PROCEDURE FOR PERFORMING OVERSPEED
TRIP OIL INJECTION TEST FROM LOCATION:
STEP-1: Press
the RHS knob and ensure build up of startup oil pressure (>8.5
ksc), Note down and release the lever.
STEP-2: Press
the LHS Knob and hold it in the pressed condition till completion of
test. Not down Aux trip fluid pressure (>5.0 ksc).
STEP-3: Rotate
the testing device hand wheel in clock wise direction to build test
oil pressure.
STEP-4: Note
down the test oil pressure at which the Over speed trip device
strikers act, Aux trip fluid pressure (0 ksc) and primary oil
pressure.
STEP-5: Rotate
the testing device hand wheel in anti clock wise direction to reduce
test oil pressure till 0 ksc.
STEP-6: Press
the RHS knob to buildup startup oil pressure and reset the trip
device and then release it after ensure resetting of both strikers.
STEP-7: Release
the LHS knob and note down Aux. trip fluid pressure (>8.5 ksc).
Resp: UCE
PROCEDURE FOR ACTUAL OVERSPEED
TEST-MAIN TURBINE
6.1:
PRECAUTIONS
6.1.1 The
persons carrying out the test must be aware of the maximum speed at
which the prime mover may be run and the need to limit over speeding
to the minimum duration.
6.1.2
Before carrying out an over speed test on a turbine generator,
precautions must be taken to ensure that the field breaker is open
and the machine is in de-excited condition. Resp: UCE
6.1.3 Check
that the healthiness of the overspeed trip device has been ensured
earlier by performing oil injection test within a period of 30 days.
Resp: UCE
6.1.4
Ensure that oil injection test (onload testing equipment) was not
carried out immediately before the actual overspeed test to avoid
freeing of the gear giving an artificial result. Resp: UCE
6.1.5
Before carrying out any overspeed test, precautions must be taken to
limit the supply of steam or fuel to the minimum necessary machine
should be warmed up sufficiently so that casing expansion are at
least 80% of full load expansion. Expansion readings are taken and
logged. Resp: UCE
6.1.6
During an overspeed test, two independent speed indicators are
desirable and both must be watched for any sign of malfunction. Resp:
C&I
6.1.7 The
turbine desk should be manned and the turbine should be hand tripped
above 3330 RPM. Resp: UCE
6.1.8 The
manual emergency trip must be manned by a person who can see clearly
the speed achieved and who will trip the prime mover if the maximum
permissible speed is exceeded or it the prime mover shows signs of
distress. This person must be in direct communication with the person
controlling the speed of the prime mover. Resp: UCE
6.2: PROCEDURE FOR DOING
ACTUAL OVERSPEED TEST DURING SHUTDOWN:
6.2.1:
During load reduction take the turbine control to hydraulic by
reducing speeder gear at about 50MW in Stage-I and 150 MW in Stage-II
and close the EHC isolation valves. (Applicable to stage-I only:
Changeover 6.6 KV Unit bus supply to Station Supply). Resp: UCE
6.2.2:
Reduce boiler firing and load gradually. Resp: UCE
6.2.3:
Charge HP/LP bypass and reduce throttle pressure to 50 ksc, while
avoiding steep drop in temperature. Resp: UCE
6.2.4:
Reduce load further after bringing the boiler load to minimum with 02
consecutive mills in service preferably C & D with 01 elevation
of oil guns. Resp: UCE
6.2.5:
Reduce the load to zero MW and then desynchronize the machine, open
field breaker. Resp: UCE
6.2.6:
Cross check the speed measurement with an offline digital instrument.
Resp: MTP
6.2.7:
Increase electrical over speed protection set point to 3330 rpm.
Resp: C&I
6.2.8:
Bring turbine speed to 3000 RPM by operating speeder gear / Starting
device. Further raise the speed and ensure maximum speed reached with
both Starting device and Speeder gear at 100% is around 3210 rpm.
