ML13333A460
| ML13333A460 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/26/1979 |
| From: | Haynes J Southern California Edison Co |
| To: | Harold Denton, Ziemann D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8001030779 | |
| Download: ML13333A460 (7) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 December 26, 1979 Director of Nuclear Reactor Regulation Attention:
Mr. D. L. Ziemann, Chief Operating Reactors Branch #2 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Loss of Offsite Power Events San Onofre Nuclear Generating Station Unit 1 Your letter of September 25, 1979, requested information concerning total and partial loss of offsite power events at San Onofre Nuclear Generating Station, Unit 1. That information is contained in the enclosure to this letter.
If you have any questions, please let me know.
Ve'ry truly yours, J. G. Haynes Chief of Nuclear Engineering Enclosure 8001030
ENCLOSURE REQUEST FOR ADDITIONAL INFORMATION LOSS OF OFFSITE POWER A. For losses of offsite power where less than all offsite power was lost:
- 1. How many circuits to the offsite network are normally available and how many were lost during the event?
There are normally seven transmission lines to San Onofre Unit 1 available for service.
These are:
3 -
138 kV lines from SDG&E 1 -
220 kV line from SDG&E 3 -
220 kV lines from SCE The number of lines lost during each event is listed in Table I, Summary of Partial Loss-of-Offsite Power Events.
- 2. What was the cause of the event?
The cause of each event is included in Table I.
- 3. Why did the other lines not fail when some did fail?
The lines are electrically independent (except at the switchyard).
Failure of one line would not cause the loss of any other line.
However, some of the lines share some common transmission line towers, so that the failure of a tower could cause the loss of more than one line.
In addition, natural phenomena, such as storms and brush fires, have caused loss of more than one line.
- 4. Was any voltage increase or decrease experienced just prior to or during the outage? If so, please give details, voltages reached, affects, etc.
Oscillograph traces of 220 kV and 138 kV bus voltages and frequency are initiated on under-voltage on the station 4 kV buses and oscillograph operation is logged by the station operator. The set point is 3500 volts on the primary or 100 volts on the secondary. Oscillograph traces are kept for approximately one year so that the absence of an oscillograph trace, alone, is not sufficient to conclude that system voltage has not dropped low enough to initiate oscillograph operation.
Oscillograph traces do not exist for the two events during the past 12 months, therefore it is concluded that voltage was not low enough during those events to initiate the oscillograph. We will review the operator's logs to determine whether any of the previous partial losses of offsite power resulted in oscillograph operation. Results of this review will be forwarded to the NRC within approximately 30 days.
-2
- 5.
Was any frequency decay experienced just prior to or during the outage?
If so, please give details, lowest frequency reached, decay rate, affects on equipment operation, etc.
As discussed in response to question A.4. above, there are no oscillograph records for the events listed in Table I. The oscillo graph records system frequency but is not initiated on under frequency at this time.
(Following the change-over to the Units 2 and 3 switchyard, oscillograph traces will be initiated by under frequency as well as under voltage).
Experience has shown that grid frequency is affected by large losses of generating capacity, and not by events similar to those listed in Table I.
- 6. How long was power unavailable from the circuit?
This information is included in Table I.
- 7. Date of Event.
This information is included in Table I.
B. For losses of all offsite power:
- 1. How long was the power off?
How long for partial recovery? Please give details.
San Onofre Unit 1 has experienced one total loss of offsite power.
That event occurred on June 6, 1973, while the plant was shutdown for refueling.
Details of this event are included in a letter from R. N. Coe (SCE) to the Deputy Director of Reactor Projects, dated July 6, 1973.
Power was completely restored in 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 59 minutes.
- 2. If turbine trip occurred, how soon after did loss of offsite power occur?
The turbine/generator was not on line at the time of the event.
- 3. If power was recovered promptly (10 minutes or less), was it due to automatic or manual actions?
Not applicable to this event.
- 4.
Was any voltage increase or decrease experienced just prior to or during the outage?
If so, please give details, voltages reached, affects, etc.
