Information Notice 1989-64, Electrical Bus Bar Failures

Electrical Bus Bar Failures

ML031180735
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	09/07/1989
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-89-064, NUDOCS 8908310301
Download: ML031180735 (7)

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 September 7, 1989 NRC INFORMATION NOTICE NO. 89-64: ELECTRICAL BUS BAR FAILURES

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

This information notice is intended to alert addressees to potential problems

resulting from the failure of electrical bus bars caused by cracked insulation

and moisture or debris buildup in bus bar housings. It is expected that reci- pients will review the information for applicability to their facilities and

consider actions, as appropriate, to avoid similar problems. However, sugges- tions contained in this information notice do not constitute NRC requirements;

therefore, no specific action or written response is required.

Description of Circumstances

(1) Palo Verde Unit 1 (Licensee Event Report No.88-010)

On July 6, 1988, a phase B to ground fault occurred on 13.8-kv non-Class lE

electrical bus E-NAN-S02. This fault ionized the air surrounding the bus and

caused all three phases to short to ground. Feeder breakers to non-Class 1E

buses E-NAN-SO1 and S02 did not open immediately, resulting in excessive

currents being supplied by the unit auxiliary transformer (UAT) and the sub- sequent rupture and ignition of the UAT. This caused the supply breakers to

buses E-NAN-SO1 and S02 and the main generator output breaker to open on a

UAT sudden overpressure signal. As expected, a reactor trip on low departure

from nucleate boiling ratio occurred because the reactor coolant pumps were

powered from buses E-NAN-SO1 and S02. The reactor was subsequently stabilized

in hot standby on natural circulation.

Failure of bus E-NAN-S02, initiated by the phase B to ground fault, was attri- buted to cracked and brittle Noryl insulation and dirt that had accumulated in

the cubicles. These conditions led to arc tracking, which caused the single

phase to ground fault. This fault subsequently propagated into a three-phase

to ground fault.

030 ..

lOO.3OO1A .

1%11 III 89-64 September 7, 1989- (2) Kewaunee (Licensee Event Report Nos.88-001 and 87-009)

On March 2, 1988, when the plant was at 93.3 percent power, a reactor trip and

associated turbine trip were generated as a result of undervoltage (UV) condi- tions on 4160-volt electrical buses 1-1 and 1-2, which supply power to the

reactor coolant pump and main feedwater pump motors.

Investigations of the UV condition on the buses revealed that an electrical fault

had occurred on the bus from the "Y" winding of the main auxiliary transformer

to buses 1-1 and 1-2 because of insulation failure. The bus bar, which was a

1/2-inch by 4-inch flat copper bar, was rated at 4000 amperes per phase and was

manufactured by the Calvert Company. The bus bar, which was encapsulated with

Noryl flame-retardant insulation, was enclosed in aluminum ducting with screened

ventilation slots on the top and bottom.

The licensee determined that the cause of the event was failure of the insulation

on the bus bar and the accumulation of water and debris around the bus, which

provided a tracking path for the fault. The bus bar runs horizontally into the

auxiliary building underneath areas where debris can fall into the bus work.

Additionally, water from a plastic drain hose, located on the floor above the

faulted section of the bus, was suspected to have dripped onto the bus work.

A similar event had occurred at Kewaunee on July 10, 1987, when a reactor trip

and-assoc-i-a-ted-turb-ne-tri-p--ooccurred-as-a result-of- an-tJV-trawsient-on-the-same--

4160-volt buses. In this case, however, a phase to ground fault occurred on

the bus bar from the "X" winding of the main auxiliary transformer to 4160-volt

buses 1-3, 1-4, 1-5, and 1-6. This bus bar was similar to the one identified

above, except that it was a flat aluminum bar that was rated at 3000 amperes.

The cause of this event was also failure of insulation on the bus bar compounded

by the accumulation of particulate debris. The bus bar was located perpendicular

to the turbine building ventilation fans, which pulled dust-filled air through a

section of the bus bar. Dust and metallic powder that had collected on the cracked

bus bar insulation provided a tracking path for the phase to ground fault.

