced
load resulting from harmonic loading.
The permissible continuous inverse current I2 is according to
IEC and ANSI standards.
3.24.1.10
Rotor retaining rings made of high-quality
austenitic nonmegnetic steel hold the end winding firmly in place and protect
them from deformation due to the centrifugal forces. The retaining rings are shrunk on to the body
of the rotor in an overhung mounting.
They are held axially, locked on the teeth by bayonet system (see
Attachment 6.54 Figure 10 Sheet 2/2).
Due to their overhung design, no forces originating due to thermal
expansion in the windings can be transmitted to the shaft. This avoids any dependence of the rotor
vibration from temperature of winding.
The retaining rings material is immune to stress corrosion cracking. The retaining rings are the most highly
stressed components in a generator. For that
reason, the supplier carries out extensive testing and at Ansaldo factory in
order to ensures that their properties comply with the specification.
3.24.1.11
An axial fan is installed at each end of the
shaft. The fan hubs are shrunk onto the
shaft. The fan blades are made of a
drop-forged-alloyed aluminum. Their
angle is adjustable according to the rotational speed and the airflow desired
and they are joined to the hub via a bolted connection.
3.25.1
There is a welded bearing pedestal at each end
of the generator. The rotor is supported
on pocket-type bearing shells, which are split horizontally. When the rotor turns, a load-supporting
lubricating film is formed automatically due to hydrodynamic forces. This protects the bearing at the turbine.
3.25.2
The bearing shells are made of steel, lined on
the inside with a white metal alloy.
Four adapter plates, around the circumference center the bearing shell
in its bearing ring. The bearing ring
itself is held in place by the bearing cap.
In order to prevent oil from entering into the machine, the bearings are
separated from the stator housing and are sealed off by means of double
labyrinth seals. See Attachment 6.54
Figure 11 Sheet 2/2.
3.25.3
Each bearing has been provided with the
arrangement for a jacking oil connection to reduce bearing friction during
startup and shutdown and to make possible the operation of the primary machine
on a turning or barring device. The bearings
are provided with lube oil from a common oil supply system with the turbine.
3.26.1
To prevent shaft currents from flowing through
the bearings, the bearing on the non-driving end has double insulation. This double insulation consists of the
adapter plates which are of insulating material and a layer of insulation
between the bearing pedestal and the bearing ring (see Attachment 6.54 Figure 7
Sheet 1/2).
3.26.2
In addition, the oil scrapers have single
insulation while the jacking oil connection has double insulation. The double insulation of the bearing allows
monitoring the condition of the insulation during operation. Therefore, the bearing pedestal has been
equipped with measuring point.
Two grounding brushes (wired to a terminal box) located on the
turbine end side provide the shaft grounding.
3.28.1
In static excitation system, the power is
supplied by a stationary thyristors bridge generally fed via a transformer
connected to the generator bus bars or to an auxiliary source. The generator field winding is fed through
slip-rings shrunk onto the generator shaft at the non-driving end. See Attachment 6.55.
3.28.2
The static excitation system includes the
following main components:
3.28.2.1
Three-phase excitation transformer.
3.28.2.2
Power converter
3.28.2.3
Static circuit breaker (crow-bar).
3.28.3
Voltage Regulator
3.28.3.1
The brushless exciter field power supply (or the
main generator field supply) is controlled by the voltage regulator. The
automatic voltage regulator (AVR) provides the field current regulation
required maintaining the desired voltage at the generator terminals.
3.28.3.2
Two voltage regulators, one automatic AVR and
manual, MVR are provided to allow the operation in case of outage of one of
them for maintenance. The AVR are provided with the following limits:
3.28.3.2.1
Maximum excitation current limit
3.28.3.2.2
Under excitation limit
3.28.3.2.3
Volt/hertz limit
3.28.3.3
A setting device (calibrator) for the two
voltage regulators is provided with an automatic follow-up of the MVR with
respect to the AVR. The firing circuits for the control of the thyristor gate
consists of an automatic field voltage regulation loop to stabilize the output
of the bridge even if the a.c. voltage of the power supply of the rectifier
changed.
