Information Notice 1991-07, Maintenance Deficiency Associated with General Electric Horizontal Custom 8000 Induction Motors
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
February 4, 1991 NRC INFORMATION NOTICE NO. 91-07: MAINTENANCE DEFICIENCY ASSOCIATED WITH
GENERAL ELECTRIC HORIZONTAL CUSTOM 8000
INDUCTION MOTORS
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
This information notice is to alert addressees to a possible problem resulting
from improper maintenance that may affect the operability of Horizontal
Custom 8000 induction motors manufactured by the General Electric Company
(GE).
The problem relates to inadequate tightening of the bolts securing the
air deflectors to the motor-end shield. 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 do not constitute NRC requirements;
therefore, no specific action or written response is required.
Description of Circumstances
On August 24, 1990, Northeast Utilities (NU), the licensee for the Millstone
Nuclear Power Station, Unit 3, notified the U.S. Nuclear Regulatory Commission
(NRC) that the lower fan shroud on the inboard side of one of the reactor
plant component cooling water pump (RPCCW) motors had come loose and impacted
the motor rotor causing a loud noise during its operation. The licensee
inspected the motor and determined that the protective glass tape on the end
turns of the drive-end winding had sustained damage; however, the mica
insulation was not damaged. Additional observations indicated that the
drive-end lower air deflector was loose and damaged with minor tears and
cracks. The licensee evaluated the available evidence and determined that the
cause of failure was the loosening of the clamps of the drive-end lower air
deflector. The licensee believes that excessive vibration caused the clamping
bolt to loosen and that a reduction in the metal contact grip of the clamps
and the air deflector (because metal had been worn away at the corner)
permitted the air deflector to loosen. GE repaired the damaged motor by
welding the lower shroud clamping bracket. A licensee inspection of the other
two RPCCW pump motors and additional motors of similar size and model
identified loosened shrouds on six motors and one with cracked upper shrouds.
The licensee tightened the loose bolts and repaired the cracks by welding.
91019//14
IN 91-07 February 4, 1991 Discussion:
Typically, the GE Horizontal Custom 8000 series motor models are assembled
with split air deflectors at both erds of the motor. The circular air
deflectors are cut through the center into two halves, and each half is
secured to the motor-end shield with clamps, hex-head machine screws, and
star-lock washers at the circumference of the air deflectors.
Similar
vertical motors are equipped with upper and lower air deflectors (constructed
from one piece, instead of two halves). In both designs, the air deflectors
direct incoming air to shaft-driven fans and cool the motor and stator. In
the vertical motor, the upper deflector is mounted directly over the fan and
is supported either by brackets or by 1/4-20 hex-head machine screws. If a
bracket or screw(s) fails, it could fall into the rotating fan and be
propelled into the winding end-turn, causing failure of the motor.
In General Electric Nuclear Energy (GENE) Service Information Letter (SIL)
No. 484 of March 29, 1989, GENE discussed problems with air deflectors installed
in vertical motors. This SIL summarized several other specific experiences
and lessons learned from the use of similar GE alternating current (AC)
induction motors in various applications in boiling water reactors (BWRs).
In paragraph 8 of this SIL, GENE (1) described the purpose of air deflectors
in vertical motors, (2) discussed the damage that may result if a bracket or
screw loosens and falls into the rotatina fan, (3) recommended that owners
ensure that their procedures for motor disassembly and overhaul should include
a provision to visually inspect the air deflector fasteners, anfd (4) recommended
that the 1/4-20 hex-head screws securing the air deflector be replaced during
each reassembly. On October 5, 1990, GENE issued Supplement 1 to SIL No. 484, which discussed several additional lessons learned from the application of the
AC induction motors.
In Paragraph 2 of this SIL, GENE discussed its experience
with loose air deflectors on Horizontal Custom 8600 Motors and recommended that
users ensure that the screws securing the air deflectors were tightened and
maintained at the required torque. The SIL requested users to contact the
GENE local representative for information pertaining to a design modification
to prevent bolt loosening for some motor models.
Because the issues discussed in the SILs only reflected BWR experience, GENE
only issued the SILs to BWR owners. Therefore, the NRC is concerned that
non-BWR owners may not have received all of the information on these problems.
Although GE normally sends service advisory letters (SALs) to other equipment
manufacturers and non-BWR owners to communicate problems identified in GE
products, GENE has informed the NRC that it had not issued SALs on this matter
because the GE facility that manufactured these types of motors ceased to exist.
Therefore, a copy of GENE SIL No. 484 and Supplement 1 to SIL 484 has been
enclosed with this information notice for the benefit of non-BWR addressees.
0
t
-1 IN 91-07 February 4, 1991 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 NRR project manager.
( v
C
et&-
Charles E. Rossi, Direct
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Kamal R. Naidu, NRR
(301) 492-0980
Attachments:
1. SIL No. 484, March 29, 1989
2. Supplement 1 to SIL No. 484, October 5, 1990
3. List of Recently Issued NRC Information Notices
Attachment 1
zI
91,07
February 4, 1991
£Page
Iof 8
SAN JOSE, CALIFORNIA
March 29, 1989 SIL No. 484 File Tab A
Category 3 R
wrMC
VIM GE AC IddUCTON MOTORS
Introduction
This SIL sizmarizes specific experiences and lessons learned from applications
of GE AC induction motors in BWRs. The information contained in this SIL has
been collected from GE Nuclear Energy's own experience base as well as those
of GE Service Shops and BWR owners. It concerns motors that either have
failed, have exhibited abnormal running characteristics such as high tempera- ture or vibration or have required replacement parts. Investigations that
followed such motor performance problems led to the data and recommendations
contained in this SIL.