(3) Millstone Unit 1 (Licensee Event Report.No. 87-001-01)

On January 13, 1987, when Unit 1 was at 100-percent power, a visual inspection

of the 4160-volt ac (VAC) load centers showed that horizontal Noryl bus bar

insulation was cracked. The problem was attributed to a manufacturing defect

on General Electric Company (GE) metal-clad switchgear type M-26 (4160 VAC) and

type M-36 (6900 VAC). Apparently, during the manufacturing process, "black"

bus bar joint compound (GE # D50H47) contaminated the Noryl insulation and over

several years caused the insulation to crack.

(4) Sequoyah Unit 1 (Licensee Event Report No.83-067)

On May 18, 1983, when Unit 1 was at 100-percent power, startup bus lB at Unit 1 failed because of a phase B to phase C fault, which propagated to ground. The

failure was attributed to degradation of Noryl insulation on the Westinghouse

Model EN-265 bus. Further investigation revealed several degraded areas in the

bus insulation at the support blocks, and startup bus 1B was declared inoperable.

IN 89-64

.

• September* 7, 1989 (5) Browns Ferry Unit 2 (Licensee Event Report No.89-008)

On March 9, 1989, a bus fault to ground occurred on the secondary (4160-volt)

side of the unit station service transformer, causing an engineered safety

feature actuation. This electrical fault also caused damage to the 4160-volt

bus, the bus duct, and the transformer bushing connections on all three phases.

The fault was attributed to (a) deterioration of the Noryl insulation above the

bus joint, (b) poor design of the bus duct, which allowed condensation to collect, and (c) inadequate implementation of the vendor-recommended preventive maintenance.

Discussion:

Failures of medium-voltage electrical bus bars, principally involving 4160-

and 6900-volt ac buses, have resulted in bus bar electrical faults and fires, electrical power system undervoltage conditions, plant transients, reactor

trips, and engineered safety feature actuations.

Failure of the bus bars has been attributed to cracked bus bar insulation (bus

sleeving) combined with the accumulation of moisture or debris in the bus bar

housings. Insulation failure, along with the presence of moisture or debris, provided undesired phase to phase, or phase to ground, electrical tracking

paths, which resulted in catastrophic failure of the buses.

__- . . - =.

-. A _ .1T

=;H

Corrective actions taken by the involved utilities included replacing damaged

bus bar sections with bus bars that were covered with insulation of a different

type, substituting "yellow" bus bar joint compound (GE # D50H109) for the "black"

joint compound previously used, modifying bus bar enclosures-to restrict ingress

and accumulation of water and debris, and instituting enhanced periodic inspections

and cleaning of bus bars and their housings.

This information notice requires no specific action or written response. If

you have any question about the information in this notice, please contact one

of the technical contacts listed below or the appropriate NRR project manager.

!C~aPr es E. i, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Mark Padovan, AEOD

(301) 492-4445 Argil Toalston, NRR

(301) 492-0831 Attachment: List of Recently Issued NRC Information Notices

Attachnent

1.N89-64 September 7, 1989 Page 1 of I

LIST OF RECENTLY ISSUED

NRCINFORMATION NOTICES

Inforrtion nDat of

Notice No. Subject Issued to

Issuance

39-63 Possible Submergence of All holders of OLs

Electrical Circuits Located 9/S/89 or CPs for nuclear

Above the Flood Level Because power reactors.

of Water intrusion and Lack

of Drainage

89-62 Malfunction of Borg-Warner 8/31/89 All holders of OLs

Pressure Seal Bonnet Check or CPs for nuclear

Valves Caused By Vertical power reactors.

Misalignment ofODisk

69-61 Failure of Borg-Warner Gate 8/30/89 All holders of OLs

Valves to Close Against or CPs for nuclear

Differential Pressure power reactors.

ES-48, Licensee Report of Defective 8/22/89 All holders of OLs

supp. 2 Refurbished Valves or CPs for nuclear

power reactors.

89-60 Maintenance of Teletherapy 8/18/89 All NRCMedical

Units Teletherapy Licensees.

89-59 Suppliers of Potentially 8/16/89 All holders of OLs

Misrepresented Fasteners or CPs for nuclear

power reactors.

