ML20002E376
| ML20002E376 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 01/21/1981 |
| From: | Fay C WISCONSIN ELECTRIC POWER CO. |
| To: | Clark R, Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| TAC-12955, TAC-12956, NUDOCS 8101270666 | |
| Download: ML20002E376 (6) | |
Text
{{#Wiki_filter:- Wisconsin Electnc powea courany 231 WEST MICHIGAN, MILWAUKEE, WISCONSIN 53201 January 21, 1981 Mr. Harold Denton, Director Office of Nuclear Reactor Regulation U. S. NUCLEAR REGULATORY COMMISSION Washington, D.C. 20555 Attention: Mr. Robert A. Clark, Chief Operating Reactor Branch #3 Gentlemen: DOCKET NOS. 50-266 AND 50-301 ADEQUACY OF STATION DISTRIBUTION SYSTEM VOLTAGES POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 Your letter of September 8,1980 requested additional information relating to the adequacy of the electrical distribution systems at Point Beach Nuclear Plant Units 1 and 2 (PBNP). This response provides additional clarification of the analysis attached to our October 12, 1979 letter on this same subject and provides the results of additional analyses. As shown on Attachment I, all safety-related loads at PBNP are supplied either from the 480 volt or the 4160 volt systems. Safety-related 480 volt loads are supplied either directly from two safety-related 480 volt busses in each unit (1-B03 and 1-804 or 2-803 and 2-B04) or from motor contrtl centers supplied from these busses. Each safety-related 480 volt bus is supplied from a 4160 volt safety-related bus through a dedicated 4160/480 volt transformer: 480 Volt Bus 4160 Volt Bus Transformer _ 1-B03 1-A05 1-X13 1-B04 1-A06 1-X14 2-B03 2-A05 2-X13 2-B04 2-A06 2-X14 All safety-related 4160 volt loads are connected to busses 1-A05 and 1-A06 for Unit #1 and 2-A05 and 2-A06 for Unit #2. The safety-related 4160 volt busses are in turn supplied by four additional 4160 volt switching busses. The switching busses are also connected to four 4160 volt busses which supply non-safety-related loads. Interconnection is according to the following table: y s // 8101270f,gg
Mr. Harold Denton January 21, 1981 l i Safety-Related Bus Switching Bus Non-Safety-Related Bus 1-A05 1-A03 1-A01 1-A06 1-A04 1-A02 i 2-A05 2-A03 2-A01 2-A06 2-A04 2-A02 The non-safety-related 4160 voit busses are supplied by the unit auxiliary transformers during normal power operation. When the unit aux-iliary is not available, the A01 and A02 supply is switched to the associated switching 'us. o Each of the 4160 volt switching busses is supplied from a separate secondary winding of the associated 13.8/4.16 KV low voltage station aux-iliary transformer according to the following table: 4160 Volt Switching Bus Low Voltage Station Aux. Transformer 1-A03 TR. 1 1-A04 TR. 1 2-A03 TR. 2 2-A04 TR. 2 Each of the 13.8/4.16 KV low voltage station auxiliary transformers is supplied from a 345/13.8 KV high voltage station transformer connected to the 345 KV bus. From the above description and Attachment I, it can oe seen that from the 345 KV bus to the safety-related loads the electrical distribution system for each unit is essentially a separate radial system. There is no automatic transfer of station auxiliary loads from one unit to the 4160 volt supply for the other unit or to common backup power sources. While inter-connections exist between the 13.8 KY and 4160 volt systems of each unit, these ties must be manually initiated. Technical specifications also preclude the operation of both units with the station auxiliaries of each unit being supplied from a single low voltage station auxiliary transformer or a single high voltage station transformer. Since each of the Point Beach units art supplied from the trans-mission grid by essentially separate and identica' distribution systems and the auxiliary electrical load in each unit is approximately the same, a worst case analysis for one unit would provide conservative results for the other unit. The worst case condition for either unit was analyzed and the results reported in our October 12, 1979 letter. The following comments address each of the points as contained in your September 8,1980 request for additional information. 1. a. Safety-related busses are not supplied from the unit auxiliary transformers. 6 .-m.,,
Mr. Harold Denton-January 21, 1981 b. The load path which was analyzed is as follows: 345 KV Bus Section 5 High Voltage Station Auxiliary Transformer #2 Low Voltage Station Auxiliary Transformer #2 4160 Volt Busses 2-A03 and 2-A04 Safety-Related 4160 Volt Busses 2-A05 and 2-A06 4160/480 Volt Transformers 2-X13 and 2-X14 480 Volt Safeguards Busses 2-B03 nd 2-B04 c. There are no other sources of offsite power. d. Loading assumptions for the case analyzed were provided in our October 12, 1979 letter. 2. A separate analysis was not performed for Unit #1. As stated above, the analysis for Unit #2 provides conservative results for Unit #1. 3. The analysis attached to our October 12, 1979 letter was based on the application of all automatically applied safety-related loads and the transfer of all non-safety-related 4160 volt busses in Unit #2 from the unit auxiliary transformer to the Unit #2 low voltage station auxiliary transformer. All large non-safety-related loads were assumed to be running and to remain running after the accident. If large non-safety-related loads had not been running, they would not automatically be started. 4. No manual load shedding was assumed for the case presented in our October 12, 1979 letter. 5. The maximum credible load was assumed for the case presented. Assumptions are contained in our October 12, 1979 letter and herein. 6. The minimum expected value of grid voltcGe is based on system load flow studies with assumptions as stated in our October 12, 1979 letter. The minimum voltage for any load supplied from each of the safety-related busses is as tabulated below.
