kwu text governing
TRANSCRIPT
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KWU TURBINE
GOVERNING SYSTEM
NOTE
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TURBINE GOVERNING SYSTEM
In order to maintain the synchronous speed under changing load/steam conditions,the KWU turbine supplied by BHEL is equipped with electro-hydraulic governor;fully backed-up by a hydraulic governor. The measuring and processing of electricalsignal offer the advantages such as flexibility, dynamic stability and simplerepresentation of complicated functional systems. The integration of electrical andhydraulic system has the following advantages:
Exact load-frequency droop with high sensitivity. Avoids over speeding of turbine during load throw offs. Adjustment of droop in fine steps, even during on-load operation.
Elements of Governing System
The main elements of the governing system are as follows:
Remote trip solenoids (RTS). Main trip valves (Turbine trip gear). Starting and Load limit device. Speeder Gear (Hydraulic Governor). Aux. follow-up piston valves. Hydraulic amplifier. Follow-up piston valves. Electro-Hydraulic Converter (EHC). Sequence trimming device. Solenoids for load shedding relay. Test valve. Extraction valve relay. Oil shutoff valve. Hydraulic protective devices.
REMOTE TRIP SOLENOIDS (RTS)
The remote trip solenoid operated valves are two in number and form a part ofturbine protection circuit. During the normal operation of the turbine, thesesolenoids remain de-energised. In this condition, the control oil from the governingrack is free to pass through them to the main trip valves. The solenoids getsenergised whenever any electrical trip command is initiated or turbine is tripped
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manually from local or UCB. Under energised condition the down stream oil supplyafter the remote trip solenoids gets connected to drain and the upstream will be
blocked. By resetting Unit Trip Relays (UTR) from UCB, these solenoids can be reset.
REMOTE TRIP SOLENOIDS
MAIN TRIP VALVES
The main trip valves (two in numbers) are the main trip gear of the turbine protectivecircuit. All turbine tripping take place through these valves. The control oil fromremote trip solenoids is supplied to them.
TURBINE TRIP GEAR
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Under normal conditions, this oil flows into two different circuits, called as the TripOil and Auxiliary Trip Oil. The Trip Oil is supplied to the Stop Valves (of HP Turbineand IP Turbine), Auxiliary Secondary Oil circuit and Secondary Oil circuits. The
Auxiliary Trip Oil flows in a closed loop formed by main trip valves and turbinehydraulic protective devices (Over Speed trip device, Low Vacuum trip device and
Thrust Bearing trip device).
The construction of main trip valves is such that when aux. trip oil pressure isadequate, it holds the valves' spools in open condition against the spring force.
Whenever control oil pressure drops or any of the hydraulic protective devices areactuated, the main trip valves are tripped. Under tripped condition, trip oil pressureis drained rapidly through the main valves; closing turbine stop and control valves.
STARTING AND LOAD LIMIT DEVICE
The starting and load limit device is used for resetting the turbine after tripping, foropening the stop valves and releasing the control valves for opening. The startingdevice consists of a pilot valve that can be operated either manually by means of ahand wheel or by means of a motor from remote. It has got port connections with thecontrol oil, start-up oil and auxiliary start-up oil circuits. The starting device canmechanically act upon the hydraulic governor bellows by means of a lever and link
arrangement.
Before start-up, the pilot valve is brought to its bottom limit position by reducing thestarting device to 0% position. This causes the hydraulic governor bellows to becompressed thus blocking the build-up of secondary oil pressure. This is known ascontrol valve close position. With the valve in the bottom limit position (startingdevice = 0%) control oil flows into the auxiliary start-up circuit (to reset trip gear andprotective devices) and into the start-up oil circuit (to reset turbine stop valves). A
build-up of oil pressure in these circuits can be observed, while bringing the startingdevice to zero position. When the pilot valve i.e. the starting device position is raised,the start-up oil and auxiliary start-up oil circuits are drained. This opens the stop
valves; ESVs open at 42% and IVs open at 56% positions of the starting device.
Further raising of the starting device release hydraulic governor bellows which is inequilibrium with hydraulic governor's spring tension and primary oil pressure(turbine speed), and raises the aux. sec. oil pressure; closing the aux. follow-updrains of hydraulic governor.
