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 electrical signal offer the advantages such as flexibility, dynamic stability and simple representation of complicated functional systems. The integration of electrical and hydraulic system has the following advantages: Exact load-frequency droop with high sensitivity.
•
speeding of turbine turbine during load throw throw offs. • Avoids over speeding droop in fine steps, even during during on-load operation. operation. • Adjustment of droop
Elements of Governing System The main elements elements of the governing governing system are 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.
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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 of turbine protection circuit. During the normal operation of the turbine, these solenoids remain de-energised. In this condition, the control oil from the governing rack is free to pass through them to the main trip valves. The solenoids gets energised whenever any electrical trip command is initiated or turbine is tripped EDC-Singrauli
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manually from local or UCB. Under energised condition the down stream oil supply after the remote trip solenoids gets connected to drain and the upstream will be blocked. By resetting resetting Unit Trip Trip Relays (UTR) from from UCB, these solenoids can be reset.
REMOTE TRIP SOLENOIDS
MAIN TRIP VALVES The main trip valves (two in numbers) numbers) are the main trip gear of the turbine turbine protective circuit. All turbine tripping take place through these valves. The control oil from remote 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 Trip Oil and Auxiliary Trip Oil. The Trip Oil is supplied to the Stop Valves (of HP Turbine and IP Turbine), Turbine), Auxiliary Secondary Oil circuit and Secondary Oil Oil circuits. The Auxiliary Trip Oil flows in a closed loop formed by main trip valves and turbine hydraulic protective devices (Over Speed trip device, Low Vacuum trip device and Thrust Bearing Bearing trip device). The construction of main trip valves is such that when aux. trip oil pressure is adequate, it holds the valves' spools in open condition against the spring force. Whenever control oil pressure drops or any of the hydraulic protective devices are actuated, the main trip valves are tripped. Under tripped condition, trip oil pressure is 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, for opening the stop valves and releasing the control valves for opening. The starting device consists of a pilot valve that can be operated either manually by means of a hand wheel or by means of a motor from remote. It has got port connections with the control oil, start-up oil and auxiliary start-up oil circuits. The starting device can mechanically 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 the starting device to 0% position. This causes the hydraulic governor bellows to be compressed thus blocking the build-up of secondary oil pressure. This is known as control valve close position. With the valve in the bottom limit position (starting device = 0%) control oil flows into the auxiliary start-up circuit (to reset trip gear and protective devices) and into the start-up oil circuit (to reset turbine stop valves). A build-up of oil pressure in these these circuits can be observed, while while bringing the starting device to zero position. When the pilot valve i.e. the starting s tarting 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 in equilibrium with hydraulic governor's spring tension and primary oil pressure (turbine speed), and raises the aux. sec. oil pressure; closing the aux. follow-up drains of hydraulic governor.
SPEEDER GEAR The speeder gear g ear is an assembly of a bellow and a spring, the tension of which can be adjusted manually from UCB by an electric motor or locally by a hand wheel. The bellow compression depends upon upon the position of the starting starting device and the speeder speeder gear position, which alters the spring tension on the top of the bellow. The bellow is also subjected to the primary oil pressure, which is the feedback signal for actual turbine speed. The zero position of speeder gear corresponds to 2800 rpm i.e. hydraulic governor comes into action after 2800 RPM. The bellow and spring assembly is rigidly linked to the sleeves of the auxiliary follow-up piston valves. The position of the sleeve changes with the equilibrium position of the bellow.
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R A E G R E D E E P S
R A E G R E D E E P S N O G N I T C A E C I V E D G N I T R A T S
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HYDRAULIC SPEED TRANSMITTER TRANSMITTER The hydraulic speed transmitter runs in the MOP bearing and operates on the principle of a centrifugal pump. The variation of pressure in the discharge line is proportional to the square of the machine speed. This primary oil pressure acts as the control impulse for the hydraulic speed governor. The transmitter is supplied with control oil via an oil reservoir. An annular groove in the speed transmitter ensures that its inside is always covered with a thin layer of oil to maintain a uniform initial pressure. Excess oil drains into the bearing pedestal. pedestal.
