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KISHOREPOWERPLANT
March 8, 2015
TURBINE 210 MW
210 MW LMW TURBINE
1. 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.
TURBINE MAIN DATA:
Rated output of the Turbine
: 210 MW.
Rated Speed
: 3000 rpm.
Rated pressure of steam before ESV
Rated live steam temperature
Rated live steam temperature at inlet of IV
Steam flow at valve wide open condition
: 130 kg/cm2.
: 535 0C
: 535 0C
: 670 Tons/hr.
Rated CW flow through condenser
: 27000 M 3 / hr.
i.
For cooling water temp.
0
C
:
24
27
30
33
ii.
Steam flow required for 210 MW
Tons/hr
:
638
645
652
662
iii.
Rated pressure at the exhaust of
LPT.
mm of Hg.
:
46.9
55.5
65.4
76.7
1. 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/cm2 and quantity of oil
going to each bearing is controlled by the orifice plate at its inlet end.
1. 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.
1. 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.
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.
1.
2.
1.
2.

1.
1.
2.
3.
For remote starting, bring the key to the ‘ON’ position in UCP and start the barring gear.
For manual starting from local panel follow the steps given below :
Open the wheel cover.
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.
Close the wheel cover.
Switch on the electric motor.
Note :
Never allow hot rotor to stand without rolling.
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.
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 :
1. 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.
1. After stopping the turbine :
1. 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 ).
2. 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 :
1. Supply of stem to the turbine and seals without running the rotors on barring gear is
strictly prohibited.
2. 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.
1. INTERLOCK & PROTECTION OF TURBINE :
1. Turbine lockout relay (TLR) will trip if,
1. Unit Lockout Relay trips (ULR).
2. Master Fuel Relay trips (MFR)
 Main Steam temperature is below 450 0C after a time delay relay ( For initial starting automatic
wipeout switch is provided).
1. Oil level in damper tank is very low.
2. DM cooling Water flow to stator winding is less than 13 M3 / hr.
3. DM cooling water specific resistivity is less than 50K. ohm/cm.
 Condenser vacuum is less than 540 mm of Hg.
 Boiler drum level is very high / low.
1. H.P. turbine exhaust temperature is above 420 0C.
2. H.P. heater level is very high ( set point 3 –this will in turn trip ULR and also te running Boiler
Feed Pumps).
3. Lub oil pressure is low ( ).3 ata ).
 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 :
1. Open Vacuum Breaker.
2. Close steam to main ejector.
3. Close steam to starting ejector.
4. Open air extraction valve of starting air ejector
Condition of (11 & 12 ) will in turn trip ULR.
xiii.
1.
2.
3.
4.
Protection extraction system troubles:
Thyrister fans supply failure.
Regulator supply failure.
Rectifier transformer temperature very high.
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.
2. The following condition will close the turbine ESVs and IVs :
1. Turbine Trip solenoid (TTS) operated.
2. Turbine over-speed trip operated (11- 12 %) .
 Turbine over-speed trip addl. Protection operated (14%).
2. Turbine relay oil pressure is less than 10 kg/cm2.
3. Turbine Manual Trip operated.
3. Closing of ESVs and IVs will in turn operate the following :
1. Generator Lockout Relay (GLR) through “Low Forward Power “Relay.
2. Close Turbine inlet M.S. valves (MS-1)
 Close extraction stream steam to Deaerator (ES-6 & ES-5)
1. Close all Extraction Non-Return valves (To open MC-53 & 54).
2. Turbine speeder gear fast reversal.
3. Open HP-LP bypass valves after tripping of GLR.
 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:
1. For healthy turbine, normally the vibrations are less than 40 microns. However, it is important to
assess 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 further speeding up of the
set (increase not in critical speed zone), investigate and remove the cause of excessive vibrations.
2. 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
1585
1881
2017
2489
4500
1. 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 :
1. 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
1.
1.
1.
1.
1.
2.

1.
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.
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.
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.
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.
During the trial runs for the heating of the flanges and studs , their heating is to be adjusted such
that :
Temperature difference between upper and lower flanges does not exceed 10 0C .
Temperature difference between left hand and right hand flanges does not exceed 10 0C .
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.