SPEEDER GEAR
The speeder gear is an assembly of a bellow and a spring, the tension of which canbe adjusted manually from UCB by an electric motor or locally by a hand wheel. Thebellow compression depends upon the position of the starting device and the speedergear position, which alters the spring tension on the top of the bellow. The bellow isalso subjected to the primary oil pressure, which is the feedback signal for actualturbine speed. The zero position of speeder gear corresponds to 2800 rpm i.e.
hydraulic governor comes into action after 2800 RPM. The bellow and springassembly is rigidly linked to the sleeves of the auxiliary follow-up piston valves. Theposition of the sleeve changes with the equilibrium position of the bellow.
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SPEEDERG
EAR
STARTINGD
EVICE
ACTINGO
N
SPEEDERG
EAR
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HYDRAULIC SPEED TRANSMITTER
The hydraulic speedtransmitter runs in the MOP
bearing and operates on theprinciple of a centrifugalpump. The variation ofpressure in the discharge lineis proportional to the square
of the machine speed. Thisprimary oil pressure acts asthe control impulse for thehydraulic speed governor.
The transmitter is suppliedwith control oil via an oilreservoir. An annular groovein the speed transmitterensures that its inside isalways covered with a thinlayer of oil to maintain auniform initial pressure.Excess oil drains into the
bearing pedestal.
CURVE SHOWING TURBINE SPEED Vs PRIMARY OIL
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AUXILIARY FOLLOW-UP PISTON VALVES
Two Auxiliary Follow-up pistonsare connected in parallel and thetrip oil is supplied to themthrough orifice. The sleeves ofthese valves are attached to thespeeder gear bellow link. The
position of the sleeve determinesthe draining rate of trip oilthrough the ports. Accordinglythe trip oil pressure downstreamof these valves changes. Oildownstream of auxiliary follow-uppistons circuit is termed as
AUXILIARY SECONDARY OIL.Hence, aux. follow-up piston
valves can be said to controlauxiliary secondary oil pressure.
SEQUENCE TRIMMING DEVICE
The function of the sequence trimming device or HP/IP TRIM DEVICE is to preventany excessive HP turbine exhaust temperature due to churning. It changes responseof main and reheat control valves. When the reheat pressure is more than 32
Kg/cm2
and load less than 20% the IP turbine tends to get loaded more than HPturbine. The steam flow through HP turbine tends to fall to very minimum, causing alot of churning and excessive exhaust temperature. The trim device operates at thismoment trimming the IP turbine control valve. The control valves of HPT open moreto maintain flow of steam, reducing the HPT exhaust temperature.
It consists of a spring-loaded piston assembly, which is supported by control oilpressure from beneath, under normal conditions. The control oil is supplied via anenergised solenoid valve. When the turbine loads is less then 40 MW and hot reheat
pressure is more than 32 kg/cm2
the solenoid valve gets de-energised cutting out thecontrol oil supply to the trim device.
The trim device trips under spring pressure. The trim device is connected to thefollow-up piston valves of IP control valves by means of a lever. Upon tripping, thetrim device alters the spring tension of follow-up pistons of IP pistons control valves,draining the secondary oil. The IP control valves openings are trimmed down.
HYDRAULIC AMPLIFIER
Hydraulic Amplifier consists of a pilot valve and an amplifier piston. The position ofthe pilot valve spool depends upon the aux. secondary oil pressure. Depending uponthe pilot spool position, the control oil is admitted either to the top or the bottom ofthe amplifier piston. The other side of amplifier is connected to the drain. Themovements of the amplifier piston are transformed into rotation of a Camshaftthrough a piston rod and a lever assembly. A feedback linkage mechanism stabilisesthe system for one particular aux. secondary oil pressure.