CURVE SHOWING TURBINE SPEED Vs PRIMARY OIL
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AUXILIARY FOLLOW-UP FOLLOW-UP PISTON PISTON VALVES Two Auxiliary Follow-up pistons are connected in parallel and the trip oil is supplied to them through orifice. The sleeves of these valves are attached to the speeder gear bellow link. The position of the sleeve determines the draining rate of trip oil through the ports. Accordingly the trip oil pressure downstream of these valves changes. Oil downstream of auxiliary follow-up pistons circuit is termed as AUXILIARY SECONDARY OIL. Hence, aux. follow-up piston valves can be said to control auxiliary secondary oil pressure.
SEQUENCE TRIMMING DEVICE The function of the sequence trimming device or HP/IP TRIM DEVICE is to prevent any excessive HP turbine exhaust temperature due to churning. It changes response of main and reheat control valves. When the reheat pressure is more than 32 2
Kg/cm and load less than 20% the IP turbine tends to get loaded more than HP turbine. The steam flow through HP turbine tends to fall to very minimum, causing a lot of churning and excessive exhaust temperature. The trim device operates at this moment trimming the IP turbine control valve. The control valves of HPT open more to maintain flow of steam, reducing the HPT exhaust temperature. It consists of a spring-loaded piston assembly, which is supported by control oil pressure from beneath, under normal conditions. The control oil is supplied via an energised solenoid valve. When the turbine loads is less then 40 MW and hot reheat 2
pressure is more than 32 kg/cm the solenoid valve gets de-energised cutting out the control oil supply to the trim device. The trim device trips under spring pressure. The trim device is connected to the follow-up piston valves of IP control valves by means of a lever. Upon tripping, the trim 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 of the pilot valve spool depends upon the aux. secondary oil pressure. Depending upon the pilot spool position, the control oil is admitted either to the top or the bottom of the amplifier piston. The other side of amplifier is connected to the drain. The movements of the amplifier piston are transformed into rotation of a Camshaft through a piston rod and a lever assembly. A feedback linkage mechanism stabilises the system for one particular aux. secondary oil pressure. EDC-Singrauli
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HYDRAULIC AMPLIFIER
1. 2. 3. 4. 5. 6. 7. 8. 9.
Amplifier piston Follow-up piston Sleeve Shaft Lever Feedback lever Pilot valve Compression spring Adjusting screw
a : Control Control oil oil b : Secondary Secondary oil b 1 : Aux. Sec oil c : Return Return oil
SOLENOIDS FOR LOAD SHEDDING RELAY A pair of solenoid solenoid valves has been been incorporated in the IP Sec oil oil line on control control valves and Aux Sec. oil line, in order to prevent the turbine from reaching high speed in the event of sudden turbine load throw-off. The control valves are operated (closed) by the load-shedding relay when the rate of load reduction exceeds a certain value. The solenoid drains the IPCV secondary oil directly. Direct draining of IP Sec oil circuit causes the reheat valves to close without any a ny significant delay. The HP control valves are closed due to draining of aux. secondary oil before the hydraulic amplifier, by the second 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 pressure corresponding 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 in the secondary oil piping to control valves. The secondary oil pressure depends upon position of sleeves of follow-up piston valves; which determines the amount of drainage of trip oil. There are in all twelve follow-up piston valves. Six of them are associated with hydraulic amplifier and six of them with EHC in the governing system. The follow-up piston valves constitute a minimum value gate for both the governors. This means the governor with lower reference set point, is effectively in control. This is also termed as HYDRAULIC MINIMUM SELECTION of governors. The drain port openings of follow-up pistons of hydraulic amplifier depends on auxiliary secondary oil pressure, upstream of aux. follow-up pistons; and that of electro hydraulic converter, on the piston of pilot spool valve of the elector-hydraulic converter (i.e. EHC output).
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FOLLOW-UP PISTON VALVES
TEST VALVE
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.
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Bolt Hand wheel Spindle Cover Oil Seal Bushing O-ring Valve Cover Valve Body Trip Oil Piston sleeve Trip Oil Piston valve Spring plate Spring Spacer Bottom cover Trip oil Drain Trip oil Startup oil
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Each of the HP and IP stop valves' servomotors receives trip oil through their associated test valves. The test valves have got port openings for trip oil as well as start-up oil. The test valves facilitate supply of trip oil pressure beneath the servomotor disc. (Stop valve open condition, under normal operation). For the purpose of resetting stop valves after a tripping, start-up oil pressure is supplied to the associated test valves, which moves their spool downwards against the spring force. In their bottom most position the trip oil pressure starts building up above the stop 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 oil above the servomotor piston and building the trip oil pressure below the disc, thus opening the stop valve. A hand wheel is also provided for manual operation of test valves.
