210 MW LMW TURBINE

A. GENERAL: The turbine is condensing, tandem compound, three cylinder, horizontal, disc and diaphragm type with nozzle governing and regenerative feed heating. The double flow LP turbine incorporate a multi-exhaust in each flow.

The complete turbine assembly is mounted on pedestals and sole plates which are designed to ensure that the components are free to expand whilst correct alignment is maintained under all conditions. Live steam from Boiler enters in two Emergency Stop Valves (ESVs) of high pressure turbine. From ESV, steam flows to four Control Valves (CVs) mounted on the casing. of High Pressure Turbine(HPT) at the central pedestal side. Control Valves in turn feed the steam to nozzle boxes located inside the HPT.

High pressure turbine comprises 12 stages , first stage being governing stage. The steam flow in HPT being in reverse direction . The blades in HPT are designed for anticlockwise rotation, when viewed in direction of steam flow.

After passing through HPT, steam flows to Boiler for reheating and reheated steam comes to the Intermediated Pressure Turbine (IPT) through two interceptor stop valves (IVs) and four Control Valves (CVs) mounted on the IPT itself.

The intermediated pressure turbine has 11 stages . HP & IP rotors are connected by rigid coupling and have a common bearing.

After flowing through IPT, steam enters the middle part of low pressure turbine through two cross over pipes. In Low Pressure Turbine (LPT) , steam flows in the opposite paths having four stages in each path. After leaving LPT the exhaust steam condenses in surface condenser welded directly to the exhaust. Part of the LP turbine.

Rotors of intermediate and low pressure turbine are connected by a semi-flexible coupling. The direction of rotation of the rotors is clockwise when viewed from the front bearing end towards the Generator. The three Rotors are supported on five bearings. The common bearing of HP & IP rotors is a combined Journal and Radial thrust bearing.

The anchor point of the turbine is located at the middle foundation frame of the front exhaust part of a low pressure cylinder. The turbine expands towards the front bearing nearly 32 mm and towards generator by 3 mm in steady operation at full load with rated parameters.

Turbine is equipped with a barring gear which rotates the rotor of turbine at slow-speed of nearly 3.4 rpm for providing uniform heating during starting and uniform cooling during shutdown.

In order to heat the feed water in the regenerative cycle of the turbine , condensate from the hot well of condenser is pumped by the Condensate Extraction Pump ( CE Pumps ) and supplied at the Deaerator through Ejectors, Gland Steam Cooler, four number L.P. Heaters and Gland Cooler. From Deaerator , the feed water is supplied to boiler by boiler feed pumps through three number H.P. heaters. Extracted steam from various points of the turbine is utilized to heat the condensate in these heat exchangers.

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TURBINE MAIN DATA:Rated output of the Turbine : 210 MW.Rated Speed : 3000 rpm.Rated pressure of steam before ESV : 130 kg/cm2.

Rated live steam temperature : 535 0CRated live steam temperature at inlet of IV : 535 0CSteam flow at valve wide open condition : 670 Tons/hr.Rated CW flow through condenser : 27000 M 3 / hr.

i. For cooling water temp. 0C : 24 27 30 33ii. Steam flow required for 210 MW Tons/hr : 638 645 652 662iii. Rated pressure at the exhaust of LPT. mm of Hg. : 46.9 55.5 65.4 76.7

B. TURBINE BEARINGS :

Three turbine rotors are supported on five bearings. The second bearing from front pedestal side is a combined radial thrust bearing while all other s are journal bearings. The rotors are located inside the turbine .The HPT & IPT rotors are joined by rigid coupling and have been provided with a common bearing. while other ends are having their own bearings.

The lubricating oil is supplied to the bearings at a pressure of about 1 kg/cm 2 and quantity of oil going to each bearing is controlled by the orifice plate at its inlet end.

i. THRUST BEARING : To carry the axial thrust and fix the rotor axially, the thrust bearing is provided. It is a Michell type with bearings surface distributed over a number of self adjusting working and surge pads to bear the axial thrust in both the directions. These pads are made of high quality phosphor bronze faced with white metal. An oil film is formed between the thrust collar and the pads and there is no metal to metal contact between them during operation of the turbine.The radial thrust bearing is supported on a spherical seating at the journal bearing centre line. The inner surface of steel housing is machined spherical, matching with bearing sphere. The bearing is in two halves bolted together. The whole radial thrust bearing is housed in middle bearing pedestal. The babbit temp. of all thrust and surge pads is monitored continuously besides babbit temp. of journal portion.

ii. JOURNAL BEARING:The journal bearings nos. 1,3,4 & 5consists of outer shell of cast steel with an inner shell lined with white metal. Both the shells are split at half joint and secured by the bolts. The pads on the outer shell are machined to bore diameter of bearing pedestals. For the fine alignment steel shims are provided under the pads. The babbit temp. of all journal bearings is monitored continuously.

C ) BARRING GEAR :

The barring gear is mounted on the LP rear bearing cover to mesh with spur gear on LP rotor coupling. The primary function of barring gear to rotate the Turbine – Generator rotors slowly and continuously at 3.4 rpm during start-up or shut-down periods when changes in rotor temperature occurs.

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When a turbine is shutdown , cooling its inner elements continues for hours together. If the rotor is allowed to remain stand still during this cooling down period , distortion of rotor begins almost immediately. The distortion is caused by the flow of hot vapours to the upper part of the casings, resulting in upper part of the turbine being at a higher temperature than lower half. Hence, to eliminate the possibility of distortion during shutdown, barring gear is used to keep the rotor revolving until the temperature change has stopped and casing have become cool. This also results in maintenance of minimum inter stage sealing clearance with higher operating efficiency.The same phenomenon is also observed during starting up of the turbine when steam is supplied to the sealings to create the vacuum. If the rotor is stationary there would be non-uniform heating of the rotor which will result in distortion of rotors. The barring gear during starting of turbine , would slowly rotate the turbine-generator rotor and thereby resulting in the uniform heating of rotor. Thus any distortion in the rotor would be avoided.During starting period , operation of barring gear eliminates the necessity of “breaking away” the turbine- generator rotors from stand still and thereby provides for a more uniform smooth and controlled starting.

SWITCHING ON THE BARRING GEAR :

Switching ‘ON’ of the barring gear can be done either by remote manual control from UCP or from local panel mounted near barring gear assembly in the turbine hall.With the help of a selector in UCP , selection to operate the barring gear can be done either from local panel or from remote switch in UCP.

a. For remote starting , bring the key to the ‘ON’ position in UCP and start the barring gear.b. For manual starting from local panel follow the steps given below :

i. Open the wheel cover.ii. Turn the wheel in clockwise direction ( looking towards barring gear from wheel

side ) and at the same time pressing the hand lever to bring the driving gear in mesh with gear on turbine rotor.

iii. Close the wheel cover.iv. Switch on the electric motor.

Note : a. Never allow hot rotor to stand without rolling.b. Prior to starting of barring gear , lubricating oil system to barring gear must be on. The oil

temperature to the barring is to be maintained between 40-50 0C as long as barring gear in operation by regulating the flow of water through oil coolers.

c. The operation of seal oil system must be ensured prior to starting of barring gear.

During a short shutdown , keep the turbine on barring gear until the turbine is again required for rolling. If the shutdown is for a indefinite period , continue to roll the rotor until the turbine has thoroughly cooled.

SWITCHING OFF THE BARRING GEAR :

a. When starting the turbine : When the speed of turbine rotor increases, due to action of the steam, the barring gear automatically switches off. The motor gets switched off by the release of the limit switch.

b. After stopping the turbine :

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i. By moving the key in ‘OFF’ position, stop the electric motor. In this case the driving gear remains in working position ( in mesh with gear on rotor shaft ).

ii. In case it is necessary to bring the driving gear out of the mesh, then open the cover wheel and rotate it in anticlockwise direction till the driving gear and also the external lever comes back to its initial position ( Non-working)..

Important : i. Supply of stem to the turbine and seals without running the rotors on barring gear

is strictly prohibited.ii. During shutdown of turbine , engage and start the barring gear only after the

rotors have come standstill. It is strictly prohibited to engage the barring gear , when the rotors are still rotating.

D. INTERLOCK & PROTECTION OF TURBINE :

1. Turbine lockout relay (TLR) will trip if,

i. Unit Lockout Relay trips (ULR).ii. Master Fuel Relay trips (MFR)

iii. Main Steam temperature is below 450 0C after a time delay relay ( For initial starting automatic wipeout switch is provided).

iv. Oil level in damper tank is very low.v. DM cooling Water flow to stator winding is less than 13 M3 / hr.

vi. DM cooling water specific resistivity is less than 50K. ohm/cm.vii. Condenser vacuum is less than 540 mm of Hg.

viii. Boiler drum level is very high / low.ix. H.P. turbine exhaust temperature is above 420 0C.x. H.P. heater level is very high ( set point 3 –this will in turn trip ULR and also te running

Boiler Feed Pumps).xi. Lub oil pressure is low ( ).3 ata ).

xii. Shaft axial shift is high ( +1.2 , - 1.7 mm.).

- ‘Low lub oil pr.’ & ‘High axial shift ‘ will also operate the following valves as under :a. Open Vacuum Breaker.b. Close steam to main ejector.c. Close steam to starting ejector.d. Open air extraction valve of starting air ejector

Condition of (11 & 12 ) will in turn trip ULR.

xiii. Protection extraction system troubles :a. Thyrister fans supply failure.b. Regulator supply failure.c. Rectifier transformer temperature very high.d. Grid control unit power supply failure during auto changeover .

All the above will in turn energise turbine trip solenoid.

xiv. “Emergency Turbine Trip “ push button will directly energise the trip solenoid.

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2. The following condition will close the turbine ESVs and IVs :

i. Turbine Trip solenoid (TTS) operated.ii. Turbine over-speed trip operated ( 11- 12 %) .

iii. Turbine over-speed trip addl. Protection operated ( 14% ).iv. Turbine relay oil pressure is less than 10 kg/cm2.v. Turbine Manual Trip operated.

3. Closing of ESVs and IVs will in turn operate the following :

i. Generator Lockout Relay (GLR) through “Low Forward Power “ Relay.ii. Close Turbine inlet M.S. valves (MS-1)

iii. Close extraction stream steam to Deaerator (ES-6 & ES-5)iv. Close all Extraction Non-Return valves ( To open MC-53 & 54).v. Turbine speeder gear fast reversal .

vi. Open HP-LP bypass valves after tripping of GLR.vii. Trip the Master Fuel Relay (MFR) , provided HP, LP bypass valves are closed and load

carrying burner or coal mill is in service , through a time delay of 6 seconds.

4. COLD START UP OF TURBINE :

The turbine is considered to be cold if the temperature of lower part of HPT casing is less than 150 0C.

ECCENTRICITY :

Before supplying steam to the turbine, when the rotors are rotating at barring speed, check the shaft eccentricity . Increase in rotor speed , by adding steam in the turbine is PROHOBITED in case the eccentricity of the rotor in barring speed is more than 0.07 mm. the eccentricity of the rotors at barring speed is also checked by putting a separate dial indicator with long stem, directly above the coupling of the rotor at the middle bearing pedestal . This mechanical dial indicator should be removed before steam rolling the set.The rotation of the rotors, alters the air gap between the eccentricity detector face and shaft collar. This change in the air gap is dependent on shaft eccentricity and relative shaft vibrations.At barring speed , the shaft vibrations are absent and therefore output from the measurement system gives the value of shaft eccentricity only. At speed higher than the barring speed, the variation of air gap is a combination of shaft with respect to the bearings. Thus the readings at speeds higher than barring speed indicate the combine effect of shaft eccentricity and relative shaft vibrations.During steam rolling , if the readings as indicated on eccentricity meter exceed 0.20 mm ( 200 micron) , the turbine should be shut down and put on barring gear and cause of excessive indication be investigated.

