ML13317A788
| ML13317A788 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/16/1981 |
| From: | Baskin K Southern California Edison Co |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8112210228 | |
| Download: ML13317A788 (7) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 K. P. BASKIN TELEPHONE MANAGER OF NUCLEAR ENGINEERING, December 16, 1981 (213) 572.1401 SAFETY, AND LICENSING Director, Office of Nuclear Reactor Regulation Attention: D. M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Gentlemen:
Subject:
Degraded Grid Voltage and Adequacy of Station Electrical Distribution System Voltages San Onofre Nuclear Generating Station Unit 1 In connection with the NRC staff's review of the subject generic issues, additional information was requested in a telephone conversation on September 22, 1981. Part of the requested information was provided in a telephone conversation with the staff on November 18, 1981.
The enclosure to this letter documents the information provided in that conversation.
If you have any additional questions on this information, please let me know.
Very truly yours, Enclosure 8112210226 911
'.T6 PDR ADOCK 05000206i P
PDR>
Enclosure Response to NRC Questions Concerning Degraded Grid Voltage San Onofre Unit 1
References:
- 1. Letter from W. C. Moody to D. M. Crutchfield, dated August 19, 1981
- 2.
Westinghouse I.L.41-201 H Type CV Relay Instructions Item 1 Following operator action to restore voltage to the Class IE buses, is the undervoltage protection scheme reset to its normal condition automatically?
Response
All undervoltage/degraded voltage relays are automatically reset following operator action to restore voltage to the 4-kV and the 480-V buses.
The CV-6 relays are reset after 32.5 seconds and the CV-7 relays are reset after 5.7 seconds, as indicated in Reference 2.
Item 2 Verify and identify any Class 1E loads supplied by stepdown transformers off of the 480-volt buses (i.e., 208V, 220V, or 230V).
Response
With the exception of non-safety related loads such as small fans or appliances there are no motors supplied by stepdown transformers off the 480 Volt source. The 208, 220, and 230-Volt values shown for some motors in Table 1 of Reference 1 (i.e., 208/220/440, 220/440, or 230/460), are only nameplate information.
They indicate that connections are available to operate these motors at voltages other than 440 or 460 volts.
Item 3 What is the time delay associated with the voltage setpoint in response to Items 1&2 of SCE's August 19, 1981 letter?
Response
The time delay of the CV-7 and CV-6 relays depend on the voltage as indicated by the time curves of the relays. The time curve of each relay is determined by the relay time dial setting, tap value voltage and potential transformer ratio (PT ratio).
The time curves for relays CV-6 and CV-7 on the 4,160-V buses, a nd relays CV-7 on the 480-V buses are shown in Figures 1, 2, and 3.
These figures are derived from the manufacturer's instruction manual (Reference 2).
-2 As examples, as shown by these figures, the following time delays can be taken from the curves:
Undervoltage Relay:
CV-6 CV-7 CV-7 Bus (Volt) 4,160 4,160 480 Time Dial Setting 2.45 1.2 7
Tap Value Voltage (Volts) 105 82 105 PT Ratio 4,200/120 4,200/120 480/120 Percent of Tap Value Voltage 80%
75%
75%
Bus Voltage (Volt) 2,940 (+3%)
2,152 (+3%)
315 (+3%)
(% of Rating) 71% (of 4,160) 52% (of 4,160) 68% (of 460)
Time Delay (second) 34 (+5%)
2.1 (+5%)
14.5 (+5%)
0% of Tap Value Voltage Bus Voltage (Volt) 0 0
0 Time Delay (second) 11.6 1.0 6.8 Item 4 What are the voltage setpoint and associated time delay of CV-7 relays on the 480-volt buses? Also what is the function of these relays?
Response
The voltage setpoint and time delay of the CV-7 relays on the 480 volt buses are provided in the response to item 3 above. The function of these relays is to protect the equipment on these buses in the event of a fault or undervoltage condition and to automatically start redundant loads on the other bus.
Specifically, in the event of an undervoltage condition on No. 1 480-V switchgear, the CV-7 relays (through auxiliary relays 27-IXI, 27-1X2, and 27-1X3) will trip and lock out the breakers of the following loads:
Screen Wash Pump A Condenser Vacuum Pump A Residual Heat Removal A Component Cooling Pump A Fire Pump A Pressurizer Group A Pressurizer Group C Recirculation Pump A Salt Water Cooling Pump A
-3 In addition, if the control switches are on AUTO, the CV-7 relays will automatically start the following standby loads if they are not operating:
Screen Wash Pump B Component Cooling Water Pumps B and C Salt Water Cooling Pump B For an undervoltage condition on No. 2 480-V switchgear, the CV-7 relays perform the same functions for the Train B loads served by No. 2 480-V switchgear. This information is shown on the following San Onofre Unit 1 drawings which are enclosed:
5146828-2 Main One Line Diagram 5148062-3 One Line Diagram 480 V Switchgear No. 1 5148063-3 One Line Diagram
.480 V Switchgears No. 2 and 3 5150885-6 Elementary Diagram 480 V Switchgears Buses 1, 2, and 3 Undervoltage Relays 5149927-1 Elementary Diagram Screen Wash Pump G43 and G43S 5150333-2 Elementary Diagram Condenser Vacuum Pumps 5150336-4 Elementary Diagram Residual Heat Removal Pumps 5149971-3 Elementary Diagram Component Cooling Water Pumps 5150349-2 Elementry Diagram Fire Pumps 5150338-2 Elementary Diagram Pressurizer Heaters Groups A and B ACB's (Control Group) 5150339-3 Elementary Diagram Pressurizer Heaters Groups C and D ACB's (Backup Group) 5149919-3 Elementary Diagram Salt Water Cooling Pumps G13A and B N-1542 Sh.
1 Elementary Diagram Recirculation Pumps Rev. 9 JLR:2927
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