ML20063M594

Responds to 820813 Request for Addl Info Re Adequacy of Electrical Distribution Sys Voltages.Theoretical & Actual Voltages for safety-related Buses Listed

ML20063M594
Person / Time
Site:	Point Beach, Prairie Island
Issue date:	09/10/1982
From:	Fay C WISCONSIN ELECTRIC POWER CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
TAC-12955, TAC-12956, TAC-47404, TAC-47405, NUDOCS 8209150262
Download: ML20063M594 (3)

Text

%QSCORSin Electnc eom couem 231 W. MICHIGAN, P.O. BOX 2046, MILWAUKEE, WI 53201 September.10, 1982 Mr. H. R. Denton, Director s l Office of Nuclear Reactor hegulation-l U. S. NUCLEAR REGULATORY COMMISSION Washington, D. C. 20555 ,

i x Attention: Mr. R. A. Clark, Chief '

Operating Reactor Branch 3 L

Gentlemen: '

o i DOCKET NOS. 50-266 AND Sd-30L ADEQUACY OF STATION ELECTRIC DISTRIBUTION POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 Your letter dated August 13, 1982' requested certain.

additional information concerning the adequacy of station 4

electrical distribution system voltages at.the Point Beach Nuclear Plant. These issues were originally discussed with Wisconsin Electric during a telephone call on July 16, 1982.

Your letter noted that the results of a verification test done in 1979 did not include the comparison of measured '

terminal voltages versus' calculated terminal voltages as requested in an NRC letter dated August 8, 1979. We have ca]culated the voltages which would theoretically have been present on the safety-related busses assuming that the voltage at the"3;45 kv bus and the loads on the safety-related busses were as measured during the verification test conducted at Point Beach Unit 1 on'ziovember 7, 1979.

The results of these calculations along with the corresponding i voltage values measured during this test are given below:

Bus Calculated Voltage MeasuredlVoltage 345 kv 354.5 kv* 354.5 kv 13.8 kv 13.836 kv 13.5 kv 1A03 4,143 v 4,140 v 1A04 4,145 v 4,140 v 1A05 4,142 v 4,150 y ,~

1A06 4,144 v 4,150 v l 1B03 468.9 v 460 v 1B04 473.4 v 470 v

• Assumed Od 8209150262 820910 PDR ADOCK 05000266 P PDR

a Mr. H. R. Denton September 10, 1982 The loads on transformers IX03 and 1X04 during these tests were approximately 60% of the transformer rating. We believe this verification test satisfies the additional verification test requirements provided with your information request except in the following areas:

1. Neither bus loading nor voltages were recorded on the 120 v safeguards busses; however, we note that the voltage on these busses is not affected by low voltage on the 480 v system. Also, control power for operation of the 480 v motor controllers is derived from a 480 v to 120 v control transformer in the motor controller itself. This voltage, therefore, varies as the 480 v bus voltage. As stated in our June 1, 1981 letter, the contactors will pick up at voltage levels down to 72.5% of 120 v, and contactors will not drop out if the voltage is maintained above 52.5% of 120 v. Control power for the 4160 v breakers is derived from the 120 v system.

2. The voltage and current measurements made during the 1979 test were taken from readings from the control board indicator instruments. The scale on these meters is such that the c' id difference between calculated and observed volt _s within the interpolation error resulting from reauing these instruments.

3. The test was performed on Unit 1 only, but because of the similarity in equipment, ratings, impedances, and other factors, we believe the results are indicative of the results which would be obtained in Unit 2 testing.

The second item contained in your information request ask'ed for an analysis showing that all Class lE equipment will be operated,within rated limits under the conditions of minimum grid voltage and maximum load, assuming the additional consideration of the inoperability of one low voltage transformer, given an accident-in one unit and an orderly shutdown of the second unit.

~

As. indicated during the July 16, 1982 conference call, we consider thi's' set of circumstances to be extremely unlikely. We would further point out that in accordance with the Point Beach Technical Specifications, item 15.3.7.B.l.c, if one of the 13.8/4.16 kv auxiliary transformers is lost, the reactor associated with the out-of-service transformer must be placed in hot shutdown. Thus, the conditions specified in your information request, as unlikely i

t

\

\i '

s  : ,

s 7 '

s N

-n -

i, , ,,

/ ,  ; .. o , ,

, , , ./ I 4

e Mr. H. R. Denton September 10, 1982

~

i i

as they may;be, would not persist for any significant period of time, since 9hutdown of one of the two operating reactors would be require &;. Nonetheless, a calculation was made assuming these conditions'(lowest grid voltage of 345 kv x 0.98). The 4 kv sa2eguards bus voltage would be approximately 3,714 v (92.8% of the 4,000 v motor rating). The corresponding lowest 480 v safe-guards equipment terminal voltage would be approximately 405 v (88% of the 460 v motor rating) if this condition persisted.

However, at the proposed degraded grid voltage relay settings of 3,872 v, the degraded grid voltage relays would operate and the safeguards loads would be transferred to the diesel generators. .

The final item from your letter concerned the physical proximity of the 1X04 and 2X04 transformers. Under existing conditions,.it is possible that a fire or similar accident in one transformer could conceivably have an effect on the other trans-former. We are presently evaluating the consequences of this potential occarrence and have under consideration a number of modifications, including placement of physical barriers or fire stops between these transformers. Our evaluation in this matter should be compJeded by November 1, 1982. At that time, we will notify you of our conclusions and propose, if necessary, modifications to be' desirable, including a schedule for completion of these changes. i Very truly yours, 7

/

, Assistant Vice President C. W. Fay Copy to NRC Resident Inspector 6