BEARING VIBRATION:

a. For healthy turbine, normally the vibrations are less than 40 microns. However, it is important to asses the trend of increase rate, than the absolute level of vibrations. If during speeding up of turbine , the vibrations gradually rise and exceed 40 microns, withhold

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further speeding up of the set ( increase not in critical speed zone), investigate and remove the cause of excessive vibrations.

b. While increasing the rotor speed, the critical speed should be passed as fast as possible to avoid the appearance of rotor vibration. Critical speed of the shaft system are given below :

I II III IV V

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c. In case there is a sudden increase in vibration while increasing speed, trip the turbine through ESV and break vacuum to decrease speed quickly. If vibrations increase during load or while increasing load, trip the set. If necessary, break vacuum to decrease speed quickly.

METAL TEMPERATURE :

a. While heating the casing of ESV, HPT & IPT and also while increasing speed and loading turbine, metal temperature should be raised gradually, avoiding sudden sharp rises. The rate of of rise of metal temperature should not exceed the limits given below :

Temperature Rate

From 100 to 2000C 20 0C per minute

From 200 to 3000C 15 0C per 5 minute

From 300 to 4000C 10 0C per 5 minute

From 400 to 5000C 10 0C per 10 minute

From 500 to 5350C 6 0C per 10 minute

The rate of heating of steam pipes should not exceed 25-30 0C per five minutes.b. While heating the main steam and reheat steam pipes, the difference in temperature of

pipes should not exceed 150C. But when the turbine is on load , this difference should not be more than 100C. While raising the speed of set up to 3000 rpm the difference of metal temperature between the left hand and right hand ESV should not exceed 30 0 C.

c. The temperature difference between the upper and lower halves of HPT & IPT casing should not exceed 50 0C near the regulation stage in case of HPT and near the zone of steam admission in case of IPT.

d. While heating of Flange & Studs, the entry of heating steam should be controlled so that the difference of temperature along the width of flange is not more than 50 0C. The temperature of outer surface of flanges should be always lower than that of inner most surface of flanges. Pressure of steam in the header supplying steam for heating of flange and studs should not exceed 2 kg/cm2.

e. During the trial runs for the heating of the flanges and studs , their heating is to be adjusted such that :

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i. Temperature difference between upper and lower flanges does not exceed 10 0C .ii. Temperature difference between left hand and right hand flanges does not

exceed 10 0C .iii. Temperature difference between flanges and studs does not exceed 20 0C and is

not negative i.e. temperature of studs must be lower than that of flanges.

f. While starting the turbine in any condition, the temperature difference between inner and outer surfaces of the wall of HPT casing should not exceed 35 0C.

CYLINDER EXPANSION :

Longitudinal thermal expansion of turbine is measured at middle and front bearing pedestals.

Thermal expansion of the casing should be symmetrical in transverse direction. While increasing the speed and loading the turbine , it is recommended to measure the clearances between pins mounted on the bearings and casing supports, so as to check the expansion of turbine in transverse direction is symmetrical.

DIFFERENTIAL EXPANSION :

It is prohibited to raise the speed of turbine rotor or the load if the relative expansion (+) or contraction (-) of the rotor reaches the maximum permissible values given below :

For Rotor of HPT : (+) 4.0 mm or (-) 1.2 mmFor Rotor of IPT : (+) 3.0 mm or (-) 2.5 mmFor Rotor of LPT : (+) 4.5 mm or (-) 2.5 mm

(+) sign indicates that Rotor is longer than cylinder and vice versa for (-) sign.

a. If HP rotor expands quicker than the HPT casing, steam supply for heating flanges and studs should be increased, but pressure in header supplying steam for heating should not exceed 2 kg/cm2.

In case of further increase in the differential expansion of rotor, stop further increase in live steam temperature and suspend further loading. If measures mentioned above are not sufficient, decrease the live steam temperature.

b. If HP rotor contracts quicker than the HP casing , stop supply of heating steam to flanges and studs, increase temperature of live steam and increase load or supply fresh steam to the front sealings of HPT and the entry of leak-off steam into heater no. 4.

c. If IP rotor expands quicker than the IP cylinder, stop the increase the temperature of steam after reheat or lower its temperature. If these measures are not sufficient, stop the increase in load too.

d. If IP rotor contracts quicker than the IP casing , increase temperature of steam after reheater and increase load or supply fresh steam to the front sealings of IPT and the entry of leak-off steam into heater no. 4.

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e. If LP rotor expands quicker than the LPT cylinder, worsen the vacuum and stop recirculation of condensate in the condenser.

f. If LP rotor contracts quicker than the LP casing, improve vacuum in the condenser.

PARAMETERS TO BE NOTED :

a. Temperature of live steam and steam after reheat should not have sharp fluctuations. Variation of steam temperature in the starting regimes and during operation of turbine should not exceed ( + 5 0C ) & ( - 10 0C ).

b. Sharp increase of speed or of load, because of deterioration of boiler regime is not permitted.

c. Starting of turbine with cold oil in lubricating and governing system is prohibited. The temperature of oil should not be less than 40 0C.

d. Temperature of lubrication oil entering the bearings after oil coolers, should be within 45 ± 5 0C. and in no case be less than 40 0C. The temperature of at the exit of bearings should not exceed 65 0C... If there is sharp rise in oil temperature up to 75 0C in any of the bearings, the turbine should be stopped.

e. The barring gear gets automatically disengaged when the rotor speed exceeds 3.4 rpm. Electric motor of barring gear also trips automatically with the help of limit switch.

f. During heating , speeding and loading of turbine, carefully watch the readings of the instruments indicating :

i. Vibration of bearings.ii. Axial shift of rotors.iii. Differential expansion of all the three rotors.iv. Metal temperature of upper and lower halves of HPT flanges and studs and upper half

of IPT flanges.v. Oil temperature at the inlet and outlet of the bearings.vi. Babbit temperature of thrust bearings.vii. Pressure and temperature of steam at the control panel.viii. Vacuum.

PROCEDURE OF START UP:

a. Pre-start checks:

1. C.W. pumps are running and condenser inlet and outlet valves are fully opens.2. All CT Fans are running.3. Condensate Pump is running on recirculation and condensate line up to LP Heater

No. 4 is charged. 4. Turbine oil tank level is normal and machine is on barring gear with AC lubricating

oil pump running. DC lubricating oil pump is on ‘Auto’.8

5. Generating casing H2 pressure is 3.5 kg/cm2 and AC Seal oil pump running with DC Seal oil pump on ‘Auto’.

6. Boiler is on oil firing.7. Boiler Feed Pump is running.8. Turbine interlocks checked and found O.K.

b. Line up of turbine , MS, CR and HR lines :

The following valves are to be opened:

1. Impulse line to all pressure gauges for steam, condensate, oil and cooling water.2. MS, HP- bypass drain valves.3. HR, CR, LP –bypass drain valves to flash box / aux. flash box and to atmosphere.4. Aux. PRDS, Gland seal steam supply line and ejector line drains.5. HP and LP cylinder steam admission pipe drains to flash box.6. HP and IP cylinder drains.7. Before seat drain of extraction NRV of extraction line to HP heater no. 7 and 5 to

flash box.8. Before seat drain of extraction NRV of extraction line to LP heater no. 2, 3 and 4 to

flash box.9. After seat drains of Nerve’s of all the extraction lines to flash box.

c. The following valves are to be kept closed :

1. Main steam stop valve (turbine side).2. Main steam stop valve bypass isolating and regulating valves.3. ESV, IV and control valves of HPT and IPT.4. Aux. PRDS to Deaerator.5. Before isolating valve of Aux. PRDS.6. Before isolating valve of gland steam controller.7. Before isolating steam valve of GC-1 ejector.8. First isolating steam valve of starting and main steam ejectors.

After ensuring the closing and opening of all the above the following procedure are to be followed:

1. Open Main steam stop valve (Boiler end) equiliser both side when M.S. pressure is 10 kg/cm2. and temperature is around 200 0C.

2. After warming up for 30 minutes open main steam stop valve.3. after opening drains of TAS line, slowly charge the turbine auxiliary steam line by

opening APRDS-1 controller (5-10%) and after sometime increase the pressure. Check that operation of APRDS is alright and spray water valves are operating.

4. Charge the steam supply header to turbine gland sealing and air ejector from TAS header by opening TAS-3, TAS-4A, and TAS-4B for heating the lines. Check that line drains are operating.

5. Maintain TAS header pressure at 14 kg/cm2 and temperature at 220 0C by raising MS pressure at 35 kg/cm2 and temperature at 280 0C.

6. Start starting Oil pump and maintain oil temperature at around 42 0C.9

d. VACUUM PULLING :

1. Close Reheater vents of Boiler and atmospheric drain of HR and Cr drains.2. Open CA valves gland sealing water line header isolating valve and maintain the header

pressure at 1.5 kg/cm2, then charge gland seal water to all the CA valves.3. Close vacuum breaker (CA-6).4. Open first isolating valve to ejectors (AS-51).5. Open steam valve to starting ejector (AS-54) and maintain steam pressure at 7.0 kg/cm2

and open air off-take valves CA-2 and CA-3.6. When condenser vacuum reaches to 150 mm of Hg, charge the turbine gland steam and

maintain the gland the gland steam header pressure at 0.15 to 0.20 kg/cm2. Charge GC-1 steam side to maintain the GC-1 vacuum 60-80 mm hg by maintaining steam pressure 1.5 to 3.0 kg/cm2. Before charging the GC-1, fill up the drain expander loop with water.

7. When vacuum reaches to 450 mm Hg open MC-39 and MC-57 ( Condensate line to condenser steam throwing device (STD),

8. Line up spray water line of HP bypass from Boiler Feed discharge line and LP bypass valves from condensate pump discharge header.

9. When the condenser vacuum reaches about 600 mm of Hg. Put both the main ejectors in service and maintain the steam pressure 5.5 kg / cm2 to 6.0 kg/cm2. Before putting the main ejectors into service fill up the ejectors drain loops.

10. Check that the HPT evacuating valves CA-21, 22 and bypass valves across CR line NRV’s (Ex-20, 21) are closed.

11. Set HP & LP bypass downstream temperatures at 320 0C and 150 0C respectively. 12. Open LP bypass and HP bypass valves manually about 5% and allow the steam to flow in

HP / LP bypass line.

Note:

Open Reheater temp. control gas dampers positively when HP/LP bypass valves are charged (If ABL make boiler ).

13. Open HP and LP bypass valves gradually and increase the firing rate, if necessary, if pressure drops.

14. Set HP bypass up stream pressure at 25 kg/cm2 and LP bypass upstream pressure at 0.5 kg/cm2 and put on ‘Auto’. Temperature of MS should be maintained around 300 0C.

Note: While heating the main steam and reheat steam lines, difference in temperature of the pipes should not exceed 15 0C.

15. when MS line metal temperature before ESV have reached to 270 0C and superheater outlet temperature of steam is above 50 0C superheat , open bypass valves of MSV for heating the pipe line up to turbine.

16. Close ESV and IV manually by operating the speeder gear hand wheel.17. Open Speeder Gear up to 7 mm.18. Open bypass valves across NRV’s in CRH (ES-20,21) and heat HP turbine up to a

temperature of 120 0C. Then close ES-20 and ES-21.

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19. Open both the ESVs by 10-20 mm as per scale by operating the hand wheel and heat ESV body steam admission pipe up to HPT control valves to 150 0C. While opening ESVs, care should be taken so that the HPT control valves remain tightly closed and steam admission pipe drains to flash box are open.

20. Check the steam pressure in HR line, which should be less than 1 kg/cm2 before starting the heating of steam admission pipe up to control valves (CVs) at IPT. If the pressure in the line is more than 1 kg/cm2, adjust and reduce the pressure by opening the LP bypass valve manually.

21. Open both side IV about 10-15 mm as per scale by opening the hand wheel and heat the steam admission pipes up to CVs up to 80 0C. Care should be taken so that during this operation IPT CVs remain closed and the steam admission pipe drains to flash box are open.