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 mm
For Rotor of IPT
:
(+) 3.0 mm or
(-) 2.5 mm
For Rotor of LPT
:
(+) 4.5 mm or
(-) 2.5 mm
(+) sign indicates that Rotor is longer than cylinder and vice versa for (-) sign.
2. 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.
4. 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.
1. 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.
4. 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.
1. If LP rotor expands quicker than the LPT cylinder, worsen the vacuum and stop recirculation of
condensate in the condenser.
1. If LP rotor contracts quicker than the LP casing, improve vacuum in the condenser.
PARAMETERS TO BE NOTED :
1. 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 ).
1. Sharp increase of speed or of load, because of deterioration of boiler regime is not permitted.
1. Starting of turbine with cold oil in lubricating and governing system is prohibited. The
temperature of oil should not be less than 40 0C.
1. 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.
1. 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.
1. During heating , speeding and loading of turbine, carefully watch the readings of the instruments
indicating :
1. Vibration of bearings.
2. Axial shift of rotors.

Differential expansion of all the three rotors.
1. Metal temperature of upper and lower halves of HPT flanges and studs and upper half of IPT
flanges.
2. Oil temperature at the inlet and outlet of the bearings.
3. Babbit temperature of thrust bearings.
 Pressure and temperature of steam at the control panel.

PROCEDURE OF START UP:
1. Pre-start checks:
1. 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’.
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.
1. Line up of turbine , MS, CR and HR lines :
The following valves are to be opened:
1.
2.
3.
4.
5.
6.
7.
8.
9.
1.
Impulse line to all pressure gauges for steam, condensate, oil and cooling water.
MS, HP- bypass drain valves.
HR, CR, LP –bypass drain valves to flash box / aux. flash box and to atmosphere.
PRDS, Gland seal steam supply line and ejector line drains.
HP and LP cylinder steam admission pipe drains to flash box.
HP and IP cylinder drains.
Before seat drain of extraction NRV of extraction line to HP heater no. 7 and 5 to flash box.
Before seat drain of extraction NRV of extraction line to LP heater no. 2, 3 and 4 to flash box.
After seat drains of Nerve’s of all the extraction lines to flash box.
The following valves are to be kept closed :
1.
2.
3.
4.
5.
6.
7.
8.
Main stream stop valve (turbine side).
Main stream stop valve bypass isolating and regulating valves.
ESV, IV and control valves of HPT and IPT.
PRDS to Deaerator.
Before isolating valve of Aux. PRDS.
Before isolating valve of gland steam controller.
Before isolating steam valve of GC-1 ejector.
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 stream stop valve (Boiler end) equiliser both side when M.S. pressure is 10 kg/cm2.
and temperature is around 200 0
2. After warming up for 30 minutes open main stream 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 0
6. Start starting Oil pump and maintain oil temperature at around 42 0
1. 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/cm2and 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.
1. When vacuum reaches to 450 mm Hg open MC-39 and MC-57 ( Condensate line to condenser
steam throwing device (STD),
2. Line up spray water line of HP bypass from Boiler Feed discharge line and LP bypass valves
from condensate pump discharge header.
3. 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.
4. Check that the HPT evacuating valves CA-21, 22 and bypass valves across CR line NRV’s (Ex20, 21) are closed.
5. Set HP & LP bypass downstream temperatures at 320 0C and 150 0C respectively.
6. 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 ).
1. Open HP and LP bypass valves gradually and increase the firing rate, if necessary, if pressure
drops.
2. 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.
1. 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.
2. Close ESV and IV manually by operating the speeder gear hand wheel.
3. Open Speeder Gear up to 7 mm.
4. 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.
5. 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.
6. 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.
7. 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:
1. 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.
2. 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.
2. 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,
3. Check that the interceptor and steam admission pipes of IPT have attained a temperature of 100
0C.
4. Close ESV and IV by operating the hand wheel.
5. Close Speeder Gear to Zero position.
6. 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.
7. Having accomplished the heating , check and note down the following readings in the log sheet
before rolling the turbine:
1. Metal temperature of pipes before MSV.
2. Metal temperature of ESV.
3. Metal temperature of steam admission lines of HPT & IPT.
4. Metal temperature of HR lines.
5. Metal temperature in the zone of regulating stage.
6. Metal temperature of IV.
7. Steam pressure and temperature before MSV,
8. Differential expansion of HP, IP & LP rotors.
9. Axial shift.
10. 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.
