ML18092B529
| ML18092B529 | |
| Person / Time | |
|---|---|
| Site: | Salem, Hope Creek, 05000000 |
| Issue date: | 04/10/1987 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML18092B528 | List: |
| References | |
| NUDOCS 8704240082 | |
| Download: ML18092B529 (6) | |
Text
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' Attachment 3.
SAFETY EVALUATION INCREASED POWER OPERATION OF SALEM/
HOPE CREEK UNITS DURING THE OUTAGE.
OF KEENEY 500 KV LINE The Salem/Hope Creek site has a total of four SOOKV offsite power transmission lines to carry the output from the three units at the site.
On March 1, 1987, due to an accident on the Delaware River, several towers supporting one of the four 500 KV lines (Keeney) were taken out of service {see Figure 1 attached).
As a result, this line will experi~nce an extensive outage estimated as one year.
Based on stability considerations for various system conditions, the licensee voluntarily reduced power to about 75% of full power output of all three units.
At this level, the design can sustain an additional loss of any critical line on the Salem/Hope Creek system without causing any of the three units to trip.
In a meeting on March 10, 1987, the licensee.proposed to increase power operation of Salem Units 1 & 2 and Hope Creek Unit 1 above 75% with only three transmission lines. Subsequently, ttie licensee under 10 CFR 50.59 submitted a safety evaluation report justif_yi ng operation of a 11 three units at increased power (above 75%) dur-ing the 500 KV Keeney line outage. The licensee has performed a stability analysis for the new system.configuration (all three units above 75% power and three exist-ing lines). The results of the stability analysis established that the critical line on the new configuration was.a fault on the Deans 500*Kv line at the Salem generating station. If this line for any reason is disconnected (i.e., line fault, operation error, etc.) while all three units are operating at increased power
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- . <. (above 75%) serious instability problems to all the three Salem/Hope Creek units could occur (tripping the three units). The analysis also indicated that output levels for three unit operation can be increased provided that Salem Unit l is automatically disconnected following any outage of the Deans 500 KV line. The automatic disconnection of Salem Unit 1 is called the "Trip-A-Unit" scheme.
The Trip-A-Unit scheme will be implemented for a fault on the Deans 500 KV line to initiate the existing Salem Unit 1 Generator Differential protection multi-
- trip circuitry and.the existing back up Salem Unit 1 Generator Differential pro-tection multitrip circuitry. Both multitrips will trip generator breakers lOX and 12X (see Figure 2 attached). Disconnect switches will be provided in the relay room to allow monitoring of the Trip-A-Unit from the control room and by the load dispatcher; and to permit the operator to disable it when required.
The regular and backup protection is fed from separate current and potential transformers.
- The control power for regular and backup protection is from dif-ferent 125 V DC batteries. Each tripping condition will activate both regular and backup scheMe separately.
In addition to the above, the Trip-A-Unit scheme will be operational only when all three Salem/Hope Creek units are operating above 75% power.
During lightning
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. and thunderstonn activity (when stonns arP. within 50 miles itS indicated by con-tracted weather services) the power output of Salem/Hope Creek will be manually reduced to 703 and the Trip-A-Unit scheme will be defeated. Moreover, no line maintenance and/or relay testing will he perfonned on the n.eans 500 KV line with the units at full power during the outage of t~e Keeney 500 KV line. If tests and/or maintenance are required, the power output will be reduced accordingly and the Trip-A-Unit scheme will be defeated.
The staff was concerned that tripping a unit on loss of a transmission line to avoid instability of the remaining operating units was unique and is not a stan-dard design practice *. The staff was also concerned that failure of the Trip-A-Unit scheme could i.ncrease the probability of loss of offsite power to all three un.:its.
At staTf's request, a meeting was held with the licensee on March ?.7, 1987 to fully understand the grid stability analysis and Trip-A-Unit scheme which will be utilized until the damaged Keeney 500 KV line is restored.
In the meeting the licensee assured the staff that even if all three Salem/Hope Creek units are lost
- (due to the failure of the Trip..;A-Unit scheme), the offsite power to safely shut-down all three units will be available from the remaininq two New Freedom lines.
The staTT concluded that although tripping a unit on loss of a transmission line is not consistent with general industry practice, it does not violate Gr>C 17 and the proposed design is acceptable. However, the staff will confirm certain as-pects of design through review of the formal submittal of the infonnation discussed in the meeting.
The licensee committed to revisP. its safP.ty evaluation report
- to include the following information requested by the staff:
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- 1.
Definiti.on of the power level restrictions for Salem/Hope Creek units during the outage of Keeney 500 KV line.
- 2.
Confirmation that failure of the Trip-A-Unit scheme will not result in Joss of offst~~ power to all Salem/Hope Creek units.
- 3.
A.clear distinction between unit(s) instability and grid instability.
- 4.
The results of an analysis that demonstrates that with all three units at 100% power and failure to trip Salem Unit 1, of~site power to Salem/Hope Creek Units will not be lost,_ and in addition, the'*resulting voltage profile at the safety-related buses for each unit in the event all Salem/Hope Creek units are lost.
- 5.
Definition of the conditions that require activation of the Trip-A-Unit scheme on loss of Deans 500 KV line.
Principal Contributor:
-o.
Chopra
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TO KEENEY IOPLJ BRANCHBURG HOPE CREEK LINOCN SALEM 8AUNSWICK SCWA,.!N
S... IT,.,8uRG CJ CI cox's co,.Nut VICINITY OF HOPE CREEK AND SALEM GENERA TING AND SWITCHING ST A Ttc~NS
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ARTIFICIAL ISLAND 5GJSKV POWER SYSTEM STABILITY SALEM - OEAliS LINE ---99 PROTECTIC8 REGU1..M
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