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HYDRAULIC AMPLIFIER
1. Amplifier piston2. Follow-up piston3. Sleeve4. Shaft5. Lever6. Feedback lever7. Pilot valve8. Compression spring9. Adjusting screw
a : Control oil
b : Secondary oilb1 : Aux. Sec oilc : Return oil
SOLENOIDS FOR LOAD SHEDDING RELAY
A pair of solenoid valves has been incorporated in the IP Sec oil line on control valvesand Aux Sec. oil line, in order to prevent the turbine from reaching high speed in theevent of sudden turbine load throw-off. The control valves are operated (closed) bythe load-shedding relay when the rate of load reduction exceeds a certain value. Thesolenoid drains the IPCV secondary oil directly. Direct draining of IP Sec oil circuitcauses the reheat valves to close without any significant delay. The HP control valvesare closed due to draining of aux. secondary oil before the hydraulic amplifier, by thesecond solenoid valve. The extraction stops valves controlled by IP secondary oil
acting through extraction valves relays also get closed. After an adjustable time delay(approx. 2 seconds) the solenoid valves are re-closed and secondary oil pressurecorresponding to reduce load builds-up in the HP and IP turbine secondary oil lines.
FOLLOW-UP PISTON VALVES
The trip oil is supplied to the follow up piston valves through orifices and flows inthe secondary oil piping to control valves. The secondary oil pressure depends uponposition of sleeves of follow-up piston valves; which determines the amount ofdrainage of trip oil.
There are in all twelve follow-up piston valves. Six of them are associated withhydraulic amplifier and six of them with EHC in the governing system. The follow-uppiston valves constitute a minimum value gate for both the governors. This meansthe governor with lower reference set point, is effectively in control. This is alsotermed as HYDRAULIC MINIMUM SELECTION of governors.
The drain port openings of follow-up pistons of hydraulic amplifier depends onauxiliary secondary oil pressure, upstream of aux. follow-up pistons; and that ofelectro hydraulic converter, on the piston of pilot spool valve of the elector-hydraulicconverter (i.e. EHC output).
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FOLLOW-UP PISTON VALVES
TEST VALVE
1.
Bolt2. Hand wheel3. Spindle4. Cover5. Oil Seal6. Bushing7. O-ring8. Valve Cover9. Valve Body10. Trip Oil11. Piston sleeve12. Trip Oil13. Piston valve14. Spring plate15. Spring16. Spacer17. Bottom cover18. Trip oil19. Drain20. Trip oil21. Startup oil
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Each of the HP and IP stop valves' servomotors receives trip oil through theirassociated test valves. The test valves have got port openings for trip oil as well asstart-up oil. The test valves facilitate supply of trip oil pressure beneath theservomotor disc. (Stop valve open condition, under normal operation). For thepurpose of resetting stop valves after a tripping, start-up oil pressure is supplied tothe associated test valves, which moves their spool downwards against the springforce. In their bottom most position the trip oil pressure starts building up above thestop valve servomotor piston while the trip oil beneath the disc gets connected to
drain. When start-up oil pressure is reduced the test valve moves up draining trip oilabove the servomotor piston and building the trip oil pressure below the disc, thusopening the stop valve. A hand wheel is also provided for manual operation of test
valves.
EXTRACTION N.R.VS AND EXTRACTION VALVE RELAY
Four pair of swing-check valves are provided in the extraction lines to the feedheaters (LP Heaters No: 2,3, Deaerator and HPH No: 5) to prevent back flow ofcondensed steam into the turbine from heaters on account of high levels in theheaters. There are two NRVs provided in each of these extraction lines and is forceclosing type. Both these valves are free-swinging check type, however the first valveis equipped with an actuator. In case of flow reversals, both the valves are closed
automatically. The actuator assists the fast closing of the first valve. The mechanicaldesign of force-closed valves is such that they are brought into free-swinging position
by means of trip oil. They are open as soon as differential pressure is sufficient. Ifthe trip oil pressure falls, the spring force closes the valve when steam pressureeither falls or is lowered (reduced load).
The extraction valve relay, its changeover valve and its solenoid valve control the tripoil to each of the actuators of force closing type valves. In case of turbine trip orsudden load reduction, by energising the associated solenoid valve, draining of trip
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oil pressure through extraction valve relay assists closing movements of FCNRVs. Inboth the cases the actuator is devoid of trip oil and its spring force closes the NRV.Extraction (4) FCNRV solenoid is also energised additionally by lower differentialpressure in the extraction line.
b : Control Oil c : Return Oil
b1 : Secondary Oil x : Trip Oil
b2 : Secondary Oil x1 : Trip Oil
COLD REHEAT SWING CHECK VALVE
Two numbers of swing check valves are provided on the CRH lines from which thesteam is drawn for HPH-6. Their pilot valves via their rotary servomotor inproportion to secondary oil pressure operate the CRH NRVs. They open out fully
when main control valves open up corresponding to 5-10% of maximum turbine out-put. Only when the control valves are closed to this threshold again, the NRVsreturn into steam flow by the hydraulic actuator, so that when the steam flow ceasesin the normal direction, they are closed by the torque of rotary servomotor. Even
when the pressure of secondary oil has not built up sufficiently, NRVs can be openedup like safety valves when the upstream pressure rises above the downstream side
pressure by one bar.
