ML19291C266
| ML19291C266 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 08/26/1977 |
| From: | JERSEY CENTRAL POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML19291C260 | List: |
| References | |
| NUDOCS 8001230250 | |
| Download: ML19291C266 (4) | |
Text
A'1TACHMEIC' IV Page 1 of 4 CYSThR C:._2K SUCLEAR rE:'i?.ATING STATICS Fort.ed River, New Jersey 08731 Licensee Event "cport Reportabic Occurrence ':o. 50-219/77-17-3L P.c na.a r t Date
-qu s t 26, '977 CCCurTenCe E.ite July 2S, 1977 Identification of Occurrence Operation in a Degraded Mode as defined in Technical Specifications, whcn the power supply was lost to Core Spray Pumps connected to "C" Bus and to S :.ndby Cas Trestr. cat System I.
This event is considered to be a reportable occurrence as defined in the Technical Specifications, paragraph 6.9.2.b.2.
Cuiditicas Prior to Occurrence Plant was shut de'.cn for annual refueling with the rode switch in the " refuel" position.
Dascription of Occurrence At 1645 on Thursday, July 2S,1977, the "C" 4160-volt Bus lost power when breakers 1C and EC opened due to activation of relays SIN (neutral overcurrent) and 26-1C/HR (lockout).
Power to Reactor Protection System I was reestablished by transferring power feed from the MG set to the transformer and the scram ecs reset.
Tie breakers US1T, US2T, and US3T were closed to supply power to plant 450-volt power systems normally fed by the "C" bus.
At that time, electricians were called to investigate the cause of the trip.
After extensive testing as listed under Corrective Action, no failed components L s:.. Los or improperly set cu...;caents coula oc rowid anu sua, sue
,e trip is unkncwn at this time.
Since the tests conducted proved the integrity of the relays, the bus and cables, the switchgear and the assochted equipment, the system was returned to normal service.
3pparent Cause of Occurrence 1792 210 The cause of the incident is unknown at this
'me.
(SEE R.O. M/ 3 FoR couSC Analysis of Occurrence The isolation of "C" bus resulted in a loss of standby emergency power to bus "1C".
In addition, the incident resulted in a ter.porary loss of one-half the sr.fety systems associated with the emergency busses.
Had a ccadition called for the cperatien of the safety systems, the redundant systems would have becn A
f, 8 0 01 2 3 0 c3 W
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ine rccunc1nt <!iesel,jr.er. tor tras proven operabic
. ;.fter the occurrence, and 1:crefore, was."ailable if a complete loss of outside po.cer sources had occurred.
',,;ndix L to the FDSAR contains a probability nalysis regarding the
'vailability of standby cooling systems and includes an analysis of off-site pcwer uailability concurrent 'eith a loss of coolant accident.
The results indicated that the reliability of available power from off-site s:;urces or frem a self-contained unit (only one diesel generator was ccasidered in the cnalysis) was quite high.
Since the station is pro-
'ed with two separate diesel generator units, having one unit out of v:
service has no effect on the results of the analysis.
In addition, the effects of single bus operation during a loss of ecolant accident was rtaly:cd in 1:cndment 32 to the FDSAR and the unit. Icading under this ccndition was found to be within the normal KVA rating of the diesel pnarator.
T'us, there is no additional safety si;nificance associated with this event h jond that aircady cnaly:ed.
Corr;ctive Action E ' cc,t rica l Teit s Pe r fo r..ed (1) The three phases of the bus and diesel cables were meggered at 2500 volts DC with all "C" Bus breakers racked in and open:
Phase A - 700 Megohms Phase B - 750 Megohms Phase C - 700 'degohns (2) Sreder EC was closed and mugger readings retaken to prove no damage or fault occu: red on the 4160-volt bus tie.
Readings similar to those
- % ve,ere found.
(3) Each of the three unit substation transformers and feeder cables were i..egge reu at.:a v u v o m ut.
(...... -.:....17 1 :_Js :n th: 'rcs
-t tM time).
US1A1/1A1P Feeder Cables - 100 Megohns US1A2/1A2P Feeder Cables - 100 Megohms USI A3/1A3P Feeder Cables - 125 Megohms (4) Current transforners were inspected and continuity checks made on the primaries and secondaries.
No problems were found.
(5) All relay wiring was checked for continuity, broken or shorted wires, and for poor connections.
.None could be found.
(6) Current was driven thrcagh each phase of the bus with an ar. meter in the seccndary to prove the ratio of the current t rans fo rme rs.
The ratio found mtched the transfor.er 400/1 ratio.
d j
RITACH'ET IV le C.
.. e '7?.
30-219/ 7 7 3L Page 3 of 4 7 -;. ' t 26, 1:17 (7) Lightning a: restc rs..cre neg;ered at 2500 '.olts DC with no indicativns found.
(S) Relay Depc.rtnent verified the proper setroint and eperation of all relays involved and those which could aave failed upstream of the bus.
All relays '.;ere found in proper operating cendition.
(9) The current transformers were by-potted to further verify their condition.
(10) All portions of the bus were physically inspected.
No evidence could be found, indeed, the bus cas in excellent ccadition.
(11) All feeder cable cc:npartments were also inspected with similar results.
(12) The bus and cables were tested with an 1000-volt DC hypot and result _s were cer): red to previous tests.
No damage or degradation.zas indicated.
(13) All secticns of the bus and leads were rec nerni:ed one at a time to verify they,could support nernal operating voltage.
All ioads were taken 'iithout incident.
(14) All relays and cabinet doors were shaken vigorously to "try" to trip relays inadvertently.
The relays could not be tripped in this manner.
The PORC recorended the continued review of testing performed to search for any possibic causes for the incident.
Contact is being made with General Electric to determine any other means of proving the integrity of the lightning arresters.
Failure Data
.No failed components were found.
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1792 212
I M 4 + E U' IV Page 4 of 4 PE.SPONSE 'IO ENCIOS~.'RE QLT.STIO::S REPORTABLE OCCURRE:CE 50-219/77-17 Section A of Enclosure Oacstions is pertinent since this event involved only one Startup Transformer.
RESPONSE
A.1 'Iko circuits are available; one circuit was lost.
A.2 Cause of event was discovered subsequently during investigation of PO 78/3 (Attacluent V). Cause was degradation of SKV cable bus.
A.3 Degradation of cable had advanced to nore discharge prone condition in one bus than the other.
A.4 No voltage excursions are pertinent to this event.
A.5 No frequency excursions are pertinent to this event.
A.6 The bus was out of service for a period of two to three hours while testing was performed to determine cause of event and ensure the bus was not faulted.
A.7 DATE OF EVENT: 7/28/77 1792 213