ML19260C539

Forwards Addl Info Re Total Loss of Offsite Power on 780728 & Partial Power Outages on 770511,1117 & 761212,in Response to NRC 791001 Request

ML19260C539
Person / Time
Site:	Beaver Valley
Issue date:	01/02/1980
From:	Dunn C DUQUESNE LIGHT CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
TAC-13110, NUDOCS 8001070380
Download: ML19260C539 (6)

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(412) 456 6000 435 S stM avenue geva a s January 2,1980 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Attention: Mr. A. Schwencer, Chief Operating Reactors Branch No. 1 Division of Operating Reactors Washington, D. C. 20555 Gentlemen:

In response to your letter dated October 1, 1979, concerning the loss of offsite power events at Beaver Valley Power Station, the attached reply addresses the one total and two partial power outages detailed in your letter. One additional partial power outage occurred at Beaver Valley Power Station and it is also addressed in the attached reply.

If you have any questions concerning this response, please contact my office.

Very truly yours, C. N. Dunn Vice President, Operations h oIS' s

1696 108 ih soot ovo 3FO _S

DUQUESNE LIGHT COMPANY Beaver Valley Power Station Unit No. 1 Loss of Offsite Power Events (May 11, 1977 incident)

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?

Two circuits are normally available to the offsite network via the 1A and 1B Syr> tem Station Service Transformers. One circuit through the IB transformer was lost during the event.

2. What was the cause of the event?

The cause of the event was a switching error at another Duquesne Light Company power station. Fuses were pulled in a circuit that feeds the No. 2 138KV bus. This caused the primary and secondary pilot wire trips to operate.

3. Why did the other lines not fail when some did fail?

Only the IB circuit was lost because the switching error affected only the No. 2 138KV bus. There was no system fault that would affect both circuits.

4. Was any voltage increase or decrease experienced just prior to or during the outage?

No voltage transient was experienced just prior to or during the outage.

5. Was any f requency decay experienced just prior to or during the outage?

No f requency decay was experienced just prior to or during the outage.

6. How long was power unavailable from the circuit?

Normal power was restored to the No. 2 138KV bus in 55 minutes.

7. Date of Event.

May 11, 1979 1696 109

Loss of Offsite Power Events (November 17, 1977 event)

A. For losses of offsite power where less than all of fsite power was lost:

1. How many circuits to the offsite network are normally available and how many were lost during the event?

Two circuits are normally available to the offsite network via the 1A and 1B System Station Service Transformers. One circuit through the 1A transformer was lost during the event.

2. What was the cause of the event?

The cause of the event was the suspected f aulty operatica of a Bus Line Backup Timer causing a lA Sy stem Station Service Trans-former pilot wire trip. At the time of the faulty operation of the timer, a traveling operator was performing switching operations on the No. 3 345KV bus. The timer relay was tested immediately af ter the f aulty operation and functioned correct 7y. The switching operation was rerun eight days later but the faulty operation could not be repeated. The timer relay was subsequently replaced.

3. Why did the other lines not fail when some did fail?

Only the 1A circuit was lost because the faulty relay provided protection to the No. 1 138KV bus. There was no system fault that would affect both circuits.

4. Was any voltage increase or decrease experienced just prior to or during the outage?

No voltage transient was experienced just prior to or during the outage.

5. Was any frecuency decay experienced just prior to or during the outage?

No frequency decay was experienced just prior to or during the outage.

6. How long was power unavailable from the circuit?

Normal power was restored to the No. 1 138KV bus in 59 minutes.

7. Date of Event November 17, 1977 1696 110

Loss of Offsite Power Events (December 12, 1976 event)

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?

Two circuits to the of fsite network are normally available via the 1A and 1B System Station Service Transformers. One circuit through the 1A transformer was lost during the event.

2. What was the cause of the event?

The cause of the event was the suspected faulty operation of a Bus Line Backup Timer causing a 1A System Station Service Trans-former pilot wire trip. The relay was tested after the event and it functicned correctly.

3. Why did the other lines not fail when some did fail?

Only the 1A circuit was lost because the faulty relay provided protection to the No. 1 138KV bus. There was no system fault that would affect both circuits.

4. Was any voltage increase or decrease experienced just prior to or during the outage?

No voltage transient was experienced just prior to or during the outage.

5. Was any frequency decay experienced just prior to or during the outage?

No frequency decay was experienced just prior to or during the outage.

6. How long was power unavailable from the circuit?

Normal power was restored to the No. 1 138KV bus in 38 minutes.

7. Date of the Event December 12, 1976 1696 iiI

o Loss of Offsite Power Events (July 28, 1978 event)

B. For losses of all offsite power:

1. How long was power off? How long for partial recovery?

All offsite power was lost for seventeen minutes. One emergency diesel generator began supplying one emergency bus in approximately ten seconds. Power became available to the other emergency bus in approximately fifteen minutes. Details of the event are as follows:

At 1536 hours0.0178 days <br />0.427 hours <br />0.00254 weeks <br />5.84448e-4 months <br />, a short circuit between the 345KV high voltage winding and the 21.5KV low voltage winding of the main transformer occurred. The high voltage impressed un the low voltage side of the ,

transformer resulted in a ground from insulation failure of the A phase low voltage termination within the main transformer and a simultaneous failure of the B phase surge arrestor within the Main Generc. tor Potential Transformer Compartment. The simultaneous occurrence of these two grounds applied a single phase short circuit across the main transformer A phase low voltage winding and the main generator A to B phase leads. The station service buses successfully transferred to the offsite sources (The No. 1 and No. 2 bus sections in the 138KV Shippingport Power Station switchyard). Fifteen seconds later as the Beaver Valley Turbine Generator coasted down, while still supplying fault current to the short circuit, the Main Generator Out of Step relays operated. The faulty out of step relay operation caused an isolation of the Beaver Valley 345KV Switchyard by tripping all 345KV line breakers and the tie to the 138KV autotransformer. In addition, three of the five 138KV breakers in the 138KV Shippingport Switchyard tripped. This action isolated the Shippingport Power Station as the only power source on the 138KV bus supplying power to the two remaining 138KV loads and the Beaver Valley Power Station System Transformers. This total load was in excess of the Shippingport Power Station ability to supply the load and the frequency declined to approximately 58 Hertz.

After attempting to reduce the output of the Shippingport Power Station for over three minutes, the Shippingport unit was tripped from the line at 1540 hours0.0178 days <br />0.428 hours <br />0.00255 weeks <br />5.8597e-4 months <br />. This removed the only source of power from both 138KV bus sections and resulted in a loss of offsite power at Beaver Valley.

Offsite power was restored to Beaver Valley 17 minutes later.

2. If turbine trip occurred, how soon after did loss of offsite power occur?

All offsite power was lost approximately four minutes after the turbine trip.

3. If power was recovered promptly (10 minutes or less), was it due to automatic or manual actions?

N/A 1696 112

4 #

4. Was any voltage increase or decrease experienced just prior to or during the outage?

We have no data indicating the extent, if any, of any voltage transient which may have occurred prior to or during the outage.

5. Was any frequency decay experienced just prior to or during the outage?

As discussed above, frequency decayed to approximately 58 Hz when Shippingport Power Station assumed all of the Beaver Valley load.

This caused all three reactor coolant pumps to trip on underfrequency relay operation. The frequency continued to decay until it reached approximately 55 Hz, at which time the Shippingport unit was manually tripped.

6. Date of D ent July 28,1978 1696 113