3.28.3.4
Its d.c circuitry is provided by both the
feeders with the relevant de-coupling diodes. The feeders (one for AVR and one
for MVR) are independent and each one is supplied by the plant battery and by
an a.c. source taken from the excitation transformer.
3.28.4
Excitation Slip-rings and Brush-holders
3.28.4.1
The slip-rings and brush-holders transmit the
excitation current from the stationary static excitation system to the rotating
field winding. The slip-rings are
grooved and have been put on an extension of the shaft at the non-driving
end. The shaft is provided with an
insulation layer and the slip-rings are then shrunk onto it to lock them in
place.
3.28.4.2
The brush-holders, together with the housing,
are mounted on a plate. The brushes and
slip-rings can be observed through windows in the casing. The brushes are made of natural graphite,
without binding agents, and are self-lubricating. They are seated in flat spiral spring
brush-holders that produce a uniform brush pressure throughout the entire wear
zone. The brushes can be taken out and
replaced during operation. The
brush-holders have been mounted on a plug-in device to make this possible. The connections on the brush rockers are designed
is such a way that polarity can be reversed which results in a more uniform
wear on the slip-rings.
3.28.4.3
The ventilation of the slip-rings housing is
provided by a radial fan, shrunk onto the shaft, in an open circuit with air
drawn in from below across single-stage mat filters. The air is discharged at the top. The filters provide effective filtration for
relatively clean air that contains no significant amount of dust or chemical
pollutants. Differential pressure
switches monitor the filter. The filters
are to be inspected whenever the differential pressure switches have gone off
and also during periodic maintenance inspections.
3.29.1
The generator is provided with an acoustical
enclosure consists of an external cover that extends over the generator and the
slip-rings housing. Lighting and arrangement for connection to the
fire-fighting system (thermostats and sprinklers) are also provided inside the
enclosure. Two fans are provided for change of air inside, so that it is
possible to access inside for inspection and maintenance.
3.29.2
The sound-proof enclosure is made of steel, the
sound absorbing material is attached to the inside of the steel frame and held
in place by a cover of perforated sheet metal screen. The sound absorbing
material consists of maintenance operations and lateral opening is provided to
withdraw the coolers.
3.30.1.1
The instrumentation built into the generator is
used primary to monitor the temperatures and the correct operation. The
standard instrumentation is as follows:
3.30.1.1.1
RTD temperature detectors PT100 in the stator
winding between the top and bottom bars into the slots spaced around the
circumference (9 nos.)
3.30.1.1.2
RTD temperature detectors PT100 in the stator
core (4 nos.)
3.30.1.1.3
RTD temperature detectors PT100 for hot air
entering the coolers, 1 for each section (4 nos.)
3.30.1.1.4
RTD temperature detectors PT100 for hot air
leaving the coolers, 1 for each section (4 nos.)
3.30.1.1.5
RTD temperature detectors PT100 on the bearing
liner, 1 each bearing (2 nos.).
3.30.1.1.6
Thermometers on the bearing oil drain, 1 each
bearing drain (2 nos.).
3.30.1.1.7
Sight glass indicators for oil circulation, 1
each bearing (2 nos.).
3.30.1.1.8
RTD temperature detector PT100 for hot air
leaving the slip-rings housing
3.30.1.1.9
Leakage detectors in the generator housing
(2nos.)
3.30.1.1.10
Differential pressure gauge across the slip
rings housing filters (2 nos.).
The functions of the generator protection and metering circuits
are:
3.31.1
To isolate and thereby prevent damage to the
generator and transformer under certain internal and external fault conditions.
3.31.2
To ensure safety of plant personnel.
3.31.3
To annunciate an alarm when a minor fault
occurs. Action to remedy the fault
prevents it from deteriorating and causing further damage.
3.31.4
Detailed description
3.31.4.1
The generator, generator transformer and the
unit transformer are refereed to as an “unit system” and the protection relays
and devices that, protect the equipment are collectively refereed to as a “unit
protection system”. When a shot circuit
fault occurs, the current flowing through an effected circuit increases substantially. Similarly, when an open circuit fault occurs,
the voltage in the effected circuit changes substantially. The protective relays sense any abnormal
current and current and voltage in their circuits and initiate either an alarm
if the fault is minor or tripping if fault is major.