The purpose of this SIL Is to assist BWR owners in selecting applications.
specifying refurbishment practices and performing field tests to improve the
reliability of GE AC induction motors.
Recommended Action
GE Nuclear Energy recommends that BWR owners review the experiences and
lessons learned that are summarized in Attachment 1 to this SIL for applica- bility to their plants. If a motor fails, a root cause evaluation should be
undertaken so that appropriate repair can be made and information can be added
to the experience base.
Please note that item 12, "Broken Or Cracked Surge Ring Brackets Should Be
Replaced", is a folloup to RICSIL 016 issued by GE Nuclear Energy on April 11,
1988.
To receive additional information on this subject or for assistance in Imple- menting a recommendation, please contact your local GE Nuclear Energy Service
Representative.
Technical Source:
J. S. Mokri
Issued by:
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J. G. Moore
Marketing Services Manager, Product Communications
Product Reference
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Plant Recommendations
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ATTACHMENT 1
Category 3 FIELD EXPERIENCES AND LESSONS LEARNED FOR GE AC INDUCTION MOTORS
1.
MOTOR OPERATION DURING BUS TRANSFERS MAY CAUSE DAMAGE:
Experience:
GE AC induction motors typically installed at BWRs are designed to
operate at both rated and reduted voltage, to start and accelerate the
standard NEMA MG1 load inertia and to start from zero speed from a single
voltage source.
As described in paragraph 15 of ANSI C50.41 (1977),
motors are typically designed to withstand a maximum supply difference of
1.33 per unit volts per hertz during bus transfers.
If operating motors are transferred from one power source to another
(e.g., bus transfers between plant transformer and startup transformer)
and if the line voltage and frequency are significantly out of phase with
the electromotive force (EMF) generated by the motor when the contactor
is opened (e.g., outside the ANSI.C50.41 criteria), the internal compo- nents of the motor may be stressed electrically and mechanically beyond
design limits.
This has been the postulated cause of motor damage at
at least one BWR.
Some motors at newer plants have been designed with
additional end-turn support rings to carry the higher loads that may
occur during fast bus transfers.
Recommended Action:
GE Nuclear Energy recommends that BWR owners review their plant design to
determine how frequently motors may be subjected to fast bus transfers
and how many redundant motors could be affected simultaneously by such
transfers.
If more than 10 fast bus transfers could occur during the
life of the plant or if a number of safety related motors could be
affected, the switching times should be investigated relative to ANSI
C50.41 criteria.
2.
ANTIFRICTION BEARING INTERNAL CLEARANCE SHOULD BE SPECIFIED:
Experience:
Motor shaft bearings are designed and specified to have certain internal
clearances between the inner race, balls and outer race.
This-clearance
is designed to be both large enough to permit radial thermal expansion of
the shaft and the bearing components and small enough to prevent excess- ive shaft movement and vibration. If the shaft temperature is high
relative to that of the bearing housing or if ambient temperatures are
high, the internal clearance is reduced. The specified clearance allows
the bearing to rotate without internal interference at high temperatures
and to support the shaft when the motor is starting and at low
temperature conditions.
Generally, manufacturers of commercial bearings do not distinguish
between standard (designated "CO")
and loose (C3) internal clearances.
The CO and C3 nomenclature is defined in the bearing standards of the
Anti-Friction Bearing Manufacturers Association (AFBMA).
- 1.1
ATTACHMENT I
Category 3
2.
ANTIFRICTION BEARING INTERNAL CLEARANCE SHOULD BE SPECIFIED: (Cont'd.)
Recommended Action:
GE Nuclear Energy recommends that BWR owners specify the internal
clearance class for bearings in procurement specifications and receiving
inspection documentation.
The class should be specified using the AEBMA
nomenclature and should be consistent with the motor's design
specification.
Motor maintenance practices and procurement dedication programs also
should include requirements for measuring the internal clearance of
bearings to assure that clearance specifications are met.
3.
SPACE HEATERS SHOULD BE ENERGIZED WHEN A MOTOR IS IN THE STANDBY MODE:
Experience:
A motor's space heaters protect its internal components from moisture
condensation if the temperature of the air around the motor is at or
below the dew point.
Stator windings impregnated with epoxy applied
under a vacuum are not affected by. .moisture as much as randomly wound or
polyester varnished windings are affected.
In all cases, however,
-
bearings, laminations, shafts and support components within a motor are
affected adversely by moisture. Although most motors originally were
provided with space heaters, some motors have been installed with no
provisions for energizing the space heaters.
Recommended Action:
GE Nuclear Energy recommends that BWR owners assure that space heaters
furnished with motors are energized when the motors are in the standby
mode.
The environmental qualification basis of some motors is contingent
upon protecting the motors from moisture with space heaters.
In such
motors, the heaters must be energized to maintain the environmental
qualification status.
To reduce the ambient heat load to motor, .GE also recommends that BWR
owners de-energize the space heaters when a motor is operating.