EXTRACTION EXTRACTION N.R.VS AND EXTRACTION VALVE RELAY Four pair of swing-check valves are provided in the extraction lines to the feed heaters (LP Heaters No: 2,3, Deaerator and HPH No: 5) to prevent back flow of condensed steam into the turbine from heaters on account of high levels in the heaters. There are two NRVs provided in each of these extraction lines and is force closing type. Both these valves are free-swinging check type, however the first valve is 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 mechanical design 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. If the trip oil pressure falls, the spring force closes the valve when steam pressure either falls or is lowered (reduced load).
The extraction valve relay, its changeover changeover valve and its solenoid valve control the trip oil to each of the actuators of force closing type valves. In case of turbine trip or sudden 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. In both the cases the actuator is devoid of trip tri p oil and its spring force closes cl oses the NRV. Extraction (4) FCNRV solenoid is also energised additionally by lower differential pressure 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 ch eck valves are provided on the CRH lines from which the steam is drawn for HPH-6. Their pilot valves via their rotary servomotor in proportion to secondary oil pressure operate the CRH NRVs. They open out fully when main control valves valves open up corresponding corresponding to 5-10% of maximum turbine output. Only when the control valves are closed to this threshold again, the NRVs return into steam flow by the hydraulic actuator, so that when the steam flow ceases in the normal direction, they are closed by the torque of rotary servomotor. Even when the pressure pressure of secondary secondary oil has not built built up sufficiently, NRVs NRVs can be opened opened up 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 pressure by conducting atmospheric air into the condenser together with the steam flowing from the LP Bypass. When the pressure in the condenser increases, the ventilation of the turbine balding is increased, which causes the turboset to slow down so that the running down time of the turboset and the time needed for passing through critical speeds are shortened.
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Electro-Hydraulic Electro-Hydraulic Governor (EHG) Electro-Hydraulic Governor (EHG) works in parallel with Hydraulic governor at all times of requirements. Basically the Electro-Hydraulic Converter (EHC) is the connecting element between the electrical and hydraulic parts of the turbine governing control system for carrying out the Electro-Hydraulic Governing of the turbine. The Electro-Hydraulic Electro-Hydraulic Governor (EHG) is beneficial in • Offering the flexibility, dynamic stability, dependability, excellent operational
reliability, 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 various electronic / selector modules configured in four modes of controls: Control mode, • Admission Control • Speed Control mode, • Load Control mode • Pressure Control mode. The Hydraulic governor and the EHG system have been designed such that the governor with lower set point takes over or assumes the system control, as such normally, the set point of the Hydraulic Governor must be set above that of the Electro-Hydraulic Governor when EHG is effective. In cases, when EHG fails to cause shut-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% above the EHG set point and it causes increase in small load when the control is transferred to Hydraulic-Governor. The tracking device is either switched on or off manually but when EHG failure or turbine trip occurs, the tracking device is switched off automatically thus tracking under faulted operation mode is prevented or prohibited. More details on tracking actions are covered in the follow-up circuits of the speed/load control modes.
Electro Hydraulic Converter Electro Hydraulic Converter converts the electrical signal in to the hydraulic signals and large positioning forces are generated in control valves. The electrical signal from governor control circuit operates the sleeve and pilot valve spool; this regulates the trip fluid drain. Under steady state condition pilot is at central position; in deflected position, the control oil is admitted above or below the amplifier piston. The motion of the amplifier piston is transmitted via a lever to a camshaft, which actuates the sleeves of follow-up piston valves, causing secondary oil pressure to change. The speed, load, and pressure signals are measured and converted into conditioned signal in electronic modules.
