05000327/LER-1993-015, :on 930614,1A Start Bus Alternate Feeder Breaker Tripped Upon Start of Unit 1 RCP Which Resulted in Start of DG Due to Current Transformer Wired Incorrectly. Restored Offsite Power & Secured Final DG

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:on 930614,1A Start Bus Alternate Feeder Breaker Tripped Upon Start of Unit 1 RCP Which Resulted in Start of DG Due to Current Transformer Wired Incorrectly. Restored Offsite Power & Secured Final DG
ML20045J011
Person / Time
Site: Sequoyah Tennessee Valley Authority icon.png
Issue date: 07/14/1993
From: Fenech R, Meade K
TENNESSEE VALLEY AUTHORITY
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-015, LER-93-15, NUDOCS 9307220275
Download: ML20045J011 (8)


LER-1993-015, on 930614,1A Start Bus Alternate Feeder Breaker Tripped Upon Start of Unit 1 RCP Which Resulted in Start of DG Due to Current Transformer Wired Incorrectly. Restored Offsite Power & Secured Final DG
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv), System Actuation

10 CFR 50.73(a)(2)(v), Loss of Safety Function

10 CFR 50.73(a)(2)(vii), Common Cause Inoperability

10 CFR 50.73(a)(2)(i)

10 CFR 50.73(a)(2)(viii)(A)

10 CFR 50.73(a)(2)(ii)

10 CFR 50.73(a)(2)(viii)(B)

10 CFR 50.73(a)(2)(iii)

10 CFR 50.73(a)(2)(x)
3271993015R00 - NRC Website

text

s Bl4 Tennessee Vaney Authonty, Post Office Hox 2000. Goddy-Daisy. Tennessee 37379-2000 Robert A. Fenech Vice President. Sequoyah Nuclear Plant July 14, 1993 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:-

TENNESSEE VALLEY AUTHORITY - SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 -

DOCKET NOS. 50-327 AND 50-328 - FACILITY OPERATING LICENSES DPR-77 AND DPR LICENSEE EVENT REPORT (LER) 50-327/93015 The enclosed LER provides details concerning the start of all four emergency diesel generators as the result of an incorrectly wired current transformer.

i This event is being reported in accordance with 10 CFR 50.73.b.2.iv as an event that resulted in the automatic actuation of an engineered safety feature.

Sincerely, Robert A. Fenech Enclosure cc: See page 2 i

1 9307220275 930714-

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U.S. Nuclear Regulatory Commission Page 2 July 14,-1993 cc (Enclosure):

INP0 Records Center Institute of Nuclear Power Operations 700 Galleria Parkway Atlanta, Georgia 30339-5957 Mr. D. E. LaBarge, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555-Rockville Pike Rockville, Maryland 20852-2739 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624 Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323-2711

MRC Form 366 U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 (6-89)

Empires 4/30/92 tICENSEE EVENT REPORT (tER)

FACIll*fY NAME (1) lDOCKETNUMBER(2) l_PAAGEW1_

_Sequoyah_!Mleitr Plant. Unit I lQlElll0jQ}L(Zj7 11]Dfl._Qj_6 TITLE (4)

_Di_eseLGenerator (D/G) St.RELR1_the Result of an Ipcorrectiv WiEed Current Tran1[ormer

_ENRLDALIS) l LER_t4 UMBER (6) l REPORT DATE (7) 1 OTHER_fACJ1111ES_lt0/DLVED_{8) l l

l l l SEQUENTIAL l l REVISION l l

l l FACILITY NAMES lDOCKETNUMBER(S)

[1QHlHj DAY jYEAR l YEAR l I NUM_9ER l l NUMBER IMONTHl DAY lYEAR I Secuoy & _ Unit 2 ID151010}H{3]Zja_

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I LICENSEE CONTACT FOR THIS LER (12)

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TELEPHONE NUMBER lAREACODEl

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A ABSTRACT (Limit to 1400 spaces, i.e., approximately fif teen single-space typewritten lines) (16)

On June 14, 1993, with Unit 1 defueled and Unit 2 in cold shutdown, Mode 5, the 1A start bus alternate feeder breaker tripped upon the start of the Unit I reactor coolant pump No. 1 motor. This resulted in the loss of voltage to the 1B-B 6.9 kilovolt shutdown board. The four emergency diesel generators (D/G) started and the 1B-B D/G supplied power to the 1B-B 6.9 kV shutdown board, as designed.