The
thermal life of a motor's insulation materials is reduced by a factor of
about 2 for each 10 degrees centigrade increase in temperature.
The
heaters are sized to keep the temperature of the winding at least three
degrees centigrade above the ambient temperature. Because the tempera- ture of winding material near the heaters is more than three degrees
above ambient, service life of the winding could be reduced significantly
if the heaters remain energized during operation.
4.
THE TEN YEAR INSPECTION RECOMMENDATION IS IMPORTANT:
Experience:
Experience and reliability data indicate that GE AC induction motors
should be inspected at ten-year intervals.
This inspection interval
-
1.2
ATTACHMENT 1
Category 3
4.
THE TEN YEAR INSPECTION RECOMMENDATION IS IMPORTANT: (Cont'd.).
applies whether a motor is operated continuously, operated intermittently
or stored.
The environmental qualification status of some motors is
contingent upon inspections at this interval.
Recommended Action:
GE Nuclear Energy recommends that BWR owners disassemble and inspect the
internal components of safety related and non-safety related totors
to confirm that none of a motor's functional components are degrading in
service. This inspection should be documented and performed at approxi- mately ten-year intervals regardless of the type of service to which the
motor has been subjected.
5.
MOTOR DRAIN PLUG O-RING AND SIGHT GLASS O-RINGS SHOULD BE REPLACED:
Experience:
Oil reservoir drain plugs typically have O-ring seals made of a low
nitrile buna material. Oil and oil operating temperature eventually
degrade this material, potentially reducing the effectiveness of the
seals.
Although GE motors are qualified for post-accident conditions, engineering studies have shown that high radiation and the typical
100-day, elevated temperature operating condition may accelerate the
degradation of low nitrile buna material seals and lead to an oil leak.
Recommended Action:
GE Nuclear Energy recommends that BWR owners replace the low nitrile buna
0-rings with medium nitrile buna-N O-rings containing at least 27%
nitrile to improve seal reliability and increase the life of the seals.
The 0-rings should be replaced at every other oil change.
The sight glass O-rings are made of similar material.
These also should
be replaced with medium nitrile buna-N O-rings containing at least 27%
nitrile when the motor is disassembled for overhauling or rewinding.
6.
HIGH CYCLE FATIGUE HAS CAUSED CONDUIT BOX GASKET FAILURES:
Experience:
The gasket between the main conduit box and the motor frame is made of a
1/4 inch thick, resilient material. The purpose of the gasket is to
support the lead cables from the frame and to provide a seal between the
conduit box and the frame.
The conduit box bolts compress the gasket.
The compressed gasket is one of the components in the bolted joint that
maintains a preload on the bolts. Over time, the gasket relaxes and the
preload on the bolts diminishes. With a reduced preload, the bolts can
loosen under normal operating conditions.
At some plants, vibratory loads have caused the bolts to fail from high
cycle fatigue.
It has been reported that this has occurred on three
motors in safety related service.
In one case the conduit box partially
cut the lead cables when the box separated from the frame.
-
1.3 -
ATTACHMENT 1
Category 3
6.
HIGH CYCLE FATIGUE HAS CAUSED CONDUIT BOX GASKET FAILURES: (Cont'd.3V
Recommended Action:
A replacement gasket with metal inserts molded into the gasket is
available.
The inserts reduce the effect of gasket relaxation and the
probability of bolt fatigue failure.
GE Nuclear Energy recommends that
BWR owners either install these replacement gaskets during the next
periodic maintenance of the motors or contact GE Nuclear Energy for a
recommended modification to the existing gaskets;.
7.
SLEEVE BEARINGS SHOULD BE INSPECTED FOR PLUGGED-OIL PASSAGES:
Experience:
The upper bearing on high thrust motors-uses'a plate bearing for thrust
loads and a sleeve bearing for radial loads.
Lubricant for both bearings
is metered through orifices and passages in the bearing housing'casting.
During motor inspections at some plants, it has been discovered'that'
chips and other debris in the oil have plugged the'oil passages' a&t their
intersections with internal 90-degree holes. These internal passages- are difficult to inspect and occasionally'have been oveilooked during, motor overhauls. Under conditions of high'ambient temperatire' and high
side load, plugged passages could jeopardize the supply of lubricant-to
the bearing assembly.
Recommended Action:
GE Nuclear Energy recommends-that BWR owners confirm that their motor
disassembly and overhaul procedures require inspecting'the' internal oil
passages and orifices for plugging and removing any plugging from this
bearing assembly when the motor is disassembled and inspected.
'
8.
AIR DEFLECTOR BRACKETS SHOULD BE INSPECTED FOR CRACKING:
9'
Experience:
Vertical motors are equipped with upper and lower air d'eflectors to
direct incoming air to shaft-driven fans.
The upper deflector is mounted
directly over the fan and is supported either by brackets or 1/4-20 hex
head machine screws.
If a bracket or screw fails, it could fall into the
rotating fan, be propelled into the winding end-turn and cause motor
failure.
One BWR owner reported a bent deflector bracket with cracks 'completely
through its thickness.
It is possible that a bracket in this condition
could fail and fall into the motor windings.