3.31.4.2
Current and voltage transformers sometimes
referred to as instrument transformers, measure the high currents and voltages
associated with the generator and transformer output currents and voltage. The current and voltage in the secondary
winding of the instrument transformers are proportional to the values being
measured but are of a much lower magnitude.
3.31.4.3
The tripping relays also activate lockout
relays, which prevents the tripped equipment from being returned to service
until the cause of trip has been found and corrected. The lockout relay must be manually reset,
either by hand, or electrically.
3.31.4.4
The generator protection and metering system
comprises the following major components:
3.31.4.4.1
Reverse power.
3.31.4.4.2
Differential protection.
3.31.4.4.3
Over voltage.
3.31.4.4.4
Earth fault (Alarm and trip).
3.31.4.4.5
Back-up differential protection.
3.31.4.4.6
Under voltage protection.
3.31.4.4.7
Over load.
3.31.4.4.8
Over current.
3.31.4.4.9
Under impedance.
3.31.4.4.10
Unbalanced load.
3.31.4.4.11
Under excitation.
3.31.4.4.12
Over fluxing.
3.31.4.4.13
Excitation fault.
3.31.4.5
Reverse power protection.
The relay
protect against the condition where current flows from the power grid into the
generator instead of the other way around.
This condition is referred to as reverse power and is caused when the
generator main circuit breaker remains closed after the gas turbine tripped or
when a sufficient load demand is not set after synchronization of the
unit. The reverse flow of the current
causes the generator t drive the prime mover, in this case the gas turbine,
which can be damaged in the motoring condition.
The relay activates the tripping of both the generator 15kV Air Blast
Circuit Breaker (ABCB) and the field circuit breaker. The gas turbine remains at full speed
no-load.
3.31.4.6
Generator differential protection
This relay
is an instantaneous ratio differential relay, which detects phase faults in the
generator windings by measuring the difference in phase currents. The phase currents, measured by current
transformers, are summed in a circuit.
This vector sum of the currents should be zero under normal
conditions. When the faults occurs
within the zone, this sum is no longer zero due to the differential current
caused by the fault. The relay activates
the flowing actions.
3.31.4.6.1
15 kV generator ABCB trip.
3.31.4.6.2
Gas turbine emergency trip.
3.31.4.6.3
Field circuit breaker trip.
3.31.4.6.4
Excitation transformer 6 kV breaker trip.
3.31.4.6.5
Start-up frequency converter trip (on start-up).
3.31.4.7
These relays protect the stator insulation
against over voltage condition, which could arise from over excitation or
system power swings. The stator insulation must be protected from these over
voltage conditions. The voltages at the generator terminals are sensed by
potential transformers, and compared with a threshold value. The over voltage
relay activates the following actions.
3.31.4.7.1
15 kV generator ABCD trip.
3.31.4.7.2
Gas turbine emergency trip.
3.31.4.7.3
Field circuit breaker trip.
3.31.4.7.4
Excitation transformer 6 kV breaker trip.
3.31.4.7.5
Start-up frequency converter trip (on start-up).
3.31.4.8
Stator earth fault protection – 100% and 95%
The stator
earth fault protection detects a phase to earth fault in the generator stator
winding which causes a current to flow in the generator neutral. The neutral of the generator is earthed
through a transformer to limit the fault current.
3.31.4.8.1
100% earth fault protection
A definite
minimum time relay is connected to the neutral earthing transformer. This relay detects the flow of neutral return
current during an earth fault condition and annunciates an alarm.
3.31.4.8.2
95% earth fault protection
A current
transformer (CT) is installed in the generator neutral conductor the neutral
earthing transformer. This CT detects
earth fault current in the generator neutral and initiates a tripping of the
generator main circuit breaker and gas turbine.
3.31.4.9
Back-up generator differential protection
The back-up
generator differential protection (also called unit overall differential
relays) are instantaneous ratio differential relay which detects phase fault in
windings of the generator, its transformer and the unit transformer. A high differential current in the circuit
being monitored often indicates an internal electrical fault in the associated
equipment. These relays are provided
with harmonic restraint to prevent a spurious trip when the circuit breakers
are first closed. When the circuits
breakers are closed to energize the generator and transformers, frequency harmonics
(multiples of the fundamental frequency of 50 hertz) are usually generated due
to the inrush of currents, the restraint feature prevents these frequency
harmonics from inadvertently tripping the circuit breaker. The relay activates the following actions:
3.31.4.9.1
132 kV CB trip.