89-58 Disablement of Turbine-Driven 8/3/89 All holders of OLs

Aux1liary Feedwater Pump Due or CPs for PWRs.

to Closure of One of the

Parallel Steam Supply Valves

89-5 7 Unqualified Electrical 7/26/89 All holders of OLs

Splices in Vendor-Supplied or CPs for nuclear

Environmentally Qualified power reactors.

Equipment

rsTrTs<<non- Clwewlonslblt r_.llst-swA x>ous§ . ..ss- Au

F

noucers Or ULS

of Material Supplied to the or CPs for nuclear

Oefense Department by Nuclear power reactors.

Supp iers

OL

• Operating License

CP

• Construction Permit

UNITED STATES

NUCLEAR REGULATORY COMMISSION FIRST CLASS MAIL

POSTAGE & FEES PAID

WASHINGTON, D.C. 20555 USNRC

PERMIT No. 0-67 OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE, $300

IN 89-64 x v September 7, 1989 (5) Browns Ferry Unit 2 (Licensee Event Report No.89-008)

On March 9, 1989, a bus fault to ground occurred on the secondary (4160-volt)

side of the unit station service transformer, causing an engineered safety

feature actuation. This electrical fault also caused damage to the 4160-volt

bus, the bus duct, and the transformer bushing connections on all three phases.

The fault was attributed to (a) deterioration of the Noryl insulation above the

bus joint, (b) poor design of the bus duct, which allowed condensation to collect, and (c) inadequate implementation of the vendor-recommended preventive maintenance.

Discussion:

Failures of medium-voltage electrical bus bars, principally involving 4160-

and 6900-volt ac buses, have resulted in bus bar electrical faults and fires, electrical power system undervoltage conditions, plant transients, reactor

trips, and engineered safety feature actuations.

Failure of the bus bars has been attributed to cracked bus bar insulation (bus

sleeving) combined with the accumulation of moisture or debris in the bus bar

housings. Insulation failure, along with the presence of moisture or debris, provided undesired phase to phase, or phase to ground, electrical tracking

paths, which resulted In catastrophic failure of the buses.

Corrective actions taken by the involved utilities included replacing damaged

bus bar sections with bus bars that were covered with insulation of a different

type, substituting "yellow" bus bar joint compound (GE # D50H109) for the "black"

joint compound previously used, modifying bus bar enclosures to restrict ingress

and accumulation of water and debris, and instituting enhanced periodic inspections

and cleaning of bus bars and their housings.

This information notice requires no specific action or written response. If

you have any question about the information in this notice, please contact one

of the technical contacts listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Mark Padovan, AEOD

(301) 492-4445 Argil Toalston, NRR

(301) 492-0831 Attachment: List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCES *C/OGCB:DOEA:NRR*RPB:ARM

(CuR~IsT~ 7 CHBerlinger TechEd

08 //8 08/31/89 08/30/89

• OGCB:DOEA:NRR *SELB:DEST:NRR*C/SELB:DEST:NRR *ROAB:DSP:AEOD *C/ROAB:DSP:AEOD

PCWen ALToalston FRosa LMPadovan JERosenthal

08/29/89 08/30/89 08/30/89 08/29/89 08/31/89

IN 89-XX

August xx, 1989 Y. vbus insulation at the support blocks, and startup bus 1B was declared in- operable.

(5) Browns Ferry Unit 2 (Licensee Event Report No.89-008)

On March 9, 1989, a bus fault to ground occurred on the secondary (4160-volt)

side of the unit station service transformer, causing an engineered safety

feature actuation. This electrical fault also caused damage to the 4160-volt

bus, the bus duct, and the transformer bushing connections on all three phases.

The fault was attributed to (a) deterioration of the Noryl insulation above the

bus joint, (b) poor design of the bus duct, which allowed condensation to

collect, and (c) inadequate implementation of the vendor-recommended preventive

maintenance.

Discussion:

Failures of medium-voltage electrical bus bars, principally involving 4160- and

6900-volt ac buses, have resulted in bus bar electrical faults and fires, electrical power system undervoltage conditions, plant transients, reactor

trips, and engineered safety feature actuations.