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VACUUM BREAKER
The function of the vacuum breakers is to cause an increase in condenser pressureby conducting atmospheric air into the condenser together with the steam flowingfrom the LP Bypass. When the pressure in the condenser increases, the ventilationof the turbine balding is increased, which causes the turboset to slow down so thatthe running down time of the turboset and the time needed for passing throughcritical speeds are shortened.
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Electro-Hydraulic Governor (EHG)
Electro-Hydraulic Governor (EHG) works in parallel with Hydraulic governor at alltimes of requirements. Basically the Electro-Hydraulic Converter (EHC) is theconnecting element between the electrical and hydraulic parts of the turbinegoverning control system for carrying out the Electro-Hydraulic Governing of theturbine.
The Electro-Hydraulic Governor (EHG) is beneficial in
Offering the flexibility, dynamic stability, dependability, excellent operationalreliability, Low transients and steady-state speed deviations at all instances.
Maintaining exact load frequency droop with high sensitivity.Providing reliable operation at times of grid isolation conditions.Operating the turbo-generator Safely in conjunction with TSE.In KWU turbines, Electro-Hydraulic Governing has been achieved through variouselectronic / selector modules configured in four modes of controls:
Admission Control mode, Speed Control mode, Load Control mode Pressure Controlmode.
The Hydraulic governor and the EHG system have been designed such that thegovernor with lower set point takes over or assumes the system control, as suchnormally, the set point of the Hydraulic Governor must be set above that of theElectro-Hydraulic Governor when EHG is effective. In cases, when EHG fails to causeshut-off, the set point that is, affected is that of Hydraulic Governor.
In such situations the Tracking Device provides a revised set point of 5-10% abovethe EHG set point and it causes increase in small load when the control istransferred to Hydraulic-Governor. The tracking device is either switched on or off
manually but when EHG failure or turbine trip occurs, the tracking device isswitched off automatically thus tracking under faulted operation mode is preventedor prohibited. More details on tracking actions are covered in the follow-up circuitsof the speed/load control modes.
Electro Hydraulic Converter
Electro Hydraulic Converter converts the electrical signal in to the hydraulic signalsand large positioning forces are generated in control valves. The electrical signal fromgovernor control circuit operates the sleeve and pilot valve spool; this regulates thetrip fluid drain. Under steady state condition pilot is at central position; in deflectedposition, the control oil is admitted above or below the amplifier piston. The motionof the amplifier piston is transmitted via a lever to a camshaft, which actuates thesleeves of follow-up piston valves, causing secondary oil pressure to change. Thespeed, load, and pressure signals are measured and converted into conditionedsignal in electronic modules.
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1. Differnetial transformer2. Amplifier casing3. Amplifierpiston4. Piston rod5. Valve bushing6. Piston valve7. Grooved ball bearing8. Spring dics9. Compression spring10.Sleeve11.Casing support12.Moving coil system
a. control oilb. Trip Oil
Electro Hydraulic Converter
Admission Valve (spool) Controller
Admission Valve (spool) Controller also referred as the position controller is Commonfor all three modes of EHG, and it supplies the operating current for driving the
plunger coil. The Position controller loop uses a PID control mode for processingoutputs that provide the driving current signal to the plunger and regulate the oildrains of HP/IP control valves (CV); thereby it controls steam supply into theturbine.
The current in the plunger coil is increased for closing the HP /IP CV and vice versafor opening of the HP /IP Control Valve. The reference signal therefore works inreverse manner (rise in the coil current for low reference condition). By using twoNos of differential transformer (housed in EHC), feedback signal from the valve lift isderived to ensure proper stationing of plunger spool.
