Attachment 1

IN 95-02
January 17, 1995
Page 1 of 2

OPERATION AND FAILURE MODES OF MAGNE-BLAST CONTROL SWITCHES

The stuck open power switch contacts are shown on the breaker connection
diagram as contacts 5 and 6 of "power switch" assembly 52-SM/LS, which
consists of three CR2940 contact blocks or switches ganged together.
Depending on the breaker configuration with the various control options
available, contacts 5 and 6 of 52-SM/LS are known as the "close permissive
switch," the "control power available/closing spring charged switch," or most
commonly, the "white light switch." The breaker electrical connection diagram
(also shown in Attachment 2) shows the three CR2940 contact blocks that
comprise power switch 52-SM/LS as normally open contacts 1, 2, 3, and 4, and
normally closed contacts 5 and 6. Note that at some plants, plant diagrams
may designate these as switches S-1 (5 and 6), S-2 (3 and 4), and S-3

(1 and 2). The three contact blocks are opened or closed simultaneously by
the interaction of their plungers and moving contact carriers, according to
the state of the breaker closing spring. A striker and cam mechanism, which
operates by the action of the breaker closing spring and its charging and
release mechanism, actuates the first contact block plunger. Its moving
contact carrier in turn operates the plunger of the next (middle) tandem
contact block, the moving contact carrier of which then operates the plunger
of the third contact block. Contacts 3 and 4 are in the anti-pump (52Y relay)
circuit and contacts 1 and 2 control the closing spring charging motor. The
switch with contacts 3 and 4 and the switch with contacts 1 and 2 are both of
the normally open (or "momentary contact") configuration with catalog number
CR2940U310. Contacts 5 and 6 are in series with the breaker closing circuit.
The switch with contacts 5 and 6 is a normally closed or "maintain contact"
configuration; catalog number CR2940U301.

In operation, immediately after the breaker closing spring discharges to close
the breaker, contacts 1, 2, 3 and 4 of power switch assembly 52-SM/LS are held
closed during the charging cycle of the closing spring and are allowed to
reopen (by means of their individual internal contact return springs) when the
breaker closing spring is fully charged. There were no reported instances of
mechanical interference and failure to return to the normally open state.
Contacts 5 and 6, held open during closing spring charging, are supposed to
reclose by means of their internal contact return springs when released upon
completion of the breaker closing spring charging cycle. However, the
CR2940U301 contact block containing contacts 5 and 6 in two of the Magne-Blast
breakers being tested failed to reclose when required, thus disabling the
closing control circuits of the breakers. The moving contact bar of the
normally-open configuration contact block (CR2940U310) was a relatively
straight piece; whereas, the moving contact bar of the failed normally-closed
configuration contact block (CR2940U301) was a complex curved piece, which
appeared to make it more susceptible to interference, apparently from excess
plastic mould flashing.

The two normally open (shelf state) configuration CR2940U310 contact blocks in
interlock switch assembly 52IS are ganged together such that they are both
held closed when the vertical lift breaker is fully elevated in its cubicle


IN 95-02
January 17, 1995
Page 4 of 4

At the request of GE NE, the breaker product department is looking into using
a different switch, at least for nuclear safety-related service, that is more
reliable for these Magne-Blast applications, and is planning to issue a
Service Advice Letter (SAL) that will address these problems. Inquiries on
this subject may be directed to GE Nuclear Energy Power Delivery Services in
King of Prussia, Pennsylvania (Phone: 610-992-6049/Fax: 610-992-6191).

This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear

Reactor Regulation (NRR) project manager. hin

Brian K. Grimes, Director
Division of Project Support
Office of Nuclear Reactor Regulation

Technical contact: Stephen D. Alexander, NRR
(301) 504-2995

Attachments:

1. Operation and Failure Modes of Magne-Blast Control Switches
2. Arrangement and Operation of AM-4.16 Control Switches

3. List of Recently Issued NRC Information Notices


Attachment 1

IN 95-02
January 17, 1995
Page 2 of 2

(they can also be closed in the test position). The contact block or switch
containing 52IS contacts 1 and 2 (in series with the breaker closing spring
charging motor circuit) is mounted on the bottom of a small bracket at the top
of the left side of the operating mechanism frame by means of two special
machine screws. The heads of these screws are to be drilled and tapped with
female threads to accept the male threads of the mounting screws of the other
52IS contact block (containing contacts 3 and 4 in the breaker closing
circuit) that is designed to be mounted onto the bottom of the first contact
block. A lever of the breaker cubicle interlock mechanism operates the
Plunger of the upper (charging motor interlock) contact block.
Simultaneously, the moving contact carrier assembly inside the upper switch
operates the plunger of the lower (closing interlock) contact block that
protrudes into the case of the upper contact block. The lack of female
threads being cut into the hole drilled in the head of one of the two special
mounting screws in the upper contact block prevented the use of one screw in
mounting the lower contact block properly. As a result, during subsequent
operations of the breaker, the lower block became loose such that its plunger
could not be depressed to close it by the moving contact carrier of the upper
contact block. The breaker closing circuit therefore did not function.


UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001

January 17, 1995

NRC INFORMATION NOTICE 95-02: PROBLEMS WITH GENERAL ELECTRIC CR2940 CONTACT
BLOCKS IN MEDIUM-VOLTAGE CIRCUIT BREAKERS

Addressees

All holders of operating licenses or construction permits for nuclear power
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to potential failures of General Electric (GE)
Magne-Blast (Types AM and AMH) and Ge/Vac (Type VVC), medium-voltage

(4.16, 7.2, and 13.8-kilovolt) circuit breakers to operate properly because of
defective GE Type CR2940 contact blocks used as control switches in the
breaker control circuits. 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 Circum

In the fall of 1993, during post-overhaul testing of some safety-related
(Class 1E) 4160-Vac circuit breakers (GE Model AM-4.16-250-8HB) at the Maine
Yankee Atomic Power Station (Maine Yankee), there were several failures of the
breakers to close electrically. In two instances, troubleshooting revealed
that although the closing springs for the breakers were fully charged, which
would allow the breakers to be closed manually, the electrical closing control
circuits in the breakers were not being completed. The cause was found to be
stuck open contacts of a CR2940U301 (normally-closed shelf state) contact
block which is one of the three contact blocks in breaker-mounted "power
switch" assembly 52-SM/LS.

In another instance at Maine Yankee, a breaker failed to close electrically
because one of two normally-open configuration CR2940U310 contact blocks used
in cubicle interlock switch assembly 52IS was not being closed as required.
The cause was found to be that the contact block had come loose from its
mounting due to a defective fastener and improper installation.

Attachment 1 to this notice explains in more detail the operation of the

switches and their failure modes and effects. Attachment 2 illustrates the
arrangement and operation of these switches.

9501100350


Attachment 2

IN 95-02
January 17, 1995
Page 1 of i

ARRANGEMENT AND OPERATION OF AM-4.16 CONTROL SWITCHES

+
OR ----po-ve-eeeeeneees Sa poo
x cs :
A h
31 52 if 52
47 1s 7 IS
3]. 59

E | 62
"TSMILS PSMILS | AUX SW

52. = 52
CLAMS AUX SW

FIG. 1 MAGNE-BLAST CONTROL CIRCUIT SCHEMATIC
(ADAPTED FROM INSTRUCTION BOOK GEI-88761)

FIG 2 REF| COMPONENT REF | COMPONENT.
1 2ndy CONNECTOR |10 | LATCH MONITOR SW
6 CAM STRIKER 12 {MOTOR FUSES

FIG. 2 - LEFT SIDE VIEW
ML-13 OPERATING MECHANISM

CIRCUIT | CONTACT | NOMENCLATURE AND FUNCTION | FIGURE 2 REF | SHELF STATE

SYMBOL CATALOG NO.
52 1 and 2 | Power Switch Assembly 8-POWER SW NO.

SM/LS Charging Motor Control 11-MOTOR CR2940U310
52 3 and 4] Power Switch Assembly 8-POWER SW NO

SM/LS 52Y Relay Enable 3-AUX_ SW CR2940U310
52 5 and 6 | Power Switch Assembly 8-POWER SW NC

SM/LS "White Light" 4-LTCH CK SW_| CR2940U301
52 1 and 2 | Interlock Switch Assembly | 2-IS (UPPER) | NO

IS Charging Motor Control 5-SWITCH CAM | CR2940U310
52 3 and 4 | Interlock Switch Assembly | 2-IS (LOWER) | NO

