ML19320B525

LER 80-042/01T-0:on 800707,w/Mayflower 500 Kv Transmission Line Out of Svc,Mabelvale 500 Kv Tripped on Ground Fault. Caused by Ground Fault & Resulting Overload

ML19320B525
Person / Time
Site:	Arkansas Nuclear
Issue date:	07/07/1980
From:	Shively C ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19320B517	List: ML19320B516 ML19320B525
References
LER-80-042-01T, LER-80-42-1T, NUDOCS 8007140405
Download: ML19320B525 (5)

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? 60 61 DoCEET Nuuttp in8 WJ la EVENT DESCRIPTION AND PROS ABLE CONSEOUENCES h l o 121 I With the Mavflower 500KV transmission line out of service & the unit 00-1 1 o 131 I eratino at 91% cower: the 500KV Mabelvale line trioned on a ground faults t o i. i i the 500KV Fort Smith line opened on the Fort Smith end, isolating all but in isi i the two 161 KV transmission lines from the AUO switchyard. The Morrilton 1o1611 East 161 KV line triooed due the resultant overload. leaving one soc.rce I lo til I of offsite power - Russellville East 161KV ine supplying SU transformer l

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CAUSF DESCRFTION AND CORRECflVE ACTIONS Laloti Transmission lines tripped due to around fault and resulting overload. i i, ii 1 l The Reactor & Turbine-Generator subs _eauently triooed. The Emergency Dies sii2i i sel Generators started and loaded per design and remained in service un-I m i til Lock-out relays were reset and 500KV bus re-energized when unit loada i s i. i i were transferred manually to startup tr.ansformers. ,

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-l- Reportable Occurrence Report No. 50-368/80-042/01T

2. . Report Date: 3. Occurrence Date:

7/7/80 6/24/80

4 Facility:

Arkansas Nuclear-0ne - Unit Two Russellville, Arkansas

5. Identification of Occurrence:

' Conditions arising from natural events, that as a resalt of the event (partial loss of offsite power due to transmission l'ne failure) require a unit shutdown & operation of safety systems or oth :r protective measures (ES bus voltage restored by automatic action of Dnergency Diesel Genera-tors). Reportable per T.S.3.8.1 and T.S.6.9.1.8.g.

6. Conditions Prior to Occurrence:

Steady-State Power X MWth Reactor Power __2360 Hot Standby Net Output Mwe

___ 840 Cold Shutdown Perecnt of Full ower 91% %

Refueling Shutdow'n Load Changes During Routine Routine Startup Operation Routine Shutdown Operation Other ('specify)

Steady state power operation with the Mayflower 500KV line (one of three 500KV lines) out of service.

7. Description of Occurrence:

At 1540 hours0.0178 days <br />0.428 hours <br />0.00255 weeks <br />5.8597e-4 months <br />, switchyard circuit breakers _ tripped apparently due to a ground fault ' isolating' the Mabelvale 500KV line. The unit's generation, along with Unit I's generation, was' transferred to the Fort Smith 500KV

-line which tripped open at the Fort Smith end, as a result of feeder overl oad. The Mabelvsle line became available again, but did not close into the ANO switchyard '500KV ring bus because of-inability -to sync-

. check. Unit II tripped from CPC generated DIER trips based on decreasing RC Pump . speed, 'apparently ~ induced from -frequency and voltage upsets 'oc-curringLon the: system grid. . The Morrilton East ^161KV line tripped on overload leaving _ only the 500KV bus segment-(Unit I generator output)

' feeding the autotransformer and the Russ .lv'lle _ East line carrying power, generation. Startup transformer y renained energized from the

. autotransformer, and ~ startup transformer #2' remained tied to the 161KV .

_ bus. The ' unit's- 4160 volt auxiliaries were transferred to startup '

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'f Reportable Occurrence No. 50-368/80-042/01T Description of Occurrence (Cont.):

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- transformer #3, while the 6900 volt buses were switched to SU#3 prior-

- to the~ occurrence. Under voltage rel_ays on the 6900 volt buses -oper-ated, shedding the Reactor Coolant Pumps and Circulating Water Pump loads. The 4160 volt auxiliary circuit indicated low voltage, strip--

ping the buses 'from startup transformer #3. Subsequently, the auto-transformer bank received lockout relay _ operation from an apparently

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faulted relay, resulting in lockout relay operation of startup trans- ,

former #3 (and Unit I's startup transformer #1), placing both units r witho_ut auxiliary bus voltage. At.this point, the switchyard buses

. were deenergized except for the Russellville East' tie to startup transformer.#2 (one source of offsite power), which remained energized.

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t D-9 Reportable Occurrence Report No. 50-368/80-042/01T

8. Designation of Apparent Cause of Occurrence:

Design Pro'cedure Manufacture Unusual Service Condition X Including Environmental Installation /

Construction Component Failure X (See Failure Data)

Operator Other (specify)

Occurrence was . caused by a loss of offsite transmission and aggravated by the resultant grid degradation.

9. Analysis or Occurrence:

Coincident with the shedding of the 6900 volt and 4160 volt buses from startup transformer #3, Emergency Diesel Generators, 2DG-1 & 2DG-2, auto-started on 2A3 and 2A4 bus under voltage. The Unit's ES buses were

- reenergized and normal' loads were sequenced on. Approximately four min-utes later the 2A1 and 2H1 buses were energized from startup transformer

1. 2. At about 55 minutes later,'all house loads were transferred back to startup transformer #3 and both Emergency Diesel Generators were secured.

The Reactor Coolant. Pumps were: sequenced on. The reactor was fed by natural circulation for a total of approximately 66 minutes. The unit was taken to Cold Shutdown conditions for Reactor Coolant Pump Seal re-placement.

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f Reportable Occurrence Report No. 50-368/80-042/01T

10. Corrective Action:

i AP&L Transmission line fault was cleared.

No plant site corrective action required as all plar:t s vstems operated per design.

11. Failure Data:

Not applicable.

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