Whenever current through the plunger coil gets interrupted or the electrical feedbackcircuit gets faulted, the reference value of the Hydraulic controller determines the
actual valve position. Although the force to the plunger coil and to the control sleeveis, considerably smaller, but the regulating signal to the secondary auxiliary oil flowas transformed is quite large. The figure below gives various connections andmodules used in EHG.
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Actual speed (nact) Measurement:
Actual speed nact is acquired by three digital speed pickups (Hall probes) in the formof pulses /frequency. Channel-2 is utilized while other two-channel pick-up remainsredundant; electronically switching ensures no affect in channel in service and alsoa full - proof monitoring. The selected sensed speed channel signal is further dividedinto three measuring signals (f/v of 0-60 Hz, low range 0-6 Hz & full range 0-60 Hzand a quartz frequency standard) for various other applications in the EHG and
other circuits.
The difference of actual speed and time dependent speed signals (nact - nRTD) formthe input error of the Speed controller which outputs control signal (in the path asexplained in selection section) through the selection modules for driving the EHC
and finally establishing the EHG.
ACTUAL SPEED MEASUREMENT
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TURBINE PROTECTION SYSTEM
Turbine protection system performs to cover the following functions: -
a. Protection of turbine from inadmissible operating conditions.
b. In case of plant failures, protection against subsequent damages.
c. It restricts occurring failures to minimum.
Standard turbine protection system comprises the following:
Mechanical/hydraulic turbine protection. Electrical turbine protections.
BLOCK DIAGRAM OF TURBINE PROTECTION AND ATT
Mechanical Hydraulic Turbine Protection
The design of mechanical hydraul ic protecti on equipment is in accordancewith hydraulic break current principle and consists of following:
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a. Two manual trip devices (main trip valves)
b. Two speed monitors (over speed trip device)
c. One hydraulic low vacuum device
d. Two solenoid valves for trip initiation (remote solenoid valves)
As explained earlier, turbine stop and control valves are tripped to close position ifthe trip oil pressure is reduced below the minimum value. The main trip valves allowrapid draining of trip oil in case they are operated either manually or automatically
by the reduction of aux. trip oil pressure. Aux. trip oil pressure can be drainedbecause of actuation of hydraulic low vacuum trip device, over speed trip device orthrust bearing trip device. The principle of functioning of individual hydraulic tripdevices is explained in details under the chapter of Automatic Turbine TestingSystem.
Remote trip solenoids act as interfaces between mechanical hydraulic and electro-hydraulic protection equipment of turbine. Upon receiving the electrical tripcommand, the solenoids get energised and close the valves. Thus control oil supply
to main trip values is cut off leading to their closure.
Electrical Hydraulic Turbine Protection
Electrical turbine trip equipments comprise two-channel redundancy and functionon operating current principle. All electrical trip criteria act on the two remote tripsolenoid valves to energise the solenoids.
The electro-hydraulic turbine protection equipment features -
-Two solenoid operated valves for trip initiation (Remote trip solenoids).-Emergency trip contactor cabinet containing trip channels 1 and 2-Monitors with signal conditioning-One substitute channel to ensure uninterrupted transmission of eventualturbine trip signals during testing by ATT.
The remote trip solenoids (RTS) have already been described. Operation of any onechannel causes energising both solenoid-operated valves leading to turbine tripeventually. Transmitters that cause a trip in the case of any electrical tripping signalare conditioned and monitored via binary signal conditioning of the ATT system or
via the central analog/binary signal conditioning.
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TURBINE PROTECTION FOR 200MW KWU SETS
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Turbine Trip Actuation Circuits
The turbine protection system is sub divided into two parts:
a. Protective circuits for the standard turbine protection equipments or criteria.b. Protective criteria from other areas.
Standard criteria are specified by the turbine manufacturer and are responsible forfull protection of turbine under various specific conditions, which are:
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1. Manual tripping devices (Turbine trip gear local operating lever)
2. Speed monitors (over speed trip devices)
3. Thrust bearing trip device
4. Hydraulic low vacuum trip device
5. Electrical low vacuum trip device
6. Lub oil pressure protection
7. Fire protection
8. Manual turbine tripping (electrical UCB switch)
Protection criteria from other areas are as follows:
Boiler trip (MFR) Boiler drum level very high ( > + 225 mm wcl ) Main steam temperature trip ( < 480 o C ) Trip from functional group control (ATRS shut-down programme) Generator trip
Like low vacuum tripping (electrical) the low steam temperature protection alsocomprises 'Arming' and 'Disarming' features to facilitate re-start of turbine, underlow main steam temperature conditions.