Note:a. The said CVs of IPT have been provided within built relief holes through which

steam leaks into IPT which may cause disengagement of rotor from barring gear, if the pressure in hot reheat line exceeds 1 kg/cm2.

b. During the process of steam admission pipe heating and HPT heating, ensure that the drain valves are open and the drain system is working normal. Check locally that there is not clogging in the drain line.

22. Check bypass valve of MSVs and NRVs in the CR lines when ESV, HPT and Steam Admission pipes of HPT are heated up to 120 0C. The steam parameters at MSV by this time shall be 25 kg/cm2 and temperature of 300 0C,

23. Check that the interceptor and steam admission pipes of IPT have attained a temperature of 100 0C.

24. Close ESV and IV by operating the hand wheel.25. Close Speeder Gear to Zero position.26. Manually close the HP bypass valves keeping LP bypass valves on “MAN” mode. When

pressure in the RH line comes to condenser pressure, manually close the LP bypass valves. Thus bypass stations are manually closed before admitting steam in the turbine for rolling the set.

27. Having accomplished the heating , check and note down the following readings in the log sheet before rolling the turbine:

a. Metal temperature of pipes before MSV.b. Metal temperature of ESV.c. Metal temperature of steam admission lines of HPT & IPT.d. Metal temperature of HR lines.e. Metal temperature in the zone of regulating stage.f. Metal temperature of IV.g. Steam pressure and temperature before MSV,h. Differential expansion of HP, IP & LP rotors.i. Axial shift.j. HPT and IPT overall expansion.

28. Before rolling turbine, ensure that condensate level, Deaerator level and drum level are within allowable limits.

29. Check that the eccentricity of the rotor is within limit (less than 70 microns).30. Open CVs of HPT and IPT completely, with the help of control gear.

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TURBINE IS READY FOR ROLLING:

31. Open the MSV bypass isolating valves of both sides.32. Open the bypass regulating valve slowly thereby allowing steam to roll the turbine.

Note: As soon as the speed of the rotor rises above 3.4 rpm check that the barring gear gets disengaged and its motor gets switched off automatically.

33. For good listening of the turbine against rubbing etc. at 500 rpm, close the MSV bypass regulating valve and listen the turbine carefully. In this process ensure that the rotor does not come at rest.

34. Being certain the turbine is in healthy condition, again raise the speed to 500 rpm by opening the regulating valve and soak the set for 10 minutes at this speed.

35. Smoothly raise the speed to 1200 rpm at the rate of about 50 rpm/ min by slow opening of the MSV bypass regulating valve. Soak the set for 20 minutes at this speed.

36. Raise the speed smoothly to 3000 rpm without pause. It is dangerous to run the set near the critical speeds and hence it is prohibited to hold the set in the critical speed zone.

Note: The control valves of HPT tend to close with the rise in sped. To keep them completely open, the speeder gear should be turned in the direction ‘Increase’.

37. Hold turbine speed at 3000 rpm for about 20 minutes for carrying out inspection, listening and soaking of turbine.

38. When turbine main oil pump develops pressure of 18 k/cm2 before NRV at about 2800 rpm, slowly close the discharge valve of Starting Oil Pump (SOP). See that the oil pressure in the governing system remains constant. Stop SOP and again open the discharge valve for operation during stopping of turbine.

39. While raising the speed, control the temperature of oil entering the bearings. Maintain oil cooler outlet temp. around 45 0C.

40. During speeding up of the turbine increase the boiler firing rate so that the steam parameters before synchronization are as follows :

M.S. steam pressure : 30-35 k/cm2.M.S. Temperature : 330 – 350 0C.R.H Temperature : 300 – 330 0C.

41. Proceed for synchronization as follows :a. With the help of control gear close control valves to such an extent that the speed

just begins to fall.b. Completely open both the MSVs and close the by-pass and regulating vlv.

42. Synchronise the machine and load the machine at 10 MW.Loading of the set:

1. After synchronizing the set hold the turbine at 10 MW load for about 30 min. to carryout soaking.

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2. The steam parameters by this time are expected to be as follows :MS pressure : 35 kg/cm2

MS temperature : 350 0CHR temperature : 330 0C.

3. After soaking the turbine for about 10 minutes at a load of 10 MW, close all the drain valves of steam lines, steam admission pipes, HR drain collector and IP drain collector.

4. During heating of turbine under load, constantly monitor the differential expansion of HPT, IPT and LPT and the overall expansion of HPT & IPT.

Note:

It is seen that during cold startup although cylinder heating is done prior to rolling of turbine HPT differential expansion tends to increase in positive side. If the HPT differential expansion tends to increase beyond +2.50 mm and the rate of increase is steep one, flange and stud heating should be applied. It is not permitted to operate the flange heating device if –

i. The differential expansion of rotor is less than 1 mm.ii. The differential expansion indicating and recording instruments are either out of order

or disconnected.

Important

Check that the temperature difference across the width of the casing flange is within 50 0C. During flange and stud heating the temperature difference between the flange and stud should not exceed 20 0C and the temperature should never be more than that of the flange.

In order to maintain proper tightening of the flange joints, it is necessary to first supply steam for heating flanges and then after sometime to studs. Separate control of steam supply for heating of each flange or studs on the left or right side after initial adjustment is not permitted. e. PROCEEDURE FOR HEATING OF FLANGES AND STUDS OF HP OR IP CYLINDER ( WHICHEVER IS REQUIRED)

a. Check that AS-21, AS-22, AS-23, AS- 24, AS-25, AS-26, AS-27, AS-28, AS-29 & AS-30 valves are open.

b. Blow-down the drains of the steam collector for flange and stud heating by opening AS-33 (HPT) and AS-41 (IPT).

c. Open the valves AS-31 (HPT) and AS-32 (IPT) and drain vacuum of approx 300 mm of Hg in the system. Then close the drain valves AS-33 and AS-41.

d. Open the valves AS-7 or AS-8 and heat the flange and studs of the required cylinder. The pressure in the header should be maintained at 1.5 kg/cm2 by adjusting the valves AS-9 and AS-10 (for HPT) or AS-11 and AS-12 (for IPT).

5. Starting of the turbine should be so regulated that the metal temperature difference between outer and inner surface of the wall of HPT casing at regulating stage does not exceed 35 0C.

6. While loading the turbine , steam temperature should be raised smoothly. The rate of increase of steam temperature should not exceed more than 3 0C per min. in the temperature zone of 400 0C to 535 0C.

7. After ensuring the satisfactory and healthy operation of the turbine at the load of 10 MW, increase the load to 30 MW in a period of 70 minutes. Hold the set at this load for 20

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minutes for soaking of turbine. Steam parameters should be continuously raised to attain following values at the end of the soaking :

MS pressure before ESV : 65 kg/cm2

MS temperature : 4300CHR temperature : 4200C

8. At this load , cut in all L.P. heaters.

9. Increase the load to 70 MW in a period of 50 minutes and hold the set at this load for 30 minutes for soaking of the turbine.

10. At 70 MW load cut in all HP heaters.

11. Put drip pump in service at around 70 MW load.

12. After soaking the turbine at the load of 70 MW , the parameters of the steam should be :MS pressure before ESV : 100 kg/cm2

MS temperature : 4800CHR temperature : 4700C

13. Smoothly and gradually increase the load to 210 MW in a period of 70 minutes and simultaneously raise the steam parameters to the rated value.

14. after the turbine has been fully heated up the overall thermal expansion of the turbine at front bearing pedestal would be around 32 mm.

15. Set the point of HP bypass valves up stream pressure at 140 kg/cm2 and downstream temperature at 380 0C and these controllers must be put on ‘Auto’

. 16. Also LP bypass valves are to be kept on ‘Auto’. Up stream pressure at 6 kg/cm2 and

downstream temperature at 200 0C

g. WARM AND HOT START UP OF TURBINE :

Type of restart of turbine depends on the degree of cooling of ESV body, HPT and IPT casings during the preceding shut down.

Depending upon the metal temperature of HPT casing in the regulating stage the type of start can be shown:

i. Above 350 0C : Hot start.ii. Between 150 0C and 350 0C : Warm start.

iii. Below 150 0C : Cold start.

Before warm / hot start, the auxiliary equipments should be started in the same manner and order as in the case of cold start. In case of warm/hot start, limit of eccentricity, bearing vibration and metal temperatures will be same as stated in the cold start up of the turbine.

GENERAL

1. Boiler is on fire and the aux. equipments e.g. B.F. Pump, CE Pp, and CW Pp are running.

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2. Starting Oil Pump (SOP) is running and machine is on barring gear, check oil pressure in lubricating and governing system and proper draining of oil from bearings.

3. Check all control and measuring instruments have been switched ‘ON’ and they are working satisfactorily.

4. Check that HPT differential expansion & IPT differential expansion are within limit i.e. above 0.0 mm and (-) 1.0 mm respectively. If these parameters are above these values on contraction side, rotor heating should be given at the time of vacuum pulling, otherwise differential expansion would go further contraction side during vacuum pulling.

5. Charge the MS line and TAS header by opening the line drains.

6. Start vacuum pulling by starting ejectors. Rotor heating may be given provided IPT differential expansion starts increasing in the negative side (below – 1.2 mm.).

7. Put HP and LP bypass lines in service when condenser vacuum is above 450 mm Hg column. Check that MSV, ESV, CVs of HPT and IPT are tightly closed.

8. Heating of body of ESV, IV and HPT & IPT steam admission pipes may be done in case the temperature of these elements is 80 0C & 100 0C less than the lower half of HPT casing in the regulating stage and in the zone of steam admission in case of IPT respectively. All the drains to flash box should be opened before starting the steam admission pipe heating.

9. In case of shutdown for less than 6 hours steam admission pipes of HPT and IPT and

bodies of ESV & IV do not get cooled significantly and therefore prior heating of these elements is not required. Just before rolling these elements may be blown for 5 min. through drains.

10. Record the metal temperature of the following :i. HPT in the zone of regulating stage.ii. IPT steam admission chamber.iii. Body of ESV & IV.iv. Steam admission pipes of HPT & IPT.v. Overall expansion and differential expansion of all the three rotors.

11. Before admitting steam to turbine, check shaft eccentricity and see that it is less than 70 microns.

12. Check the temperature of upper and lower halves of HPT. The difference between respective upper & lower halves should not be more than 50 0C.

13. Differential expansion of HPT, IPT & LPT should be more than 0.0 mm, -1.2 mm and + 1.0 mm respectively before rolling of turbine.

14. Before rolling, check that condenser vacuum is above 700 mm of Hg and only main ejector is in service.

INSTRUCTIONS TO USE THE CHART :

1. The curves drawn are for various main steam pressure available before MSV at the time of rolling the unit.

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2. The diagonal lines drawn at the lower part of the chart now directly indicates the various HPC metal temperature at the regulating stage at the time of rolling the unit.

3. For exact matching ( Which is always preferred ) use the abscissa at no.2 . For maximum allowable positive mismatch use the abscissa at no. 1 and for maximum allowable negative mismatch use the abscissa at no. 3. Positive mismatch means steam hotter than metal while negative mismatch steam cooler than metal.

4. The required main steam temperature for the matching for various steam pressure can be obtained from the ordinate of the graph.

For example, say at the time of rolling the unit, the metal temperature at regulating stage is 380 0C and main steam pressure is 70 ata.

Then, as shown by dashed lines on the chart, the main steam temperature before ESV, required for rolling are:

For + Mismatch : 513 0C.For + Exact Match : 468 0C.For - Mismatch : 423 0C.

WARM START :

1. Read the actual temperature of HP casing at the regulating stage, which for this type of start up should be in between 150 0C to 350 0C.

2. By using the temperature matching chart herewith, determine the desired steam temperature and pressure for rolling the turbine on the basis of metal temperature existing in the regulating stage of HP turbine. However, steam temperature must be more (at least 25 0C) than the hottest metal temperature of ESV and steam admission pipes of HPT.

