Guidelines for Repair_Replacement

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16ELECTRICAL APPARATUS SERVICE ASSOCIATION, INC. • www.easa.com

Guidelines for

Repair/Replace Decisionsand Performance Optimization

Electrical ApparatusService 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




By Austin M. BonnettEducation and Technology Consultant

Electrical Apparatus Service Association, Inc.

St. Louis, Missouri

Chuck Yung

Technical Support Specialist


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, insome 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 inChicago, Illinois, June 25, 2001.

MOTOR REPAIR BEST PRACTICE GUIDES

The Electrical Apparatus Service Association (EASA)

has available the following repair guidelines to assistin 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.




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 and60 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 MANUFACTURERSAND 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 PROTOCOLOne 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 bedeveloped 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

EPACTLevel Efficient

PremiumEfficient

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





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 theapplication? 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 not only operating

cost and payback period, but also downtime and associ-

ated factors such as capital depreciation, lost

opportunities and customer good will. A replacement

EPACT motor that fails within a year or two may have a

significantly higher cost than a repair that optimizes the

motor for its unique application.





Annual energy savings of several hundred dollars are

quickly wiped out by unscheduled downtime when a

motor fails unexpectedly.

Much of today’s literature emphasizes efficiency and the

cost of energy as stand-alone factors in the repair-re-

place decision matrix. Frequently, the cost of the motor –

or its repair – is a small fraction of the total cost of down-time when lost production is factored in.

Considerations (other than efficiency and simple pay-

back) include reliability, performance and anticipated

motor life as well as availability of a replacement. Of these,

the most critical may be reliability. A motor customized

to its application will offer the greatest chance of long

life. (See Appendix C for a list of repair options.) “Zero

downtime” is a noble goal, one that requires commitment

and planning.

NEMA MG 1-1998 defines Unusual Service Conditions(Appendix B). Most readers will recognize many of these

as the norm for real-life motor applications. By itself, this

fact may be justification for repair and customization of

a failed electric motor.

It makes economic sense to identify the weak link in any

process, and to detect imminent failure before it occurs.

When the weak link is strengthened, the entire process

becomes stronger. A motor subject to accidental wash-

down should be of a suitable enclosure, and can be

modified to further protect the motor from this hazard.

Likewise, since more than 50% of electric motor failures

start as bearing failures, bearing temperature detectors

or vibration probes are logical options in many cases, as

shown in Figure 3.

With today’s rapidly changing technology, the motormanufacturer is hard-pressed to incorporate emerging

technology within a 2- to 3-year period. One advantage

the service center has is its ability to deal with each

unique motor and apply new technology as it develops

to address specific concerns about that particular motor’s

application and environment.

This means the end user can take advantage of unique

technology that meets their unique needs.

B e a r i n g s E n v i r o n m e n t

L u b r

i c a t i o

n

D r i v e

n l o

a d

W i n d

i n g s

L i n e v o l

t a g e

Bearing 51%*

Stator winding 16%*(May have been voltage,

water, overload, etc.)

External 16%*(Environment, voltageand load — will likelyoccur again)

Shaft/coupling 2%Rotor bar 5%

Unknown 10%*(No root causefailure analysis

performed)

* For each component shown, appropriate measures

to either prevent or predict the failure could greatly

reduce three-quarters of motor failures.

FIGURE 3: FAILURES BY COMPONENTS

Reference: IEEE Petro-Chemical paper PCIC-94-01

TABLE 1: LEVELS OF REPAIR

Level 1 Basic reconditioning. Includes replacing

bearings, cleaning all parts and replacing

lubricant. Also adds seals and other acces-

sories as agreed with customer.

Level 2 Includes Level 1 with the addition of varnish

treatment of stator windings, repair of worn

bearing fits and straightening of bent shafts.

Level 3 Includes Level 1 as well as rewinding the sta-

tor (replacing windings and insulation).

Level 4 Includes rewinding of the stator plus major

lamination repair or rotor rebar. May include

replacement of the stator laminations or

restacking of laminations. Shaft replacement

would normally fall into this category. In short,

Level 4 involves major repairs that are costly

enough to justify examining the option of re-

placement.

Level 5 Motors that would normally be replaced ex-cept for special circumstances faced by the

customer (i.e., no spare or unacceptable lead

time for a replacement). Level 5 includes

misapplied motors, inadequate enclosures

and pre U-frame motors. A motor that should

be replaced, if not for the owners’ inability to

operate without it.

