PLA-1735, RO Re Failure of Startup Transformer T10.Cause Under Investigation.Transformer Will Be Disassembled for Repair at Which Time Evaluation of Failure Will Be Conducted. Transformer W/Automatic Tap Changer Will Be Installed
| ML20076J646 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 06/30/1983 |
| From: | Kenyon B PENNSYLVANIA POWER & LIGHT CO. |
| To: | Allan J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| PLA-1735, NUDOCS 8307060069 | |
| Download: ML20076J646 (3) | |
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PP&L Pennsylvania Power & Light Company Two North Ninth Street
- Allentown, PA 18101 + 215 / 7705151 Bruce D. Kenyon Vice President-Nuclear Operations 215/770-7502 JUN 3 01983 Mr. J. M. Allan Acting Regional Administrator, Region I U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406 SUSQUEHANNA STEAM ELECTRIC STATION STARTUP TRANSFORMER REPAIRS ER 100450 FILE 841-4 PLA-1735 Docket No. 50-387
Dear Mr. Allan:
This letter is provided to confirm and document the information provided to Region I and NRR representatives in a phone conference on June 28, 1983.
Startup Transformer T10 at Susquehanna has failed in service. The exact nature of the fault has yet to be determined.
It is our expectation that a complete evaluation cannot be made until the transformer is disassembled for repair.
We will provide a report on the failure when the evaluation is complete.
Our best estimate is that repair will take 3 months.
PP&L is replacing the failed startup transformer, which has automatic load tap changers, with a transformer having a manual tap changer. The replacement transformer was removed from this application when PL established a need for automatic load tap changing in order to maintain Emergency Safeguards System voltage levels during supply system (grid) voltage fluctuations. All other capabilities of the Emergency Safeguards System are retained including all interlocks, indications, alarms, protective features, and backup on-site diesel generators, except as discussed below.
The plant electrical system, with the replacement transformer installed, meets the design criteria for non-LOCA response under all system operating voltage conditions. To assure adequate starting and operating voltages for LOCA loads, PP&L will supply the replacement startup transformer by a radial feed from the switchyard at our Montour Steam Electric Station, which has two units. This will be accomplished by operating with the ^ circuit breaker open at the remote end of the Montour-Mountain Line (Mountain substation). We will maintain the required voltage by automatic voltage regulation at Montour where operation of either unit is sufficient to assure the necessary voltage at Susquehanna.
B307ih60069 B30630 PDR ADOCK 05000387 O
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Page 2 SSES PLA-1735 JUN 3 01983 ER 100450 File 841-4 Mr. J. M. Allan The Susquehanna Emergency Safeguards System is protected against low supply voltage by a Degraded Grid Protection System which automatically transfers the busses to the emergency diesel generator if necessary.
This system was installed to assure that ESS equipment receives sufficient voltage to start under degraded voltage conditions on the offsite supply system.
If neither Montour unit is operating we will consider that we have only one source of offsite power and will thus enter the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> LCO which requires restoration of the offsite power source or shutdown. Based on past experience we anticipate this to occur once in six months. Procedures will be in place for both the Montour plant operators and the Power System Dispatcher to notify the Susquehanna plant if both Montour units trip off the line.
We have investigated all failure modes and concluded that all functions will occur normally with the replacement transformer installed, except for the following:
1.
If the offsite power source through startup transformer T20 is out of service, all offsite power to the ESS busses flows through ESS Trans-former 101. Plant operators will realign the plant electrical system to restore ESS transformer 201 to service.
Until the realignment is completed, we will be in a 24-hour LCO and then a 72-hour LCO until transformer T20 is restored.
2.
If ESS Transformer 201 is out of service, all offsite power to the ESS busses flows through Startup Transformer 10 and ESS Transformer 101.
Plant operators will realign the plant electrical system so that offsite power flows into the plant through Startup Transformer #20 and through the 13KV tie breaker and ESS Transformer 101. Until the realignment is completed we will be in a 24-hour LCO, and then a 72-hour LCO until ESS Transformer 201 is restored.
During the time required for these realignments, adequate starting voltage is assured by the Degraded Grid Protection System mentioned above. Appropriate plant procedures will be reviewed to identify any necessary changes.
To assure the operability of the replacement startup transformer, a series of tests will be performed.
Prior to energization, the transformer will be subjected to a number of integrity tests including Meggar, insulation power factor (Doble), transformer excitation, and transformer turns ratio tests.
To verify the transformer performance as modeled in voltage studies we will conduct an open circuit voltage test and a power test at a load greater than 30% of nameplate.
F Page 3 SSES PLA-1735 JUN 3 01983 ER 100450 File 841-4 Mr. J. M. Allan The above evaluation is based on supplying only Unit 1 ESS loads during a LOCA. Existing equipment will automatically shed any Unit 2 ESS loads on a Unit 1 LOCA signal assuring the validity of this evaluation. A startup transformer with automatic tap changer will be re-installed before Unit 2 fuel loading.
Our current plans are to complete the installation and testing of the manual tap changer transformer by June 30, with the plant returned to service by July 3.
If you require any additional information, please call.
Ve truly yours, BIbD.'Kenyo
' Vice President-Nuclear Operations cc:
G. Rhoads - USNRC R. Perch - USNRC 1
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