ML18139A873

Part 21 Rept Re S&W Notification That out-of-phase Transfer Might Occur When Emergency Buses Are Transferred from Offsite Power Source to Emergency Diesel Generators After Reaching Rated Speed & Voltage.Originally Reported 801114

ML18139A873
Person / Time
Site:	Surry, North Anna
Issue date:	11/19/1980
From:	Sylvia B VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
REF-PT21-80-310-000 932, NUDOCS 8012040669
Download: ML18139A873 (4)

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November 19, 1980 Mr. James P. O'Reilly, Director Serial No. 932 Office of Inspection and Enforcement NO/ESG:ms U. S. Nuclear Regulatory Commission Docket Nos. 50-280 Region II

• 50-281 101 Marietta Street, Suite 3100 50-338 Atlanta, *Georgia 30303 50-339 License Nos. DPR-32 DPR-37 NPF-4 NPF-7

Dear Sir:

Under the provisions of the. Technical Specifications and 10 CFR 21, NRC Region II was notified on November 14, 1980 that a potential significant deficiency or ~ubstantial safety haz_ard existed at Surry Units 1 and 2 and North Anna Units 1 and 2.

• In accordance with the reporting requirements of 10 CFR 21, the following,

• information is submitted: -

A. Name and address of reporting individual:

Hr. B. R. Sylvia, Manager Nuclear Operations and Maintenance Virginia Electric and Powe.r Company P. 0. Box 26666 0 Richmond, Virginia 23261" B. Facility, activity and/or component affected:

Surry Units 1 and 2 North Anna Units 1 and 2 C. Name of firm constructing the facility or supplying the component, activity or service:

Stone & Webster Engineering Corporation Boston, Massachusetts 02107

e VIBOJNa ELECTBJC AND PoWEB COMPANY TO Hr. 'James P~ of.illy 2 D. Description of defect, deficiency or failure to comply:

Stone* & Webster Engineering Corporation informed Vepco that under certain conditions, an out of phase transfer might occur when the emergency buses are transferred from the offsite power source to the emergency diesel generator after the generators have reached rated speed and voltage because there is no definitive phase relationship between the offsite source and the emergency diesel generator vol-tages and no time permissive for collapsing the residual voltage.

,.On November 14, 1980, Stone & Webster Engineering Corporation confirmed a significant out of phase transfer could occur under the following conditions:

1. : A Safety Injection signal is received and the diesels start and run on standby.

2. Offsite power is lost, the emergency buses isolate from the offsite supply and are transferred to the diesel generators.

As built, there was no time permissive to allow for collapsing of

• residual bus voltages. Therefore, an out of phase transfer might have caused severe motor end-turn forces as well as high torsional stresses that could cause motor rotor, coupling or driven equipment .

shaft failures.

• A study of this transfer effect on th~- low head *

• safety injection motors indicates that the resultant volts per Hertz may not be within the recommended allowable limit for a safety transfer per ANSI CS0.41-1977.

E. Date of determination of reportability: November 14, 1980 F. Similar components, .activities or services: None G. Corrective Action which has been, is being or will be taken, the

• individual responsible and the length of time to complete the action:

A time delay circuit has been installed on the Surry Unit 2 and North Anna Unit 1 emergency diesel generator output breakers to allow a .2.0 second time delay between the opening of the offsite supply .breakers and closing of the emergency diesel generator breakers. A 1. 96 second time delay is sufficient for the residual voltages to dissipate to allowabl~ levels.

The modifications will be completed on Surry Unit 1 and North Anna Unit 2 prior to startup from their current out~ges.

e V1aonnA Eu:cra1c AND Pow.zB CoKPANY To Mr. James P*. of.illy H. Other information:

Any additional information regarding the above topic will be submitted in the Licensee Event Reports.*

Should y~u require further information, please contact this office.

I Very truly yours,

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B. R?s;1v;;

• Manager - Nuclear Operations and Maintenance cc: Mr. Victor Stello, Director (3)

Office of Inspection and Enforcement

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