Resp: UCE
6.2.9:
After ensuring that all the precautions are met, raise the turbine
speed from local by rotating the over speeding knob. Resp: UCE
6.2.10:
Note the speed at which the turbine trips, along with the
corresponding primary oil pressure and record it. Resp: UCE
6.2.11:
Normalise Electrical overspeed setpoint. Resp: UCE/C&I
NOTE: The maximum
permissible speed at which the test is to be carried out should be
decided before doing the test, and informed to all persons involved
in the test.
6.3: PROCEDURE FOR DOING ACTUAL
OVERSPEED TEST DURING STARTUP AFTER OVERHAUL:
6.3.1
Before the turbine is rolled, its Stop valves operation, Governing
characteristics, CRH NRV operation and Extraction lines FCNRVs
operation must be checked for smooth operation over the maximum
travel practicable in such circumstances. Resp:
Re-commissioning Incharge / TMD
6.3.2
Before the turbine is rolled its governor should be set to commence
controlling the speed at the lowest speed possible. Operation of the
governor, control gear and all valves must be observed for signs of
sticking or other malfunction. Resp: Re-commissioning
Incharge / C&I / TMD
6.3.3:
Before rolling the turbine Turbine tripping (Closure of Stop valves)
must be ensured through Remote HMI trip, Local Governing rack trip
lever and also through electrical over speed protection by
simulation as part of Protection & Interlock checking, Protocol
must be signed. Resp: Re-commissioning Incharge
6.3.4:
When the turbine generator is being returned to service, the steam
tightness of the Steam Control Valves must be proved by ensuring the
turbine does not accelerate from the barring gear speed when the
Turbine stop valves are opened and control valves are in closed
condition. Resp: Re-commissioning Incharge /TMD
6.3.5:
During first run-up after overhaul, Shaft speed should be measured
with a digital Tachometer and speed indicator readings compared with
Tachometer reading. Resp: Re-commissioning Incharge / MTP
6.3.6:
After the turbine has been rolled to 3000 rpm, perform oil injection
test (preferably before electrical testing of generator) and ensure
both strikers act, record Primary oil pressure and Test oil pressure
at which the strikers act. Resp: Re-commissioning Incharge Resp:
Re-commissioning Incharge
6.3.7:
Allow the overall expansion to reach 80% of full load expansion.
During the course of electrical testing, the steam temperatures may
be increased gradually to achieve the expansions. Resp:
Re-commissioning Incharge
6.3.8:
Cross check the speed measurement with an offline digital instrument.
Resp: MTP
6.3.9:
Increase electrical over speed protection set point to 3330 rpm.
Resp: Re-commissioning Incharge / C&I
6.3.10:
Bring turbine speed to 3000 RPM by operating speeder gear / Starting
device. Further raise the speed and ensure maximum speed reached with
both Starting device and Speeder gear at 100% is around 3210 rpm.
Resp: Re-commissioning Incharge / TMD
6.3.11:
After ensuring that all the precautions are met, raise the turbine
speed from local by rotating the over speeding knob. Resp:
Re-commissioning Incharge / TMD
6.3.12:
Note the speed at which the turbine trips, along with the
corresponding primary oil pressure and record it. Resp:
Re-commissioning Incharge
NOTE: The
maximum permissible speed at which the test is to be carried out
should be decided before doing the test, and informed to all persons
involved in the test.
7.0: PROCEDURE FOR ACTUAL
OVERSPEED TEST OF TDBFP DRIVE TURBINE
7.1
Oil injection test to be done before stopping TDBFP as per the
procedure given below:
Step-1:
Open control oil supply v/v to test oil generating device.
Step-2:
Push & hold lever of over speed test device downwards completely.
This will ensure stop v/v in open condition.
Step-3:
Holding lever downward, rotate hand wheel slowly in clockwise
direction to generate/increase test oil. Note test oil pressure at
which over speed protection device operates.
Step-4:
Rotate hand wheel anticlockwise completely to reduce test oil
pressure.
Step-5:
Energise Remote trip engage to reset the device. Release the lever
and De-energise Remote trip engage after device resets.
Step-6:
Close control oil supply v/v to test oil generating device.