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 0
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 :
1. With the help of control gear close control valves to such an extent that the speed just begins to
fall.
2. 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.
2. The steam parameters by this time are expected to be as follows :
MS pressure
: 35 kg/cm2
MS temperature
: 350 0C
HR temperature
: 330 0C.
1. 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.
2. 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 –
1. The differential expansion of rotor is less than 1 mm.
2. 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.
1.
1.
2.
3.
4.
5.
6.
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.
PROCEEDURE FOR HEATING OF FLANGES AND STUDS OF HP OR IP
CYLINDER ( WHICHEVER IS REQUIRED)
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.
Blow-down the drains of the steam collector for flange and stud heating by opening AS-33
(HPT) and AS-41 (IPT).
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.
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 AS10 (for HPT) or AS-11 and AS-12 (for IPT).
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 0
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 0
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 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
: 4300C
HR 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
: 4800C
HR 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’. Upstream pressure at 6 kg/cm2 and downstream
temperature at 200 0C
1. 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:
1. Above 350 0C
: Hot start.
0
0
2. Between 150 C and 350 C : Warm start.
 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.
1. 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.
1. Check all control and measuring instruments have been switched ‘ON’ and they are working
satisfactorily.
1. 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.
1. Charge the MS line and TAS header by opening the line drains.
1. 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.).
1. 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.
1. 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.
1. 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.
1. Record the metal temperature of the following :
1. HPT in the zone of regulating stage.
2. IPT steam admission chamber.
 Body of ESV & IV.
1. Steam admission pipes of HPT & IPT.
2. Overall expansion and differential expansion of all the three rotors.
1. Before admitting steam to turbine, check shaft eccentricity and see that it is less than 70 microns.
1. Check the temperature of upper and lower halves of HPT. The difference between respective
upper & lower halves should not be more than 50 0C.
1. 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.
1. 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.
2. The diagonal lines drawn at the lower part of the chart now directly indicates the various HPC
metal temperatures 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.
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 :
1. Body of ESV & IV.
2. Steam admission pipe of HPT & IPT.
 Steam admission chamber of IPT.
1. 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.
2. The parameters of steam are raised to get the desired matching temperature with the help of HPLP by-pass station.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. 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.
9. After attaining the desired steam temperature and pressure suitable for rolling of the turbine, hold
the firing rate of boiler.
10. 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.
11. 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.
12. Open fully both the turbine side main steam stop valves (MS-1) and also valves in the drain lines
of the transfer pipes.
13. Before rolling check that HP-LP by-pass valves are on ‘Auto’ mode. LP by-pass pressure setting
should be at 6 ata.
14. Completely open ESV & IV with the help of speeder gear. Turbine will start rolling through IPT.
15. 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.
16. Start opening of CVs of IPT and raise the speed of turbine to 3000 rpm without pause.
17. Ensure that MOP takes over at 2800 rpm and then stop the SOP.
18. Synchronise the set and take around 30 MW load on the unit. Close all the drains.
19. 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.
20. Ensure that the evacuating valves CA-21 & CA-22 in the HP casing drain lines gets closed
automatically when steam flow starts through HPT.
21. 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.
22. 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.
23. 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.
24. Stop rotor heating steam supply of HPT & IPT when differential contractions reduced and got
stabilized.
25. 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.
2.
3.
4.
Inform the boiler operator that turbine would soon be shutdown.
Check the SOP and AC & DC Lub. Oil pumps and ensure their ‘Auto’ cut in.
Check the non-seizure of ESV & IV . Check that bypass valves of MS-1 are closed.
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 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.
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 0
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 0
20. Stop the condensate supply to valves and pumps glands sealing and also cooling water in ESV
& IV
21. After the turbine is shutdown , drains of steam admission pipes and cylinders should not be
opened till the metal temperature falls below 200 0 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 0
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.
2.
3.
4.
5.
Start the starting oil pump.
Check that MS-1 valves have closed on auto , otherwise close these valves manually.
Put the turbine on barring gear when rotor s have come to rest.
Try to detect the fault and restart the turbine if the fault is over.
