ML17054A304
| ML17054A304 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 12/22/1983 |
| From: | GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML17054A301 | List: |
| References | |
| GEK-11393B, NUDOCS 8312280495 | |
| Download: ML17054A304 (8) | |
Text
GEK-11393B TESTING OF THE OVERSPEED 'TRIP SYSTEM See ELECTRICAL TRIP AND ALARMSYSTEM, PROTECTIVE CIRCUITS, for functional descrip-tion.
TEST A TESTS
'SEE TABLE I FOR' Test designation
- Devices tested
- Schedule
- Test conditions
- Test procedure
- Indications In Table I, it is assumed that all tests are suc-cessful and without any complications.
THE FOLLOWING:
DESCRIPTION COVERS POINTS OF SPECIAL,INTEREST AND INSTRUC-TIONS FOR MOST LIKELY OCCURRING AB-NORMAL BEHAVIOURS OF THE SYSTEM.
Test A is a routine functional test of the over-speed trip device and the mechanical trip valve.
The AND/OR statementunderschedule inTable I is to be interpreted as: If the unit is. startedweekly or more often,, the on line "Once a Week" test can be omitted.
This test "exercises" the overspeed trip and the mechanical trip valve and is, therefore, useful to keep these devices operable and to prevent an ex-cessive rise of the trip speed.
Although the test can be performed at any load, including full load, it is, for psychological reasons preferred to do it at low load.
Together withthe closing test of all steam valves this constitutes a complete test of allparts of the overspeed trip system except the relay trip valve.
IN ALL CASES OF MALFUNCTION, THE OP-ERATOR MUST MAKE HIS DECISIONS WITH A THOROUGH KNOWLEDGE OF THE SYSTEM AND ACT IN THE BEST INTEREST FOR SAFE OP-ERATION BUT WITHOUT UNNECESSARY LOSS OF GENERATION.
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In'able I this is indicated under the test condi-tions 'as '!ROTOR HOT."
PDR ADO 95 8312PP 839 ppep CK OSOOOy1O
- --.....PDR OVERSPEEDING Alltests that call for overspeeding of the unit (Tests B,
C. and E) must be conducted with a THOROUGHLYWARMED-UP TURBINE AND GEN-ERATOR ROTOR.
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On a cold or warm startup, Tests Aand D should be made and after they are successfully completed, the unit should be synchronized and'run atinitial or higher load for several hours before it is taken off the line to conduct overspeed tests.
It is essential that the ROTOR BORES have reached STEADY-
'TATE,TEMPERATURE conditions BEFORE OVERSPEEDING the unit.
UNSUCCESSFUL TEST A-If in Test A the mechanical trip valve should fail to trip, the solenoid oil trip valve should be, observed.
Ifthis valve seems to work, it must be concluded that the overspeed tripdevice is sticking.
In this case the BACKUP OVERSPEED TRIP CIR-CUITS should be tested immediately (Test D). If Test D Is successful the unit can he lefton the line up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
As soon as convenient within this period, the followingprocedure should be used:
- l. Unload the unit ~corn latel
- 2. Open circuit breaker
- 3. Push "LOCKOUT"
- 4. Push "MEDIUM"startup rate S. Push"OIL TRIP" AND "OVERSPEED" si-multaneously.
- 6. Ifthe mechanical trip valve trips below 110 percent
- speed, return to rated speed, reset and conduct Test B (this time without pushing the oil trip).
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GEK-11393B TESTING OF THE OVERSPEED TRIP SYSTEM Ifthe tripspeedin TestB iswithin thetolerances (see Diagram of Control Mechanism, Tab 4 of-'-Me'-
chanical Instruction Book) the unit can be returned to service.
- 7. If the overspeed trip device fails to trip at 110 percent speed with oil trip on or is above tol-erance in Test B the unit MUST BE SHUT DOWN IMMEDIATELYand the overspeed trip must be re-paired to;pass Test A and B or C.
If, following anUNSUCCESSFUL TEST A, TEST D'IS ALSO UNSUCCESSFUL, THE UNIT MUST BE
'HUT 'DOWN IMMEDIATELYAND THE DEFEC-TIVE DEVICES AND CIRCUITS MUST BE RE-PAIRED.
TEST B Test B is a preferred test to establish the exact trip speed after the system test (C) has been suc-cessful but the trip speed was readjusted or a con-firmation on the trip speed value is desired (every 6 to 12 months).