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1. Differnetial transformer 2. Amplifier casing 3. Amplifierpiston 4. Piston rod 5. Valve bushing 6. Piston valve 7. Grooved ball bearing 8. Spring dics 9. Compression spring 10. Sleeve 11. Casing support 12. Moving coil system a. control oil b. Trip Oil
Electro Hydraulic Converter
Admission Valve (spool) Controller Controller Admission Valve (spool) (spool) Controller also referred referred as the position controller controller is Common for 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 processing outputs that provide the driving current signal to the plunger and regulate the oil drains of HP/IP control valves (CV); thereby it controls steam supply into the turbine. The current in the plunger coil is increased for closing the HP /IP CV and vice versa for opening of the HP /IP Control Valve. The reference signal therefore works in reverse manner (rise in the coil current for low reference condition). By using two Nos of differential transformer (housed in EHC), feedback signal from the valve lift is derived to ensure proper stationing of plunger spool. Whenever current current through the plunger plunger coil gets interrupted interrupted or the electrical feedback feedback circuit 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 sleeve is, considerably smaller, but the regulating signal to the secondary auxiliary oil flow as transformed is quite large. The figure below gives various connections and modules 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 form of pulses /frequency. Channel-2 is utilized while other two-channel pick-up remains redundant; electronically switching ensures no affect in channel in service and also a full - proof monitoring. The selected sensed speed channel signal is further divided into three measuring signals (f/v of 0-60 Hz, low range 0-6 Hz & full range 0-60 Hz and 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) form the input error of the Speed controller which outputs control signal (in the path as explained 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 PROTE CTION SYSTEM SYSTE M Turbine protection protection system performs to cover cover the following functions: a. Protection of turbine t urbine from inadmissible operating conditions. b. In case case of plant failures, failures, protection protection against subsequent subsequent damages. c. It restricts occurring failures to minimum. Standard turbine protection system comprises the following:
Mechanical/hydraulic Mechanical/hydraulic turbine protection.
Electrical turbine protections.
BLOCK DIAGRAM OF TURBINE PROTECTION AND ATT
Mechanical Mechanical Hydraulic Turbine Protection Th e design of me ch an ic a l hy dr a ul ic pr ot ec ti on eq ui pm en t is i n ac co rd an ce with hydraulic hydraulic break current current principle and consists consists of following: following: EDC-Singrauli
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a. Two manual manual trip devices devices (main (main trip valves) b. Two speed monitors (over speed speed trip device) device) c. One hydraulic low vacuum device d. Two solenoid valves for trip initiation initiation (remote solenoid solenoid valves) As explained earlier, turbine stop and control valves are tripped to close position if the trip oil pressure is reduced below the minimum value. The main trip valves allow rapid 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 drained because of actuation of hydraulic low vacuum trip device, over speed trip device or thrust bearing trip device. The principle of functioning of individual hydraulic trip devices is explained in details under the chapter of Automatic Turbine Testing System. Remote trip solenoids act as interfaces between mechanical hydraulic and electrohydraulic protection equipment of turbine. Upon receiving the electrical trip command, 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 function on operating current principle. All electrical trip criteria act on the two remote trip solenoid valves to energise the solenoids. The electro-hydraulic electro-hydraulic turbine protection protection equipment equipment features - Two
solenoid operated valves for trip initiation (Remote trip solenoids). solenoids).
- Emergency - Monitors
trip contactor cabinet containing trip channels 1 and 2
with signal conditioning
- One
substitute channel to ensure uninterrupted transmission of eventual turbine trip signals during testing by ATT.
The remote trip solenoids (RTS) have already been described. Operation of any one channel causes energising both solenoid-operated valves leading to turbine trip eventually. Transmitters that cause a trip in the case of any electrical tripping signal are conditioned and monitored via binary signal conditioning of the ATT system or via the central analog/binary analog/binary signal conditioning. conditioning.
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TURBINE PROTECTION PROTECTION FOR 200MW KWU KWU SETS
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Turbine Trip Actuation Actuation Circuits Circuits The turbine protection system is sub divided divided into two parts: parts: a. Protective circuits for the standard sta ndard turbine protection equipments or criteria. b. Protective criteria from other areas. Standard criteria are specified by the turbine manufacturer and are responsible for full protection of turbine under various specific conditions, which are: EDC-Singrauli
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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 functional group control control (ATRS shut-down shut-down programme) programme) Generator trip
Like low vacuum tripping (electrical) the low steam temperature protection also comprises 'Arming' and 'Disarming' features to facilitate re-start of turbine, under low main steam temperature t emperature conditions. conditions.