3. Ensure that the evacuating valves CA-21 & CA-22 and the valves across NRVs in cold reheat lines (ES-20 & ES- 21) are closed.

4. With the help of HP-LP bypass valves, raise the steam parameters of boiler to desired value. Simultaneously heat MS, CR & HR lines, if required.

5. Open bypass valves of MS-1 and ESV by 15-20 mm and heat the steam admission pipes up to control valves.

6. Check the steam pressure in hot reheat line, which should be kept less than 1 kg/cm2, before the heating of steam admission pipes of IPT. If the pressure is more than 1 kg/cm2 adjust the pressure accordingly. Open IV by 10-15 mm and heat the steam admission pipe up to control valve of IPT. Care should be taken that the control valves of IPT, during this operation should remain tightly closed. And barring gear does not disengage.

7. After completion of heating, note down various metal temperatures. Ensure that the desired matching steam temperature is available at ESV.

8. Check also that the differential expansion of HPT, IPT and LPT are more than 0.0 mm, -1.2 mm and + 1.0 mm respectively. Check also that HPT and IPT casing upper and lower temperature differential is less than 50 0C.

9. Manually close the HP by-pass valves and open the LP bypass valves. When the pressure in the reheat line comes to vacuum, close the LP by-pass valves also. Thus HP-LP by-pass valves are closed before rolling the turbine.

10. Bring down the speeder gear to zero position and unlock the ESVs and IVs fully and close MS-1 bypass regulating valves.

11. With the help of speeder gear, fully open ESVs, IVs and CVs of HP & IP turbine.16

12. Slowly open the by-pass regulating valves of MS-1 and roll the turbine. Raise the speed up to 500 rpm.

13. As soon as the speed of the rotor rises above 3-4 rpm check and ensure that the barring gear gets disengaged and its motor gets switched off automatically.

14. Listen the turbine rubbing etc. at 500 rpm. Check the vibrations of the bearings.15. After ensuring that the turbine is in healthy state, raise the speed to 1200 rpm within 3- 4

minutes by further opening of by-pass regulating valves of MS-1. Soak the turbine at this speed for 2 – 3 minutes. Note all the parameters and ensure that these are within limit.

16. Raise the speed to 3000 rpm without pause. Hold the turbine speed at 3000 rpm for 5 minutes with a view to carryout the inspection, listening and soaking of turbine.

17. Ensure that Main Oil Pump takes over at 2800 rpm, and then stop SOP.18. Synchronise the set and load the set to 20-30 MW. All the drains must be closed after some

load has been taken on the turbine.19. The raising of steam parameters and loading of the set is carried out as per attached curve

for ‘warm start’.20. After loading the unit put HP-LP bypass valves on ‘Auto’.21. The second Boiler Feed Pump, LP Htrs., HP htrs. Should be cut in depending upon load

conditions of the set.

HOT START :

1. Read the actual metal temperature of the regulating stage of HPC which for this type of start up should be above 350 0C.

2. Read the actual metal temperature of the following :i. Body of ESV & IV.ii. Steam admission pipe of HPT & IPT.iii. Steam admission chamber of IPT.

3. With the help of steam temperature matching chart attached herewith, determine the desired steam temperature and pressure for rolling the turbine on the basis of metal temperature existing in the regulating stage of HP casing. However, the steam temperature before ESV at the time of rolling of the turbine must be more (at least 25 0C.) Than hottest metal temperature of the elements indicated in the Para (2) above.

4. The parameters of steam are raised to get the desired matching temperature with the help of HP-LP by-pass station.

5. After ensuring all the pre-start conditions of HP-LP bypass system, put the HP-LP by-pass valves in service and then put HP by-pass station on ‘Auto’ mode. LP by-pass station also is set on ‘Auto’ and pressure be set at 6.0 ata.

6. Put the temperature control loops of HP by-pass valves on ‘Auto’ and set the temperature set point at 50 0C higher than the Cold Reheat pipes metal temperature. The set point of temperature would have to be slided upward to meet the boiler requirements and ensuring the allowed heating rate of CR pipe lines and Reheater. The temperature set point should not exceed 380 0C. The temperature set point of LP bypass station to be set at 200 0C with ‘Auto’ mode.

7. Ensure that the by-pass valves across NRVs of CRH lines ( ES-20 & ES-21) are closed. Open the evacuating line valves (CA-21 & CA-22) to release the entrapped steam from HP casing.

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8. It may be required to put HPT & IPT rotor heating for arresting HPT * IPT differential contraction. MS temperature should be raised at least 50 0C higher than the HPT & IPT cylinder temperature before putting the rotor heating.

9. Raise the steam parameters of boiler . The HP by-pass valves shall be kept on open condition and swallow the entire steam generated by the boiler, until the flow passing capability of the HP by-pass valves corresponding to set pressure is fully utilized.

10. Raise the boiler parameters to the value required under Para (3) . As the difference of pressure, between the actual value and set point, exceeds the limit, an alarm shall appear. At this stage , the pressure set point should be manually slided upwards, but always ensuring that the set point value is 2 to 3% lower than the actual pressure value indicated in the instrument.

11. After attaining the desired steam temperature and pressure suitable for rolling of the turbine, hold the firing rate of boiler.

12. Heat the steam admission pipes between IV and CV of IPT by opening IV by 5 to 10 mm. The valves in the drains of these pipes should be kept full open, prior to opening IV. After heating these pipes corresponding to steam temperature, close IV fully. Care should be taken during this operation to lower the LP by-pass station pressure set value below 1 kg/cm2 so that the turbine does not get rolled off the barring gear.

13. Check also that the differential expansion of HPT, IPT and LPT are more than 0.0 mm, -1.2 mm and + 1.0 mm respectively. Check also that HPT and IPT casing upper and lower temperature differential is less than 50 0C.

14. Open fully both the turbine side main steam stop valves (MS-1) and also valves in the drain lines of the transfer pipes.

15. Before rolling check that HP-LP by-pass valves are on ‘Auto’ mode. LP by-pass pressure setting should be at 6 ata.

16. Completely open ESV & IV with the help of speeder gear. Turbine will start rolling through IPT.

17. As soon as the speed of the rotor rise above 3.4 rpm check and ensure that the barring gear gets disengaged and its motor gets switched off automatically.

18. Start opening of CVs of IPT and raise the speed of turbine to 3000 rpm without pause.19. Ensure that MOP takes over at 2800 rpm and then stop the SOP.20. Synchronise the set and take around 30 MW load on the unit. Close all the drains.21. Continuously monitor the steam temperature of HP & LP by-pass station. Immediately

after opening of CVs of IPT, monitor the pressure in HR lines. Automatically ‘Pressure Control Loop’ of LP by-pass station will not allow dropping pressure below 6 ata in the HR line. In case it falls below this value, LP bypass control should be taken in manual for controlling the pressure in reheat line around 6 ata.

22. Ensure that the evacuating valves CA-21 & CA-22 in the HP casing drain lines gets closed automatically when steam flow starts through HPT.

23. Immediately increase load of the turbine @ 5 MW per minute until HP bypass valves get closed automatically and entire steam passes through HPT. Hold the load at this stage.

24. Further loading of the set is done as per the curves for HOT start. The steam parameters are raised by increasing boiler firing rate. The time for loading the set during hot restart depends on the thermal condition of HPT & IPT.

25. While loading the set, ensure that the metal temperature difference between inner and outer surfaces of the wall of HPT casing does not exceed 35 0C. In case this requirement is not being fulfilled stop further loading of the set until these requirements is met.

26. Stop rotor heating steam supply of HPT & IPT when differential contractions reduced and got stabilized.

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27. The second Boiler Feed Pump, LP heaters and drip pumps should be put into service depending upon the load condition of the set.

SHUTDOWN OF TURBINE :

A planned shutdown i.e. gradual load reduction leading to subsequent shutdown is desirable as compared to abrupt trip out, which is normally done during emergency condition only. If no proper sequence is followed during shutdown. It may result in inducing thermal stresses, differential expansions, distortions and misalignment of turbine flow path elements. Proper shutdown procedure will reduce the down time for restarting of the set and also it will avoid under stressing of turbine parts. The shorter is the shutdown required, the greater must be the coordination and precision of the operator during shutdown.

The turbine can be stopped by pressing the knob of turbine shutdown switch on the front right side of the front pedestal. The same action can be achieved by engaging the solenoid of the shutdown switch by remote operation from UCR. This solenoid also gets energized and trips the turbine when the ‘Turbine Lockout Relay’ is operated due to any fault in the unit necessitating the tripping of turbine.

Planned Shutdown :

For planned shut down of the set, following procedure should be followed:

1. Inform the boiler operator that turbine would soon be shutdown.2. Check the SOP and AC & DC Lub. Oil pumps and ensure their ‘Auto’ cut in.3. Check the non-seizure of ESV & IV . Check that bypass valves of MS-1 are closed.4. Normally, the turbine is unloaded by closing gradually the CVs through remote operation

of speeder gear. The unloading should be carried out @ 3 MW per minute at rated parameters. The rate of unloading mainly depends differential contraction of rotors. Firing rate of boiler is to be controlled accordingly.

5. After reducing the load to 120 MW cutout HP heaters on steam side as well as drip side.6. Switch off one of the B.F. Pumps 7. At about 70 MW load check that drip pump gets switched off under automatic controller

action.8. While unloading and stopping the turbine , sharp fall in metal temperature of steam

distribution elements of HPT & IPT should be avoided.9. While unloading the turbine , constantly monitor the differential expansions of Rotors,

temperature of flanges & studs, vibration of bearings, shaft eccentricity etc.10. In case differential expansion of rotors tends to exceed the permissible limit, take necessary

measure. For minimizing the contraction rate of HP & IP, rotor heating may be applied ( after the blowing down the pipes ). Care should be taken so that steam temperature is higher than the metal temperature of HPT and IPT as case may be.

11. Having unloaded the turbine to about 10 MW load, start the Starting Oil Pump (SOP) . Then trip the turbine. Check that ESVs IVs and CVs get closed. Also check that Generator Circuit Breaker has opened through ‘Low Forward Relay’.

12. Check that MS-1 have closed on ‘Auto’ otherwise close these valves manually.13. If there is jamming in ESV or IV, immediately close MS-1 ( If these are not closed on auto)

and ensure that turbine speed starts reducing.

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14. When the speed has dropped to 2800 rpm, check that oil pressure in the lubrication system is normal.

15. If for some reason , the turbine is to be stopped quickly vacuum should be broken. For this purpose , cut off steam supply to main ejectors and open the vacuum breaker valve CA-6. When the vacuum falls to 100 mm of Hg. Cut off gland seal steam supply and steam supply to GC-1 ejector.

16. When the oil temperature at the outlet of the bearings drops to 45 0C , stop cooling water supply to oil coolers.

17. When rotor comes to stop , immediately start the barring gear and roll the rotors continuously till temperature of lower part of HP casing at regulating stage drops to 150 0C.

18. Isolate TAS header by closing the main isolating valve. Also close MS stop valves MS-2 and MS-2A or SH-7 & 7A).

19. Keep the condensate pump running on recirculation until LP exhaust hood temperature comes to 50 0C.

20. Stop the condensate supply to valves and pumps glands sealing and also cooling water in ESV & IV servomotors.

21. After the turbine is shutdown , drains of steam admission pipes and cylinders should not be opened till the metal temperature falls below 200 0C. If the turbine is to be started before the metal temperature drops to 200 0C, then the drain are only opened during preparation for restarting.

22. CW Pumps can be stopped when LPT exhaust hood temperature falls to 50 0C.23. After the turbine is stopped and the rotor is on barring gear, check shaft eccentricity and

record it in the log book.

