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PHILADELPHIA ELECTRIC COMPANY2301 MARKET STREET

P.O. BOX 8699

PHILADELPHIA. PA.19101

(215) 841 4502

S. J. KOWALSKIvics-PassIDENT

10CFR50.55Ce)uu............

Mr. W. T. Russell, AckninistratorU. S. Nuclear Regulatory Conmission Docket No. 50-353Attn: Document Control Clerk CPPR-107Mall Station P1-137 :

Washington, DC 20555 |

Subject: Limerick Generating Station - Unit 2Significant Deficiency Report - SDR No. L2-88-11Inadequate Degraded Grid UndervoltageRelay Setpoints

Reference: Interim Report for SDR No. L2-88-11, datedFebruary 7, 1989

Flie: QUAL 2-10-2 (SDR No. L2-88-11)

Dear Mr. Russell:

As conmitted to in the referenced Interim Report, we are submit-ting the attached Significant Deficiency Report SDR No. L2-88-11concerning inadequate degraded grid undervoltage relay setpoints.This condition has been determined to be reportable per 10CFR

Part 50.55Ce).

The cause of the condition was a cognitive personnel error by autility employed engineer who failed to properly follow Implementingprocedures. To prevent recurrence, the details of the event have beendiscussed with the engineer involved who now recognizes the need forstrict procedural adherence. In addition, new undervoltage relayswill be installed and transformer tap settings changed to providecompliance with the design basis. This work will be completed priorto Unit 2 Fuel Load.

mmk In conclusion, we consider SDR No. L2-88-11 closed with the0050 - Issuance of this report. If you have any further questions, please

go contact us.

Gog Sinc rely,/No ' / /"O

f4-g AttachmentGo

1"4M Copy to: W. T. Russell, USNRC, Region 1 AdministratorR. A. Granm, USNRC, LGS 2 Senior Resident InspectorR. J. Clark, USNRC, LGS 2 Project Manager , g

CBT/ds/03298904

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. - |Mr. W. T. Russa11, Administrator J

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Dockst No. 50-353, CPPR-107 j-...

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bec: C.'A. McNolli (S26-1) 3

S. , Kowalski (S25-1) ||'

E. J. Bradley (S23-1)L. B. Pyrih (N2-1)E. P. Fogarty (S7-1)D. R. Helwig (S7-1)G.-A. Hunger, Jr. (S7-1) jA. J. Marie (N2-1)H. D. Honan (N2-1)D. P. Helker (57-1)G. M. Leitch (LGS)d. S. Kemper (S25-1)P. J. Duca, Jr. (LGS)C. R. Endriss (LGS)d. M. Corcoran (LGS)R. M. Krich (N7-1)P. S. Thurman (N2-1).

R. J. Lees (N2-1)D. B. Fetters (N4-1)D. N. Sundt (N2-1)W. d. Boyer (N2-1)C. B. Tuttle (N2-1)W. J. M!ndick N2-1)DAC (NG-8)

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NUCLEAR ENGINEERINGENGINEERING DIVISION

N2-1, 2301 Market Street

Significant Deficiency ReportSDR No. LD-88-11

Inadequate Degraded Grid Undervoltage Relay SetpointsNRC Construction Pennit No. CPPR-107

Description of Deficiency:

The Linerick Final Safety Analysis Report (FSAR) Section 8.1.6.3.6,"BTP-PSB-1, Adequacy of Station Electric Distribution Systen Voltages,"cannits to compliance with NRC Branch Technical Position PSB-1," Adequacy of Station Electric Distribution System Voltages." Compliancewith the guidance provided in Branch Technical Position (BTP)-PSB-1required a protection schene which would maintain adequate voltagelevels to Class 1E equipment at all times. BTP-PSB-1 recognized theinadequacy of existing undervoltage protection schenes which typicallyprovided only a single level (i.e., a loss of power relay) ofundervoltage protection. BTP-PSB-1 states in part that a second level '

of undervoltage protection with a time delay is needed to protect theClass 1E equipme ,t under degraded power supply conditions which wouldnot actuate a loss of power relay typically set at 70% of nominal.However, as a result of the Unit 2 Independent Design and ConstructionAssessment (IDCA) being perfonned for Unit 2 and a parallel review ofGeneric Letter 88-15, " Electric Power Systens - Inadequate Control OverDesign Processes," the undervoltage relay setpoints on the Unit 14.16kVsafeguard buses were found to be too low to ensure adequate voltage tothe 480V Class 1E loads for all operating conditions.