Failure of the bus bars has been attributed to cracked bus bar insulation (bus

sleeving) combined with the accumulation of moisture or debris in the bus bar

housings. Insulation failure, along with the presence of moisture or debris, provided undesired phase to phase, or phase to ground, electrical tracking

paths, which resulted in catastrophic failure of the buses.

Corrective actions taken by the involved utilities included replacing damaged

bus bar sections with bus bars that were covered with insulation of a different

type, substituting "yellow' bus bar joint compound (GE # D50H109) for the

"black" joint compound previously used, modifying bus bar enclosures to re- strict ingress and accumulation of water and debris, and instituting enhanced

periodic inspections and cleaning of bus bars and their housings.

This information notice requires no specific action or written response. If

you have any question about the information in this notice, please contact the

technical contacts listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Mark Padovan, AEOD

(301) 492-4445 Argil Toalston, NRR

(301) 492-0831 Attachment: List of Recently Issued NRC InformatioL X ces

• SEE PREVIOUSS CONCURRENCES D/DOEA:NRR C/ EA:NRR*RPB:ARM

CERossi CHBerlinger TechEd

08/ /89 08/31/89 08/30/89

• OGCB:DOEA:NFRR *SELB:DEST:NRR*C/SELB:DEST:NRR *ROAB:DSP:AEOD C/ROAB:DSP

PCWen ALToalston FRosa LMPadovan JERosentha

08/29/89 08/30/89 08/30/89 08/29/89 08/3S/89

IN 89-XX

August xx, 1989 a . _j e5) Browns Ferry Unit 2 (Licensee Event Report No.89-008)

On March 9, 1989, a bus fault to ground occurred on the secondary (4160-volt)

side of the unit station service transformer, causing an engineered safety

feature actuation. This electrical fault also caused damage to the 4160-volt

bus, the bus duct, and the transformer bushing connections on all three phases.

Inadequate insulation and the collection of condensation led to the deteriora- tion of the Noryl sleeving at the factory-cut end. The deterioration extended

appropriately 1/4 inch above the bus flex connector.

The fault was attributed to (a) inadequate insulation above the bus joint, JbJ poor design of the bus duct, which allowed condensation to collect, and

c inadequate implementation of the vendor-recommended preventative main- tenance.

Discussion:

Failures of medium-voltage electrical bus bars, principally involving 4160- and

6900-volt ac buses, have resulted in bus bar electrical faults and fires, electrical power system undervoltage conditions, plant transients, reactor

trips, and engineered safety feature actuations.

Failure of the bus bars has been attributed to cracked bus bar insulation (bus

sleeving) combined with the accumulation of moisture or debris in the bus bar

housings. Insulation failure, along with the presence of moisture or debris, provided undesired phase to phase, or phase to ground, electrical tracking

paths, which resulted in catastrophic failure of the buses.

Corrective actions taken by the involved utilities included replacing damaged

bus bar sections with bus bars that were covered with insulation of a different

type, substituting "yellow" bus bar Joint compound (GE $ D50H109) for the

"black' joint compound previously used, modifying bus bar enclosures to re- strict ingress and accumulation of water and debris, and instituting enhanced

periodic inspections and cleaning of bus bars and their housings.

This information notice requires no specific action or written response. If

you have any question about the information in this notice, please contact the

technical contacts listed below or the appropriate NRR project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Mark Padovan, AEOD

(301) 492-4445 Argil Toalston, NRR

(301) 492-0831 Attachment: List of Recently Issued NRC Information Notices

D/DOEA:NRR C/OGCB:DOEA:NRR RPB:ARM

/ CERossi CHBerlinger TechEd RS

a SE n, L 08/ /89 08/ /89 08/30/89 OGCB:DOEA:NRR SEYM:DEST:NRR C/S kflEST:NRR ROAB:DSP C/ROAB:DSP:AEOD

PCWen ALTp .ston FRoWUY 114 LMPadovan JERosenthal

08h1/89 08Y"1'/89 08) 89 08A1/89sA rft)8/ /89