Recommended Action:
GE Nuclear Energy recommends that BWR owners assure that their!.procedures
for motor disassembly and overhaul require a visual inspection of the air
deflector brackets. The 1/4-20 screws should be replaced during each
-
1.4 -
ATTACHMENT 1
Category 3
8.
AIR DEFLECTOR BRACKETS SHOULD BE INSPECTED FOR CRACKING: (Cont'd.)
reassembly.
These screws often have been overtorqued during a previous
reassembly and, therefore, may be partially fractured.
9.
TERMINAL LUGS SHOULD BE INSPECTED FOR CRACKING:
Experience:
As a result of NRC Bulletin 88-27, attention has been given recently to
damaged feeder cable termination lugs. Some lugs have identification
stamps near the transition which produce stress risers. On others, stiff
cable splices require extra force to insert the termination into the
conduit box.
This contributes to mechanical failures of the lugs.
At
one plant, a motor had improperly crimped termination lugs which fell off
the leads during an inspection.
The lead was shortened and stripped to
install a new lug, necessitating lead replacement.
Recommended Action:
GE Nuclear Energy recommends that BWR owners consider either increasing
the length of motor lead cables to reduce mechanical stresses or
installing oversized conduit boxes when motors are in the service shop-.
10.
SHAFT END-PLAY ADJUSTMENT IS CRITICAL TO BEARING LIFE:
Experience:
Shaft end-play is necessary to allow unrestrained thermal expansion of
the rotor during transient conditions and to minimize axial shuttling of
the rotor. At some plants, bearings, shaft sleeves and bearing housings
have been damaged because of. improper end-play adjustment.
Because motor instruction manuals are written in a general format for
several different bearing configurations, the appropriate shaft end-play
may not be evident from drawings in the manuals. For example, angular
contact bearings mounted in the DF configuration do not require shaft
end-play adjustment. However, the same bearings mounted in the DT
configuration do require end-play adjustment of the top shaft nut.
Recommended Action:
GE Nuclear Energy recommends that BWR owners either consult the text of
motor manuals to determine the types of bearing assemblies used on their
motors and the methods of end-play adjustment that should be used for
each bearing assembly when motors are reassembled or contact GE Nuclear
Energy for guidance.
11.
ANTIFRICTION BEARING INNER RACE TO BEARING CARRIER DIMENSION IS CRITICAL
TO BEARING LIFE:
.Experience:
Antifriction bearing life and load capability depend on specified close
- 1.5 -
ATTACHMENT 1
Category 3
11.
ANTIFRICTION BEARING INNER RACE TO BEARING CARRIER DIMENSION IS CRITICAL
TO BEARING LIFE: (Cont'd.)
tolerances.
If the inner race is not mounted on the carrier with a tight
fit, relative movement between the race and the carrier is possible.
This can cause unacceptable wear. Bearing manufacturers discuss this
failure mechanism in their commercial catalogs. Measurements of several
vertical motors recently inspected in a GE Service Shop showed that the
fit between the bearing inner race and the shaft was outside the design
limit and required corrective action.
Recommended Action
GE Nuclear Energy recommends that when a motor is disassembled and
available for dimensional inspection, BWR owners measure the bearing to
bearing carrier dimensions to confirm that these dimensions are within
specified design limits for the motor.
12.
BROKEN OR CRACKED SURGE RING BRACKETS SHOULD BE REPLACED:
Experience:
A variety of methods has been used in GE motors to support end-turns
-
against electromechanical loads that develop during starting transients
and bus transfers. Surge ring brackets are used on some vertical motors.
Cracks in surge ring brackets have been reported in NRC Information
Notice 87-30 and in RICSIL 016, "ECCS Motor Bracket Failures", issued by
GE Nuclear Energy on April 11, 1988.
Recommended Action:
GE Nuclear Energy recommends that BWR owners replace surge ring brackets
on motors whose brackets are broken or missing.
If motor inspections
have confirmed that the bend radius of the brackets is no less than 1/4 inch or if a motor's original brackets have been replaced with brackets
with no less than a 1/4 inch bend radius, no additional bracket inspec- tions are necessary.
For motors whose bracket bend radii are less than 1/4 inch and for motors
whose brackets cannot be inspected through the air vents, either inspec- tions in accordance with NRC Information Notice 87-30 should be continued
or plant unique justifications should be prepared for alternative
actions.
13.
HIGH VOLTAGE INSULATION TESTS OF INSERVICE MOTORS SHOULD BE AVOIDED:
Experience:
High voltage motor insulation testing at levels comparable to those used
in the motor manufacturer's factory (e.g., NEMA MG1) usually should be
avoided once the motor has been placed into service. However, after
reassembling a motor in a service shop or power plant or if the condition
of the winding is questionable, it may be appropriate to perform high
voltage tests on the motor at a reduced voltage.
- 1.6 -
ATTACHMENT 1
Category 3
13.
HIGH VOLTAGE INSULATION TESTS OF INSERVICE MOTORS SHOULD BE AVOIDED:
(Cont'd.)
At some plants, test voltages approaching NEMA MG1 levels have resulted
in damage to the windings, necessitating additional repair.
Recommended Action:
GE Nuclear Energy recommends that when high potential tests of GE AC
induction motors are required, BWR owners conduct such tests in
accordance with methods described in IEEE 95 to avoid damaging the
winding. High voltage insulation testing of motors that have been in
service should not be conducted at NEMA MG1 factory voltages.
