ML18139A387
| ML18139A387 | |
| Person / Time | |
|---|---|
| Site: | Surry, North Anna  |
| Issue date: | 06/26/1980 |
| From: | Sylvia B VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Harold Denton, Varga S Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8007010422 | |
| Download: ML18139A387 (4) | |
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e RESPONSE TO "LOSS OF OFFSlTE PO\\v1ER SURVEY" Attachment Page 1
REFERENCE:
NRC letter dated May 9, 1980 from S. A. Varga -
Operating Reactors Branch No. 1.
A review of Surry's experiences has been performed which indicated two partial losses of offsite power have been experienced; there have been no complete losses of offsite power.
The following are the responses to the survey questions:
A.
Partial Loss of Offsite Power
- 1)
HOW MAJ.TI CIRCUITS TO THE OFFSITE NETWORK ARE NORMALLY AVAIL-ABLE AfID HOW MANY WERE LOST DURING THE EVENT?
CASE 1 -
There are two independent circuits from offsite trans-mission
- network available to energize the 4160 VAC and 480 VAC emergency buses -
(two auto transformers which feed Bus 5 and Bus 6 respectively). Bus 5 was the only source lost, this resulted in a loss of two reserve station service transformers and a Unit l trip of the turbine and reactor.
CASE 2 -
Initial conditions same as Case 1, except between event dates an additional source was added, transformer.1f4, which was added to supply buses 5 and 6.
The entire Bus tf2 cleared itself as a result of a fault on the #2 auto-transformer.
The #4 transformer energized the 34. 5 Bus 116 automatically.
There was no effect on either operating unit.
- 2)
WHAT WAS THE CAUSE OF THE EVENT?
CASE 1 -
The Buses 5 and 6 were tied together through the T562 Breaker.
During testing on the LT-12 Breaker, the T562 breaker was mistakenly left in auto; it should have been in manual.
When the LT-12 breaker was closed with its disconnects open, the breaker logic required the T562 to open, thus de.:energizing the Bus #5.
Case 2 - Whiie closing the Hi side breaker of the tf2 auto trans-former returning lightning arrestors* to service, a ground fault occurred.
This opened all of the #1 auto transformer breakers.
Atta.
Page 2
- 3)
WHY DID THE OTHER LINES NOT FAIL WHEN SOME DID FAIL?
Case 1 - T~e event occurred as a result of breaker. logic - nothing failed.
Case 2 - The tripping scheme functioned as designed, protecting the reset of the distribution system.
- 4)
WAS ANY VOLTAGE INCREASE OR DECREASE EXPERIENCED JUST PRIOR TO OR DURING THE OUTAGES?
IF SO, PLEASE GIVE DETAILS:. LOWEST FREQUENCY REACHED, DECAY RATE, AFFECTS ON EQUIPMENT, OPERA-TION, ETC.
CASE 1 - None
.CASE 2 - None
- 6)
HOW LONG WAS POWER UNAVAILABLE FROM THE CIRCUIT?
CASE 1 - Approximately 45 minutes.
Case 2 - Power to the emergency buses ~as never interrupted.
- 7)
DATE OF EVENT CASE 1 - June 9, 1974.
CASE 2 - November 10, 1978 B.
For Losses of All Offsite Power:
NOTE:
There have been no such events at Surry.
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NORTH ANNA POWER STATION RESPONSE TO 11LOSS OF OFFSITE POWER SURVEY'.'
Attachment Page 3 A thorough review of North Anna station records was conducted and. it has been determined that no occurrences of the type mentioned in the survey have occurred.