7.2
Record test oil & speed in protect check register. If oil
injection test is not satisfactory, reason is to be investigated. If
speed cannot be raised to 5400 rpm (approximately) due to low load
conditions, then at least try to ensure buildup of test oil pressure.
Resp:
UCE/ TMD
Preparation for Overspeed test:
7.3
TDBFP is to be stopped as per shutdown procedure & kept on
barring. TDBFP to be isolated from steam side. Both vacuum p/p can be
taken in service if required. Resp:
UCE
7.4
When turbine casing temperature reaches less than 120 degree, stop
barring of TDBFP .TDBFP is to be isolated from oil side and permit to
be issued for decoupling of turbine from main pump & gearbox (BP)
side. Resp:
UCE /TMD
7.5
After decoupling of turbine, charge oil system & put TDBFP on
barring. Adjust turning gear valve to maintain barring speed 500 rpm
(approx). Resp:
UCE /TMD
7.6
TDBFP governing characteristic to be checked. Resp:
TG desk engr/TMD/C&I
7.7
Ensure closing of control valves before opening ESV. Resp:
TG desk engr
Procedure for
Overspeed test:
7.8
Ensure tripping of turbine (closure of stop valves) through Local
trip gear, Remote HMI trip and electrical overspeed protection (by
reducing setpoint below barring speed). Resp:
TG desk engr/C&I
7.9
Charge TDBFP from steam side with aux PRDS v/v as per procedure.
Charge Extraction source also if available (i.e If Main turbine is in
service).Resp:
TG desk engr.
7.10
During speed rising, close monitoring is required for control valve
opening, if control valve is not opening as per speed control output,
trip BFP and investigate reasons. Resp:
UCE/TMD
7.11
Roll TDBFP turbine as per the allowed rate and soak at 2000, 4000 and
5400 rpm for 30 min each. Offline speed to be measured by MTP at
above speeds. Turbovisory parameters also to be observed. Soak the
turbine at this speed till casing temperature reaches 200 deg C.
Resp:
TG desk engr /MTP
7.12
Carry out Oil Injection test three times to ensure the healthiness of
over speed trip device and consistency in test oil pressure at which
bolt acts is to be established. Procedure for oil injection test
given in 7.1 to be followed. Resp:
UCE/MTP/TMD
7.13
Turbine electrical protection set point to be raised 6100 from 6000
rpm & Speed reference blocking to be increased to 6100 rpm from
5800rpm. “OS Test” Push button to be pressed (Turns green) to
remove blocking of Nrtd at 5800 rpm. Resp:UCE/
C&I
7.14
Before going for actual over speeding ensure Remote trip engage is in
De-energised condition as this will not let the device act. Resp:
UCE/C&I
7.15
Turbine speed to be increased in steps of 100rpm till 5900 rpm &
later in step of 50 rpm. Operation executive/TMD executive should be
present in local to trip TDBFP if speed goes beyond 6100 rpm. MTP
engineer should be present in local to measure speed offline.
Turbovisory parameters to be kept under observation. Resp:
HOD operation /HOD TMD /HOD(C&I)MTP
7.16 Note the speed at which
turbine trips. Maximum TSI parameter to be noted. Resp: UCE/TMD
7.17
Restore OS protection setpoint to 6000 rpm and Speed reference
blocking to 5800 rpm. Press the “OS test” button in mimic (Turns
Red) to restore 5800 rpm limit on Nrtd. Resp:
UCE/C&I
8.0
FREQUENCY OF ACTUAL
OVERSPEED TEST
A Turbine on which on load oil
injection test being carried out successfully on monthly basis, shall
be given an actual overspeed test at intervals of 24 months or as per
manufacturer's recommendation whichever is less.
If the on load overspeed test mechanism
by oil injection is not functioning, then the actual overspeed
should be carried out while stopping the machine for planned shut
down or before taking the machine again in to service
If, for any reason, it is not possible
or practicable to carry out an actual overspeed test at least once
every 12 month, then this should be reported to the Director of
Operation, and formal dispensation sought on each and every occasion.