FORCED SHUT DOWN / TRIP OUT OF TURBINE :

During forced shutdown/trip out of turbine due to some fault, ESV, IV and control valves will get closed immediately and the generator circuit breaker will open through low forward power relay. In that case the following operations should be done immediately :

1. Start the starting oil pump.2. Check that MS-1 valves have closed on auto , otherwise close these valves manually.3. Put the turbine on barring gear when rotor s have come to rest.4. Try to detect the fault and restart the turbine if the fault is over.5. If the fault persists , boiler fire is to be killed and vacuum may be killed as described in

normal shutdown procedure.

A typical H.P. Control Valve Characteristic in Cold Condition:

Relay oil pressure : 16 kg/cm2 .H.P. Cylinder 1st. stage Metal Temperature : 38 0C.

LIFT OF H.P. CONTROL VALVESHP Cam angle position degree ( 0 )

CVSM position( mm )

Valve-1( mm )

Valve-2( mm )

Valve-3( mm )

Valve-4( mm )

0 0 0 0 0 010 140 3 4 0 0

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20 155 6 8 0 030 170 7 10 0 040 178 9 13 0 050 205 11 16 0 060 220 13 18 0 070 240 18 23 0 080 256 23 29 0 090 272 24 (Full open) 36 3 Starts opening100 290 24 38 (Full open) 14 5105 300 24 38 18 (Full open) 11 (Full open)

H.P. Control Valves Starts open at :

Cam Angle Position

C.V.S.M. Position

Valve No.-1

ValveNo.-2

Valve No.-3

Valve No.-4

0 0 120 mm Start - - -100 122 mm - Start - -740 250 mm - - Start -900 272 mm Full Open - - Start1000 290 mm - Full Open - -1500 300 mm - - Full Open Full Open

GAPS in between H.P. Cam and Roller Assembly:

Control Valve Gap

Valve No.-1 5.0 mmValve No.-2 5.0 mmValve No.-3 8.0 mmValve No.-4 8.0 mm

I.P. control Valves Starts open at :

IPCV Angle position

CVSM Position

LIFT OF CONTROL VALVEValve No.-1

ValveNo.-2

Valve No.-3

Valve No.-4

5 10 Start Start - -45 50 - - Start -90 95 - - - Start290 300 (Full open)

Lift-98 mm(Full open) Lift-98 mm

(Full open) Lift-82 mm

(Full open) Lift-80 mm

ESV & IV starts open at :

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Speeder Gear Position (mm) ESV Lift (mm) IV Lift (mm)5.0 - Starts opening.6.3 Starts opening -7.5 - Full open8.0 Full Open -

TURBINE GOVERNING SYSTEM

1. Introduction :

High pressure hydro-mechanical Governing system has been provided for the steam turbine to maintain the speed at the desired set points during start up and normal operation. It also serves to prevent undesired over speeds following sudden loss of export load. The control action of the proportional type with a steady state overall speed regulation (i.e. proportional band) of 4 ± 1% . This proportional band is necessary in order to realize :

a. Stable speed control in isolated operation of the set.b. The desired degree of load distribution between sets running in parallel.

All the operations of starting and loading the set can be performed by manually operating the speeder gear hand wheel located at front pedestal or by operating speeder gear motor remotely from unit control panel.

Special features :

i. In the event of generator breaker opening following a full load loss, governing system prevents the over speeding of the set to a dangerous level and quickly stabilizes the set on house load or on no load, This is achieved by electro hydraulic transducer (EHT) receives signal only for two seconds.

ii. The governing system envisages anticipatory over speed control gear termed as ‘Differentiator’. The differentiator causes anticipatory closure of the control valves depending on the magnitude of acceleration being experienced by the turbine. This action prevents speeding of the set to a dangerous level.

iii. Transient speed rise is anticipated to be not more than 7 to 8% over normal speed, even in case of total loss of export load.

iv. Speed governor can control speed in the range approx. 300-3450 rpm when the set is not synchronized.

v. Load limiter has been provided to avoid accidental overloading of the set. The set point of load limiter can be chosen over entire range from no load to full load.

vi. Governing gear operates on constant oil pressure principle.vii. Initial steam pressure unloading gear (ISPUG) has been provided to unload the set in

case initial steam pressure drops by more than 10% of the rated steam pressure.

A. GOVERNING SYSTEM : The governing or regulation process is achieved by a combination of mechanical and / or hydraulic signals causing interactions of elements mentioned below :a. Speed Governor.b. Follow-pilot valve.

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c. Summation pilot valve.d. Intermediate pilot valve.e. Control valve servo motor.f. Load / speed control pilot valve g. Differentiator ( Anticipatory gear ).h. Electro hydraulic Transducer (EHT).i. Speeder Gear.j. Initial Steam Pressure Unloading Gear (ISPUG).k. Lever.l. Load Limiter.

B. Protection System;

Protection system functions similar to governing system by a combination of mechanical and hydraulic signals on various elements mentioned below :

a. Emergency governor.b. Emergency governor lever.c. Emergency governor indicators.d. Emergency governor testing cock.e. Emergency governor pilot valve.f. Emergency stop valve servomotor.g. Interceptor valve servomotor.h. Turbine shutdown switch.

II. DESCRIPTION OF GOVERNING SYSTEM ELEMENTS :

A. Speed Governor :

Speed Governor Pilot Block performs malfunctions during startup of turbine and during normal service when the turbine is being run in a grid or otherwise. The speed governor pilot block performs these functions through the following elements :

i. Follow pilot valve.ii. Summation pilot valve.iii. Load / speed control pilot valve.iv. Speeder gear.v. Lever.

Function of the above elements :

i. Follow pilot spool follows the movement of governor sleeve and actuates the summation pilot valve through lever.

ii. Summation pilot valve receives signal from follow pilot valve and load / speed control pilot valve through the lever and actuates differentiator and intermediate pilot valve.

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III. Load/ Speed control pilot valve is instrumental in converting mechanical signal from speeder gear into hydraulic signals to emergency governor pilot valve, emergency stop valve servomotor and interceptor valve servomotor. It actuates the summation pilot valve through lever. It performs the following functions :

a. To bring the main pilot spool of the emergency governor pilot valve (EGPV) in operative position after turbine trip out. This process is called charging of the emergency governor pilot valve.

b. To open emergency stop valve and interceptor stop valve.

c. To control speed while the set is at no load.

d. To assist in synchronization of the set.

e. For changing the load of the set while the turbine is working in parallel with other turbines in the grid.

IV. Speeder gear essentially actuates the load / speed control pilot valve. The speeder gear can be actuated either by operating the hand wheel at front pedestal or by remote operation from unit control panel.

V. Lever inter-connects the load/speed control valve , follow pilot valve and summation PILOT VALVE.

Equilibrium of various elements and process of propulsion:

i. Equilibrium of follow pilot spool.The pilot spool remains in equilibrium as a result of 13 ata ( oil at 20 ata enters through an orifice of dia 3.2 mm ) pressure acting on the left face of the bobbin and pressure 5 ata acting on the right face of the bobbin. Oil flows to open drain from the chamber ( 5 ata oil pressure ) through radial and central holes and nozzles of 5 mm dia. Oil flow is restricted by governor sleeve which is approximate 1.3 mm away from nozzle face.

ii. Force acting on summation pilot spool.A continuous hydraulic force due to 20 ata pressure acting on the right face of the bobbin, keeps the spool pressed against the lever. However, this force is feeble as compared to the force exerted by follow pilot valve and load / speed control pilot valve through lever. Thus the position of the spool is dictated by the position of the follow pilot spool and load / speed control pilot spool. Primary sensitive line oil enters and leaves through ports to open drain.

iii. Force for actuation load speed control pilot spool

Pilot spool is subjected to hydraulic forces which are self balanced by 20 ata oil pressure. The propulsion force for the pilot spool is provided by speeder gear only.

OPERATION : a) Speed decreasing i.e. load increasing on the set :

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Under the conditions the speed governor sleeve moves towards left. This restricts oil flow from the chamber. This in turn increases the pressure in the chamber. The equilibrium of the pilot spool gets disturbed and it moves towards left until the distance between nozzle face and governor sleeve is again restored. It can, therefore, be said that the pilot spool is hydraulically coupled with governor sleeve and follows its motion.

The leftward movement of the pilot spool pushes the lever towards left through tie-rod.

The lever pulls pilot spool of summation pilot valve towards left hand side. It temporarily transmits the increased oil pressure signal to the intermediate pilot valve through the primary sensitive oil line. The increased pressure also gets transmitted to differentiator . the pressure increase in primary sensitive oil line actuates the intermediate pilot valve in such a manner that the pressure in the primary sensitive oil line gets restored to its normal value 7.7 ata Similarly the pressure in the line to differentiator also gets restored to its normal value of 8.9 ata

b) Speed increasing i.e. load decreasing on the set:The mode of operation in this case would be just reverse of the events described above.

c) Large load dump: Under these conditions, the follow pilot spool actuates the pilot spool of summation pilot valve to move towards right rapidly. This causes sharp drop if pressure in the primary sensitive oil line. At the same time due to movement of the bobbin sharp drop in oil pressure takes place in the oil connected to differentiator. The differentiator senses the rate of drop of pressure and gives command for anticipatory closure of control valve.

d) Charging of emergency governor pilot valve :Following a trip out by actuation of emergency governor pilot valve (EGPV), it is essential to bring EGPV in operative position again. For achieving this , it is necessary to bring the spool of load / speed control pilot valve to extreme left position so that oil supply to chamber connected to charging line is blocked

e) Opening of ESV and IV servomotors :Anticlockwise rotation of speeder gear moves pilot spool of load / speed control pilot valve towards right which uncovers the ports and this in turn leads the supply of 20 ata Oil in ESV and IV servomotors. IV servomotor begins to open when the pilot spool of load / speed control valve has moved by 4.6 mm and get completely opened at 5.9 mm travel of the spool. Similarly ESV servomotors begin to open at 5.5 mm travel and get completely opened at 6.65 mm travel of the spool.

f) Speed control at no load :Anti-clockwise rotation of the hand wheel of speeder gear moves pilot spool of load / speed governor control valve towards right. Any movement of pilot spool towards right causes movement of summation pilot spool towards left through lever because middle pin acts as fulcrum. The speeder gear can be operated by the DC motor also. The motion is transferred through worm and worm gear.

9.6 mm travel of spool of load / speed control pilot valve would bring the pilot spool of summation pilot valve in such a position that the bobbin just begins to cover the pots which

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would cause increased pressure signal in the primary sensitive oil line resulting in opening of control valves ( as explained afterwards).

As speed increases , follow pilot spool would move towards right and the lever would just push the summation pilot spool towards right by about twice the travel of follow pilot spool. Thus net movement of summation pilot spool towards left , due to anti-clockwise rotation of speeder gear, is the difference of travel of load/ speed control pilot spool towards right and double the travel of follow pilot spool towards right. The negative travel of summation pilot spool due to increase in speed is counteracted by further anti-clockwise rotation of speeder gear. Thus speed control at no load can be done by operating pilot spool of load / speed control pilot valve by speeder gear.

Foe synchronization of the set with grid , speed of the set can be brought to match the frequency of the grid and then set may be connected to grid.

When the set is in grid of large capacity , its speed is governed by the grid frequency only and load / speed control pilot valve would then control the load when actuated by the speeder gear.

B) Intermediate Pilot Valve :The intermediate pilot valve amplifies the hydraulic signals from summation pilot valve, differentiator, electro-hydraulic transducer and EGP valve. The amplified hydraulic signal is in turn , transmitted to control valve servomotor.

Oil at 20 ata Enters in the chamber from bottom hole . Oil from the chamber also flows into another chamber, through the ports and central hole in bobbin of pilot spool, which is connected to primary sensitive oil pressure.

Another chamber at the top is connected to the secondary sensitive oil line on one side and to the suction line of main oil pump through ports on the other side. The pressure in the secondary sensitive oil line is maintained at 10.3 ata Under steady state.