3.31.4.9.2
6 kV unit board incoming CB trip.
3.31.4.9.3
15 kV generator ABCB trip.
3.31.4.9.4
Gas turbine emergency trip.
3.31.4.9.5
Excitation transformer 6 kV breaker trip.
3.31.4.9.6
Start-up frequency converter trip (on start-up).
3.31.4.9.7
6 kV station board incomer auto change over.
3.31.4.10 Under
voltage protection
These
relays protect the stator insulation against under voltage conditions, which
could arise from under excitation or system power swings. The stator insulation must be generator
terminals are sensed by potential transformers, and compared with a threshold
value. The voltage relay activates the
following actions.
3.31.4.10.1
15 kV generator ABCD trip.
3.31.4.10.2
Field circuit breaker trip.
3.31.4.10.3
Excitation transformer 6 kV breaker trip.
3.31.4.11 Under
frequency trip
This relay
protects the generator and gas turbine from system frequencies excessively
below the synchronous frequency of to 50 Hz.
An under frequency condition usually indicates system generation
inadequacy. The relay activates the 132
kV CB trip. The gas turbine remains at full speed sustaining its own load. The generator can be re-synchronized to the
power grid when conditions allow.
3.31.4.12 Generator
overload
This relay
protects the generator forms sustained thermal overloads caused by high
currents. The relay monitors the
parameter (stator current) and activates the 132 kV CB trip. The gas turbine
remains at full speed sustaining its own load.
The generator can be re-synchronized to the power grid when conditions
allow.
3.31.4.13 Generator
over current protection
The over
current relay detects excessive current levels the stator circuit of the
generator, for example as a result of short circuit or insulation failure
fault. Over current is different from
over load conditions, which is not considered to be an instantaneous
fault. While over load may involve
currents of up to a twice normal, an over current condition means a fault
current several times the normal operating current. The relay activates the 132 kV CB trip. The
gas turbine remains at full speed sustains its own load. The generator can be re-synchronized to the
power grid when conditions allow.
3.31.4.14 Under
impedance protection
The under
impedance relay detects phase fault in the generator circuit. There are two under impedance relays; 1st
stage and 2nd stage. The 1st
stage relay activates the following actions.
3.31.4.14.1
15 kV generator ABCD trip.
3.31.4.14.2
Gas turbine emergency trip.
3.31.4.14.3
Field circuit breaker trip.
3.31.4.14.4
Excitation transformer 6 kV breaker trip.
3.31.4.14.5
Start-up frequency converter trip (on start-up).
The 2nd stage relay activates the following actions.
3.31.4.14.6
132 kV CB trip.
3.31.4.14.7
6 kV unit board incoming CB trip.
3.31.4.14.8
15 kV generator ABCB trip.
3.31.4.14.9
Gas turbine emergency trip.
3.31.4.14.10 Field
circuit breaker trip.
3.31.4.14.11 Excitation
transformer 6 kV breaker trip.
3.31.4.14.12 Start-up
frequency converter trip (on start-up).
3.31.4.15 Unbalanced
load
This relay
detects unequal currents in the three phases of the stator windings. During normal operation, the current in the
three phases should be the same. Unequal
currents is indicative of a fault is one or more phases. The relay activates the 132 kV CB trip. The
gas turbine remains at full speed sustaining own load. The generator can be re-synchronized to the
power grid when conditions allow.
3.31.4.16 Under
excitation protection
This relay
activates the following actions.
3.31.4.16.1
15 kV generator ABCD trip.
3.31.4.16.2
Gas turbine emergency trip.
3.31.4.16.3
Field circuit breaker trip.
3.31.4.16.4
Excitation transformer 6 kV breaker trip.
3.31.4.16.5
Start-up frequency converter trip (on start-up).
3.31.4.17 Over
fluxing protection
The relay
protects against stator magnetic core saturation during over voltage
conditions. Magnetic core saturation can
lead to an increase in magnetic core temperature. It is usual to use the voltage to frequency
ratio as a measure of over fluxing, this relay activates 132 kV CB trip. The
gas turbine remains at full speed sustaining its own load. The generator can be re-synchronized to the
power conditions when allow.