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 VALVES
HP 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
0
10
140
3
4
0
0
20
155
6
8
0
0
30
170
7
10
0
0
40
178
9
13
0
0
50
205
11
16
0
0
60
220
13
18
0
0
70
240
18
23
0
0
80
256
23
29
0
0
90
272
24 (Full
open)
36
3
Starts
opening
100
105
290
300
38 (Full
open)
14
5
38
18 (Full
open)
11 (Full
open)
Valve
No.-1
Valve
No.-2
Valve
No.-3
Valve
No.-4
24
24
H.P. Control Valves Starts open at :
Cam Angle
Position
C.V.S.M.
Position
00
120 mm
Start
–
–
–
100
122 mm
–
Start
–
–
740
250 mm
–
–
Start
–
900
272 mm
Full Open
–
–
Start
1000
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 mm
Valve No.-2
5.0 mm
Valve No.-3
8.0 mm
Valve No.-4
8.0 mm
I.P. control Valves Starts open at :
LIFT OF CONTROL VALVE
IPCV Angle
position
CVSM
Position
Valve
No.-1
Valve
No.-2
Valve
No.-3
Valve
No.-4
5
10
Start
Start
–
–
45
50
–
–
Start
–
90
95
–
–
–
Start
290
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 :
Speeder Gear Position
(mm)
ESV Lift (mm)
IV Lift (mm)
5.0
–
Starts opening.
6.3
Starts opening
–
7.5
–
Full open
8.0
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 :
1. Stable speed control in isolated operation of the set.
2. 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:
1. 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.
2. 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.
 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.
1. Speed governor can control speed in the range approx. 300-3450 rpm when the set is not
synchronized.
2. 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.
3. Governing gear operates on constant oil pressure principle.

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.
1. GOVERNING SYSTEM :
The governing or regulation process is achieved by a combination of mechanical and / or
hydraulic signals causing interactions of elements mentioned below :
1. Speed Governor.
2. Follow-pilot valve.
3. Summation pilot valve.
4. Intermediate pilot valve.
5. Control valve servo motor.
6. Load / speed control pilot valve
7. Differentiator (Anticipatory gear ).
8. Electro hydraulic Transducer (EHT).
9. Speeder Gear.
10. Initial Steam Pressure Unloading Gear (ISPUG).
11.
12. Load Limiter.
1. Protection System;
Protection system functions similar to governing system by a combination of mechanical and
hydraulic signals on various elements mentioned below :
1.
2.
3.
4.
5.
6.
7.
8.
1.
Emergency governor.
Emergency governor lever.
Emergency governor indicators.
Emergency governor testing cock.
Emergency governor pilot valve.
Emergency stop valve servomotor.
Interceptor valve servomotor.
Turbine shutdown switch.
DESCRIPTION OF GOVERNING SYSTEM ELEMENTS :
1. 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 :
1. Follow pilot valve.
2. Summation pilot valve.
iii. Load / speed control pilot valve.
1. Speeder gear.
2.
Function of the above elements :
1. Follow pilot spool follows the movement of governor sleeve and actuates the summation pilot
valve through lever.
1. 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.
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 :
1. 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.
1. To open emergency stop valve and interceptor stop valve.
1. To control speed while the set is at no load.
1. To assist in synchronization of the set.
1. For changing the load of the set while the turbine is working in parallel with other turbines in the
grid.
1. 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.
2. Lever inter-connects the load/speed control valve , follow pilot valve and summation PILOT
VALVE.
Equilibrium of various elements and process of propulsion:
1. 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.
1. 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.
1. 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 :
1. Speed decreasing i.e. load increasing on the set :
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
1. 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.
1. 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.
1. 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
1. 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.
1. 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
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.
1. 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 :
1. 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
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.
1. 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.
1. 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 :
10. 10.3 ata Pressure acting upwards, on the lower face of bobbin I (lower).
11. 20 ata Pressure acting downwards on the upper face of bobbin IV ( on differential area of bobbin
IV & V)
 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 :
1. Pressure in the chamber acting upwards on lower face of bobbin I ( lower ).
2. Pressure in the chamber acting downwards on the upper face of bobbin I ( on differential area of
bobbin I & II ).
 Control Valve forces acting downwards on the piston through linkage and stem.
Operation :
1. 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.
1. b) Speed increasing i.e. load decreasing :
1. 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.
1. 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.
 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.
1. 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 oil line pressure would rise resulting in
opening of control valves and thus loading the machine.
1. 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.