As these five levels imply, the damage resulting from

a motor failure varies widely as do the associated re-

pair costs. An evaluation process that fails to consider

the various levels of “repair” is too simplistic to yield

an accurate assessment.





Bearings

• Replace bearings*

• Add seals*

• Install automatic

lubrication device

• Special grease

• Change bearing type*

Windings

• Core damaged?

• Rewind?

Other options

• Upgrade enclosure

• Improve sealing of

the enclosure

• Upgrade paint for corrosion

resistance

Moisture

• Special coatings

• Shaft seals

• Seal leads

• Gaskets

• Seal brackets

• Space heaters

Corrosion

• Special paints

• Varnish treatment

• Stainless steel shaft

Inverters

• Spike-resistant wire

• Higher corona-inception voltage

• Upgrade winding bracing

Heat

• Add RTDs

• Improve fan design

• Heat exchanger

• Upgrade insulation class

Abrasion

• Special energy-absorbing coatings

• Improve wedging

• Upgrade enclosure and add filters

Severe starts

• Better shaft material

• Stronger shaft design

• Additional winding bracing

• Change starting method

Mechanical damage

to shaft and housing

• Is is repairable?

• If replacing shaft, is

there a better material?

• Is stainless steel

warranted?

• Are shaft modifications

warranted?

• Optimize voltage?

• Special coatings?

• Inverter duty?

• Optimize slot fill

• Winding RTDs?

• Repair/restack core

• Replace core

• Change starting method to

reduce in-rush current

• Add space heaters

• Precision balance rotor

• Increase air flow

Special considerations

* Adding seals or changing bearing types may affect efficiency.

Illustration courtesy of Siemens AG

FIGURE 4 : POSSIBLE MOTOR UPGRADES AND MODIFICATIONS

Whether the concern is winding temperature, vibration

or bearing temperature, specific accessories can be in-

corporated into the repair process to enhance motor

life and permit the end-user to monitor the critical fea-

ture.

Consider winding temperature alone: There are 4 dif-

ferent RTD resistances, 14 different thermocouples andnumerous thermistors and bimetallic switches in com-

mon use. Clearly, a stock motor cannot cover all these

options. These features are a special order from motor

manufacturers and usually require long lead times. The

service center is able to tailor the motor repair to match

the monitoring equipment used by the user, incorporat-

ing special features without impacting the repair

turnaround.

Vibration monitoring is available as a continuous, on-

line system. Accelerometers are but one item that can

be retrofitted to improve the user’s ability to predictequipment failure. Non-contact shaft probes, acceler-

ometers intended for continuous monitoring and periodic

data collection, accelerometers integral to a sophisti-

cated continuous monitoring system; all are available





Table 2 illustrates the effect on efficiency and winding

temperature.

Low voltages are especially common in rural areas,

where the motor may be operating at a considerable dis-

tance from the nearest substation. Irrigation pumps and

municipal pump stations are two examples.

While many manufacturers can deliver a motor to opti-

mize non-standard line voltage, typical manufacturer lead

times of five to eight weeks may be prohibitive. The ser-

vice center can accomplish the same voltage optimization

during a motor repair.

An added benefit: It is common practice for manufactur-

ers to produce motors with up to 12 leads, so that the

motor may be used on multiple voltages, often as a part-

winding start or wye-start, delta-run. This means the

electrician may deal with 9 to 12 leads in the junction

box, increasing the chances of a ground failure from

abraded leads. When an electric motor is repaired, the

service center has the option of installing only the num-

ber of leads required. With only 3 or 6 leads, there is

more room in the junction box and less chance of lead

damage or misconnection during installation.

Note: Tri-voltage motors represent a compromise be-

tween the possible applied voltages. This improves

potential availability, to the detriment of efficiency at cer-

tain applied voltages.

VIBRATION MONITORING AND IMPROVEMENT

A Blanchard grinder begins to vibrate, and pieces of valu- able precision plate are scrapped before the cause is

identified.

technology today. Once a user makes the financial com-

mitment to a particular system, it is rarely practical to

abandon it in favor of another emerging technology. That

makes the service center a partner in maintaining the

system(s) selected by each end user.

With most companies returning to their “core business,”

and outsourcing maintenance, the competent servicecenter is best qualified to assess the cause of each mo-

tor failure and develop a plan to reduce the possibility of

a repeat failure. The service center warranty ensures

the repairer has a vested interest in identifying the root

cause of the motor failure, and performing a quality re-

pair.

