ML20102A988
| ML20102A988 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 07/20/1992 |
| From: | Sieber J DUQUESNE LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9207280099 | |
| Download: ML20102A988 (3) | |
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f hver va ?ey Power Station SNppingport, PA 15077-000d (412) 39 1 5255 I
JOHN D. SCBER vice Preudent - Nuclear Group July 20, 1992 U.
S. Nuclear Regulatory Commission Attn:
Document Control Desk Washington, DC 20555-
Subject:
Boavar Valley Power Station, Unit No. 1 and No. 2 BV-1 Docket No. 50-334, Licenso No. DPR-66 BV-2 Docket No. 50-412, License No. NPF-73 Combir4ed Inspection Report 50-334/91-80 and 50-412/91-80 Electrical Distribution System Punctional Inspection Attached is a supplemental response to our previous' submittal of June 12, 1992, which provided a schedule for the resolution of the Unresolved Items resulting from the above referenced inspection.
This response is being provided as a result of a telephone conference on July 10, 1992 between Mr.
J.
E. Beall of USNRC Region I and Mr. Nelson R. Tonet of my staff on this subject.
It further clarifles the timing of our efforts to address the unresolved item
" Setting of Degraded Grid Relays."
If there are any questionn conct ning this response, please contact Mr. Nelson R. Tonet at (412) 393-5210.
Sincerely, h
Mb J.
D.
Sieber i
Attachment cc:
Mr.
L. W.
Rossbach, Sr. Resident Inspector Mr.
T.
T.
Martin, NRC Region I Administrator Mr. M.
W.
Hodges, Director, Division of Reactor Safety Mr.
A.
W.
DeAgazio, Project Manager Mr.
M.
L.
Bowling (VEPCO)
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DUQUESNE LIGHT COMPANY Nuclear Group Beaver Valley Power 3tation Units 1-and 2 Combined NRC Inspection 50-334/91-80 and 50-412/91-80 Electrical Distribution System Functional Inspection Supplemental Response for Unresolved Items Unresolved Item (50-334/91-80-04 and 50-412/91-80-04) - Setting of Degraded Grid Relays Description of Unresolved Itqm A review was performed of degraded grid relay settings and reset capability, coordination with_the EDG start and fast bus transfer schemes, and applicable schematics.- This review determined that the degra0.ed grid relays on the 4160 V and'480 V safety 1related buses were set at 90% +/-1.6% of their respective nominalEbus-voltage.
Therefore, the minimum theoretical voltages allowed on the switchgear and on the load center buses, before the appropriate automatic action takes place,-are 3677 V_and 424 V, respectively.
To ensure that the specified settings-adequately-protect the safety-related motors from undervoltage conditions,-the continuous ratings-of the motors were also surveyed.
A sampling of several14160 V and 480 V motors revealed 'a continuous _ rating of 90% of the nominal 7
(nameplate) voltage, i.e.,
3744 V and 414 V (460 V x 0.9),
respectively.
A comparison of the above values shows that, under degraded voltage conditions, the 4160 V motor-would be operating at a voltage below their minimum continuous rating and that a 10 V margin exiats for the 480 V motors.
In addition,.when the cable voltage drop from the bus to the. motors is.taken into consideration,'the voltage at the motors' terminale could be considerably less than the motors' continuous rating.
The 90% relay setting was verified through a review:of several Relay-Setting-Sheets and is in accordance with the-guidelines contained in BV-1 and BV-2's " Protective Relay Philosophy.and Practices for 4160 V and 480 V Systems", Engineering-Standard No. ES-E-004, Revision 0,
-dated September 11, 1989, and ES-E-003', Revision 0,' dated February-14, 1989, respectively.
The +/-1.6% tolerance was calculated-in a Westinghouse analysis of the relay loop.
The team discussed the concern with the licensee who pointed out that the settings were in agreement with Item 6 of Table 3.3-4aof BV-1 and BV-2's Technical Specification.
The licensee also indicated _that the-transformer tap settings kept the. bus voltage near the nominal values.
However, they uere unable tx) provide antanalysis.to show that the motors could be operated below their continuous rating-should a degraded voltage condition exist.
~The setting of the der aded grid relay 1 and/or the capability of the safety related moteru ?a operate below their continuous setting is unresolved pending appropriate analysis or justification by the licensee.
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- i Supplemental Response for' Unresolved Items 50-334/91-80-04 and 50-412/91-80-04 rage.2 4
gricinal Resronse Proposed' Resolution:
The current degraded grid relay setpoints;were established recognizing that equipment will operate below 90% of-nameplate voltage for periods of time with minimal impact on'the equipment and-j_
that corrective actions would be taken to improve degraded. grid conditions.
The electrical' grid in the BVPS~ area is-very strong and does not operate at degraded voltage conditions or normally experience voltage excursions of a magnitude to cause'3cw voltage concerns.
F The degraded grid relay setpoints;will'be addressed by the-upgrade of applicable electrical-calculations.- Pending completion-of this effort,'the;use of interim setpoints'willnbe investigated and-implemented,Eif appropriate.
Final.setpoint determination will be made after completion.of the necessary calculational-efforts.
Scheduled-Date:
50-334/91-80-04
_ Interim 1setpoints implemented
'Sthl refueling
. outage
' Final lsetpoints' implemented - 11th refueling outage 50-412/91-80 Interim setpoints implemented:- 4th refueling:
outage Final setpoints implemented - 5th refueling outage-J Supplemental Response The Nuclear-Engineering Department is.analyzingfthe--issuelof degraded o
grid relay setpoints-to establish a basis forDimplementing1 interim-setpoints, if_ deemed _ appropriate.
Any interim setpoints Will' bet sufficiently conservative.to' address the concerns of this Unresolved Item.
Following completion of wnt'ytical efforts to upgrade
- existing electrical calculationc, any..uterim setpoints-willibe readjusted.
accordingly.- The1 schedule to accomplish 1these setpoints is as stated.
in our June-12, 1992. submittal and as identified above (i.e.,
the;9th i
refueling' outage and the 4th refueling outage 1at Unit 1 and: Unit?2, i
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