Equilibrium: The pilot spool remain in equilibrium due to pressure at 15.4 ata acting downwards on differential area of bobbins I and II and pressure 7.7 ata At lower face of bobbin I acting upwards.The hydraulic face on the remaining faces of the bobbins are self balanced.

Operation :

a) Speed decreasing i.e. load increasing :Under these conditions the pressure in primary sensitive oil line would increase causing the upward movement of pilot spool which would result in :

1. Bobbin I would reduce the area of opening of ports, thus reducing the quantity of oil entering the chamber. The pilot spool would move only to such an extent as to restore the pressure in primary sensitive oil line to 7.7 ata

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2. Bobbin II under simultaneously reduce the area of opening of ports and thus reducing the quantity of oil drain from secondary sensitive oil line to the suction line of main oil pump. This would cause the transient pressure increase in secondary sensitive oil line resulting in further opening of control valves.

b) Speed increasing i.e. load decreasing :

1. For small load changes the mode of operation would be just reverse as stated above.

2. In case the large load dump, differentiator would cause additional oil drain from primary sensitive oil line which would result in further downward movement of pilot spool of intermediate pilot valve causing anticipatory closure of control valve.

3. In case of generator breaker opening , electro-hydraulic transducer would also come additional pressure reduction signal in primary sensitive oil line for two seconds thereby causing the closure of control valves.

c) Emergency condition :

During action of the protection system, main pilot spool of emergency governor pilot valve moves downwards causing drain of primary sensitive oil . It would give a sharp decrease pressure signal in primary sensitive oil line causing downward movement of pilot spool of intermediate pilot valve , which would actuate control valves servomotor to completely close the control valves.

C ) Control Valve Servomotor :

The servomotor receives hydraulic signal from intermediate pilot valve and actuates four control valves of HP turbine and four control valves of IP turbine through racks, pinion, cams etc.

Equilibrium :

At steady state , the pilot spool of servomotor pilot valve remains in equilibrium under the action of the following forces :

i. 10.3 ata Pressure acting upwards, on the lower face of bobbin I (lower).ii. 20 ata Pressure acting downwards on the upper face of bobbin IV ( on differential

area of bobbin IV & V) iii. 1 ata Pressure acting downward on the upper face of bobbin V (upper ),

In steady state piston of control valve servomotor is in equilibrium under the action of following force :

i. Pressure in the chamber acting upwards on lower face of bobbin I ( lower ).ii. Pressure in the chamber acting downwards on the upper face of bobbin I ( on

differential area of bobbin I & II ).iii. Control Valve forces acting downwards on the piston through linkage and stem.

Operation :27

a) Speed decreasing i.e. load increasing :

Under these condition , oil pressure in secondary sensitive oil line increases. Due to unbalance the pilot valve moves upwards. As a result control oil flows into the lower chamber of control valve servomotor through ports which disturbs the balance of piston and it moves upwards resulting in opening of control valves. Oil above the piston flows into a chamber of servomotor pilot valve through ports from where it flows into suction line of MOP.

Movement of piston upwards causes downward movement of pilot spool of feed back pilot valve by feed back action lever. This movement decreases oil supply to chamber through ports and as soon as the servomotor opens up to the desired level, pressure in the secondary sensitive oil line gets restored to 10.3 ata This process is known as feed back action.

When pressure 10.3 ata is restored , pilot spool of servomotor pilot valve moves down to its middle position and stops further oil flow into the lower chamber and also oil flow from the upper chamber of control valve servomotor. Thus oil under and above the piston in the main servomotor is entrapped arresting the movement of piston.

b) Speed increasing i.e. load decreasing :

i. Under the condition, oil pressure in the sensitive oil line decreases. Due to unbalance the pilot spool of servomotor pilot valve moves downwards. As a result control oil flows into the upper chamber of control valve servomotor through port, which disturbs the balance of piston and it moves downwards resulting in closing of control valves. Oil below the piston flows into a chamber of servomotor pilot valve through ports from where it flows into the suction line of MOP.Movement of piston downwards causes upward movement of pilot spool of feed back pilot valve by feed back action of lever. This movement increases oil supply to chamber through ports and as soon as servomotor closes up to the desired level, pressure in the secondary sensitive oil line gets restored to 10.3 ata.When pressure 10.3 ata is restored, pilot spool of servomotor pilot valve moves up to its middle position and stop further oil flow into the upper chamber and also the oil flow from the lower chamber of control valve servomotor. Thus oil in the main servomotor is entrapped.

ii. During large load dump , primary sensitive oil would drain from the summation pilot valve as well as in differentiator. Additional drain of primary sensitive oil in the differentiator would cause anticipatory closure of control valve.

iii. During opening of generator circuit breaker causing action of EHT, 2 seconds pressure reduction signal in primary sensitive oil causes the anticipatory closing of control valves.

iv. Main steam pressure drop causing action of initial steam pressure unloading gear decreases secondary oil line pressure resulting closing of the control valves and thus unloading the turbine. If main steam pressure is restored, secondary sensitive

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oil line pressure would rise resulting in opening of control valves and thus loading the machine.

c) Operation of protection system to trip the turbine :

Under these conditions, primary sensitive oil is connected to open drain through emergency governor pilot valve resulting in downward movement of pilot spool of intermediate pilot valve to lower stop. It causes sufficient pressure drop in secondary sensitive oil line leading to instantaneous and complete closure of control valves.

D) Differentiator :

The differentiator essentially causes anticipatory closure of control valves of HPT & IPT, in case the load throw-off is more than 50% of the nominal thus preventing undue speed rise of turbine.

Equilibrium :

Following forces keep the pilot spool in the equilibrium position :

i. Control oil pressure 20 ata acting downwards on the upper face of bobbin.ii. Oil pressure 8.9 ata acting upwards on the lower face of bobbin.

Piston is in equilibrium due to following forces :

i. Control oil pressure 20 ata acting downwards on the upper face of bobbin.ii. Oil pressure 4.85 ata acting upward on lower face of bobbin.

Operation :

a) Speed decreasing i.e. load increasing :

Oil pressure temporarily increases under the pilot spool which results in upward movement of pilot spool relative to piston causing flow of control oil from one chamber to other. It results in movement of piston upwards till ports are again covered by bobbin of pilot spool with some time lag ( Time constant of piston is more than time constant of pilot spool) . In this process primary sensitive oil pressure is not affected by differentiator. So under these conditions differentiator does not participate in governing process.

b) Speed increasing i.e. load decreasing :

Oil pressure temporarily decreases under the pilot spool , which results downward movement of pilot spool relative to piston. As a result of this oil chamber is connected to open drain. Thus due to decrease of pressure in the chamber, piston moves down till ports are again covered by bobbin of pilot spool. Piston follows motion of pilot spool in downward direction also.

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When load fall is less than 50% of the rated load the primary sensitive oil pressure is not affected by the differentiator.

c) Abnormal condition ( large load dump) :

When load dump is more than 50% of the rated value, resulting in pre-determined acceleration of the set, pilot spool moves downwards much faster than the piston. As a result of this piston lags pilot spool by a distance more than overlap of 0.5 mm and the ports get uncovered. It causes drain of primary sensitive oil in addition to its drain in summation pilot valve , resulting in anticipatory closure of control valves. Speed rise is limited to 7 to 8% of the rated value under large load dump condition, by differentiator. Thus chances of unit trip by speed increase to 11 to 12% are eliminated.

E) Electro-Hydraulic Transducer (EHT) :It is instrumental in converting electrical signal derived from generator circuit breaker into hydraulic signal in the primary sensitive oil line. This is achieved by two main elements.

a. Electromagnetic transducer :It converts electrical signal from generator circuit breaker into movement of one plunger.

b. Hydraulic amplifier :It converts movement of plunger of electromagnetic transducer into an amplified hydraulic signal to primary sensitive oil line resulting in closure of control valves.

Equilibrium :

a. Electromagnetic transducer EMT) :When energized , sliding system of EMT experiences an upward force due to interaction of magnetic flux of permanent magnet and operating coil. The sliding system moves upwards until the tension of the spring equalizes the magnetic forces.

b. Hydraulic amplifier :Primary pilot spool is in equilibrium under the influence of downward forces due to pressure 4.6 ata acting on upper face of bobbin and upward force due to pressure 13 ata In the chamber acting on the lower face of primary pilot spool.

Secondary pilot spool is in equilibrium under the influence of force from right on bobbin due to pressure 11.8 ata and force from left on bobbin due to control oil pressure 20 ata

Operation :a. Generator circuit breaker opens :

Under these conditions, a time bound electrical signal (current) is transmitted to the operating coil of EMT. Because of the interaction between the magnetic forces of operating coil and permanent magnet sliding system of EMT would move up thereby clearance between oil guard and nozzle and face ( upper face of bobbin of

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primary pilot spool ) would increase . This increased clearance would cause more drain through nozzle end face to initial value.

As a result of action stated above clearance between nozzle and taper part of primary pilot spool would increase. It would result in more drain through nozzle and ultimately decrease the pressure in right hand chamber of bobbin of secondary pilot spool. Equilibrium of secondary pilot spool gets disturbed and it moves towards right till the clearance comes to initial value. ( Movement of secondary pilot spool is three times the movement of primary pilot spool). Due to the movement of secondary pilot spool towards right, it would uncover the ports causing the drain of primary sensitive oil from the chamber. This will cause temporary pressure drop in primary sensitive oil line resulting in closure of control valves.

After 2 seconds as soon as the electrical signal is cut-off , sliding system of EMT would move down to its middle position and the processes as stated above would occur in reverse order. Thus the drain oil of primary sensitive oil will block. In this manner, it may be noted that EHT impulse in the primary sensitive oil line is superimposed on the other governing signal for a duration of 2 seconds only.

b. Load / Speed changes when generator circuit breaker remains closed :Under these condition no electrical signal is transmitted to EHT and therefore electro-hydraulic transducer does not influence the governing system.

F) Initial Steam Pressure Unloader:

Initial steam pressure unloading gear (ISPUG) essentially reduces the load on the turbine in case initial steam pressure falls below 90% + 2% of the rated value i.e. below (117 + 2) ata It is achieved by partial closure of control valves. Unloading gear would proportionally unload the set to no load if the initial steam pressure drops from (117+2) ata to 91 ata ( i.e. 90% + 2% to 70%)

Oil Circuit:Under normal opening condition port in the liner is covered by pilot spool coupled with actuator and the chamber fed with oil from secondary sensitive oil line is not permitted to flow through ports. There is an overlap of 150 between the edges of ports to avoid leakage.a) Control action when main steam pressure starts falling down :

Electrical signal from pressure transmitter is blocked till pressure falls from 130 ata to (117 +2 ) ata. At pressure (117+2) ata, actuator receives electrical signal and rotates the pilot spool such that pointer indicates ‘1’ on scale. Under this condition overlap of 150 between the edges of ports reduces to zero. On further steam pressure drop , pilot spool starts uncovering the port which will lead to drain secondary sensitive oil into suction of MOP. This would result in temporary oil pressure drop in secondary sensitive oil line causing closure of control valves. When initial steam pressure drops from 90% to 70% the set is completely unloaded from full load to no load. Unloading is proportional to the pressure drop in the range 90% to 70% i.e. if pressure drop is 5% unloading would be 25% . If pointer indicates ‘2’ on scale unloading is 25% at’3’ by 50% and so on.

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b) Control action when main steam pressure building-up :Pressure rise in the range 70% to 90% of the normal would cause movement of pilot spool in reverse direction. It would reduce the uncovered area of the ports and thus increase pressure in secondary sensitive oil line. As a result control valve would open to reload the set proportional to the steam pressure rise.

G) Load limiter :Load limiter avoid the accidental overloading of the set beyond set point. The set point can be carried over entire load range. It is mounted on the front end of the front pedestal of turbine.

Operation :Operation of load limiter is unidirectional. It restricts movement of pilot spool of summation pilot valve towards left, as soon as the bolt (located at the interconnection point of lever and summation pilot valve) presses limiter rod. But load limiter does not affect movement of pilot spool when the later moves towards right ( load decreasing).