EXAMPLES OF UPGRADESAND MODIFICATIONS

Once a cause of failure is determined, the service cen-

ter can work with the equipment owner to identify specific

remedies to extend MTBF. The following are but a few

examples of frequent problems — and solutions — ser-

vice centers encounter.

VOLTAGE OPTIMIZATION

A municipal pump station is located at the end of the

power transmission line. Motor failures are common, and

winding temperatures are higher than identical motors

operating at the water treatment plant in town. Repeated

measurements have confirmed chronic low voltage.

When a winding failure is the result of low applied volt-

age, the replacement motor — regardless of efficiency — will be subject to the same low line voltage. The solu-

tion, then, is to redesign the motor to optimize

performance at the actual applied voltage. It is common

to apply a 230 volt motor to a 200 or 208 volt application.

Compounding the problem, the utility supplying 208 volts

is allowed to deviate and may supply even lower voltage.

FIGURE 5: ROTOR BALANCING

Rotor being dynamically balanced in a service center.

stloV 802 032

)%(ycneiciffE 6.08 4.48

)%(rotcafrewoP 0.58 7.28

)spma(tnerrucdaollluF 5.03 9.62

)spma(tnerruchsurnI 921 841

)C°(esirerutarepmeT 19 27

)%(pilS 9.5 1.4

Design B, 4-pole, tri-voltage motor (208-230/460)

TABLE 2: EFFICIENCY AND WINDINGTEMPERATURE





Vibration sensors are vital when the application is a pre-

cision grinder or similar vibration-sensitive equipment.

Installation of vibration probes can be accomplished by

the service center with minimal intrusion into the motor.

Accelerometers can be installed on the frame or in the

junction box, while non-contact shaft probes may be pre-

ferred for sleeve bearing machines. A finishing grinder in

a machine shop must hold close tolerances to minimizescrap. Vibration from a defective bearing can be expen-

sive.

Another good candidate for vibration sensors is a pump

motor operating in a remote location. Continuous moni-

toring by instrument is infinitely better than a weekly visit

by a plant operator.

The service center can install the appropriate vibration

sensing accessories on eligible motors in the course of

each repair.

Manufacturers’ standard motors are balanced to NEMA

MG 1-1998, Part 7 specifications while the service cen-

ter can routinely balance to one-quarter of NEMA or

better. While precision manufacturing has a legitimate

need for this, many end-users request special balance

tolerances because they recognize that there is a reli-

ability factor associated with vibration.

BEARING TEMPERATURE PROTECTION

The cause of a plant fire is tracked back to a bearing

failure. The bearing, unmonitored, failed catastrophically.

Vibration damaged the pump seal and the pump leaked,

by which time the bearing temperature was high enough

to ignite the spewing liquid.

Bearing temperature protective devices (Figure 6) can

be installed during routine repairs to provide early warn-

ing of increased temperature. Excessive lubrication

intervals, high ambient temperature, imminent bearing

failure and other general machinery faults may cause

an increase in bearing temperature before damage oc-

curs. A bearing RTD is not intended to just protect the

bearing, but rather to protect the machinery by alerting

personnel when an equipment fault results in an increase

in bearing temperature. Depending on the critical nature

of the machine, feedback can take the form of a light in

the control room, or automatic shutdown of the equip-

ment.

The service center can install the appropriate tempera-

ture detectors to interface with instrumentation already

in use at the plant.

The cost to fit an electric motor with bearing thermals

may be only a few hundred dollars. That cost should be

weighed against the possible consequences of failure,

not against the cost of the motor.

CORROSION RESISTANCE

A chemical plant removed a 600 hp motor for routine

repairs. The corrosive environment had rusted through

the motor frame in numerous places, even the mounting

Weatherproof terminal head

BearingSpring-loaded, fluid-seal holder

Probe element

Bracket outer wall

Customer's

conduit

entrance

FIGURE 6: BEARING TEMPERATUREDETECTORS

Courtesy of Minco

FIGURE 7: TYPICAL MOTOR ENCLOSUREUPGRADES

Courtesy of Siemens AG





A B C

FIGURE 8: STRESS RAISERS

The lines indicate the path of stresses in the shaft. Where stresses converge, the chance of failure is much higher. The sharp

inside corner of shaft C is 40% weaker than it would be with an appropriate radius.

feet. Although running when removed from service, the

motor was beyond repair and had to be replaced.