With a degraded grid condition, adequate safeguard bus voltages naynot be assured with the existing protective relay setpoints. This couldoccur if an equipnent fallure (e.g., failure of the load tap changer)(LTC) resulted in degradation of the safeguard bus voltage to between90% and 95.7% of naninal (4160V). In this range, safeguard bus voltageis too low to ensure proper operation of the 480V Class 1E loads but toohigh to cause relay trip and subsequent transfer to the alternate powersource. The refore, if the safeguard bus voltage degraded to th; rangebetween 90% and 95.7% of nominal, proper operation of the Class 1Eloads is not assured. This is contrary to the position in Section8.1.6.3.6 of the FSAR which states that the plant undervoltageprotection design is in conpliance with BTP-PSB-1.

The relay setpoints were calculated to result in compliance withthe guidance of BTP-PSB-1. To ensure adequate voltage levels are {maintained to the 480V Class 1E loads, a relay setting of 92% of nominal '

voltage, with a tap changer setting of 5% boost (i.e., secondary voltagei

of 504V vs 480V) on the 4160/480V transformer was calculated to be'

necessary. The 5% boost tap setting increases the secondary voltage(480V side) by 5% (i.e., 24V). The most accurate undervoltage relay

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*Significant Deficiency Report.

SDR No. L2-88-11.

Page 2 of 3

available at the tine that the calculation was perforned was a BrownBoveri nodel ITE-27D which provides a 12% setpoint tolerance with a 3%pickup to dropout ratio. The dropout ratio is a relay characteristicwhich specifies the difference between the trip setpoint and the valuerecuired for the relay to reset. Therefore, for a 92% setting thiswould translate to a nexintm relay actuation at 94% and a neximum resetat 97%. These actuation and reset voltage levels were considered toohigh since they may have created the possibility for spurious trips,which would be contrary to guidance of BTP-PSB-1. In addition, the highreset value (i.e., 97%) could prevent relay reset during recovery froman electrical transient and thus cause an unnecessary trip of thesupplying offsite power source and transfer to the alternate powersource. Considering these facts, a 90% relay setting was chosen byPhiladelphia Electric Canpany.

During plant construction, the 4160/480V transformer taps were setat 5% boost, in concert with the previous voltage studies. With these ;

tap settings, there were Instances of equipnent danege due toovervoltage in the power supply to the 480V loads. Therefore, the the4160/480V transformer taps were reset to nominal boost (0%). Thisresnited in the primary side voltage potential non-operability rangewidering from 90% to 92% of nominal, to 90% to 95.7% of nominal. Therelay vould have permitted secondary side voltage to drop below theminimun voltage necessary to ensure proper operation of the 480V Class1E loads. However, further analysis to ensure compliance with the FSARwas mistakenly determined not to be necessary due to the assumption thatthe undervoltage relay setpoints were based solely on primary sidevoltage levels and did not consider tap setting effects on the secondaryside voltage levels.

Safety Implications:

Degraded voltages on the 4kV safeguard busses in the range between90% and 95.7% could result in inoperability of 480V, Class 1E loadswithout the relays operating to isolate the Class 1E power systen fromthe degraded source.

Corrective Actions: I

The undervoltage relays in question are being replaced with BrownBoveri nodel ITE 27-N relays with a tolerance of 10.2% with a pickup todrop out ratio of 0.5%. New voltage regulation calculations have beenperforned to provide the exact setting of the relay. The tight setpointtolerance and pickup to dropout ratio of the new relay provides theperformance necessary to prevent spurious tripping of the supplyingoffsite source and also allows re'ay reset at a value only 0.5% abovethe trip setpoint. Therefore, an unnecessary transfer of the offsitepoaer supply to the alternate source is renote. In concert with therelay change, the 4160/480V transformer taps will be set to 2-1/2%boost. These changes provide compliance with the design basis detailedin FSAR Section 8.1.6.3.6, which cannitted to the guidance of BTP-PSB-1.These changes provide voltage levels and protection of equipnent incompliance with BTP-PSB-1.

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*Significant Deficiency Report*

.SDR No. L2-88-11., ,

Page 3 of 3-

Actions Taken to Prevent Recurrence:

This event was discussed in detail with the engineer involved, whonow recognizes the need for strict procedural adherence.

A review of the Quality Assurance (QA) plan covering constructionof Limerick Generating Station and the associated design controlprocedures in place, showed these procedures to be adequate to precluderecurrence of this event.

CBT/ds/03308901

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