3.31.4.18 Excitation
fault
This relay
activates the following actions:
3.31.4.18.1
15 kV generator ABCB trip.
3.31.4.18.2
Gas turbine emergency trip.
3.31.4.18.3
Field circuit breaker trip.
3.31.4.18.4
Excitation transformer 6 kV breaker trip.
3.31.4.18.5
Start-up frequency converter trip (on start-up).
3.31.5
GT Generator Design Data
3.31.5.1
Generator type – WY21Z-097LLT
3.31.5.2
Rated output – 200000 kVA
3.31.5.3
Rated power factor– 0.8
3.31.5.4
Rated voltage – 15000 V
3.31.5.5
Voltage variation range – ±5%
3.31.5.6
Rated frequency – 50 Hz
3.31.5.7
Frequency variation range – ±** %
(acc. to IEC 34)
3.31.5.8
Rated current – 7698 A
3.31.5.9
Number of poles – 2
3.31.5.10 Rated
speed – 3000 rpm
3.31.5.11 Overspeed
(test for 2 min) – 3600 rpm
3.31.5.12 Excitation
system type – STATIC
3.31.5.13 Excitation
current at rated load – 1376 A
3.31.5.14 Excitation
voltage at rated load (at 105oC) – 299 V
3.31.5.15 Stator/Rotor
winding cooling type – Indirect/direct
4.1
The gas turbine generator system automation is
inclusive of sub-group control program (SGC) and sub-loop control program (SLC)
that automatically operates all the auxiliaries by command signal generated by
module [1MBY01-EC001] during plant start-up and shut-down. The command signal
is initiated via the OIS control desk located in the Central Control Room (CCR)
or from the gas turbine Local Control Panel.
4.2
The gas turbine auxiliaries can also be started
from the local control panels that consist of emergency push buttons for safety
reasons. For this please refer to the individual system description documents
and system operating procedures documents.
4.3
The system automation for the gas turbine
generator is described in the System Operating Procedures Document LP-OP-GTG
and all command and permissive signals for start/stop command can be obtained
from gas turbine project document no. 4600-J-1-MBY-I018 (SW Configuration PCU #
01) and document no. 4600-J-1-MBY-I019 (SW Configuration PCU # 02).
5.1
4600-T-X-MB*-S002
Gas Turbine
Type V 94.2 (Operation and Maintenance Manual)
5.2
4600-T-X-MB*-S004
Gas Turbine
Type V 94.2 (Field Assembly Manual)
5.3
4600-T-X-MBD-S001
PID – Gas
Turbine Diagram
5.4
4600-T-X-MBN-SOO1, Rev 0
PID – Fuel
Oil System (Sheet 1, 2 and 3 of 3)
5.5
4600-T-X-MBM-S001, Rev 0
PID -
Combustion Chamber Control
5.6
4600-T-X-MBQ-S001, Rev 0
PID –
Ignition Gas
5.7
4600-T-X-MBA-S003, Rev 0
PID -
Drainage System
5.8
4600-T-X-MBP-S001, Rev 0
PID – Fuel
Gas System
5.9
4600-A-X-MKF-S001, Rev 0
PID – Gas
Turbine Generator Air Cooling System
5.10
4600-A-X-MBV-S001, Rev 0
PID - Gas
Turbine and Generator Lube Oil Cooling System
5.11
4600-T-X-MBR-S001, Rev 0
PID –
Exhaust System
5.12
4600-T-X-MBA-S001, Rev 0
PID – Blow
Off System
5.13
4600-T-X-MBA-S002, Rev 0
PID –
Compressor Cleaning
5.14
4600-T-X-MBV-S001, Rev 0.
PID Lube
and Lifting Oil System
5.15
4600-T-X-MBV-SOO1, Rev 0
PID – Lube
Oil System
5.16
4600-T-X-MBX-S001, Rev 0
PID – Trip
Oil System
5.17
4600-T-X-MBX-S001, Rev 0
PID –
Control Oil System
5.18
4600-A-X-MAV-S001, Rev 0
PID –
Turbine Lube Oil Purification System
5.19
4600-T-1-MBU-S002, Rev 0
PID – GT
Demi-Water Skid
6.1
Major Assemblies of Gas Turbine Unit
6.2
Sectional and Cut-away Views of Gas Turbine.