When a motor (new or rebuilt) is placed into a known

corrosive atmosphere, the service center can take pre-

cautions to greatly improve motor life. At the simplest,corrosion-resistant paint can be used to protect the frame.

In extreme cases, the shaft can be chrome plated, or

replaced with a stainless steel shaft to better resist cor-

rosive materials. When caustic solutions are evident,

aluminum parts may be quickly eroded. Preventive mea-

sures may be as simple as dipping the rotor with varnish

to protect it. The rotor might even be rebarred using

bronze alloy of similar resistivity to avoid changing the

torque characteristics (rotor cage resistance should be

maintained to avoid changing motor performance). The

rotor should also be balanced after work is done to the

rotor. A precision balance requires only slightly more time

than a “standard” balance.

The exploded view of an open motor (Figure 7) illus-

trates the ease with which various degrees of weather

protection can be accomplished by the addition of cov-

ers, filters or guards. While an open motor is ill-suited to

outdoor operation, the upgraded WPII enclosure was de-

signed for outdoor service.

HIGH-TORQUE APPLICATIONS

An electric motor driving a hammer mill application fre-

quently experiences a broken shaft.

There are several ways to approach this problem de-

pending on the application. One would be to replace the

shaft using material with higher tensile strength than the

original shafting. The corners should all be radiused to

minimize potential stress raisers (Figures 8 and 9). The

keyway can be machined in a manner to reduce the stress

raisers at the end of the keyway (a sled-type keyway as

opposed to a milled keyway.) In extreme cases, the key-

way can be milled with a radius bottom and fitted with a

custom key. It is not necessary to modify the keyway in

the coupling.

Most service centers can machine custom shafts and

keyways to address concerns about fatigue-related fail-ures.

WASH DOWN AND FLOODING

When a power outage occurs, the sump pumps stop and

the pit floods. Electric motors must be removed, cleaned

and dried before production can be restored.

Accidental wash down and flooding cause many electric

motor failures. To increase reliability, special seals are

installed on the shaft openings to exclude water from

the bearings (Figure 10). Special water-resistant grease

can be used to pack the bearings, to further resist wash-ing of lubricants. Sealed bearings may be preferred when

the installation precludes regular maintenance.

The service center can seal T-leads using special pot-

ting compounds to prevent water from entering through

the lead opening. End brackets can be sealed with sili-

cone during the assembly process. These are

inexpensive steps, but are very effective for a motor sub-

ject to flooding or inadvertent wash down. Examples of

VENT FAN

BEARING

ROTOR CORE

BEARING

COUPLING/PULLEY

A B C D E F G H I J

FIGURE 9: STRESS RAISERS

All of the highlighted areas create stress raisers. Points F,H, I and J are usually the most vulnerable because of shaft

load at these points. It is hard for a shaft to fracture atpoints A, B, C, D or E.





candidates for this sort of modification include motors

operating below grade in pump rooms, as well as cool-

ing tower motors.

PROTECTION FROM ABRASIVE DUST

An electric motor operates downwind of a rock quarry

and abrasive dust sandblasts the windings.

Unprotected windings do not last very long in this typeof environment. The service center can topcoat the wind-

ings with a special material that absorbs impact energy,

thus protecting the windings. Filters can be added to

exclude the dust from the motor enclosure, or additional

covers can be installed to upgrade the enclosure.

Motors operating in rock quarries, cement mills or power

plants benefit from this treatment. Motors operating near

agricultural fields may also benefit. These treatments can

also be applied to new motors before they are placed

into service.

RECONNECTION

To reduce starting torque, a wye-start/delta-run connec-

tion can be used. In some cases a motor can be

reconnected, while in other cases a rewind is required.

Other starting options include a VFD or a solid-state soft-

starter.

There will always be applications where reduced start-

ing current will be required. In most cases a Design A

motor will still be justified, when coupled with an appro-priate starter sized for the current. Typical paybacks when

comparing energy savings against capital investment

range between 1 and 3 years, based on the cost of en-

ergy and hours of running time. Wye-delta starting

reduces inrush current to 37% and provides one-third

the torque. Part-winding start methods reduce inrush cur-

rent to one-half to two-thirds while supplying one-half

the starting torque.

The service center can often reconnect an existing wind-

ing to reduce starting current and torque. (See Figure 11.)