When load limiter is rotated clockwise, limiter rod moves towards right and pushes pilot spool of summation pilot valve towards right which resets in closure of control valve.

It may be noted that control valve servomotor can be completely closed by operating the load limiter hand wheel clockwise. But the reverse is not true i.e. control valve servomotor may not get opened by operating the load limiter hand-wheel anti-clockwise.

Equilibrium :

Load limiter is not subjected to any hydraulic forces. It consists of mechanical elements with a micro-switch having electrical contacts.

Procedure for adjusting the set point of load limiter :

i. By actuating the speeder gear , bring the turbine load to a load slightly lower than the value for which load limiter is required to be adjusted.

ii. Load limiter hand wheel is rotated clockwise to such an extent that annunciation ‘load limiter operated’ appears in unit control room.

iii. Now the load limiter hand wheel is rotated anti-clockwise by about 2.0 mm in the load limiter scale so that ‘load limiter operated’ annunciation disappears in unit control room.

Note :As soon as the annunciation ‘ load limiter operated’ in UCP appears , immediately steps should be taken to reduce the load in the set so that the annunciation disappears.

III ) DESCRIPTION OF PROTECTION SYSTEM :

a) Emergency Governor :In the unlike event of speed increasing to 111-112% of value , emergency governor strikes fly-out of the emergency governor body to trip the set through levers and other hydraulic circuit. It is necessary that the emergency strikers should be tested periodically during

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normal service of turbine. Since over-speeding of turbine is not possible when the set is interconnected with the grid, the effect of over-speeding is simulated by injecting oil under the strikers. These objectives are achieved by :

1. Emergency Governor.2. Levers.3. Testing cock.4. Indicators.

1. Emergency Governor :The emergency governor is mounted on the front end of HP rotor and is dynamically balanced with it. It is coupled to shaft of MOP by a gear coupling. Two strikers have been provided for reliability and for on-load testing. Centre of gravity of the strikers is away from centre line of rotation. Initial compression of the spring is adjusted so that the strikers fly out at 11 to 12% over-speed. Centrifugal force on the strikers is counteracted by the spring force during normal speed of the turbine.

2. Emergency Governor Levers:Levers are mounted on a bracket which is fixed with emergency governor pilot valve. A handle is provided outside the front pedestal which can adjust position of levers relative to strikers. Any one or both the levers can be adjusted to receive signal from emergency governor. During normal operation each lever placed opposite to corresponding strikers to receive signal.

3. Testing cock ;Testing cock is provided inside the front pedestal on left hand side. It can be operated by a knob outside the front pedestal.

4. Indicators : Indicators are mounted on a bracket which is fixed with differentiator. Rubber wheels are placed just opposite to respective strikers at about 1 mm.

Oil circuit of Emergency Governor :

i. Control oil at 20 ata is fed to the chamber of cock. When oil injection knob is in the middle position there is no oil supply to any nozzle.

ii. Turning of oil injection knob anti-clockwise knob anti clockwise would cause control oil to flow from the chamber of the cock to the nozzle of striker no.1. From nozzle oil flows into the chamber around striker no.1 through ports. When oil supply to the nozzle is out turning the injection knob , the accumulated oil of the chamber around striker no.1 drains through ports inside the front pedestal.

iii. Turning of oil injection knob clockwise would cause control oil flow from chamber of the cock to the nozzle of striker no.2, where from it flows around the chamber of striker no.2. on cutting oil supply to nozzle , accumulated oil around the striker drains into front pedestal similar to striker no. 1.

Operation:

a) Operation at 11% to 12% over-speed :As soon as the speed of the turbine rises to 11%-12% of the normal speed (i.e. 3330 to 3360 rpm) centrifugal force on the strikers overcome force of the springs and the strikers fly-out. Once the strikers begin to move out , distance between the centre of gravity of the

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strikers and centre line of rotation increases, thus causing further increase of centrifugal force. Thus strikers , once dislodged from stable position, would continue to move out until checked by the ‘stop’ of the body.When the strikers strike one end of the levers, the other end would press the impulse pilot spool of emergency governor pilot valve and would ultimately lead the tripping of turbine through hydraulic circuit. Apart from actuating the trip system, the strikers press corresponding rubber wheels. The axle of the wheel would act as a fulcrum and the rod lifts the flap up. Movement of the flap is visible at the top of front pedestal and also indicate the operation of the corresponding striker.

Operation during testing by oil injection :Either striker can be tested at one time. If desired , the lever opposite to the striker under test is disengaged in such a manner that it would not trip the set but flap would opo up to indicate that the striker moved out due to centrifugal force of the injected oil around the striker.

b) Emergency Governor Pilot Valve :It is an intermediate element to convert the mechanical signal , received from emergency governor through level to a hydraulic signals from follow pilot valve and turbine shutdown switch. Hydraulic signal is transferred to emergency stop valve servomotor, interceptor valve servomotor and control valve servomotor.

Equilibrium :

During normal service of turbine, the spring keeps the impulse pilot spool upwards.

i. Hydraulic forces acting on main pilot spool during normal service of turbine :when there is no impulse from protection system, the lower face of upper bobbin of main pilot spool is exposed to an oil pressure of 20 ata. At the same time the upper face of the bobbin (upper) of the main pilot spool is also subjected to same pressure. However the exposed area at lower face is greater than exposed area of upper face. Therefore the pilot spool experiences an upwards thrust.

ii. During transient period when protection system actuates the EGP valve :

under these conditions the protection line oil drains and the pressure in the chamber drops. The downward force acting on the upper face of pilot spool becomes greater than the upward force acting on the lower face and main pilot spool moves downwards. As soon as the main pilot spool begins to move downwards, the area of the upper face exposed to 20 ata gets increased. This provides additional force to accelerate the downward movement of pilot spool.

Operation :

a) Over-speed trip signal from emergency governor ( at 11% to 12% over speed):

If either or both the strikers operate, corresponding levers would press impulse pilot spool downwards from its top position against the spring force. The lower bobbin of impulse

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pilot spool would uncover the ports which would result in draining of protection oil inside the front pedestal. As a result net force downwards on main pilot spool increases.As soon as the main pilot spool starts downwards control oil pressure acts downwards on a bigger area resulting in further increase of force downwards. It would result in accelerated movement of main pilot till lower stops.

Downward movement of pilot spool would cause drain of oil from line to ESV & IV servomotors and primary sensitive oil line resulting in complete closure of ESV & IV and CVs. Further oil supply from load speed control valve is also blocked as the ports are covered by the bobbin of main pilot spool.

As soon as the main pilot spool begins to move down, the force pressing the impulse pilot spool gets reduced and consequently the impulse pilot spool moves upward relative to main pilot spool. This would restore 20 ata pressure in protection line. However the net resultant force on main pilot spool would still be downwards because now area of upper face of upper bobbin of main pilot spool exposed to 20 ata pressure is larger.

b) Charging of Emergency governor pilot valve :

Once the main pilot spool has moved down , it can not be moved up until the pressure in chamber , receives oil from load/speed control pilot valve is relieved totally. This can be done only by turning the speeder gear clockwise, until load/ speed control pilot occupies extreme left position. As the pressure in the chamber of EGP pilot valve mentioned above , gets reduced the forces acting on the lower face of the upper bobbin would push the main spool upwards. Control oil is now supplied to the chamber by turning the speeder gear anti-clockwise and the emergency governor pilot valve would be ready i.e. charged to receive impulse from protective system. The process has been termed as ‘CHARGING OF EGP VALVE’.

c) Overspeed trip signal from follow pilot valve (at 14% to 15%):

In the unlike event, should speed increase to 114% to115% of the normal speed, protection oil would drain through ports of follow pilot valve which would result in sharp drop of oil pressure in protection oil line. This would result the tripping of the turbine.

After tripping of the set speed goes down and as soon as the ports of the follow pilot valve are covered by bobbin of follow pilot spool, pressure in protection line gets restored. But the net force on the main pilot spool of EGP would still be downwards as described in (a) above.

d) Trip signal from turbine shut down switch:

If turbine shut down switch is operated manually or automatically by energizing the turbine trip solenoid, protection oil would drain through ports of pilot valve. It would result in sharp drop of oil pressure in protection oil line. This would result in tripping of turbine.

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After trip signal, the bobbin of pilot spool of shut down switch covers the ports and protection line pressure gets restored. But the net force on the main pilot spool of EGP would still be downwards as described in (a) above.

C. Emergency stop valve servomotor. Two emergency stop valve servomotors have been provided to totally cut off steam supply to H.P. turbine in case of emergency conditions. The emergency stop valves remains in fully open position when turbine is in service. Two servomotors, one for each emergency stop valve, have been provided. These are mounted over emergency stop valves.

EQUILIBRIUM:In equilibrium position the lower bobbin of pilot spool remains in equilibrium under the action of the following forces:1. Oil pressure acting upward on lower face of pilot spool.2. Force of springs acting downwards.

OPERATION: a) Manual operation by hand wheel.

By turning hand wheel clockwise, the screw compresses the spring forcing the pilot spool through rod to move downwards. Oil under the piston of ESV gets released and the piston downwards due to spring force, thus closing the stop valve. Downward movement of piston would reduce compression of spring of pilot spool by feed back lever and would bring the pilot spool back to its middle position.

By turning hand wheel anticlockwise reverse action would take place i.e. piston moves upwards, opening the stop valve. Pilot spool would come to middle position by feed back action.

b) Operation by speeder gear.Actuating the speeder gear anticlockwise would permit the oil flow to ESV servomotor through load/speed control pilot valve and emergency governor pilot valve. At 5.5mm position of speeder gear oil pressure at lower face of pilot spool becomes 10 ata which would bring the pilot spool to its middle position. Further anticlockwise rotation of speeder gear would open the servomotor which come to its upper stop at 6.65mm position of speeder gear. By feed back action pilot spool would again come to its middle position.

Clockwise movement of speeder gear would restrict oil flow and reduce the pressure under pilot spool. It would result in downward movement of pilot spool releasing oil under the ESV piston. Thus servomotor would again come to its middle position.

c) Emergency operation of servomotor.In emergency condition when protection system operates, the chamber under the pilot spool is connected to open drain through emergency governor pilot valves resulting in sudden fall of oil pressure. Under these conditions servomotor would immediately close the stop valve cutting off complete steam supply to H.P. turbine.

D. Interceptor Valve Servomotor:

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Two interceptor valve servomotors have been provided for totally cut off steam supply to intermediate pressure turbine in case of emergency conditions. The servomotors remain fully open when turbine is in operation.

EQUILIBRIUM:In equilibrium position the lower bobbin of the pilot spool covers the ports. Pilot spool remains in equilibrium under the action of oil pressure acting upwards on the lower face of the pilot spool and force of pair of springs acting downwards.

OPERATION:a) Manual operation by hand wheel. By turning the hand wheel clockwise, screw moves downwards through warm wheel and it pushes the pilot spool downwards. Oil under the piston of IV get released and the piston moves down due to spring force, thus closing the interceptor valve. Downward movement of the piston would reduce compression of the springs of pilot spool by feed back lever and would bring the pilot spool back to its middle position.

By turning hand wheel anticlockwise, reverse action would take place i.e. piston moves upward, opening the interceptor valve. Pilot spool would again come to middle position by feed back action.

b) Operation by speeder gear. Actuating the speeder gear anticlockwise would permit the oil flow to IV servomotor through load/speed control pilot valve and emergency governor pilot valve. At 4.6mm position of speeder gear oil pressure at lower face of pilot spool becomes 5 ata which would bring the pilot spool to its middle position. Further anticlockwise rotation of speeder gear would open the servomotor, which will come to its upper stop at 5.9mm, of speeder gear. By feed back action the pilot spool would again come to its middle position.

