Information Notice 1994-54, Failures of General Electric Magne-Blast Circuit Breakers to Latch Closed

Failures of General Electric Magne-Blast Circuit Breakers to Latch Closed
	ML031060555
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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	08/01/1994
From:	Grimes B; Office of Nuclear Reactor Regulation
To:	;
References
	IN-94-054, NUDOCS 9407270127
	Download: ML031060555 (15)
	v • d • e

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 August 1, 1994 NRC INFORMATION NOTICE 94-54: FAILURES OF GENERAL ELECTRIC MAGNE-BLAST

CIRCUIT BREAKERS TO LATCH CLOSED

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

PurDose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees to a condition in which certain General Electric

(GE) medium-voltage Magne-Blast circuit breakers may begin to randomly fail to

latch closed. It is expected that recipients will review the information for

applicability to their facilities and consider actions, as appropriate, to

avoid similar problems. However, suggestions contained in this information

notice are not NRC requirements; therefore, no specific action or written

response is required.

Description of Circumstances

The Maine Yankee Atomic Power Station (Maine Yankee) and the Millstone Nuclear

Power Station (Millstone) have recently experienced failures of safety-related

GE Magne-Blast 4160-Vac circuit breakers to latch closed (also called "going

trip-free"). Failures occurred during post-overhaul, preoperational, and

in-service surveillance testing. At Maine Yankee, failures occurred shortly

after an overhaul of the breakers, during troubleshooting of an indirectly

related problem with limit switches. The affected breakers have failed to

latch on a random basis during up to about two-thirds of attempted closures, both electrically and manually. At both plants, the affected breakers were

among those recently overhauled by the GE Apparatus Service Division of

Philadelphia, with quality assurance coverage provided by GE Nuclear Energy

(NE) Power Delivery Services (PDS) of King of Prussia, Pennsylvania. Failure

analysis, inspection, and testing of one of the affected breakers from Maine

Yankee were performed at the GE Apparatus Service Division under the direction

of GE NE PDS and the design engineer from the breaker manufacturer, GE

Specialty Breaker Plant. The results were consistent with onsite testing at

both Millstone and Maine Yankee. The failure analysis activities, observed by

NRC and licensee representatives, identified the primary failure mode, apparent principal root causes, and the most effective remedies.

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IN 94-54

- August 1, 1994 Discussion

The breaker models considered to be potentially affected at the present time

include (1) Type AM-4.16-350-1H and (2) Type AM-4.16-250-6, -7, -8, or -9HB.

GE is currently evaluating other Magne-Blast models for potential

susceptibility. Among these models, only breakers equipped with one prop

reset spring (prop spring), and in which all "Tuf-Loc" (Teflon-coated

fiberglass) bushings (especially the prop bushings) have been replaced with

aluminum-bronze bushings, have recently experienced unreliable latching.

However, it should be noted that this failure ultimately results from a

combination of contributing factors and not all breakers of the potentially

affected type and configuration are prone to failure. In addition, there have

been a few instances (although not recently) of one-prop spring breakers with

Tuf-Loc prop bushings that have failed to latch due to other unsatisfactory

conditions within the breaker such as excessive wear, hardened or insufficient

lubrication, and/or being severely out of adjustment. No failures are known

to GE or the NRC to occur in breakers equipped with two prop springs (included

as original equipment since 1968, or added during maintenance or repair). The

failure analysis testing appeared to confirm the GE position that breakers

with two prop springs should not experience this problem. The details of the

failure mode are discussed in Attachment 1 to this information notice.

Attachment 2 shows the prop springs.