During this test the speed control system is not affected and when the "OVERSPEED" button is re-leased the unit will return to rated speed auto-matically.
Since after this test resetting of the mechanical trip valve above approximately 102 percent is not possible and there is a risk of mechanical damage on the trip mechanism if the reset is attempted above 102 percent speed, it is recommended towait until the unit is again controlling at rated speed before the mechanical trip valve is reset.
TEST C Test C is the ultimate system test that should be conducted after installation or maintenance on the system in order to verify the proper functioning of the system after all partial checks have been satisfactory.
This test can replace Test B if it is conducted every 6 to 12 months; however, more frequent ap-plication of Test C is not recommended because the fast closing of the valves represents heavy duty.
Special care should be used when resetting (with master reset).
The speed should not be above 102 percent. It is best to wait until the unit has coasted down to rated speed before resetting.
Since all valves trip closed and the speed set returns to "VALVES CLOSED," the unit will keep decelerating until the emergency trip system is reset and the speed selection rated speed is made by pushing the corresponding button, It is desirable to select the "FAST" startup rate in order to mini-mize the delay in valve opening.
UNSUCCESSFUL TEST C In case the trip speed is not within tolerances, consult Test B.
If any turbine valve did not close fast or the speed set did not return to "VALVES CLOSED" or the emergency trip system did.not "seal in" in tripped position, the unit should be shut down and the defective portion of the system should be r'e-paired.
This test can also be used to take data for the speed regulation of the control valves and the inter-cept valves. If this is desired, the vacuum should be very good and the excitation of the generator should be removed in order to have the unit coast down as slowly as possible so that the valve opening is much slower than the built in opening rate limit.
UNSUCCESSFUL TEST B Sticking of the overspeed trip device oi the me-,
chanical trip valve would be uncovered by Test A, rather than Test B.
If, in Test B, the trip occurs too low the unit can be returned to service; however, the operator must realize that the unit will likely trip out on overspeed iffull load should be lost.
If the TRIP SPEED IS ABOVE.TOLERANCE or THE TRIP DOES NOT OCCUR, THE UNIT MUST BE SHUT DOWN IMMEDIATELYTO REPAIR THE DEFECTIVE MECHANISM.
Except for obtaining the trip speed, the system operation can equally well be tested with the manual trip at the front standard or the MASTER TRIP button.
During initial startup, these tests should precede Test C preferably without steam pressure in the boiler and, therefore, at standstill.
TEST D Test D is a circuit test for the backup overspeed trip.
Since the backup overspeed trip (BUOT)actuates the master trip relay by energizing a circuit (at approximately 112 percent speed),
the circuits can be tested by opening the trip circuit of the BUOT and lowering its speed reference just'below rated speed temporarily.
This is all done automatically when the "BACKUP OVERSPEED TRIP TEST" button on the monitor panel is depressed.
A successful test will result in lighting the "BUOT" light on the monitor panel.
TESTING OF THE OVERSPEED TRIP SYSTEM GEK-11393B II TABLE I
'EST DES IGNATION DEVICES TESTED SCHEDULE Overspeed trip Once a week Mechanical trip valve (MTV) and/or (Steam valves remain open) at each startup TEST CONDITIONS Bated speed on line hs soon as rated speed ls reached, off line TEST PROCEDURE
- 1. Push "LOCKOVT"
- 2. Push "OIL TRIP" until MTV trips (a few seconds)
Push "RESET" until MTV ls reset (a fc>> seconds)
- 4. Lockout "NORMAL" automatic (approximately 10 seconds)
INDICATIONS "LOCKOUT"light on MTV 'TRIPPED" light on MTV "RESETTING'ight off - on - of[
"RESET" light on "NORMAL-light on "IOCP'OUT" light off B
Ovcrspced trip 5 to 12 (trip speed) months Mechanical trip valve (MTV)
(steam valves remain open)
Of[ line ROTOR NOT OVEBSPEED For trip speed tolerances see diagram of control mechanism tn Tab 4 of mechanical volume of instruction book I. Push "LOCKOUT"'.
Push "FAST",startup rate S. Push 'OVERSPEEIy'nd keep depressed
- 4. At 50 rpm below trip speed push "MEDIVM"startup rate Keep 'OVEBSPEED" depressed
- 5. At trip speed Record trip speed Release "OVERSPEED"
- 0. Let unit slow dawn to rated speed lt wBI hoM speed there.