Clockwise movement of speeder gear would restrict the oil flow and reduce oil pressure under the pilot spool. It would result in downward movement of pilot spool releasing oil under the IV piston. Thus servomotor would close the interceptor valve. By feed action pilot spool would again to its middle position.

c) Emergency operation of servomotor. In emergency conditions when protection system operates, the chamber under the pilot spool is connected open drain through emergency governor valves, resulting in sudden fall in oil pressure. Under these conditions servomotor would immediately close interceptor valve cutting off completely steam supply to intermediate pressure turbine.

E. Turbine Shut Down Switch. The turbine shut down switch is provided to facilitate turbine tripping. One chamber of the pilot spool is connected to the additional protection oil line. When pilot spool uncovers ports, oil in the additional protection line is connected to open drain.

OPERATION:a) Normal operation by knob.

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When the knob is pressed downwards, pilot spool is lifted up by lever, thus uncovering the ports which would result in draining of oil in additional protection line. All the control valve, emergency stop valves would close.

b) Operation by solenoid. By operating the control switch of solenoid from unit control room or when tripping circuit gets energised, due to any fault the solenoid would get energised, pulling the lever upwards, thus draining of additional protection oil, causing tripping of set.

4. INTERFACE ACTION OF THE GOVERNING SYSTEM ELEMENTS UNDER VARIOUS MODES OF OPERATIONS:

A. Interface action of Governing system elements for speeder gear:

a) Increasing of speed by actuating the speeder gear: When the turbine is stand-still and the servomotors are closed, the port of the summation pilot spool is in the totally uncovered position. To raise the speed, it is essential to turn the speeder gear in anticlockwise direction. This would cause the summation pilot spool to move towards left hand side. As the summation pilot spool covers the ports, the pressure in the primary sensitive oil line increases and this actuates the intermediate pilot valve in such a manner as to restore the pressure in the primary sensitive oil line. However the actuation of intermediate pilot valve would increase the pressure in secondary sensitive oil line transiently. The increase of pressure in the secondary oil system causes the upward movement of control valve servomotor pilot spool and this results in supply of oil under the piston of the servomotor. The servomotor moves up there by opening the control valves and admitting steam to the turbine.

The upward movement of the servomotor causes the downward movement of the feed back pilot spool and restores the pressure in the secondary sensitive oil line. As soon as the pressure in the secondary sensitive oil line is restored, the servomotor pilot spool returns to its mean position, thereby checking any further upward movement of the piston of control valves servomotor.

b) Decreasing of speed by actuating the speeder gear: The speed of the turbine can be decreased by moving the speeder gear in clockwise direction. The sequence of operation would be just reverse of what has been described in paragraph (a).

B. Interface action of the governing system element when turbine is in service and it is not interconnected to grid:

Any difference between the export load and the power generated by turbine, would result in the change of speed. The governing system would come into action and it would suitably actuate the control valves to bring the system in equilibrium at the new speed within the steady state overall speed regulation limits. Since it is desirable to maintain the

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network frequency at 50Hz, the speed of the set can be brought to 3000 rpm by actuating the speeder gear suitably. The speeder gear would have to be moved in clockwise direction to reduce the speed and anticlockwise to increase the speed. In other words the speeder gear shifts the static characteristic (speed Vs load) of the governing system above or below the mean position. The shifting of the characteristics dose not alter the shape of the characteristics.

C. Interface action of the governing system elements when the turbine is operating in a grid:

When the turbine is running in an interconnected grid, its speed is controlled by the network frequency. If it is desired to change the load on the turbine, the same can be achieved by actuating speeder gear. Anticlockwise movement of speeder gear would mean increasing the load on the set i.e. the characteristics would shift upwards from its previous position. For decreasing the load on the set, speeder gear should be moved clockwise.

5. TESTING OF TURBINE PROTECTION:A. Testing of overspeed protection system.

The turbine overspeed protection system can be tested either by overspeeding the set or by injecting the oil during the normal service of turbine.

Testing schedule:It is recommended to observe the following schedule/events for testing overspeed protection system.

a) After erection or maintenance of the turbine.b) After any maintenance work connected with the elements in front standard.c) After any adjustment or maintenance of the governing and protection system.d) After shut down, if its period exceeds 15 days.e) Routine testing normal service of turbine. This should be done by injecting oil under the

striker and the corresponding lever should be disengaged from the system to avoid spurious tripping.

a) Procedure for testing the overspeed protection system by actual

overspeed.This testing can be most conveniently carried out during a start up before synchronizing the set to the grid in following manner:

1. Bring the set to 3000 rpm.2. Trip the turbine by pressing the turbine shut down switch knob.3. Quickly turn the speeder gear clockwise to charge the EGP valve.4. Keep both the strikers in engaged position for tripping.5. Slowly increase the speed of the set until overspeed protection system operates.6. Observe the speed and the striker which tripped the turbine.

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7. Observe the speed at which flap moves down i.e. the speed at which the striker rests itself.

8. Recharge the EGP valves.9. Disengage the striker which tripped the turbine.10. Increase the speed of the set until the other striker trips the turbine.11. Observe the speed at which the tripping occurred.12. Observe speed at which flap moves down i.e., the speed at which the striker

rests itself.13. Both the tripping should occur in the speed range of 3330 to 3360 rpm. If it is

not achieved, shut down the turbine and adjust the setting of strikers.14. It is desirable to test the overspeed protection system by oil injection after every

overspeed test. This is done to check the efficacy of the oil injection.

NOTE:IT IS NOT RECOMMENDED TO INCREASE THE SPEED OF THE TURBINE BEYOND 3360 RPM UNDER ANY CIRCUMSTANCES DURING TESTS OR OTHERWISE.

b) Procedure for testing the overspeed protection system by oil injection (Turbine connected to grid)

a. The test can be done during the normal service of the turbine.b. Disengage the lever from striker No. 1 by pushing in the handle from middle

position.c. Turn the oil injection knob anti-clockwise.d. Observe that the flap for striker No. 1 pops up.e. Bring oil injection knob in the middle position and observe that the flap

moves down.f. Bring the handle to middle position.g. Disengage the lever from striker No. 2 by pulling out the handle from middle

position.h. Turn the oil injection knob clockwise.i. Observe that the flap for striker No. 2 pops up.j. Bring oil injection knob in the middle position and observe that the flap

moves down.k. Bring the handle to middle position.

c) Procedure for testing the overspeed protection system by oil injection with turbine at no load.

The overspeed set point of the emergency strikers can be checked by oil injection method in the following manner. This test can be most conveniently carried out before the synchronization of the set and after the overspeed test of the set.

a. Bring the auxiliary oil pump into service.b. Reduce the speed of the set to 2700 rpm.

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c. Disengage the lever for striker No. 1 by pushing in the handle from its middle position.

d. Turn the oil injection knob in anticlockwise direction.e. Raise the speed of the set slowly.f. Observe the sped at which flap pops up. If it pops up at a speed equal to or less

than 2970 rpm, it can be construed that the overspeed set point of the striker is within 3330 and 3360 rpm.

g. Increase the speed of the set to 3150 rpm.h. Stop oil injection by turning the oil injection knob to neutral position.i. Maintain the speed 3150 rpm for 30 seconds.j. Reduce the speed slowly and observe the speed at which the flap moves down. If

the flap comes down at a speed 3065+45/35 or 3065-45/35 rpm, it may be construed that the striker No. 1 is in a healthy state.

k. Repeat the test for striker No. 2.

NOTE:IT IS NOT RECOMMENDED TO INCREASE THE SPEED OF THE TURBINE BEYOND 3360 RPM UNDER ANY CIRCUMSTANCES DURING TESTS.

B. Tests for checking tightness of emergency stop valves.

This test can be most conveniently conducted before start up. The procedure for conducting the test is as follows:

1. Bring the set to 3000 rpm by full arc system admission in the turbine. This essentially means that control valves and emergency stop valves are fully open and the main steam stop valves are partially open.

2. Quickly close both the emergency stop valves actuating the hand wheel provided at ESV servomotors.

3. Plot the coasting down curve and measure the time required for reducing the speed from 3000 rpm to 1500 rpm. If the time taken is less than 8 minutes, it can be construed that the emergency stop valves are sufficiently tight.

C. TESTS FOR CHECKING THE TIGHT CLOSURE OF HPT CONTROL VALVES.

This test can be most conveniently conducted before synchronization of the set in the following manner:

a. Bring the turbine to 3000 rpm by seeder gear. It may be noted that the main steam stop valves should be fully open for conducting this test.

b. Move the speeder gear in clockwise direction until the HPT and IPT control valves are totally closed but ESV and IV are fully open.

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c. Observe the time taken by the set to coast down from 3000 rpm to 1500 rpm. If it takes less than 10 minutes then it can be construed that the HTP control valves are having tight closure.

NOTE:WHILE CONDUCTING THIS TEST IT SHOULD BE ENSURED THAT THE STEAM, FROM ANY SOURCE OTHER THAN TURBINE, SHOULD NOT ENTER THE REHEAT CIRCUIT.

D. TESTS FOR CHECKING THE TIGHT CLOSURE OF INTERCEPTOR VALVES.

The test can be most conveniently conducted during the start up when turbine is being run at 3.4 rpm by the barring gear. Procedure for test is as follows:

1. Connect special differential manometer for measuring differential pressure between the condenser pressure and the pressure in the chamber after the first stage of I.P. Turbine.

2. Keep the MSV and its by-pass, ESV, IV and CV closed.3. Check the steam from HTP by-pass station is not being supplied to the reheat

circuit.4. Turn the speeder gear in anti-clockwise direction and open the ESV, IV and control

valves of IPT.5. By turning the hand wheel of interceptor valve servomotors, close both the

interceptor valves completely.6. Bring in service the HPT by-pass station PRDS-2 and raise the pressure in the

reheat circuit to as high a value as permitted from other turbine considerations.7. When the pressure in the cold reheat circuit is more than 4 ata, the differential

pressure manometer is less than 40 mm of Hg, it can be construed that the interceptor valves are having the tight closure.

8. After conducting the test remove the special differential pressure manometer.

E. TESTS FOR CHECKING THE PROPER FUNCTIONING OF ESV AND IV SERVOMOTORS.

This test is essentially carried out to verify that the servomotors for the ESV and IV are in a healthy state and also to verify that the stems of the stop valves are free to move and there is no seizure. This test can be conducted either by partially closing the servomotor or by completely closing the servomotor. Partial closure test can be conducted at least once in every 8 hours when turbine is in service and carrying a load not than 170MW, the full closure test should be conducted once in a fortnight when the set is carrying a load not more than 120MW. All the four stop valves i.e. two ESV and two IV should be tested one after the other and not simultaneously.

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Procedure for test involving partial closure of stop valve is as follows:

1. Check that the set is carrying a load less than 170MW.2. Turn the hand wheel on the servomotor by 15 to 20 mm.3. Reopen the servomotor fully.4. In case of ESVs the proper functioning of the damper should be checked in the following manner:

a. When the servomotor has moved down by 5mm from its uppermost position, the pressure under the servomotor should be recorded.

b. The oil pressure under the piston in this piston of servomotor should be 9.6+1 or 9.6-1 ata

c. After a major overhaul of the turbine or a major stoppage, the characteristic curve for the damper should be plotted and compared with the initial characteristics which had been drawn at the time of commissioning.

Procedure for test involving full closure of stop valve is as follows: 1. Check that the load is not more than 120MW.2. Turn the hand wheel on the servomotor and completely close the servomotor under test.3. Reopen the servomotor fully.

F. SCHEDULE FOR CONDUCTING TESTS.Following periodicity of the test should be observed during the normal service of the turbine.1. Tests once in a shift a) Partial closure of ESV. b) Partial closure of IV.

2. Test once in a fortnight. a) Complete closure of ESV. b) Complete closure of IV. c) Functioning of oil pressure switch.

3. Test once in 3 months. Overspeed protection system by oil injection. 4. The turbine overspeed protection system should be tested by actual overspeeding after every shut down. However frequency of such test should be limited to twice a year.

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