14.
PREDICTIVE MAINTENANCE METHODS HAVE PROVEN USEFUL IN TROUBLESHOOTING:
Experience:
Some BWR owners have found that the following methods have reduced the
amount of motor troubleshooting required in certain situations and have
been useful in diagnosing motor problems:
a.
Devices for monitoring bearing shock pulse can be installed when-the
motor is disassembled. These devices measure antifriction bearing
spike energy and can be trended to assist in predictive maintenance.
b.
Samples of the oil reservoir lubricant can be analyzed periodically
for contaminants and particles of bearing metal.
Trending of the
analysis results assists in predictive maintenance.
c.
Techniques for rotor bar testing and stray field monitoring have
been developed to assess a motor's condition by analyzing the
frequency spectrum of the motor's current or stray magnetic fields.
These data can be trended or compared with measurements from similar
motors at the plant to determine the motor's condition.
Recommended Action:
GE Nuclear Energy recommends that BWR owners who have had problems with
motors consider predictive maintenance methods both for troubleshooting
problem motors and for predicting motor overhaul schedules.
End of Attachment 1
-
1.7 -
1.40
Attachment 2
I1IN 91-07 GE Nuclen! February 4. 199:
Page I of 6
Geneait Electric Company
175 Curtner Avenue, San Jose C4 95125 S IL SeM=snfonwfidLet
October 5, 1990
SIL No. 484 Supplement 1 Category 3
EXPERIENCE WITH GE AC INDUCTION MOTORS
Introduction
This Supplement 1 to SIL No. 484 summarizes specific experience and lessons
earned from applications of GE AC induction motors. The information
contained in this Supplement has been collected since SIL No. 484 was issued in
March 1989 and is from GE Nudear Energy's experience base as well as those
of GE Service Shops and GE BWR owners. It concerns conditions identified as
a result of investigating motor performance problems or in the course of
performing routine motor inspections and maintenance.
The purpose of this Supplement is to inform GE BWR owners of motor operat- ing and maintenance practices which can contribute to improved reliability of
GE AC induction motors. These are identified in the attachment to this SIL
To receive additional information on this subject or for assistance in Imple- menting a recommendation, please contact your local GE Nuclear Energy Ser- vice Representative.
Technical
Source
Notice
Issued by
Product
Reference
L. S. Mokri
This SL pertains only to GE BWRs. GE Nuclear Energy prepared this SIL ex- dlusiveyas a service for owners of GE BWRs. GE Nuclear Energy has not con- sideredor evaluated the applicability, if any, of information contained in this
SIL to any plant or facility other than GE BWRs. Determination of applicability
of information contained in this SIL to a specific GE BWR and implementation
of recommended action are the responsibilities of the owner of that GE BWR.
No warranty or representation expressed or implied is made with respect to the
accuracy, completeness or usefulness of this information. General Electric
Company assumes no responsibility for liability or damage which may result
from the use of this information.
l. G. Mooe
Customer Service Communications Manager
A72 -Plant Recommendations
Attachment
Experience with GE AC Induction Motors
Experience
1. Motor Fan Bolt Engagement
Many GE AC induction motors installed at GE BWRs are designed with fan
mounting bolts which also are used to secure rotor balancing weights. Thread
engagement of the mounting bolt in the rotor is a nominal 5/8 inch for 1/2'-13 bolts. At a GE BWR/4 it was discovered that a pump motor in service had one
of twelve fan mounting bolts, also used to secure balancing weights, engaged
only 1/4 inch in the threaded hole in the rotor spider subassembly.
GE Nuclear Energy recommends that when motors are disassembled for rotor
maintenance or inspection GE BWR owners verify the amount of thread
engagement of motor fan/spider subassembly bolts which also secure rotor
balancing weights.
Recommended
Action
One at a time, remove all bolts that secure rotor balancing weights. If bolt en- gagement is less than 5/8 inch, replace the original bolt with an SAE Grade 5 safety related bolt of sufficient length to satisfy the 5/8 inch engagement
requirement. Replace balancing weights as necessary, tighten the 1/2 inch bolts
to 70 to 75 ft-lbs and rebalance the rotor.
Experience
2. Loose Air Deflector on Horizontal Custom 8000 Motors
Horizontal Custom 8000 series motor models are typically assembled with split
type air deflectors at both ends of the motor. The circular air deflectors are cut
through the center into two halves and are secured to the motor end shield with
three clamps, bolts and star lock washers at the circumference of the air deflec- tors. Loose air deflectors have damaged motor stator windings and rotor cool- ing fins.
Recommended
Action
GE Nuclear Energy recommends that GE BWR owners take appropriate action
to assure that the bolts securing air deflectors on Custom 8000 motors are tight- ened and maintained at the required torque. A design modification is available
for some motor models to prevent bolt loosening. Information about the modi- fication is available from local GE Nuclear Energy Service Representatives.
Experience
3. Maintenance of Cooling Water Flow Rates and Temperatures
Motors with oil cooling coils require that the cooling water flow rate be greater
than a minimum value and that cooling water inlet temperature be less than a
maximum value to control bearing oil temperature during transient or accident
conditions. Oil temperature usually can be maintained within operating limits
with less than the minimum cooling water flow rate during normal operation if
Supplement 1
Category 3 Page 2
both the cooling water and ambient air temperatures are relatively low.