- 1-A05 93.8%
2-A05 93.8%
- 1-A06 93.8%
2-A06 93.8%
- 1-803 85.8%
2-803 85.8%
- 1-B04 85.8%
2-804 85.8%
- Since cable sizes and lengths from the supplying bus to the loads are not always identical, the maximum voltage for Unit #1 safety-related loads was calculated assuming bus voltages as determined i
for Unit #2 and actual Unit #1 connection configurations. l l
Mr. Harold Denton January 21, 1981 i 7. As described in an attachment to our September 17, 1976 letter to Mr. George Lear, a voltage on the 345 KV bus of 350 KV or lower is alarmed both in the plant control room and at the System Control Center. The Power Supply Supervisor then will perform necessary switching operations or generation adjustments to restore the voltage level on the 345_ KV bus to its normal level. In addition, voltage levels on the 345 KV bus which would result in voltages below the equipment rating of safety-related loads would result in the transfer of safety-related loads to backup onsite power sources. 8. These values were provided for the case analyzed in the Attachment to our October 12, 1979 letter and will be repeated here. 345 KV Bus Section 5 345.69 KV 100.2% High Voltage Station Auxiliary Transformer #2 (High Side) 345.69 KV 100.2% (Low Side) 12.82 KV 92.9% 13.8 KV Bus H06 12.82 KV 92.9% Low Voltage Station Auxiliary Transformer #2 (HighSide) 12.82 KV 92.9% (Low Side) 3.906 KV 93.9% 4160 Volt Busses 2-A05 & 2-AC5 3.906 KV 93.9% 4160/480 Volt Transformers 2-X13 and 2-X14 (2-X13 High Side) 3.906 KV 93.9% (2-X13 Low Side) 430 Volts 90.0% (2-X14 High Side) 3.906 KV 93.9% (2-X14 Low Side) 431 Volts 90.0% 480 Volt Busses 2-B03 430 Volts 90.0% 2-804 431 Volts 90.0% 9. Safety-related motors supplied by the 480 volt busses are rated at 460 volts +10% -20% and would have no difficulty running at the voltages determined by this analysis. A separate test of the voltage required to pick-up and cause drop-out of the motor starters was conducted. Minimum pick-up voltage was found to be 85 volts (340 volts on 480 volt system). Maximum drop-out voltage was found to be 62 volts (248 volts on 480 volt system).
- 10. An Attachment to our letter of July 28, 1977 requesting Technical Specification Change #45 contains a description of the multi-layered under-voltage protection scheme at Point Beach. The first layer of this scheme, which separates 4160 volt safety-related busses from offsite power, is intended to protect against degraded
.Mr. Harold Denton January 21, 1981 grid voltage. All lower levels of undervoltage protection are essentially loss of voltage protection and have voltage settings much lower than those determined as being possible by this analysis. The location of the relays which provide this first layer of pro-tection, their interconnection logic, and the voltage settings have been changed several times since the original request for Technical Specification Change #45 was submitted. The present proposed arrangement is described in our letter of September 22, 1980. As indicated in the tables attached to the September 22, 1980 letter, the relays intended to provide degraded grid voltage protection are to be set at 3675!2% volts. This relay setting is conservatively below the 3906 volts determined as being possible by this analysis. Unwanted separation of safety-related loads from offsite power due to degraded grid voltage is, therefore, highly unlikely. Technical Specification Change Request #45 is still pending. The present setting of the relays which provide degraded grid voltage protection is 3255 volts !3%, which is again conservatively below the 3906 volts determined as being possible by this analysis.
- 13. Assumptions made for this analysis are as stated in our October 12, 1979 letter as supplemented herein.
We trust that this additional information will allow you to complete your analysis of PBNP degraded grid voltage. Very truly yours, o C. W. Fay, Director Nuclear Power Department Attachment Copy to: NRC Resident Inspector Point Beach Nuclear Plant
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