IS Closing Circuit Enable 9-CLSG SPRNG | CR2940U310



IN 95-02
January 17, 1995
Page 2 of 4

Discussion

Power Switch Failures

During a recent overhaul of the 4160-Vac Class 1E breakers at Maine Yankee by
a team from GE Apparatus Service Division (Philadelphia), the over 10-year-old
original CR2940 contact blocks were replaced. Internal examination of the
failed switches revealed that the moving contacts (5 and 6) of the normal ly-
closed contact block were stuck in the open position. This appeared to result
from mechanical interference that prevented reclosure of the contacts by their
internal return springs. These observations raised the question of the
reliability of at least this batch of new CR2940s (their date codes, e.g.,
"MA316="_ indicated 1993 manufacture). The NRC is pursuing this issue with the
CR2940 manufacturer (GE Electrical Distribution & Control or ED&C), the
breaker manufacturer (GE Specialty Breaker Plant or SBP), and GE Nuclear
Energy (GE NE). Preliminary reports indicate that the affected contact blocks
came from a batch or batches that had some excess plastic injection mould
flashing that was apparently interfering with the movement of the moving
contact bar or its carrier assembly. GE ED&C is continuing to investigate to
determine the root cause(s) and scope of the problem, but has already
instituted some initial corrective actions and preventive measures at its
factory in Puerto Rico.

GE SBP has informed the NRC that contacts 5-6 are provided when another
accessory function called [trip] latch checking is supplied as an option. In
some applications, contacts 5 and 6 provide a white light indication on the
switchgear panel that the closing spring is charged and also that control
power is available (hence the term "white light switch").

According to a technical evaluation by the Maine Yankee Plant Engineering
Department, done as part of a modification screening pursuant to Section 50.59
of Part 50 of the Code of Federal Regulations (10 CFR 50.59), contacts 5 and 6
are not required for a close-permissive function to inhibit Closing attempts
during closing spring charging, because the Magne-Blast mechanism design does
not permit breaker closure before the closing spring is fully charged.
Although contacts 5 and 6 have no required function at Maine Yankee, they can
disable the breaker electrical closing circuit should they stick open. In
consultation with GE, Maine Yankee has determined that no required function of
the breaker would be impaired if contacts 5 and 6 are bypassed. However, in
this condition, the light would not indicate closing spring status. The
suitability of such a modification for a given plant would need to be
determined through a technical evaluation.

For certain safety-related loads (e.g., low-pressure safety injection pumps),
the breakers are normally open, but close on engineered safety feature
actuation signals during design basis events. To ensure the reliability of
the affected breakers until the white light switches could be jumpered out,
Maine Yankee required electricians to check the continuity across contacts


IN 95-02
January 17, 1995
Page 3 of 4

5 and 6 immediately after each Magne-Blast breaker closure. In this manner,
the ability of the breaker to be reclosed electrically (by a control room
operator, by an engineered safety feature actuation signal, or by the
emergency diesel generator load sequencer) following a loss of offsite power
in winch: @ breaker has been opened for initial load shedding, can be
confirmed.

Interlock Switch Failure

The two normally open (shelf state) configuration CR2940U310 contact blocks in
interlock switch assembly 52IS are ganged together such that they are both
held closed when the vertical lift breaker is fully elevated in its cubicle or
in the test position. However, in one breaker, the hole drilled in the head
of one of the two special mounting screws in the upper contact block
(fastening it to its mounting bracket) had no female threads tapped into it.
Consequently, the technician installing the new lower contact block as part of
the overhaul was not able to use both screws. Apparently the lower contact
block nevertheless was mounted onto the upper block by only one screw. As a
result, during subsequent operations of the breaker, the lower block became
loose. Its plunger could not be depressed to close it by the moving contact
carrier of the upper contact block, and the breaker closing circuit therefore
did not function.

Several other special fasteners among those in the contact blocks used for the
Maine Yankee breaker overhaul were found to contain deviations such as
incomplete threading and/or shallow screwdriver slots. The manufacturer has
determined that the problems occurred when a screw making machine shut itself
down due to a broken tool. On this occasion, a number of defective screws
that passed through during the shutdown sequence were not captured. The
manufacturer corrected the problem and believes that it is limited to a few
screws in contact blocks with MA3XX= (1993) date codes. The manufacturer has
instituted tighter controls to prevent recurrence and has inspected its stock.
In addition, GE Nuclear Energy has reported upgrading its process for
dedicating the commercial grade components used in manufacturing and
overhauling safety-related breakers. Defective fasteners may be identified by
examination of each contact block upon delivery.

Another problem reported has been CR2940 contacts in the charging motor
circuit becoming welded shut when interrupting charging motor current. In
normal operation, one of the CR2940s in 52SM/LS interrupts motor running
current and very few instances of welding have been reported. However, during
manual interlock lever operation with control power applied, if motor fuses
are not removed, one of the 52IS contact blocks will momentarily energize the
charging motor. When the contacts reopen, they must interrupt motor starting
current (which is much higher than the current normally seen) sometimes
severely pitting or even welding the contacts. In addition, new contact
blocks occasionally have been found to not function during receipt/acceptance
testing (sometimes as part of commercial grade dedication), some due to
incorrect installation of internal parts.