However, a low now rate risks motor availability during abnormal operating
conditions. Measurements of actual cooling water flow rates at some plants
have identified motors operating with substantially less than the required
minimum flow rate. Furthermore, corrosion product buildup or biological
- rowth can degrade the flow rate. USNRC Generic Letter 89-13 contains more
information on this.
Recommended
Action
GE Nuclear Energy recommends that GE BWR owners verify that all motors, particularly motors in the Emergency Core Cooling System, are supplied with at
least the minimum recommended cooling water flowv rate. Cooling water tem- peratures also should be maintained within recommended limits.
Experience
4. Motor Oil Cooling Coll Corrosion
GE AC induction motors equipped with oil reservoir cooling coils often contain
untreated water in the coils. A cooling water leak in the upper oil cooling coil of
a pump motor at a GE BWR/4 caused the oil reservoir to overflow onto motor
internals, rendering the motor inoperable. Inspections of motor oil coolers on
other motors at the same plant revealed three more cooling coils with corrosion
sufficiently advanced that failure could have occurred at any time. For more
information on this event, please refer to SIL No. 523, Motor Oil Cooling Coil -
Corrosion,' issued August 29, 1990.
Recommended
Action
Severe corrosion leading to failure can develop in cooling coils where water
chemistry, coil materials and operating conditions combine to create an adverse
environment. GE Nuclear Energy recommends that GE BWR owners investi- gate for the presence of corrosion in oil cooling coils. SIL No. 523 provides spe- cific guidelines which may be useful in this effort. If oil level monitors have
been installed, verify that the high and low level alarms are operable.
Experience
S. Space Heater Electrical Lead Replacement
Motor space heaters are installed with the heater electrical leads enclosed in
protective sleeves. Motor inspections at some plants have revealed that the
protective sleeves were degraded.
Recommended
GE Nuclear Energy recommends that GE BWR owners include inspection of
Action
space heater leads and sleeves as part of motor 10-year inspection plans. De- graded sleeves should be replaced with
lass
F-A-I fiberglass-acrylic seeves.
Experience
6. Maintenance of Bearing Insulation
Motor bearing housings generally are designed and installed to be insulated
Supplement 1
Category 3 Page 3 I-
electrically from the motor frame. If the electrical isolation is violated, stray
electric current can flow through the bearing, significantly reducing bearing life.
At some plants, proximity probes have been mounted on motor bearing hous- ings. Grounding paths can be created unintentionally through the probe mount- ing fixture, through a conductive sheath on the instrument cable or through a
grounding connection integral to the instrument.
GE Nuclear Energy recommends that GE BWR owners be aware of the signifi- cance of the insulated bearing assembly and the potential for reduced bearing
life if the electrical isolation is not maintained. Provisions for electrical insula- tion between any instrument mounted on the bearing housing and the motor
frame must be included in any installation. After installing any instrumentation
on an insulated bearing assembly, verify that the bearing assembly is electrically
isolated from the motor frame.
Recommended
Action
Experience
7. Precautions for Tandem Angular Contact Bearing ApplicatIons
Motors in high thrust and reversing thrust applications generally use angular
contact bearings in duplex configurations. Tandem configurations increase the
axial load (thrust) capability of the motor in one direction by distributing the
load between multiple bearings. Face-to-face configurations provide for thrust
capability in both axial directions. For load sharing to occur as designed, individual bearing dimensions must be compatible. If bearing dimensions are
not compatible within a bearing pair, one of the bearings can take a
disproportionate share of the load. This causes accelerated wear and can lead
to early bearing failure. Both types of duplex bearing applications require the
inner and outer bearing races to be ground to specific, close dimensional
tolerances to avoid both excessive preload and endplay.
Recommended
Action
GE Nuclear Energy recommends that GE BWR owners be aware of the need
for tighter dimensional tolerances for duplex bearing applications.
Experience
8 Bearing Wiping During Initial Motor Operation
Recirculation pump motor guide bearing wiping occurred recently on two GE
BWR motors. In both cases the motors were forced to operate outside the
design limits (low oil level after receiving a low level alarm in one case and no
cooling water in the other case). An oil sample from the reservoir of the failed
bearing of one of the motors was analyzed and although the Direct Reading
Ferrography result showed an increase in particles, the operator concluded that
the motor was normal. Low oil level caused a rapid increase in bearing
temperature which led to the bearing wiping.
At two other GE BWRs with similar motors, a combination of factors also
caused upper guide bearing wiping. These factors included differential thermal
Supplement 1
Category 3 Page 4
expansion which reduced the running clearance and caused the bearing wiping.
Oil temperature increased rapidly when the motor was restarted following bear- ing replacement. There was evidence that the motors may have been operating
in this condition for a long time with no adverse consequences under normal op.
erating conditions. Operability of motors with wiped bearings may be question- able under abnormal conditions.
Recommended
Action
If increased bearing oil temperature is observed after motor start-up or if the
motor has been operated with lower than the recommended oil level, a bearing
may have been wiped and, unless analysis of the oil shows no change in oil prop- erties, bearing inspections should be planned and implemented. Minor changes
in oil properties, even though otherwise acceptable, may indicate that the
bearing has wiped. If shaft proximity probes indicate increasing clearance or if
there are other indications of a wiped bearing, justification for continued
operation of the motor should include an evaluation of its ability to operate in
abnormal conditions. Bearing design changes have been installed on some
motors that have experienced wiped bearings to improve lubricant flow and
avoid wiping caused by differential thermal expansion.
