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Guidelines for Repair/Replace Decisions 16
ELECTRICAL APPARATUS SERVICE ASSOCIATION, INC. www.easa.com
Guidelines for
Repair/Replace Decisions
and Performance Optimization
Electrical Apparatus
Service Association, Inc.
1331 Baur Blvd.
St. Louis, Missouri 63132 USA
314-993-2220 FAX 314-993-1269
www.easa.com
This paper was presented by Austin H. Bonnett, EASA Education and Technology Consultant
at EASA's Convention in Chicago, Illinois, June 25, 2001 1
ELECTRICAL APPARATUS SERVICE ASSOCIATION, INC. www.easa.com
By Austin M. Bonnett
Education and Technology Consultant
Electrical Apparatus Service Association, Inc.
St. Louis, Missouri
Chuck Yung
Technical Support Specialist
Electrical Apparatus Service Association, Inc.
St. Louis, Missouri
ABSTRACT
For general-purpose motors, there are many cases where
replacing a failed motor with a new one of EPACT effi-
ciency levels or better is the best choice. However, in
some cases, the motor will fail again unless the root cause
of failure is addressed through some modification to the
motor or the system.
There are also many cases where repairing the existing
motor is the best choice. This is especially true if an up-
grade is required to address the cause of failure, or in
some cases, where cost, availability or unique perfor-
mance is an issue. The motor service center is in an
excellent position to make these assessments. The pur-
pose of this paper is to explore both choices and present
some of the many options available.
Quite often when a motor fails, the procedure is to re-
move the damaged motor from service and replace it
without a thorough evaluation of the root cause of the
failure. Depending on the motor size and the amount of
damage, the old motor may be repaired and placed into
spares inventory or even scrapped.
The problem with this approach is that the replacement
motor, whether new or rebuilt, may fail again for the same
reason. If a root cause failure analysis is conducted, it is
often possible to identify and correct the underlying
cause. All that may be required is to modify the motor,
driven equipment or system to extend the
mean time
between failures
(MTBF) significantly.
In most cases, where a standard motor is no longer suit-
able for the application, the service center is able to make
the required modification faster than the motor manu-
facturer can produce a unique model.
The application checklist in Appendix A can be used to
assist in this analysis.
INTRODUCTION
The Electrical Apparatus Service Association (EASA) has
established Recommended Practices for its 2500 mem-
bers around the world to assure that the repair process
does not degrade the motor performance characteris-
Reliable Solutions Today!
GUIDELINES FOR REPAIR/REPLACE DECISIONS
AND PERFORMANCE OPTIMIZATION
This paper was presented at EASA's Convention in
Chicago, Illinois, June 25, 2001.
MOTOR REPAIR BEST PRACTICE GUIDES
The Electrical Apparatus Service Association (EASA)
has available the following repair guidelines to assist
in providing quality motor repairs.
ANSI/EASA AR100-1998,
Recommended
Practice for the Repair of Rotating Electrical Ap-
paratus
, Copyright 1998.
Association of Electrical and Mechanical Trades
(AEMT)
Good Practice Guide: The Repair of
Induction Motors, Best Practices to Maintain En-
ergy Efficiency
, Crown Copyright 1998.
EASA
A Guide to AC Motor Repair and Re-
placement
, Copyright 1999.
These documents can be obtained from EASA head-
quarters in St. Louis to be used as reference
documents when selecting or working with a motor
repair facility.
Appendix D includes several sample pages from these
documents. 2
ELECTRICAL APPARATUS SERVICE ASSOCIATION, INC. www.easa.com
Guidelines for Repair/Replace Decisions and Performance Optimization
tics. This paper provides the reader with a repair guide-
line to implement these procedures with their local repair
organizations.
Criteria are presented to determine when the repair of
the motor is not practical and may lead to reduced effi-
ciency levels. In some cases, it is possible to improve
the level of operating efficiency during the repair pro-
cess.
EASA members rebuild electrical equipment, primarily
motors and generators. Many EASA service centers also
rebuild peripheral equipment such as pumps and
switchgear.
EASA is in the process of conducting a major test pro-
gram to verify the results of these Recommended
Practices. This paper will include an update on this work
in progress.
EASA/AEMT MOTOR REWIND STUDY
INTRODUCTION
Previous studies were conducted on motors in the 10 hp
range at four-pole speeds, which do not reflect the true
degree of difficulty associated with rewinding the typical
failed motor. The EASA/AEMT Motor Rewind Study is
focusing on motors that are more typically rewound for
both the NEMA and IEC designs.