Over Speed Trip Device Two hydraulically operated over speed trips are provided to protect the turbine against over speeding in the event of load coincident with failure of speed governor. OVER SPEED TRIP DEVICE
1. 2. 3. 4. 5.
Bearing pedestal Spindle Spring Piston Piston body
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Spring Pawl Over speed trip bolt Shaft journal Limit switch
c: Return Oil u: Auxiliary Stratup Oil x: Auxiliary Trip Oil
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When the preset preset over speed is reached, the eccentric fly bolt activates the piston piston and limit switch via a pawl. pawl. This connects connects the auxiliary trip oil to drain drain thereby thereby depressurising depressurising it. The loss of auxiliary trip medium medium pressure causes the main trip valve to drop, drop, which in turn causes the trip oil pressure to collapse. 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 the vacuum. If the vacuum is too weak to counteract the spring tension, the spring moves valve 6 downwards. The pressure beneath valve is thereby dispersed and the auxiliary trip medium circuit is connected to drain. The resultant depressurisation of the auxiliary trip oil actuates main trip valves MAX51 AA 005 and MAX51 AA 006 thereby closing all turbine valves. The electrical tripping on low vacuum occurs through a pressure switch on the vacuum line to mechanical hydraulic low vacuum trip device also at the same condenser pressure. When turbine is started up again, this pressure switch is interlocked against a second pressure switch, which monitors this condition and prevents continuation of tripping initiation when condenser pressure is high.
Thrust Bearing Trip Trip Device The function of the thrust bearing trip is to monitor the shaft position in the bearing pedestal and, if a fault occurs, to depressurize the auxiliary trip medium and thus the trip oil in the shortest possible time, thereby tripping the turbine.
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1. Compression spring 2. Bearing pedestal 3. Piston 4. Valve body 5. Turbine shaft 6. Pawl 7. Torsion spring 8. Piston 9. Compression spring 10. Limit switch 11. Knob a: c: u: x:
Test Oil Return Oil Aux. Startup Oil Aux. Trip Oil
The two rows of tripping cams, which are arranged on opposite sides of turbine shaft, have a specific clearance, equivalent to the permissible shaft displacement, relative to pawl of the thrust-bearing trip. If the axial displacement of the shaft exceeds the permissible limit, the cams engage pawl, which releases a piston to depressurise depressurise the auxiliary trip oil and at the same time to actuate limit switch. Electrical tripping of turbine is achieved by fire protection along with closure/stoppage of total control oil supply to turbine governing system by tripping the 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 mm below the normal working level 'O'). 'O'). Please refer to the associated logics at the end of this chapter. Also fire protection-1 (automatic actuation) gets bypassed if the barring gear 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
To open the stop valves and generate auxiliary secondary oil and secondary oil
FUNCTION
:
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 val ve 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 SOURCE
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: To operate LPBP valves : Control oil
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KWU
LMW
1.
The types of governor used is Electro-hydraulic backed up by Hydraulic governor
The types of governor used is Hydromechanical
2.
Governing type used is throttle governing
Nozzle type governing is provided
3.
Speed of the m/c is controlled right rig ht from turning gear speed by Electro-hydraulic governor
Speed of the m/c is controlled by Governor from 300-3450 rpm
4.
Regulation range of Electro-hydraulic governor 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 rise a) 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% a) HP ESV: 0.35 Sec
7.
Closing time of servomotors a) HP i) ESV: 0.2 Sec ii) Control Control valve: 0.4 Sec b) IP
i) IV: 0.8 Sec ii) Control Control valve: 0.8 Sec.
8.
Control oil pressure – 8.0 Kg/cm2
9.
Size of HP Stop valve (ESV) i) 160 mmφ - 2 nos ii) zie of HP control valves 128 mmφ - 2 nos) (0.8 times of ESV) iii) Size of IV valves - 320 mmφ (2 nos) iv) Size of IP control valves - 256 mmφ (02 nos)
b) IP: IV: 0.4 Sec c) Control valve servomotor: 0.5 Sec. Control oil pressure – 20.0 Kg/cm2 Size of control valves 1,2,3,4 (4 nos) – 125,150,150.150 mmφ
Size of IV valves – 320 mmφ (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 outside and 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 case of 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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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. Actual over speed test is carried out by by means of Speeder gear after selecting the respective governor by means of selector of emergency governor lever. 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.