Over Speed Trip Device
Two hydraulically operated over speed trips are provided to protect the turbineagainst over speeding in the event of load coincident with failure of speed governor.
OVER SPEED TRIP DEVICE
1. Bearing pedestal2. Spindle3. Spring4. Piston5. Piston body
6. Spring7. Pawl8. Over speed trip bolt9. Shaft journal10. Limit switch
c: Return Oil
u: Auxiliary Stratup Oilx: Auxiliary Trip Oil
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When the preset over speed is reached, the eccentric fly bolt activates the piston andlimit switch via a pawl. This connects the auxiliary trip oil to drain therebydepressurising it. The loss of auxiliary trip medium pressure causes the main trip
valve to drop, which in turn causes the trip oil pressure to collapse.
Low Vacuum Trip Device
In the hydraulic low vacuum trip device, a compression spring set to a specific
tension pushes downwards against diaphragm, the topside of which is subject to thevacuum. If the vacuum is too weak to counteract the spring tension, the springmoves valve 6 downwards. The pressure beneath valve is thereby dispersed and theauxiliary trip medium circuit is connected to drain. The resultant depressurisation ofthe auxiliary trip oil actuates main trip valves MAX51 AA 005 and MAX51 AA 006thereby closing all turbine valves.
The electrical tripping on low vacuum occurs through a pressure switch on thevacuum line to mechanical hydraulic low vacuum trip device also at the samecondenser pressure. When turbine is started up again, this pressure switch isinterlocked against a second pressure switch, which monitors this condition andprevents continuation of tripping initiation when condenser pressure is high.
Thrust Bearing Trip Device
The function of the thrust bearing trip is to monitor the shaft position in the bearingpedestal and, if a fault occurs, to depressurize the auxiliary trip medium and thusthe trip oil in the shortest possible time, thereby tripping the turbine.
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1. Compressionspring
2. Bearing pedestal3. Piston4. Valve body5. Turbine shaft6. Pawl7. Torsion spring8. Piston9.
Compressionspring
10.Limit switch11.Knoba: Test Oil
c: Return Oilu: Aux. Startup Oil
x: Aux. Trip Oil
The two rows of tripping cams, which are arranged on opposite sides of turbineshaft, have a specific clearance, equivalent to the permissible shaft displacement,relative to pawl of the thrust-bearing trip. If the axial displacement of the shaftexceeds the permissible limit, the cams engage pawl, which releases a piston to
depressurise the auxiliary trip oil and at the same time to actuate limit switch.
Electrical tripping of turbine is achieved by fire protection along withclosure/stoppage of total control oil supply to turbine governing system by trippingthe emergency stop valve on the control oil line. The fire protection trip is achieved
by manual Pushbutton in UCB or automatically by very low MOT level (- 150 mmbelow the normal working level 'O'). Please refer to the associated logics at the end ofthis chapter. Also fire protection-1 (automatic actuation) gets bypassed if the barringgear valve is 'not closed'.