It should be noted that, depending on the severity of the various contributing

conditions, the onset of failure to latch reliably in these breakers may vary, and a breaker that has successfully passed rigorous post-maintenance testing

and further receipt inspection and preoperational testing may subsequently

start failing to latch reliably in service. In recent instances, failures to

latch have begun to occur after about 35-50 operations (cycles) following

overhaul or repair of the operating mechanism. Once started, the failure

frequency has been observed during testing, to vary from 1 failure to latch in

as many as 50 consecutive operations to 16 failures in 24 attempts. The

operating characteristics of a given breaker (in particular, adequacy and

consistency of prop action as explained in Attachment 1) can indicate the

likelihood of unreliable latching. According to GE, the desired prop action

positions the prop fully forward against its stop, thus providing maximum

engagement under the prop pin (called prop wipe). However, affected breakers

that start (or are likely to start) failing to latch reliably typically

exhibit inconsistent (and often less than the design minimum) prop wipe even

when they do latch.

The NRC and licensees have expressed concerns regarding increased suscepti- bility to unwanted tripping with less than minimum design prop wipe caused by

vibration or shock (e.g., during a seismic event). The Magne-Blast design

engineer has stated that because of the geometry and magnitude of forces

acting on the prop, once the mechanism has successfully latched (even if only

barely), it would be extremely unlikely for the shocks or vibration associated

with seismic events to cause the prop to move backwards and olut from under the

prop pin. Nevertheless, a breaker that is latched, but with less than the

design minimum prop wipe, is not in a condition for which it was analyzed or

in which it was tested during seismic qualification.

IN 94-54 August 1, 1994 Normal prop wipe can be confirmed with the breaker in its cubicle and closed

(in test position if necessary) in most installations by visual inspection

(using an inspection mirror and light) without having to get too close to

energized components or hazardous mechanism parts if the switchgear cabinet

door can be opened with appropriate safety precautions. Pending issuance of a

service advice letter (SAL) by the manufacturer on this problem or a safety

communication by GE NE, Attachment 2 illustrates an inspection hole in the

right side of the mechanism frame through which the prop and prop pin position

may be viewed. While the fully forward prop position (to the stop) is the

desired condition (maximum wipe), the absence of failures to latch along with

consistent and greater than minimum allowed prop wipe is, according to GE,

indicative of continued reliable latching. However, because minimum prop wipe

is not a published design specification, and because certain other factors

(e.g., opening spring adjustment) may influence latching reliability, GE has

requested that any licensee experiencing Magne-Blast breaker latching problems

or noticing changed, inconsistent or apparently abnormally low prop wipe, particularly following overhaul or repair including prop bushing replacement, contact GE NE PDS at (610) 992-6049.

Pending installation of a second prop spring in affected breakers, Maine

Yankee has shifted, to the extent possible, its available dual prop spring

breakers to locations where operability requires assured latching reliability

for closure or reclosure during a design-basis event. For the remaining

potentially affected breakers, Maine Yankee is planning expedited inspections

with the assistance of GE NE PDS to aid in its operability determinations.

Related Generic Communications

Information Notice 84-29, "General Electric Magne-Blast Circuit Breaker

Problems," dated April 29, 1984.

Information Notice 90-41, "Potential Failure of General Electric Magne-Blast

Circuit Breakers and AK Circuit Breakers," dated June 12, 1990.

Information Notice 93-91, "Misadjustment Between General Electric 4.16-KY

Circuit Breakers and Their Associated Cubicles," dated December 3, 1993.

Information Notice 94-02, "Inoperability of General Electric Magne-Blast

Breaker Because of Misalignment of Close-Latch Spring," dated January 7, 1994.

IN 94-54

August 1, 1994 This information notice requires no specific action or written response. If

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

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Stephen Alexander, NRR

(301) 504-2995 Kamalakar Naidu, NRR Sikindra Mitra, NRR

(301) 504-2980 (301) 504-2783 Attachments:

1. Details of Failure Mode and Contributing Factors

2. Magne-Blast Prop Mechanism Diagram

3. List of Recently Issued NRC Information Notices

47 g AnJ-L

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Attachment 1 IN 94-54 August 1, 1994 DETAILS OF THE FAILURE MODE AND CONTRIBUTING FACTORS

