05000280/LER-1980-070-01, /01T-0:on 801114,S&W Informed Util That Out of Phase Transfer Might Occur When Emergency Buses Transferred from Offsite Source.Caused by Undeterminable Design Error. Time Delay Circuit Installed

/01T-0:on 801114,S&W Informed Util That Out of Phase Transfer Might Occur When Emergency Buses Transferred from Offsite Source.Caused by Undeterminable Design Error. Time Delay Circuit Installed

ML18139A863
Person / Time
Site:	Surry
Issue date:	11/26/1980
From:	Joshua Wilson VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML18139A862	List: 05000280/LER-1980-070, Forwards LER 80-070/01T-0 05000280/LER-1980-070-01, /01T-0:on 801114,S&W Informed Util That Out of Phase Transfer Might Occur When Emergency Buses Transferred from Offsite Source.Caused by Undeterminable Design Error. Time Delay Circuit Installed
References
LER-80-070-01T, LER-80-70-1T, NUDOCS 8012030717
Download: ML18139A863 (3)

LER-1980-070, /01T-0:on 801114,S&W Informed Util That Out of Phase Transfer Might Occur When Emergency Buses Transferred from Offsite Source.Caused by Undeterminable Design Error. Time Delay Circuit Installed

Event date:
Report date:
2801980070R01 - NRC Website

text

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~~~~ L~©I o I s I o I o I o I 2 I s I o 1011 I 11 11 4 I s I o I© 111 1 1 2 1 6 I s I o 10 60 61 DOCKET NUMBER 68 69 EVENT DATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE.CONSEQUENCES@)

I Stone and Webster Jngineerinq Corrp:my info:c:med VEPCO that because there is no defi ni ti::sre

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• 1Phase Relationship between the off-site source and them:; Voltages and no tine pennis-1sive for collapsing the residual voltage, an out-of-phase transfer might occur when the,I

~ency buses are transferred from the off-site S01.llX:e to the ECG.

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1reportable per T.S. 6.6.2.a. (9).

The health and safety of the public were not affected. I 7

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43 44 47 I The cause of this design error has not been determined. A time delay circqit was

!III] I installed on the FOG output breaker to allCM a 2. O second time delay between the open-0:W I ing of the off-site supply breakers and closing of them::; breakers. 'Ibis was accom-

[I))J I plished as a temporary nodification. A design change will be canpleted to provide final I lIITI I resolution.

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,..,~'ITACHMENT 1, PAGE 1 OF

• SURRY POvER STATION, UNIT 1 IXCKET NO:

50-280 REPORT NO:

80-070/01~0 EllENT DATE:* : 11-14-80 SUBJ.OCT:

EMER3E~Y BUS 'OOT OF PHASE TRANSFER

1.

DESCRIP!'ION OF 'EVENT:

On November 12, 1980, Stone and Webster Engineering Corporation infonned VEPm that, under certain conditions,.an out of phase transfer might occur when the emergency buses are transferred from the off-site p:::Mer som:c:e to the emergency diesel generator after the generators have reached rated speed and voltage because there is no definitive phase relationship between the off-site source

• and the emergency diesel generator voltages and no tine penni.ssi ve for collap-sing the residual voltage.

On Novanber 14, 1980, Stone and Webster Corporation confinned a significant*out of phase transfer oould occur under the following conditions:

1.

A Safety Injeclion signal is received and the diesels start and nm on standby.

2. Off-site power is lost, the emergency buses isolate from the off-site supply and are transferred to the diesel generators.

'Ihis event is reportable per Technical Specification 6.6.2.a.(9).

2.

PROBABLE CONSmuENCES:

As built, there was no time pennissive to allow for collapsing of residual bus voltages. 'Iherefore, an out of phase transfer might have caused severe noter *end-tum forces as well as high torsional stresses that could cause rrotor rotor, ooupling or driven equipnent shaft failures.

A study of this transfer effect on the low head safety injection rrotors indicates that the resultant volts per Hertz ma.y not be within the recorrMendecl.allowable limit for a safe transfer per ANSI CS0.41-1977. '!he scenario described above has a very low probability of occurring and has nnt been ext>P.rienced at Suny; therefore the health and safety of the public-were not. affected.

3.

CAUSE

'!he cause of this, !design error has not been detennined.

4.

IMMEDIATE CO~ ACTION:

In order to*alleviate the p:,ssibility of a significant out of phase transfer condition, a time delay circuit was installed on the emergency diesel generator output breakers to allow a 2.0 second tine delay between the opening of the off-site supply breakers and closing of the emergency diesel generator breakers.

A 1.96 second tine delay is sufficient for the residual voltages to dissipate to allowable levels.

The installation of the tine delay was accanplished as a temporary m::xlification.

e A'ITACHMENT 1, PAGE 2 OF 2 SURRY J?a,l1ER STATION, UNIT 1 IXCKET N'.):

50-280 REPORI' N'.):

80-070/0lT-0 EVENT DATE:

11-14-80 C)

SUBJECT:

E:MER:;ENCY BUS *CXJT. OF PHASE TRANSFER

5.

SUBSF.QUENT CORRECTIVE ACTION:

e A design change will be corrpleted to provide final resolution.

6.

• GENERIC IMPLICATIONS:

The above corrective action has resolved any generic implications at Sun:y.