13.
In all types of starts HP control valves v alves control from 0 to 100%. IP control valves have controlling function along with HP control c ontrol valve up to 40%, further control is done by HP control valves.
14.
Actual over speed test is carried out by means of separate test lever provided in Hydraulic governor. Both over speed governor are tested together.
15.
Electrical pressure controller is provided to unload the M/C in case ca se the main steam pressure drops by more than 10% of 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 the governing rack.
No such device is provided
18.
IP control valves opens after HP control c ontrol valves
HP control valves opens after IP control co ntrol valves
19.
20. 21. 22. 23. 24.
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 T he speed controller is then in stand by mode and stands ready to provide station load in case of load shedding. Stop & control valves are provided pr ovided in same casing Control valves are mounted away from turbine Control valves movement is in horizontal direction Each control valve can be tested for spindle freeness during operation Each control valve has a separate servomotor
EDC-Singrauli
Such facility does not exist, as the Turbi ne is not provided with Electro hydraulic governing system.
Stop & control valves are mounted in different casing Control valves are integral parts of turbine Control valves movement is in vertical direction Such facility is not available during operation of the M/C Only one servomotor operates all HP & IP control valves.
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PROBLEM Change over valve not getting reset OBSERVATION Change over valve in trip condition and control oil pressure low SOLUTION On line full flow filter self 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 at speed 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
EDC-Singrauli
39
PROBLEM LP By pass Not Resetting OBSERVATION Getting reset after bypassing condensate pressure mechanical switch SOLUTION Open the switch found bellow found damaged. It was replaced. Normal operation of LP BP observed RECOMMENDATION
Bellow changed OR If operation required before replacement. Ensure temperature switch working properly. Replace bellow at the earliest. PROBLEM Electro Hydraulic Converter Hunting OBSERVATION Calibration of EHC checked with Calibrator and found oscillating SOLUTION Opened the EHC and one leaf out of three leaves spring of electro hydraulic converter found damaged. Spring was replaced. Stabilization voltage set to negative (-1 mV). Problem was solved. PROBLEM LP Bypass Water Injection Valve Not Closing OBSERVATION Signal Oil Pressure was low and W I actuator drain line was hot SOLUTION Signal oil inlet was wrongly connected with valve actuator.
EDC-Singrauli
40
PROBLEM HP CV Oscillating (Hunting) OBSERVATION HPCV & HP Secondary Oil Pressure Hunting SOLUTION Damping device was opened and ball ball was found missing. It was put back, oscillation of valve stopped.
PROBLEM Startup Speed Not Rising OBSERVATION Startup device and speeder Gear liver link was broken SOLUTION Lever was changed, problem was solved RECOMMENDATION
Same problem was repeated after about a month. Spring setting was set right and stroke of starting device and speeder gear was readjusted. Problem solved permanently.
EDC-Singrauli
41
PROBLEM HP Control Valve Not Opening OBSERVATION HP Secondary oil pressure was not building up. This was checked in Hydraulic mode as well as EHC mode SOLUTION Follow up pilot block inspection cover was opened and one of the three control pilot was found loose and fell down. It was placed in position. RECOMMENDATION
Pilot was tightened in position with a small screw and little glue smooth operation of HPCV PROBLEM HP Stop valve Not opening OBSERVATION Test valve was checked and found clearance of slide and sleeve more. SOLUTION Test valve was replaced. Problem solved. RECOMMENDATION
Quality of oil/FRF to be maintained for no corrosion / mechanical pitting. Avoid frequent operation of manual testing devices.
EDC-Singrauli
42
PROBLEM
IP Stop Valve Not Opening OBSERVATION
Test valve was checked and found OK. Flow of Trip oil to SV actuator was felt, as line was hot. SOLUTION Actuator was opened and a nut was found in between piston and disc RECOMMENDATION
Fault at assembly shop do not attempt to open the Hydraulic Actuator without the expert guidance. PROBLEM
CRH NRV not opening OBSERVATION
Supply and return line was found hot. SOLUTION Servomotor was opened and servicing was done its seal was found damaged. It was replaced. RECOMMENDATION
Change all the gasket and seals if opened in governing system and control oil system.
EDC-Singrauli
43