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FIRE PROTECTION-1 CHANNEL-1
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FIRE PROTECTION-2 CHANNEL-1
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FIRE PROTECTION OIL TANK LEVEL MONITOR
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TRIP OIL
FUNCTION :To open the stop valves and generate auxiliary secondary oil
and secondary oil
SOURCE : Control oil
SUPPLY DEVICE : Main Trip Gears
AUXILIARY TRIP OIL
FUNCTION : To engage and operate the main trip valves
SOURCE : Trip oil
SUPPLY DEVICE : Main Trip Gears
AUX. SECONDARY OIL
FUNCTION : To provide the position signal for the hydraulic governor
SOURCE : Trip oil
SECONDARY OIL
FUNCTION : To provide the position signal for the control valve servomotor
SOURCE : Trip oil
PRIMARY OIL
FUNCTION : To supply speed signal to hydraulic governor
SOURCE : Control oil
SUPPLY DEVICE : Hydraulic Speed Transmitter
START UP OIL
FUNCTION : To supply control signals for the stop valves
SOURCE : Control oil
SUPPLY DEVICE : Starting Device
AUX. START UP OIL
FUNCTION : To reset the Hydraulic Protective devices
SOURCE : Control oil
SUPPLY DEVICE : Starting Device
TEST OIL
FUNCTION : To test the hydraulic trip devices
SOURCE : Control oil
SIGNAL OIL
FUNCTION : To operate LPBP valvesSOURCE
:Control oil
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KWU LMW
1. The types of governor used is Electro-hydraulicbacked up by Hydraulic governor
The types of governor used is Hydro-
mechanical
2. Governing type used is throttle governing Nozzle type governing is provided
3. Speed of the m/c is controlled right fromturning gear speed by Electro-hydraulicgovernor
Speed of the m/c is controlled by
Governor from 300-3450 rpm
4.Regulation range of Electro-hydraulicgovernor can be varied from 2.5 to 8% in steps
of 0.5% (Regulation range of hydraulic
governor is 7%)
Regulation range is 4%1%
5.Transient speed risea) When control valves are mounted near
casing is 8%
b) When control valves are mounted away
from casing as in BHEL sets is 8.5%
Transient speed rise is 6 to 7%
6. Dead band of Governing system: 0.01% Dead band of Governing system: 0.3%
7.
Closing time of servomotors
a) HP i) ESV: 0.2 Sec
ii) Control valve: 0.4 Sec
b) IP i) IV: 0.8 Sec
ii) Control valve: 0.8 Sec.
a) HP ESV: 0.35 Sec
b) IP: IV: 0.4 Sec
c) Control valve servomotor: 0.5 Sec.
8. Control oil pressure 8.0 Kg/cm2 Control oil pressure 20.0 Kg/cm2
9.Size of HP Stop valve (ESV)i) 160 mm - 2 nos
ii) zie of HP control valves 128 mm - 2 nos) (0.8
times of ESV)
iii) Size of IV valves - 320 mm (2 nos)
iv) Size of IP control valves - 256 mm (02 nos)
Size of control valves 1,2,3,4 (4 nos)
125,150,150.150 mm
Size of IV valves 320 mm (2nos)
Size of IP control valves (4nos)
10.Automatic turbine testing is provided to check
the protective devices while M/C is in
operation
Automatic testing device is not provided
to check the protective devices while
M/C is in operation
11.All Gov.elements like Main trip valve, EHC
follow up piston block etc. are kept outsideand assembled in separate cabinet
All Gov. elements like Fly weight
governor, Summation pilot, Follow pilot;
Emergency Gov. pilots are mounted in
front pedestal.
12.Trimming device provided for IP control valves
is used for controlling HP exhaust temp. in caseof following low load operation.
(HP Exhaust or CRH pressure>32 KSC and
Generator load < 20%)
There is no trimming device provided for
IP control valves
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EDC-Singrauli 38
13.In all types of starts HP control valves controlfrom 0 to 100%. IP control valves have
controlling function along with HP control
valve up to 40%, further control is done by HP
control valves.
In cold and warm start HP control valves
control from 0 to 100%. There is no control
on IP control. In case of hot start, IP
control valves control the M/C up to
30MW. Further control is by HP control
valves for HP & LP bypass system.
14.Actual over speed test is carried out by means
of separate test lever provided in Hydraulic
governor. Both over speed governor aretested together.
Actual over speed test is carried out by
means of Speeder gear after selecting
the respective governor by means ofselector of emergency governor lever.
15.Electrical pressure controller is provided to
unload the M/C in case the main steam
pressure drops by more than 10% of rated
value.
Initial steam pressure unloading (ISPUG)
hydraulic device has been provided to
unload the M/C in case main steam
pressure drops more than 10% of the
rated value.
16.Load shedding Relay is provided to control the
acceleration rate during sudden reduction in
output load.
The electrical signal is converted into
hydraulic signal by actuation of EHT.
17.Hydraulically driven Emergency shut-off valve
is provided to interrupt the supply to thegoverning rack.
No such device is provided
18. IP control valves opens after HP control valves HP control valves opens after IP controlvalves
19.
The output signal of speed controller
(electrical) is automatically matched to the
output signal of load controller from the rated
power on down to station load. The speed
controller is then in stand by mode and stands
ready to provide station load in case of load
shedding.
Such facility does not exist, as the Turbine
is not provided with Electro hydraulic
governing system.