6.3
Principles of Rectifier Drive and Starting
System Control Block Diagram.
6.4
Air Inlet Assemblies.
6.5
Air Inlet Damper Motor.
6.6
PID - Air Intake System.
6.7
Gas Turbine Rotor and Hirth Couplings
6.8
Compressor Intake Casing.
6.9
Compressor Variable Inlet Guide Vane.
6.10
Compressor Stator Blade Carrier.
6.11
Compressor Rotor and Stator Blade.
6.12
Compressor Exhaust Diffuser:
6.13
Intermediate Shaft.
6.14
Gas Turbine Support System.
6.15
Compressor Blow-Off System Schematic.
6.16
Sectional View of Combustion Chamber.
6.17
Combustion Chamber Internals.
6.18
Secondary Air Ring Mechanism.
6.19
Fuel Burner Assembly:
6.20
Light Fuel Oil Burner (detail).
6.21
Ignition Gas System:
6.22
Ignition Gas Cylinder Room.
6.23
Turbine Stator.
6.24
Turbine Rotor and Stator Blade.
6.25
Turbine Inner Casing
6.26
Center Casing
6.27
Hydraulic and Manual Turning Gear
6.28
Exhaust Casing
6.29
Exhaust Diffuse
6.30
Exhaust Ducting
6.31
Cooling and Sealing Air System
6.32
Compressor Bearing
6.33
Turbine Bearing
6.34
Shaft Glands Types
6.35
Lube Oil System
6.36
Main/Auxiliary and Emergency Lube Oil Pumps
6.37
Shaft Lift Oil Pump Assembly
6.38
Gas Turbine Generator Lube Oil Cooling System
6.39
Lube Oil Filters
6.40
Oil Vapor Extractor and Thermostatic Valve
Details
6.41
Control Oil System Schematic Diagram
6.42
Control Oil Supply Simplified Diagram
6.43
Electrohydraulic Converter and Control Oil Pump
6.44
Fuel Gas Schematic Diagram and Fuel Gas Filter
6.45
Fuel Gas Emergency Stop Valve and Fuel Gas
Control Valve
6.46
Differential Pressure Indicator
6.47
Light Fuel Oil System (Simplified)
6.48
Fuel Oil Emergency Stop Valve and Fuel Oil Ball
Valve Assembly
6.49
Fuel Oil Shut-Off Valve and Fuel Oil Control
Valve Assembly
6.50
Electrohydraulic Converter Sectional View
6.51
GT Generator Cooling System
6.52
GT Generator Water – Air Coolers
6.53
GT Generator Stator Winding
6.54
GT Generator Rotor (Sheet 1 and 2)
6.55
Static Excitation System.
Attachment 6.1
Attachment 6.2
Attachment 6.3
Attachment 6.4
Attachment 6.5
Attachment 6.6
Attachment 6.7
Attachment 6.8
Attachment 6.9
Attachment 6.10
Attachment 6.11
Attachment 6.12
Attachment 6.13
Attachment 6.14
Attachment 6.15
Attachment 6.16
Attachment 6.17
Attachment 6.18
Attachment 6.19
Attachment 6.20
Attachment 6.21
Attachment 6.22
Attachment 6.23
Attachment 6.24
Attachment 6.25
Attachment 6.26
Attachment 6.27
Attachment 6.28
Attachment 6.29
Attachment 6.30
Attachment 6.31
Attachment 6.32
Attachment 6.33
Attachment 6.34
Attachment 6.35
Attachment 6.36
Attachment 6.37
Attachment 6.38
Attachment 6.39
Attachment 6.40
Attachment 6.41
Attachment 6.42
Attachment 6.43
Attachment 6.44
Attachment 6.45
Attachment 6.46
Attachment 6.47
Attachment 6.48
Attachment 6.49
Attachment 6.50
Attachment 6.51
Attachment 6.52
Attachment 6.53
Attachment 6.54
Attachment 6.55