As discussed above in B.1., the total loss of offsite power event occurred while the unit was shutdown for refueling. The event was initiated when the station's normal source of offsite power ("C" auxiliary transformer) was cleared for work and the alternate offsite
-3 power source (the main transformer and auxiliary transformers "A"l and "B") tripped from operation of the unit differential relay. The cause of the differential relay operation was determined to be an inadvertent grounding at a terminal block of the main generator current transformer leads between the differential relay and the test switch. Therefore, because 1) the unit was not operating, and 2) the cause of the loss-of offsite power event was at the station as opposed to on the system grid there was no change in grid frequency or voltage prior to the event and no detectable changes during the event.
- 5. Was any frequency decay experienced just prior to or during the outage?
If so, please give details, lowest frequency reached, decay rate, affects on equipment operation, etc.
See response to B.4. above.
- 6. Date of Event.
June 6, 1973 C. Were there any other losses of offsite power events other than we have listed? If so, please give details of each event.
No, there has been only one such event.
Table I Summary of Partial Loss-of-Offsite Power Events San Onofre Nuclear Generating Station, Unit 1 Date Line*
Duration(min.)
Cause 1-20-68 San Mateo 28 Unknown 3-25-68 San Luis Rey 17 Switching error 4-2-68 San Mateo 12 Unknown 6-11-68 Chino 2
Line tripped or relayed at one terminal only 6-13-68 Villa Park 8
Switching error 1-6-69 Chino 133 Unknown 2-6-69 San Luis Rey 433 Wind storm 2-24-69 San Mateo 1200 Wind blew pole over Villa Park 1200 Chino 389 8-22-69 San Luis Rey 2
Fire under line 1-12-70 San Mateo 1
Accidental tripping of OCBs.
5-19-70 Chino 37 Tripped to remove object 12-21-70 Capistrano 2
Wind storm 6-22-71 Santiago 2
Incorrect relay operation 6-22-71 Chino 5
Contractor shorted line 9-15-71 Chino 3
Incorrect relay operation 10-31-71 Mission 448 Tie point relay operation 1-15-72 Mission 465 Hardware failure 5-25-72 Chino 19 Accidental Trip-out
-2 8-9-72 San Luis Rey 425 Contractor shorted line 8-12-72 San Luis Rey 56 Incorrect relay setting 8-12-72 Capistrano Momentary Load unbalance 8-12-72 Mission 78 Lightning 4-1-73 Santiago 5
Incorrect relay operation 8-6-73 San Luis Rey 30 Unknown 8-15-73 Capistrano 11 Fault during hot wash 8-16-73 San Mateo 27 Crane contacted line 9-17-73 Chino 5
Insulator flash over 11-29-73 Mission 8
Trouble off system 2-23-74 Capistrano 8
Unknown 4-15-74 Mission 2
Unknown 11-7-74 San Mateo 301 Pot head failure 2-15-75 Capistrano 333 Hardware failure 4-23-75 San Luis Rey 8
Foreign object in line 8-12-75 Capistrano 4
Unknown 9-23-75 Mission 67 Fire under line 9-24-75 Mission 5
Unknown 1-21-76 San Mateo 127 Fire under lines Capistrano 177 Santiago 265 Chino 20 1-30-76 Capistrano 131 Conductor failure 3-31-76 San Mateo 1
Fault during hot wash 9-24-76 Chino 2
Lightning
-3 5-12-77 Capistrano 255 Connector failure 7-23-77 Capistrano 3
Lightning 11-29-77 Mission Momentary Fire under line 3-8-78 Mission 150 (approx.)
Sustained three phase fault at switchyard of another plant 5-22-78 Villa Park 9
Unknown 5-28-78 Capistrano 18 Substation trouble 6-4-78 Villa Park 0.5 Accidental Trip-out 6-15-78 Mission Momentary Unknown 6-17-78 Villa Park 10 Unknown 12-19-78 Chino 4
Lightning 9-15-79 Mission 134 Fire under line Line designations San Mateo 138KV SDG&E San Luis Rey 138KV SDG&E Capistrano 138KV SDG&E Mission 220KV SDG&E Villa Park 220KV SCE Chino 220KV SCE Santiago 220KV SCE