The cause of the failures to latch cited in the body of the Information Notice

is related to a component of the Type ML-13 breaker operating mechanism called

the prop (see Attachment 2). The breaker will fail to latch closed when the

prop does not travel forward fast enough (relative to the motion of the

closing linkage) to be in the proper position under the prop pin of the

closing linkage as it rises above then descends onto the prop during the

closing cycle (whether manually or electrically initiated). Absent a trip

condition upon closing, the prop is permitted (by the rotation of the main

cam) to be pulled forward under the prop pin by the prop reset spring (or

springs when two are fitted). If the slower speed of the prop relative to the

pin is such that the pin passes down in front of the prop instead of landing

on top of it (called latching) as it is supposed to, the linkage will

"collapse" causing the moving contact arms to immediately drop down to the

open position. This condition or action is also called the trip-free

condition because it occurs in the same manner as if a trip signal were

present at the breaker tripping mechanism when the breaker attempts to close, thus preventing the prop from moving forward and latching.

According to GE, and as apparently confirmed by testing, several conditions

must be present to render a given breaker susceptible to this failure mode.

Most fundamental are the individual breaker model and configuration, mechanism

type, and vintage. Within these constraints, certain modifications or

upgrades that have (or have not) been performed on a given breaker influence

its susceptibility. Finally, the condition of the breaker mechanism in terms

of age and type of moving parts, wear, lubrication, and adjustment can

ultimately be the determining factor with regard to latching reliability.

Due to their particular combination of operating (opening and closing) spring

configurations, all 4.16-kilovolt (Kv)-rated, vertical-lift, air-magnetic

(Magne-Blast) breakers of 350-million volt-ampere (MVA) interrupting rating

(Type AM-4.16-350-1H) that are fitted with only one prop spring are considered

by GE to be potentially affected. Also potentially affected, owing also to

their particular operating spring configurations, are those 4.16-Kv, 250-MVA-

rated Magne-Blast breakers with one prop spring that have a 78-kilo-ampere

(kA) close-latch rating (called a "high momentary" rating), which includes

Models AM-4.16-250-6, -7, -8, or -9HB (the "H" suffix indicates the ML-13 type

mechanism and the "B" indicates the high momentary rating).

Within this population, the major factor determining susceptibility is the

number of prop springs installed. With one anomalous exception (a breaker

suspected of being grossly out of adjustment), only breakers with one prop

spring have thus far been reported to experience unreliable latching.

Breakers of these models built before about 1968 were originally fitted at the

factory with a single prop spring. After this time, breakers with close and

latch ratings of 77 Ka or 78 Ka were factory fitted with two prop springs, in

order, according to GE, to make the breakers less sensitive to fit and

adjustment tolerances and to facilitate factory setup. The failure analysis

testing indicated that breakers built with or modified subsequently to add a

second (upper) prop spring, and that are not otherwise in severely out of

tolerance condition, should not be susceptible to this failure mode.

Attachment 1

IN 94-54 August 1, 1994 The breaker manufacturer, in GE Service Advice Letter (SAL) No. 073-348.1, issued in December 1990, recommended replacement of the main (lower) prop the

spring with an improved spring (called the "gold" prop spring because of

color of its cadmium plating). NRC Information Notice 90-41, "Potential

Failure of General Electric Magne-Blast Circuit Breakers and AK Circuit fitted

Breakers," also addressed this problem. The gold prop spring has been original

in breakers built since 1971, due to fatigue failures reported in the

spring. Although SAL 073-348.1 did describe the dual prop spring

configuration, it did not address the addition of a second prop spring. See

Attachment 2.