The event has been determined to have been caused by an incorrectly wired current transformer in the alternate feeder breaker protection circuitry. Plant equipment response during this event was consistent with that specified in the Final Safety Analysis Report for a loss of offsite power event.

I l

i4RC Form 366(6-89)

-,..U.S. NUCLEAR REGULATORY COMMISSION TApprovsd.0MB No. 3150-0104 (6-89)-

Exp1res 4/30/92

- LICDeSEE EVDIT REPORT (LER) '

TEXT CONTINUATION FACILITY NAME (1) lDOCKETNUMBER(2)l LER NUMBER (6) l l

PAGE (31-

.l l-l l$EQUENTIAL;l l REVISION l l l.l l Sequoyah Nuclear Plant, Unit 1 l.

lYEAR I l NUMBER' -l

'l NUMBER l l l _ l,. l -

lDj5]A10j 913 12 17 19 13 l-l 0 l ' 1 1 5 l-l 0 1 0 l 01 2l0Fl 01 6' TEXT (If more space is required, use additional NRC Forn, 366A's) (17)

I.

PLANT CONDITIONS

4 Unit I was defueled and Unit'2 was in cold shutdown,- Mode 5.

II.

DESCRIPTION OF EVENT

A.

Event-On June 14,1993, the '1A start bus alternate feeder breaker '(EIIS Code EA).

tripped upon.the start of the Unit.1 reactor coolant pump-(RCP):No. 1 motor (EIIS Code AB). This resulted in the lossLof w itage to the 1B-B.6.9 kilovolt (kV) shutdown board (EIIS Code EB). 'The'four emergency-diesel. generators (D/Gs) (EIIS Code EK) started and the 1B-B D/G s'upplied power ~~to the11B-B.6.9-kV shutdown board,'as designed.

The 1A start bus had been transferred to the alternate feeder breaker. earlier

'the previous day as the result of maintenance.being performed on_the normal feeder breaker. A very light load existed on.the boards at that time as the result of the current-dual unit outage. On June 14, the, Unit 11 RCP No. 1-motor-was started af ter having been recently reinstalled from maintenance activities. Upon start of the RCP motor, a neutral-overcurrent' relay. actuated and, in turn, actuated the lock-out relay for the alternate feeder. breaker to the 1A start bus. As a result, the 1A and-1C 6.9 kV_ unit boards, as well as-the 1B-B shutdown board, experienced a loss of voltage and all four D/Gs started. The IB-B D/G tied on to the -1B-B shutdown board to ' supply power. - The-boards were verified to have no grounds, the RCP motor was not shorted, and there were no signs of damage to the shutdown board, unit boards, or start bus enclosure.

This event is being reported in accordance with 10 CFR 50.73.b.2.iv as an event that resulted in the automatic actuation of an engineered safety feature.

B.

Inapgrable Structures. Components or Systems That Contributed to the Event None.

C.

Dates and Approximate Times-of Maigr Occurrmacna October 15, 1992 Electrical Maintenance' discovered a significant crack on the "B" phase load current transformer (CT) for the 1A start bus alternate feeder breaker.

November 3, 1992 The cracked CT was replaced with a new CT from the same manufacturer.