Experience
9. Motor Lead Bushing and Conduit Box Gasket
The original SIL No. 484 recommended replacement of original conduit box gas- kets with gaskets of an improved design during the next periodic maintenance
because of gasket relaxation and subsequent bolt loosening and fatigue failure.
The bolts securing the conduit box to the motor frame are safety related for
Class IE motors and should be replaced with new safety grade bolts when the
conduit box gasket is replaced.
GE Nuclear Energy recommends that GE BWR owners be aware of the safety
related function of the conduit box bolts for Class IE applications. Complete
kits including the new gasket design, metal inserts and bolts for both safety and
non-safety applications are available through local GE Nuclear Energy Service
Representatives.
Recommended
Action
Experience
10 Cooling Coil Damage During Motor Installation
At some GE BWRs, motor cooling coils have been damaged inadvertently when
cooling water supply piping was connected to motors. If excessive torque is ap- plied to the coolng coi tube, brazed connections inside the motor can be dam- aged and potentially cause a coil to leak cooling water into the oil reservoir. GE
vertical AC induction motors of recent design are equipped with special cooling
water fittings which do not transmit torque to the cooling coil
GE Nuclear Energy recommends that GE BWR owners include appropriate
precautions in motor maintenance procedures to prevent excessive torque from
Recommended
Action
SIL No. 484 s-
Supplement 1
Category 3 Page 5
being applied when cooling water piping is installed. A replacement fitting of
the new design is available through local GE Nuclear Energy Service Represen- tatives.
Experience
11. Motor Oil Cooling Coil Removal
Motor oil cooling coil reliability and maintenance problems may be avoided by
replacing water cooled coils with air cooling on some motors where the normal
and accident ambient temperatures remain below 140 degrees Fahrenheit.
Recommended
GE Nuclear Energy recommends that GE BWR owners consider converting cer- Action
tain oil cooled motors to air cooling. Information on such conversions is avail- able through local GE Nuclear Energy Service Representatives.
Experience
12. Motor Improvements and Upgrades
Before performing major maintenance on motors, it may be appropriate to con- sider adding motor upgrades and improvements during the maintenance project.
Available improvements include the following:
o
Inst:iation upgrading from Class B to Class F
o
Bearing spike energy probe installation
o
Internally mounted stator and rotor condition monitors
o
Temperature detector installation, if not originally installed
o
Oil reservoir conversion to air cooling
o
Dirt resistant coating application for motor windings
o
Motor stator cooling improvements
o
Oil level monitor
Recommended
GE Nuclear Energy recommends that GE BWR owners consider motor im- Action
provements and upgrades for improved motor reliability, ease of maintenance
and/or added performance monitoring capability. Information about such im- provements is available from local GE Nuclear Energy Service Representatives.
End of Attachment
Supplement 1
Category 3 Page 6
Attachment 3
February 4, 1991 LIST OF RECENTLY ISSUED
HRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
91-06
91-05
91-04
91-03 Lock-up of Emergency Diesel
Generator and Load Sequehcer
Control Circuits Preventing
Restart of Tripped Emergency
Diesel Generator
Intergranular Stress Corrosion
Cracking in Pressurized Water
Reactor Safety Injection
Accumulator Nozzles
Reactor Scram Following Control
Rod Withdrawal Associated with
Low Power Turbine Testing
Management of Wastes Contaminated
with Radioactive Materials ("Red
Bag" Waste and Ordinary Trash)
Brachytherapy Source Management
Supplier of Misrepresented
Resistors
Requirements for Use of
Nuclear Regulatory Comm- Jission-(NRC-)Approved
Transport Packages for
Shipment of Type A Quanti- ties of Radioactive Materials.
Fitness for Duty
1/31/91
1/30/91
01/28/91
01/07/91
01/07/91
01/04/91
12/31/90
12/24/90
91-02
All holders of OLs or
CPs for nuclear power
reactors.
All holders of OLs or
CPs for pressurized
water reactors (PWRs).
All holders of OLs or
CPs for nuclear power
reactors.
All medical licensees.
All Nuclear Regulatory
Commission (NRC) medi- cal licensees author- ized to use byproduct
material for medical
purposes.
All holders of OLs or
CPs for nuclear power
reactors.
All registered users
of NRC-approved
packages.
All U.S. Nuclear
Regulatory Commission
(NRC) material and
non-power reactor
licensees.
91-01
90-82
90-81 OL - Operating License
CP - Construction Permit
I
IN 91-07 February 4, 1991 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 NRR project manager.
,,/,A-Charles E. Rossi, UirecZ
6
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Kamal R. Naidu, NRR
(301) 492-0980
Attachments:
1. SIL No. 484, March 29, 1989
2. Supplement 1 to SIL No. 484, October 5, 1990
3. List of Recently Issued NRC Information Notices
- See previous concurrences.