- 7. Push "RESET" (not master reset)
- 8. Lockout "NORMAL" automatic (approximately 10 seconds)
"LOCKOUT"light on "FAST" light on "OVERSPEED" and "ACCELERATING-light on "MEDIUM"light on (5 percent/minute rate)
MTV TRIPPED" light on I
"AT SPEED'ight on rated speed on speed Indicator MTV "RESETTING" light of[ - on - off "RESET" light on "NORMAL"light on "LOCKOUT"light ol[
Overspecd trip system (trip speed)
Allsteam valves At startup atter main-tenance work on trip system or valves.
Off line Rotor hot Overspeed For trip speed tolarances see diagram of control mechanism
- 1. Push "FAST" startup rate
- 2. Push "OVERSPEED" and keep depressed At 50 rpm below rated trip speed push "MEDIUM"startup rate Keep "OVEBSPEED'epressed
- 4. At trip speed Record trip speed Release "OVEBSPEED" Check valve closures
- 5. Let unit slaw dawn to rated speed or less
- d. Push "MASTER BESET" until ETS "BESET" light comes on T. Push RATED TRIP SPEED
- 8. Push "FAST" startup rate
- 9. Let unit accelerate to rated speed "FAST" light on "OVERSPEED" and "ACCELERATING" light on "hiEDIUM"light on (5 percent/minute rate)
MTV "TIUPPED'! light on ETS 'TRIPPED" light on Speed set "VALVFS CLOSED" on MTV "RESETTING" off - on - off MTV "RESET" on FIS "RESET" on Rated speed set light on "ACCELERATING"light on "FAST" light on "AT SPEED" llglu On rated speed on speed Indicator Backup ovcrspced trip (BUOT) circuits Backup overspced trip system (trip speed)
Allsteam valves Once a week and after each star tup 12 to 24 months Rated speed on line (or olf lint lfdcslrcd)
Off linc Rotor hot Load set at 40 percent'VERSPEED eLoad set must be increased because "OVEBSPEED" top limit Is generally set below trip speed of BUOT.
For value of trip speed sea Llncup Diag. or BUOT Schematic.
- 1. Push -BVOT TEST" on monitor panel.
Keep depressed for a few seconds.
- l. Push loading rate "10-
- 2. Put load set to 40 percent (push "INCREASE" long enough)
- 2. Push "FAST" startup rata
- 4. Push 'iLOCKOVTee
- 5. Push 'OVEBSPEED" and keep depressed
- g. At trip speed of mechanical overspeed trip: keep
'OVERSPEED" depressed
'l. At trip speed o[ BVOT Release "OVEBSPEED" Record trtp speed Check valve closure
- 8. Same as 5 through 9 of test "C-.
"BUOT TEST" light on (indicates test successful)
"10" percent/minute light on Load set 40 percent. unit willacceierat<
approximately 4 percent ln 4 minutes "FAST-tight on "LOCKOUT"light on "OVERSPEED" and "ACCELERATING" light on Mechanical trip valve
-TRIPPED" light on "LOCKOUT"light of[
MTVlight "TRIPPED" ETS light 'TIVPPED" Speed set "VALVES CLOSED" Load set running back to rero.
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GEK-11393B TESTING OF THE OVERSPEED TRIP SYSTEM Releasing the test. button will restore, the cir-cuits to normal operation within. about 5 seconds.
Test A must not be conducted simultaneously with Test D.
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UNSUCCESSFUL TEST D If the "BUOT" light does not come on, check speed setting.
If an attempt to correct the speed setting is un-successful, the unit can be KEPT OPERATING AT ANY LOAD BUT, TESTS INVOLVINGTHE LOCK-OUT (A, B and E) MUST'OT BE PERFORMED under these conditions.
If the backup overspeed sensing circuit or the relay appears to be inoperative, the corresponding circuit card can be replaced with a preset spare.
TEST E Test E is the BACKUP OVERSPEED TRIP SYS-TEM TEST.
This testshould beperformed after initialstartup and at 12 to 24,months intervals thereafter.
More frequent application of this test is not ad-visable because of the high overspeed and the heavy valve duty involved.
Test D and a reading on the backup overspeed reference voltage should always precede this test.
The same precautions for resetting as in Test C are applicable.
If the test is not successful, all tests involving the "LOCKOUT"should be omitted until the defec-tive parts of the system have been repaired, GENERAL
ELECTRIC 4-74 (3M)