NRC form 366(6-89)

f1RC Form 366A U.S. NUCLEAR REGULATORY COMMISSION Approvsd OMB No. 3150-0104 Expirss 4/30/92 (6-89)

+

LICENSEE EVENT REPORT (LER)

TEXT CONYINUATION Adll1YNAME(1) l000KETNUMBER(2)}

LIE _UUtfELR_16) l I

PAQi_{3) l l

l l SEQUENTIAL l l REVISION l l l l l Sequoyab Nuclear Plant, Unit 1 l

jlEARI I NQ@ER l l NUMBER I l l l~l IMMdd0l3 12 17 19 13 l-l 0 l 1 15l-l01 0101310f.}0l6 TLXT (If more space is required, use additional NRC Form 366A's) (17) l June 13, 1993 The 1A start bus is transferred to the alternate feeder breaker in order to perform maintenance on the normal feeder breaker.

l June 14, 1993 While attempting to start the Unit 1 RCP No. 1, the 1A start bus alternate feeder breaker tripped, causing a loss of voltage to the 1A and 1C unit' boards and the 1B-B shutdown board and subsequent start of all.four D/Gs.

l June 15, 1993 Investigation revealed that a CT on the "B" phase of the alternate feeder breaker was wired incorrectly. The CT had been replaced in November 1992. The replacement CT (same manufacturer) had the "X1" and "X2" positions in l

opposite locations from the original CT.

The i

electricians when replacing the CT and laid the leads down with the X1 and X2 wires in the same position as the original CT, not knowing the replacement CT was opposite the origit,a1 CT.

The CT wiring error went undetected i

until sufficient load existed (RCP *notor start) on the boards to create the phase imbalance that rerulted in the breaker trip. No records could be found that indicated j

the alternate feeder breaker had ever been placed in service until the day before this event occurred.

D.

Rther Systema _nr_S.econdary Functions Affrcted None.

l E.

Method of Discov_ery The D/G start was the result of the loss of voltage to the 1B-B shutdown board and was, thus, discovered by Operations personnel The incorrectly wired CT was discovered by Maintenance personnel investigating the cause of the 1A start bus alternate feeder breaker trip.

F.

QpSratDr Action Operations personnel, upon ensuring that a stable offsite power source existed, secured the three D/Gs that were not loaded to the shutdown boards. Once offsite power was restored to the 1A start bus, the final D/G was also secured.

G.

Safety Svatem_ Response The D/Gs started, as designed, upon the loss of voltage to the 1B-B shutdown board. The IB-B D/G properly tied onto the IB-B shutdown board and provided the power to the board until offsite power could be restored to the board.

NRC form 366(6-89)

iU.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 Expires 4/30/92 (6-89)

LICENSEE EVENT REPORT (LER)

' TEXT CONTINUATION-j l

FACIllTY NAME (1) lDOCKETNUMBER(2)l LER NUMBER (6) l l

PAGE (3) l l

l l SEQUENTIAL l-l REVISION l l l l l Sequoyah Nuclear Plant, Unit 1 l

lYEAR l l NUMBER l l NUMBER l l l ll i

!Ol510[Qhj3 l2 17 19 13 l-l 0 l 1 1 5 l-l 0 l 0 l 01 410Fl 01 6 TEXT (If more space is required, use adfitional NRC form 366A's) (17) l III.

CAUSE OF EVENT

1 A.

Imediate Cause l

The immediate cause of this event was an' incorrectly wired CT on.the "B" phase i

of the 1A start bus alternate feeder breaker. - This caused the breaker to trip and resulted in.the loss of voltage to the 1B-B shutdown board.

l B.

Root CauSE The root cause of this event was the failure to uniquely identify.the CT secondary wiring in accordance with site procedures in order to ensure. correct-retermination of the wires. The individuals that. removed the. cracked CT indicated that the "B" phase CT control wiring was removed. Proper.

identification would have indicated that two uniquely identified wires were removed from the X2 pocition of the CT and one uniquely identified wire was removed from the X1' position.

C.

Conj;ributine Cauan A contributing cause was that the postmaintenance test (PMT) for the installation of the CT was ineffective'in detecting the wiring error. -This was the result of a lack of technical knowledge involving cts and a lack of l-specific guidance in site procedures concerning the proper PMT for a CT.

IV.