TECH EDITOR
JMain*
12/17/90
OFC
- YIB:DRIS:NRR
- SC:VIB:DRIS
- C:VIB:DRIS
- D:DRIS:NRR
- C:GCB
- D:OEA
:
:--------CHB-
NAME :KNaidu*
- CVanDenburgh* :EBaker*
- BGrimes*
- CBerlinger*
- CERossi*for
DATE :1/07/91
- 1/08/91
- 1/14/91
- 1/15/91
- 1/22/91
- 1/29/91 OFFICIAL RECORD COPY
Document Name: IN 91-07
IN 914X'
j4-amry.lt
1991 V Page 3 of
This information notice requires no specific action or written response. f
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate NR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Kamal R. Naidu, NRR
(301) 492-0980
Attachments:
1. SIL No. 484, March 29, 1989
2. Supplement 1 to SIL No. 484, October 5, 1990
3. List of Recently Issued NRC Information Notices
DISTRIBUTION
VIB R/F
DRIS R/F
EBaker
KNaidu
CVanDenburgh
BGrimes
CBerlinger
see previous concurrence
TECH EDITOR
JMain*
12/17/90
09I
OFC
- VIB:DRIS:NRR
- SC:VIB:DRIS
- C:VIB:DRIS
- D:DRIS:NRR
- C:GCB
- Da.Ed
NAME :KNaidu*
- CVanDenburgh* :EBaker*
- BGrimes*
- CBerlinger*
- CERossi
DATE
- 1/07/91
- 1/08/91
- 1/14/91
- 1115491
- 1/j.1/
OUFILIPIL KCWKU COPY
LUocument
Ndame: UCuu
u
IN 91-XX
January XX,
1991 Page 3 of
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 NRC region
.
Charles E. Rossi, Director
/
Division of Operational Even
Assessment
Office of Nuclear Reactor
egulation
Technical Contact:
Kamal R. Naidu, NRR
(301) 492-0980
Attachments:
1. SIL No. 484, March 29, 1989
2. Supplement 1 to SIL No. 484, October 5, 1990
3. List of Recently Issued NRC Information Notices
DISTRIBUTION
VIB R/F
DRIS R/F
EBaker
KMaidu
J
CVanDenburgh
BGrimes
/
CBerlinger
- e previous concurrence
TECH EDITOR
JMain* 97p
12/17/96 OFC
- VIB:DRIS:NRR
- SC:VIB:DRIS
- C:YIB:DRIS
- D:DRIS:NRR
- C:GCB(.jf5
- D:OEA
___*______---
- --------------------
NAME :KNaidu*
- CVanDenburgh* :EBaker*
- BGrimes*
- CBerlinger
- CERossl
DATE :1107191
- 1/8/91
- 1/14/91-
- 1/15/91
- 143W91
- 1/
/91 OMrWtiAL RECORKLD COu
uocuieni Rafe;
bt
OUUU
IN 91-XX
January XX, 1991
Page 3 of
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 NRC regional office.
Charles E. Rossi, Director
/
Division of Operational Ev ar(Assessment
Office of Nuclear Reactor
gulation
Technical Contact:
Kamal R. Naidu, NRR (301) 492-0980
,'
Attachments:
1. SIL No. 484, March 29, 1989
2. Supplement 1 to SIL No. 484, March 29, 1990
3. List of Recently Issued NRC Information Notic
DISTRIBUTIO
'IB R/F
D S R/F
EBaper/
/
KNatd
CV ~hnburqf
B inek
Xerlin r
' /*
see previous concurrence
OFC
- VIB:DRIS:NRR
- SC:VIB:DRIS
- C
- D:
K
C:GCB
- D:OEA
_-
-
-
-
-
-
-
-
--
--
__
_
_
_
_
_
_
_
.a
-
-
- _----____--
__-- -_---__
NAME
- KNaidu*
- C;an e
EBaker
- B
s
- CBerlinger
- CERossi
--
-
-
--
-
-
--
-
-
--
--
--
-
--.--
-
-
-
-
---
-
-
-
DATE
- 1/07/91
- 1/W /91
- 1W///91
- 1 (g91
- 1/
/91
- 1/
/91
OFFICIAL RECORD COPY
Document Name: GE8000
IN 91-X'
January XX,
9'91 Page 3 of
This information notice requires no specific action or written respo e. If
you have any questions about the information in this notice, pleas
contact
the technical contact listed below or the appropriate NRC regio
office.
Charles E. Rossi, Dir tor
Division of Operati
al Events Assessment
Office of Nuclear eactor Regulation
Technical Contact:
Kamal R. Naidu, NRR (301) 492- 80
Attachments:
1. SIL No 484, March 29, 1989
2. Supplement 1 to SIL No 484, March 29,
0
3. List of recently issued NRC Informati
otices
DISTRIBUTION
VIB R/F/
DRIS R/F
EBaker
KNaidu
CVanDenb rgh
BGrimes
CBerli ger
OFC
IS:NRR
- SC:VIB:DRIS
- C:VIB:DRIS
- D:DRIS:NRR
- C:GCB
- D:OEA
no-
-
-
NAME
- Naidu
- CVanDenburgh :EBaker
- BGrimes
- CBerlinger
- CERossi
___---:----
_
_
_
__
_-____
__
____
DATE :1/r/91
- 1/ /91
- 1/ /91
- 1/ /91
- 1/ /91
- 1/ /91
OFFICIAL RECORD COPY
Document Name: GE8000