ML19263D634

Forwards Evaluation of Degraded Grid Voltage Protection Plan.Accepts Design Re Protection from Degraded Voltage Conditions & Implementation Schedule Stated in

ML19263D634
Person / Time
Site:	North Anna
Issue date:	03/20/1979
From:	Parr O Office of Nuclear Reactor Regulation
To:	Proffitt W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
References
NUDOCS 7904130088
Download: ML19263D634 (5)

Text

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4s UNITED 5TA TES

,l= %,) D { 4 NUCLEAR REGULATOnY COMMISSION Y I E

WASHINGTON, D. C. 20555

TAR 2 01979 Docket Nos. 50-338 and 50-339 i

Mr. W. L. Proffitt Senior Vice President -

Power Operations Virginia Electric & Power Company P. O. Box 26666 Richmond, Nirginia 23261

SUBJECT:

NORTH ANNA POWER STATION UNITS 1 AND 2 - PROTECTION FROM DEGRADED GRID VOLTAGE CONDITIONS / INTERACTION OF 0FFSITE AND ONSITE POWER SYSTEMS In your letters of September 12, 1978, October 24, 1978, and January 12, 1979, you provided information in response to our letters of July 28, 1978, September 27, 1978, and December 1,1978 regarding protection from degraded voltage conditions / interaction of offsite and onsite power systems.

We have reviewed the information provided by you and have concluded that your design regarding protection from degraded voltage conditions is acceptable. Our evaluation of this matter is presented in the Enclosure. As stated in your letter of October 24, 1978, we agree that the implementation schedules of this design for Units 1 and 2 are as follows:

first refueling outage on Unit 1 and prior to initial operation on Unit 2.

Sincerely, Db an

. Parr, Chief Light Water Reacto.

Branch No. 3 Division of Projets Management

Enclosure:

As Stated cc w/ enclosure:

See next page 7904130088

i MAR 2 01979 Mr. W. L. Proffitt 2

cc:

Mrs. James C. Arnold John J. Runzer, Esq.

P. O. Box 3951 Pepper, Hamilton S Scheetz Charlottesville, Virginia 22903 123 South Broad f.treet Philadelphia, Peinsylvania 19109 Mr. Anthony Gambaradella Office of the Attorney General Clarence T. Kipos, Jr., Esq.

11 South 12th Street - Room 308 1700 Pennsylvania Avenue,. N.W.

Richmond, Virginia 23219 Washington, D. C.

20006 Carroll J. Savage, Esq.

Richard M. Foster, Esq.

1700 Pennsyl unia Avenue, fi. W.

211 Stribling Avenue Wasi.ington, D. C.

20006 Charlottesville, Virginia 22903 Mr. James C. Dunstan Michael W. Maupin, Esq.

State Corporation Conmission Huntois, Williams, Gay & Gibson Conaonwealth of Virginia P. O. Box 1535 Blandon Building Richmond, Virginia 23212 Richmond, Virginia 23209 Mrs. June Allen 412 Cwens Drive Huntsville, Alabama 35801 Mr. James Torson Alan S. P;senthal, Esq.

501 Leroy Atomic Safety and Licensing Socorro, New Mexico 87801 Appeal Board U.S. Nuclear Regulatory Commission Mrs. Margaret Dietrich Washington, D. C.

20555 Route 2, Box 568 Gordonsville, Virginia 22942 Michael C. Far.ar Esq.

Atomic Safety and Licensing William H. Rodgers, Jr., Esq.

Appeal Bcird Georgetown University Law Center U.S. Nuclear riegulatory Commission 600 New Jersey Avenue, N.W.

Washington, D. C.

20555 Washington, D. C.

20001 Dr. John H. Buck Mr. Peter S. Hepp Atomic Safety and Licensing

' Executive Vice President Appeal Board Sun Shipping & Dry Dock Company U.S. Nuclear Regulatory Commission P. O. Box 540 Washington, D. C.

20555 Chester, Pennsylvania 19013 Mr. R. B. Briggs Atomic Safety and Licensing Associate Director'.

Board Panel 110 Evans Lane U.S. Nuclear Regulatory Commission Oak Ridge, Tennessee 37830 Washington, D. C.

20555

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Mr. W. L. Proffitt MAR 2 01979 cc:

Mr. Michael S. Kidd U. S. Nuclear Regulatory Commission P. O. Box 128 Spotsivania, Virginia 22553 Dr. Paul W. Purdom Department of Civil Engineering Drexel University Philadelphia, Pennsylvania 19104 Dr. Lawrence R. Quarles Apartment No. 51 Kendal-at-Longwood Kennett Square, Pennsylvania 19148

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__k ENCLOSURE EVALUATION OF NORTH ANtlA DEGRADED GRID VOLTAGE PROTECTION We have reviewed the applicant's design with respect to degraded grid voltage protection and the interaction of the onsite power system with the offsite power system. We compared the North Anna 1 and 2 design to our established position on this subject and have reached the following conclusions. Our position is in four parts and each is separately addressed below.

Part 1 of the position requires undervoltage protection for low grid voltages. The undervoltage relays traditionally used to detect loss of offsite power at the emergency busses have had setpoints around 70-75 percent of nominal bus voltage. This protection alone does not pro-tect the plant loads from damaging los voltages which are maintained above this setpoint. Therefore, we have required an additional protective trip at approximately 90 percent of nominal bus voltage with a time delay to avoid spurious trips due.to short duration transients such as those occurring when starting larger motors. The North Anna design did not originally incorporate this degraded voltage protection.

The design now

!ncorporates this protective feature in a manner that satisfies the appropriate requirements of the IEEE Std 279-1971. We find this aspect of the design to be acceptable.

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h v E t'h Part 2 of our position requires that the diesel generator bus load shedding feature be automatically bypassed once the diesel genert. tor f.

is supplying power to the bus. This is required so that the voltage h

f drops encountered during load sequencing on the diesel generators will I

not interact with the load shedding feature and negate the loading sequences. Our position further requires that once the diesel generator 7

breaker is subsequently opened the load shedding feature shall be auto-Vf matically restored. The applicants design is in full conformance with this requirement. When the diesel generator breaker is open, there is a w

pemissive in the logic which allows load shedding (following c 2.2 second delay to allow fast transfer to a preferred offsite source) when under-

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vnitage is detected on the emergency bus. This pemissive is removed

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when the diesel generator breaker is in the closed position. We find 3

this acceptable.

Part 3 of our position deals with incorporating tests and test frequencies

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into the Technical Specifications to assure. continued adherence to this position throughout the plant lifetitie. These provisions have been 4

incorporated into the Technical Specifications proposed by the applicant t

and this is acceptable.

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.t Part 4 of our position requires that the tap settings on the plant dis-

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tribution transfomers be optimized and verified at the preoperational 1

e testing stage by measurement. The applicant has demonstrated by analy-sis that the transfomer tap settings have been fully evaluated and 3

optimized. We find this aspect of the design to be acceptable pending k

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verification oy actual in-plant.;easura.:ents.

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