ANALYSIS OF EVENT

i One of the signals upon which the D/Gs are designed to start is a loss of voltage to the shutdown boards. The shutdown board, through the protective relays, will strip the load from the board, allow the D/G to come.up to speed, tie the D/G to the board, and then sequence the required loads back on the board..This is the sequence that occurred for this event. All safety-related equipment functioned as designed.

cts are designed to-monitor the current in a circuit. The cts used in-the 1A start bus alternate. feeder breaker are 4000/5-amp, wye-wired cts. The cts sum the current in all three. phases of.the circuit and send the resultant value to the breaker protective relays. The current total for a three-phase system should be zero for a normal circuit. However, with the "B" phase CT wired incorrectly, a current imbalance was sensed and a signal was sent to the protective relays to trip the 1A start bus alternate feedet breaker. Thus, with the CT wired incorrectly, the equipment functioned as designed.

Plant equipment response during this event was consistent with that specified in the Final Safety Analysis Report for a loss of offsite power event. Therefore, the event did not adversely affect the health and safety of the public.

i US Form 366(6-09) m

l HRC form 366A U.S. NUCLEAR REGULATORY COMMISSION Approved OMB No. 3150-0104 Expires 4/30/92 (6-89)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION fthklkHAME(1) lDOCKETNUMBER(2)}

LIR_tlUMBER (6) {

l PADE (3) l l

l l SEQUENTIAL l l REVISION l l l l l Sequoyah Nuclear Plant. Unit 1 l

jlEARl l_FUMBER I l NVtEIRJ l l l l IDMIE1DlD33d2 l7 l2_l3._l-l 0 l 1 l_5 l--! O l 0lOlljAFjJJJ_

TEXT (If more space is required, use additional NRC Form 366A's) (17)

V.

CORRECTIVE ACTION

i A.

IJInediate_ Correntive Action t

The immediate corrective action associated with this event included securing i

the three D/Gs that were not supplying power to the shutdown boards, restoring offsite power, and then securing the final D/G. An investigation was then l

I initiated to determine why the 1A start bus alternate feeder breaker tripped.

l Upon discovery of the incorrectly wired CT, all 6.9-kV cts that had been replaced were identified to ensure that proper installation had occurred. This i

investigation did not discover any further discrepancies. However, subsequent testing on a 6.9-kV common board CT revealed an incorrectly wired CT in the 2A

)

start bus normal feeder breaker circuitry.

Procedures were developed to j

perform phase testing on all 6.9-kV cts that had not been tested upon j

l replacement. The open work documents were also reviewed to ensure phase i

testing of any future replacement cts. The incorrectly wired cts were corrected.

l l

B.

Action to Prevent Recurrence The site procedure that governs configuration control of maintenance activities has been revised to clearly require unique identification of each configuration change.

Site Standard Practice (SSP) 6.31, " Maintenance Management System Pre-or Post-Maintenance Testing," will be revised to specify the proper PMT for CT replacement.

VI.

ADDITIONAL INFORMATION

A.

failesLcomponenta None.

B.

fERYinuS_Simi1ar Eventa A review of previous reportable events was conducted to identify any similar events. Several events were identified with similar causes, i.e., inadequate PMT, inattention to detail, and inadequate verification. Actions have been taken in response to previous events to ensure that management expectations were clearly conveyed, understood, and concurred with by site personnel.

It should be noted that the work for the replacement of the CT was planned in March 1992. This was before the specified corrective actions were in place.

Subsequent planning of work activities associated with CT replacement in February and again in April 1993 resulted in the proper PMT being specified.

N2C form 366(6-89)

.x

.1 NRC f orm 366A U.S. NUCLEAR REGULATORY COMMISSION Approvzd OMB No. 3150-0104 (6-89) s Expirss 4/30/92 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACIl!TY NAME (1) lDOCKETNUMBER(2)l LEILN3tMDER (6) l l

PASE (3) l l

l l SEQUENTIAL l l REVISION l l l l l Sequoyah Nuclear Plant Unit 1 l

lyEARl I NUMBf1 l l NUMBER _l-l l l l 1015!0101013 12 17 19 13 1 - I o I 1 1 5 1--I o 1 0 I of 610rl of 6 TEXT (If more space is required, use additional NRC Form 366A's) (17)

VII.

COMMIIMENT SSP-6.31 will be revised by August 27, 1993, to ensure that the proper PMT for cts is specified.

NY form 366(6-89)