Recent breaker overhauls/repairs that included replacement of the Tuf-Loc

(Teflon-coated fiberglass) prop bushings with aluminum-bronze prop bushings, in conjunction with cleaning and relubrication of the closing linkage and

renewal of worn parts have not been demonstrated conclusively to be the sole

cause of the recently reported failures to latch. However, they appear to

have been the common precipitating events. In breakers of the affected models

with one prop spring that have had all the Tuf-Loc bushings (except for the

prop bushings) replaced with aluminum-bronze, the recently reported failures

to latch have begun to occur after about 35-50 operations (cycles) after prop

completion of overhaul or repair that included replacement of the Tuf-Loc

bushings with aluminum-bronze. Since 1975, these breakers have been fitted

with aluminum-bronze sleeve bearings or bushings in their mechanisms (except

for the prop bushings) for improved wear characteristics. Many of the older in

Magne-Blast breakers, in accordance with GE SAL 073-318.1 (and .1A), issued

1977, and 318.2, issued in 1979, have had their original Tuf-Loc bushings "GE

replaced with the aluminum-bronze bushings. IE Information Notice 84-29, Magne-Blast Circuit Breaker Problems," also addressed this issue. The factory

bushing replacement kits, supplied under catalog no. 0156C9403G001, did not

include replacement bushings for the prop. Hence, most prop bushing

replacements have been performed only recently.

When other conditions in a breaker are conducive to marginal latching, it

appears that the new bushings, in conjunction with reduced friction in the

closing linkage from the overhaul, cleaning and new lubricant, may shift the

force and speed balance in the mechanism. The shift can be sufficient to

speed up the motion of the closing linkage and prop pin relative to the prop

(which also may actually be slightly retarded) beyond design margins. Under

these conditions, a single prop spring can no longer move the prop forward

fast enough to latch reliably, or if it does latch, to ensure the desired prop

wipe. Where the second prop spring has been installed in conjunction with the

mechanism overhaul, failure to latch reliably in the manner described hereinnot

has not been reported, and according to GE, as confirmed by testing, would

be expected to occur. Disassembly and detailed inspection of the Maine Yankee

breaker operating mechanism after testing revealed no additional significant

factors contributing to the failures to latch experienced by the test breaker.

Therefore, the test results appear to have confirmed the factors to which

close-latch reliability is most sensitive.

Attachment 2

1, IN 94-54 August 1, 1994 Page 1 of I

MAGNE-BLAST OPERATING MECHANISM PROP DIAGRAMS

1. Handle

2. Trip Coil Support

3. Trip Coil

4. Trip Armature

5. PROP SPRING

5A. SECOND PROP SPRING

(if fitted)

6. Cam Follower Roller

7. Trip Shaft

8. Trip Latch

9. Trip Latch Roller

10. Roller Support

11. Crank Shaft

12. Cranks

13. PROP PIN

14. PROP

15. Drive Shaft

16. Cam

17. PROP BUSHING

FRONT OF BREAKER

Figure 1 (Adapted From Figure 7 of GE Instruction Book GEI-88761)

Figure 2: Right Side View of ML-13 Operating Mechanism

(From Figure 4 of GE Instruction Book GEI-88761)

Attachment 3

' IN 94-54 August 1, 1994 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

91-45, Possible Malfunction of 07/29/94 All holders of OLs or CPs

Supp. 1 Westinghouse ARD, BFD, for nuclear power reactors.

and NBFD Relays, and

A200 DC and DPC 250

Magnetic Contactors

94-42, Cracking in the Lower 07/19/94 All holders of OLs or CPs

Supp. 1 Region of the Core Shroud for boiling water reactors

in Boiling-Water Reactors (BWRs).

94-53 Hydrogen Gas Burn Inside 07/18/94 All holders of OLs or CPs

Pressurizer During Welding for nuclear power reactors.

94-52 Inadvertent Containment 07/15/94 All holders of OLs or CPs

Spray and Reactor Vessel for nuclear power reactors.

Draindown at Millstone

Unit 1

94-51 Inappropriate Greasing 07/15/94 All holders of OLs or CPs

of Double Shielded Motor for nuclear power reactors.