1. 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 :
1. Control oil pressure 20 ata acting downwards on the upper face of bobbin.
2. Oil pressure 8.9 ata acting upwards on the lower face of bobbin.
Piston is in equilibrium due to following forces :
1. Control oil pressure 20 ata acting downwards on the upper face of bobbin.
2. Oil pressure 4.85 ata acting upward on lower face of bobbin.
Operation :
1. 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.
1. 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.
When load fall is less than 50% of the rated load the primary sensitive oil pressure is not affected
by the differentiator.
1. 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.
1. 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.
1. Electromagnetic transducer :
It converts electrical signal from generator circuit breaker into movement of one plunger.
1. 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 :
1. 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.
1. 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 :
1. 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 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.
1. 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.
1. 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.
1. 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 150between 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.
1. b) Control action when main stream 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.
1. 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 :
1. 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.
2. Load limiter hand wheel is rotated clockwise to such an extent that annunciation ‘load limiter
operated’ appears in unit control room.
 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 :
1. Emergency Governor :
In the unlike event of speed increasing to 111-112% of value , emergency governor strikes flyout 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 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.
3. Testing cock.
4.
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 :
1. 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.
2. 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.
 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:
1. 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 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.
1. 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.
1. 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.
1. 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 :
1. 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 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.
1. 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’.
1. 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.
1. 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.
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.
1. 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:
1. 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.
1. 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.
1. 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.
1. Interceptor Valve Servomotor:
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:
1. 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.
1. 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.
1. 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.
1. 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:
1. a) Normal operation by knob.
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.
1. 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:
1.
Interface action of Governing system elements for speeder gear:
1. 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.
1. 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).
1. 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 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.
1. 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:
6. 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.
1.
2.
3.
4.
5.
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.
1. 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.
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.
1. b) Procedure for testing the overspeed protection system by oil injection (Turbineconnected
to grid)
1. The test can be done during the normal service of the turbine.
2. Disengage the lever from striker No. 1 by pushing in the handle from middle position.
3. Turn the oil injection knob anti-clockwise.
4. Observe that the flap for striker No. 1 pops up.
5. Bring oil injection knob in the middle position and observe that the flap moves down.
6. Bring the handle to middle position.
7. Disengage the lever from striker No. 2 by pulling out the handle from middle position.
8. Turn the oil injection knob clockwise.
9. Observe that the flap for striker No. 2 pops up.
10. Bring oil injection knob in the middle position and observe that the flap moves down.
11. Bring the handle to middle position.
1. 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.
1.
2.
3.
4.
5.
6.
Bring the auxiliary oil pump into service.
Reduce the speed of the set to 2700 rpm.
Disengage the lever for striker No. 1 by pushing in the handle from its middle
Turn the oil injection knob in anticlockwise direction.
Raise the speed of the set slowly.
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.
7. Increase the speed of the set to 3150 rpm.
8. Stop oil injection by turning the oil injection knob to neutral position.
9. Maintain the speed 3150 rpm for 30 seconds.
10. 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.
11. 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.
1. 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.
1. 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:
1. 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.
2. Move the speeder gear in clockwise direction until the HPT and IPT control valves are totally
closed but ESV and IV are fully open.
3. 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.
1. 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.
1. 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.
Procedure for test involving partial closure of stop valve is as follows:
1.
2.
3.
4.
Check that the set is carrying a load less than 170MW.
Turn the hand wheel on the servomotor by 15 to 20 mm.
Reopen the servomotor fully.
In case of ESVs the proper functioning of the damper should be checked in the following
manner:
5. When the servomotor has moved down by 5mm from its uppermost position, the pressure under
the servomotor should be recorded.
6. The oil pressure under the piston in this piston of servomotor should be 9.6+1 or 9.6-1 ata
7. 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.
2.
3.
1.
Check that the load is not more than 120MW.
Turn the hand wheel on the servomotor and completely close the servomotor under test.
Reopen the servomotor fully.
SCHEDULE FOR CONDUCTING TESTS.
Following periodicity of the test should be observed during the normal service of the turbine.
1.
2.
3.
2.
3.
4.
5.
3.
1. Tests once in a shift
a) Partial closure of ESV.
b) Partial closure of IV.
Test once in a fortnight.
a) Complete closure of ESV.
b) Complete closure of IV.
c) Functioning of oil pressure switch.
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.