20. Stop & control valves are provided in samecasing
Stop & control valves are mounted indifferent casing
21. Control valves are mounted away fromturbine
Control valves are integral parts of
turbine
22. Control valves movement is in horizontaldirection
Control valves movement is in vertical
direction
23. Each control valve can be tested for spindlefreeness during operation
Such facility is not available during
operation of the M/C
24. Each control valve has a separate servomotor Only one servomotor operates all HP & IPcontrol valves.
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EDC-Singrauli 39
PROBLEMChange over
valve not getting
reset
OBSERVATIONChange over valve in trip
condition and control oil
pressure low
SOLUTION
On line full flow filterself cleaning by knob
rotation
RECOMMENDATION
On line full flow filter self
cleaning by regular
knob rotation
PROBLEM
Emergency
Governor operating
within operating
speed range
OBSERVATION
Unit frequently tripping in
over speed during rolling atspeed lower than 3000 rpm.
SOLUTION
Check test oil pressure.
Check proper latching of
reset unit. Check the
position and mass of the
over speed bold
RECOMMENDATION
Period testing of O/S
Governor by simulation
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EDC-Singrauli 40
PROBLEMLP By pass Not
Resetting
OBSERVATION
Getting reset after bypassing
condensate pressuremechanical switch
SOLUTIONOpen the switch found
bellow found damaged.It was replaced. Normal
operation of LP BP
observed
RECOMMENDATION
Bellow changed OR If
operation requiredbefore replacement.
Ensure temperature
switch working properly.Replace bellow at the
earliest.
PROBLEMElectro Hydraulic
Converter Hunting
OBSERVATION
Calibration of EHC checked
with Calibrator and foundoscillating
SOLUTIONOpened the EHC and one leaf out of
three leaves spring of electro hydraulic
converter found damaged. Spring wasreplaced. Stabilization voltage set to
negative (-1 mV). Problem was solved.
PROBLEM
LP Bypass WaterInjection Valve Not
Closing
OBSERVATIONSignal Oil Pressure was low and
W I actuator drain line was hot
SOLUTION
Signal oil inlet was wrongly
connected with valve actuator.
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EDC-Singrauli 41
PROBLEM
HP CV Oscillating
(Hunting)
OBSERVATION
HPCV & HP Secondary Oil
Pressure Hunting
SOLUTIONDamping device was opened
and ball was found missing. It was
put back, oscillation of valve
stopped.
PROBLEM
Startup Speed NotRising
OBSERVATIONStartup device and speeder
Gear liver link was broken
SOLUTION
Lever was changed,
problem was solved
RECOMMENDATION
Same problem was
repeated after about amonth. Spring setting was
set right and stroke of
starting device andspeeder gear was re-
adjusted. Problem solved
permanently.
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EDC-Singrauli 42
PROBLEMHP Control Valve
Not Opening
OBSERVATION
HP Secondary oil pressure
was not building up. This waschecked in Hydraulic mode
as well as EHC modeSOLUTION
Follow up pilot blockinspection cover was
opened and one of the
three control pilot wasfound loose and fell down.
It was placed in position.
RECOMMENDATION
Pilot was tightened in
position with a small
screw and little gluesmooth operation of
HPCV
PROBLEMHP Stop valve Not
opening
OBSERVATION
Test valve was checked and
found clearance of slideand sleeve more.
SOLUTIONTest valve was
replaced. Problem
solved.
RECOMMENDATION
Quality of oil/FRF to be
maintained for nocorrosion / mechanical
pitting. Avoid frequent
operation of manualtesting devices.
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PROBLEM
IP Stop Valve NotOpening
OBSERVATION
Test valve was checked and
found OK. Flow of Trip oil toSV actuator was felt, as line
was hot. SOLUTION
Actuator was opened
and a nut was foundin between piston
and disc
RECOMMENDATION
Fault at assembly shopdo not attempt to open
the Hydraulic Actuator
without the expert
guidance.
PROBLEM
CRH NRV not
openingOBSERVATION
Supply and return line was
found hot.
SOLUTION
Servomotor wasopened and servicing
was done its seal wasfound damaged. Itwas replaced.
RECOMMENDATION
Change all the gasketand seals if opened in
governing system and
control oil system.