Bearings

94-50 Failure of General 07/14/94 All holders of OLs or CPs

Electric Contactors for nuclear power reactors.

to Pull in at the

Required Voltage

94-49 Failure of Torque 07/06/94 All holders of OLs or CPs

Switch Roll Pins for nuclear power reactors.

94-48 Snubber Lubricant 06/30/94 All holders of OLs or CPs

Degradation in High- for nuclear power reactors.

Temperature Environments

94-13, Unanticipated and Unin- 06/28/94 All holders of OLs or CPs

Supp. 1 tended Movement of Fuel for nuclear power reactors.

Assemblies and other

Components due to Improper

Operation of Refueling

Equipment

OL = Operating License

CP = Construction Permit

IN 94-54 August 1, 1994 This information notice requires no specific action or written response. If

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

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

orig /s/'d by CIGrimes/for

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Stephen Alexander, NRR

(301) 504-2995 Kamalakar Naidu, NRR Sikindra Mitra, NRR

(301) 504-2980 (301) 504-2783 Attachments:

1. Details of Failure Mode and Contributing Factors

2. Magne-Blast Prop Mechanism Diagram

3. List of Recently Issued NRC Information Notices

SEE PREVIOUS CONCURRENCE

VIB:DRIL VIB:DRIL SC/VIB:DRIL TECHED

SAlexander* KNaidu* GCwal ina* MMejac*

05/19/94 04/14/94 05/19/94 04/18/94 C/VIB:DRIL:NRR D/DRIL:NRR EELB:DE:NRR C/EELB:DE:NRR

LNorrholm* CERossi* SMitra* CBerlinger*

05/24/94 05/27/94 07/06/94 07/11/94 OGCB:DORS:NRR AC/OGCB:DORS:NRR D/:DORS:NRR

PWen* ELDoolittle* BKGrimes(Y-

07/13/94 07/14/94 OT/94

07D NAM 1 OFFICIAL RECORD COPY DOCUMENT NAME: 94-54. IN

NOTE: The PMs for Maine Yankee (E. Trottier) and Millstone-1 (J. Andersen)

have been informed of the development of this information notice, and

their comments have been incorporated.

Steve Alexander of the Vender Inspection Branch has consulted with GE on

the technical accuracy of this information notice. GE's comments have

been incorporated.

Peter Wen, 7/13/94

IN 94-XX

July XX, 1994 This information notice requires no specific action or written response. If

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

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Stephen Alexander, NRR

(301) 504-2995 Kamalakar Naidu, NRR Sikindra Mitra, NRR

(301) 504-2980 (301) 504-2783 Attachments:

1. Details of Failure Mode and Contributing Factors

2. Magne-Blast Prop Mechanism Diagram

3. List of Recently Issued NRC Information Notices

SEE PREVIOUS CONCURRENCE

VIB:DRIL VIB:DRIL SC/VIB:DRIL TECHED

SAlexander* KNaidu* GCwal ina* MMejac*

05/19/94 04/14/94 05/19/94 04/18/94 C/VIB:DRIL:NRR D/DRIL:NRR EELB:DE:NRR C/EELB:DE:NRR

LNorrholm* CERossi* SMitra* CBerlinger*

05/24/94 05/27/94 07/06/94 07/11/94 OGCB: QRS:NRR AO/ :DORS:NRR D/:DORS:NRR

PWen tV\1 E 4ff^1ttl e BKGrimes

07/13 /94 07/" /4 07/ /94 4 OFFICIAL RECORD COPY DOCUMENT NAME: GEMAGNET.IN

NOTE: The PMs for Maine Yankee (E. Trottier) and Millstone-I (J. Andersen)

have been informed of the development of this information notice, and

their comments have been incorporated.

Steve Alexander of the Vender Inspection Branch has consulted with GE on

the technical accuracy of this information notice. GE's comments have

been incorporated.

Peter Wen, 7/13/94

IN 94-XX

July XX, 1994 Normal prop wipe can be confirmed with the breaker in its cubicle and closed