OBJECTIVE OF STUDY
The major objectives of the study include:
Issue a best practice guide for motor rewinds.
Determine whether low- and medium-voltage ma-
chines respond similarly.
Investigate the impact of repeated rewinds of the
same motor.
Establish the correlation between the
static core
loss test
and the
running core loss test
.
Evaluate the impact of physical damage to the sta-
tor core.
SCOPE OF PRODUCT EVALUATED
There will be at least 27 motors used in the study, most
of which will be in the 50 to 200 hp range. Both 50 and
60 Hertz will be included, as well as low- and medium-
voltage, IEC and NEMA frames, ODP and TEFC
enclosures and two- and four-pole speeds.
PARTICIPATING MANUFACTURERS
AND INSTITUTIONS
At least seven different motor manufacturers have com-
mitted to provide motors, technical data and assistance
for the study. The Dowding and Mills facility in Birming-
ham, UK will facilitate all motor modifications and repairs
that are part of the study. The University of Nottingham
will perform the basic load testing on their dynamom-
eters in Nottingham. There may be additional tests
performed at Dowding and Mills.
ROUND ROBIN TESTING AND TEST PROTOCOL
One motor will be selected for round robin testing to en-
sure the accuracy of the Nottingham University facility.
These tests will be conducted at the U.S. Electrical Mo-
tors Motor Technology Center in St. Louis, Mo. and the
Invensys Brook Crompton UK plant. Both IEEE and IEC
methods of efficiency testing will be conducted. All test-
ing will include (at no load and full load) a loss segregation
method that allows for detailed analysis.
OTHER DELIVERABLES
It is expected that due to the large size of the sample
and the data collected additional deliverable might be
developed as part of a supplementary document. It may
be possible to update an EASA tutorial on other aspects
of motor repair that affect overall motor performance and
efficiency. Winding configuration, span, slot fill, flux den-
sity and mechanical factors will be considered.
SCHEDULE
The motors are all now at the University of Nottingham
FIGURE 1: REPAIR OR REPLACE OPTIONS
Failed motor
Options
Repair
Replace
EPACT
Level Efficient
Premium
Efficient
Customized
motor
Redesign/Upgrade
Optimize horsepower
to load
Optimize voltage
Change speed
Inverter-duty winding
Increase insulation
class
Modify
Improve enclosure
Add seals
Make bearing
modifications
Restore
Repair to original
condition 3
ELECTRICAL APPARATUS SERVICE ASSOCIATION, INC. www.easa.com
Guidelines for Repair/Replace Decisions and Performance Optimization
FIGURE 2: REPAIR OR REPLACE DECISION PROCESS
Failed motor
Additional considerations include increased reliability, life expectancy and benefits of additional features, upgrades
or modifications.
What is the condition of the
stator core?
Is the motor suitable for the
application?
Investigate replacement with suitable motor (size/enclosure).
Is return on investment of EPACT
motor acceptable?
Is it an EPACT motor?
Has catastrophic failure occurred,
or is there evidence of prior
catastrophic failure?
Is the rotor damaged, or is there
severe damage to other
mechanical parts?
Is the cost of repair greater than
the cost to replace the motor?
Is replacement motor available?
Are replacement funds available?
Is lead time of replacement motor
acceptable?
Significant damage or high losses
Yes
Yes
No
Yes
No
No
No
OK
Yes
Yes
Yes
Yes
Yes
No
No
No
No
Repair motor
Replace motor
Yes
No
Special cases
(e.g., very expensive
motors)
and testing is under way. lt is expected that this evalua-
tion will be complete by the end of 2001. The co-chairmen
are David Walters and Austin Bonnett. The technical
group will review progress monthly and have already held
one meeting in Birmingham.
REPAIR-REPLACE DECISION MODEL
In the past, the decision whether to repair or replace an
electric motor has been one of economics. Replacement
of an older electric motor with a more efficient model
often makes sense for a motor operating continuously.
However, in most cases the decision is more complex
(Figures 1 and 2). A motor operating infrequently, a mo-
tor with special mounting or design features, an EPACT
motor or a motor larger than those covered by EPACT
are all examples where the repair option may be the bet-
ter choice.
When comparing the cost to replace or repair an electric
motor, the equation should include