ML19312E139

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Forwards Response to NRC 800505 Ltr Re Loss of Offsite Power Events.One Partial Loss of Offsite Power Has Occurred as Described in LER 77-15 Dtd 770628.No Total Loss of Offsite Power Events Experienced
ML19312E139
Person / Time
Site: Three Mile Island Constellation icon.png
Issue date: 05/30/1980
From: Herbein J
METROPOLITAN EDISON CO.
To: Reid R
Office of Nuclear Reactor Regulation
References
TLL-242, NUDOCS 8006030335
Download: ML19312E139 (2)


Text

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Metropolitan Edison Company j q a Post Office Box 480

' Middletown, Pennsylvania 17057 717 944 4041 Wnter's Direct Dial Number May 30, 1980 TLL 242 Office of Nuclear Reactor Regulation Attn: R. W. Reid, Chief Operating Reactors Branch No. 4 U. S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Sir:

Three >111e Island Nuclear Station, Unit I (TMI-1)

Operating License No. DPR-50 Docket No. 50-289 Loss of Offsite Power Events Enclosed please find our response to your letter of May 5,1980. Please note that there have been no total loss of offsite power events at TMI-I. One partial loss of offsite power has been experienced as described in TMI-I Licensee Event Report 77-15 dated June 28, 1977. I Sincerely, o

/

.usO

~-

J. G. Herbein Vice President TMI-I e

JCH: Lk"d: hah Enclosure cc: J. T. Collins B. J. Snyder

/

S\g on Corrpany .s a Memoer cf tre Genera! Puti+c Ut: .t es System 8 0 0 6 0 3itt 03.Metroochtan E)s

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  • 3 Enclosure 1 TLL 242 LOSS OF OFFSITE POWER SURVEY

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

1

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

, Response-Two station service auxiliary transformers are normally available.

One auxiliary transformer tripped during this event.

I 2. What was the cause of the event?

l Response-The trip occurred due to a wiring error in the current transformer i circuit for the 230 KV bus differential circuit. The error caused the load on the TMI-II auxiliary transformer 2A to appear .as a fault on the bus.

l l

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

Response-The load on TMI-II transformer 2B was not sufficient to energize the bus

differential relay for the redundant circuit. (A similar error existed in the wiring for that circuit)
4. Was any voltage increase or decrease experienced just prior to or during the outage? If so, please give details, voltages reached,

{

affects, etc.

.i.

Response-The balance of plant buses transferred to the A transformer and the

] D 4KV ES bus was energized by the emergency diesel as designed. No

abnormal voltage conditions were experienced.

l i 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.

4 Response-No frequency decay was experienced.

1

6. How long was power unavailable from the circuit?

Response-The B transfermer was returned to cervice in approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.

7. Date of event.

Response-The date of~this event was May 29, 1977.

B. For losses of all offsite power:

Not applicable.

l