ENERGY EFFICIENCY IMPROVEMENT

There are occasions when rewinding a motor where the

opportunity may exist to enhance the motor performance

and reliability by modifying the winding configuration and

copper content. For many designs, the copper loss (I2R)

is the largest loss component (Figure 12). In some cases,

this loss can be reduced by converting from a concen-

tric, machine-wound configuration to a traditional,

hand-inserted lap winding. In many cases, the copper

FIGURE 10: NON-CONTACT BEARING ISOLATOR

The standard-design non-contact bearing isolator consists

of two parts: The stator, which is press-fitted into a bearinghousing and is designed to retain lubricant in the housing,

and the rotor, which in combination with the stator, isdesigned to keep contamination out of the bearing housing.

Courtesy of Inpro/Seals Company

FIGURE 11: ALTERNATIVE METHODSOF CONNECTION

wye start - delta run

double delta

part winding





content (slot fill) can also be increased. Figure 13 shows

the contrast between a relatively low slot fill (40 to 50%

where the wire is PD2 / 4) and one of a much higher per-

cent slot fill (60 to 64%).

This modification will improve heat transfer, reduce the

copper loss and winding temperature and improve mo-

tor efficiency. There will be less coil movement, andincreased resistance to moisture, due to better varnish

retention. Even though these improvements are difficult

for the service shop to quantify, they are none the less

real and will usually improve motor performance and re-

liability. With this modification, the motor’s service factor

will be improved and it will be able to withstand wider

variations in voltage, ambient and starting conditions.

Table 4 shows the possible efficiency improvements that

can be made for a generation of T frame motors pro-

duced during the 1970s and ’80s. Not all motors offer

this opportunity, but for those that do this option should

be considered as a possible product improvement.

CONCLUSION

By incorporating effective technology as it becomes avail-

able, it is possible to reduce downtime, improve

productivity and operate more efficiently. Reduced costs

make an organization more profitable. Savings can be

redirected to improve other “weak links.” The savvy main-

tenance professional is always looking for ways to

improve processes, and the competent service center is

able to assist in this task.

When evaluating the operating cost of an electric motor,

the cost of energy is only one variable (and often not thebiggest one) in the equation. The key to maximizing pro-

ductivity is to eliminate downtime. While zero downtime

is not always possible, any significant reduction in down-

time improves profitability. When downtime is measured

in thousands of dollars per hour, the payback reaped

from extending motor life can be enormous.

The economics of the repair or replace decision process

are complex. All variables must be considered in order

to select the best option.

TCAPE-erplanigirO 52 enihcaM 0.34 5.88 7.88

TCAPE-erpdnuoweR 52 paL 0.26 2.09 8.09

ecnereferTCAPE 52 7.19

TCAPE-erplanigirO 05 enihcaM 0.64 7.19 6.19

TCAPE-erpdnuoweR 05 paL 0.06 4.29 6.29

ecnereferTCAPE 05 0.39

TABLE 4: ENERGY EFFICIENCY IMPROVEMENT

Typical 4-pole, open dripproof, general purpose, T-frame motors of pre-

energy efficient design.

Horsepower

Windingtype

Spacefactor(%)*

Namep

lateNNE(%)

Full-loa

defficiency(%)

*Percent space factor =

Total number of wires per slotD 2

4 of wire

Total slot area - area of insulation

wire diameter

×

×

=

3 14

100

.

D

Stator core losses15-20%

Rotor losses15-20%

Stator winding losses35-40%

Stray load losses10-15%

Friction and windage losses5-10%

FIGURE 12: TYPICAL DISTRIBUTION OF LOSSES

The laminated core, stator windings and rotor account for

as much as 80% of the total losses for the typical electric

motor. While losses are generally associated with lost

efficiency, they represent energy converted to heat.

NEMA Standards MG 10-1994, Table 2-2 (National Elec-

trical Manufacturers Association, Rosslyn, VA, 1994).

FIGURE 13: EXAMPLES OF SLOT FILL

Low slot fill Improved slot fill





• Principles of Large AC Motors . Electrical Apparatus

Service Association, Inc., St. Louis, MO, 2000.

• Intelligent Motors Take the Lead in Predictive Main-

tenance . Matt O’Kane, U.S. Electrical Motors, St.Louis, MO. Presented at EASA Convention 2000,

Anaheim, CA, April 5, 2000.

• Ongoing Issues With AC Electric Motors . Austin

Bonnett, Education and Technology Consultant, Elec-

trical Apparatus Service Association, Inc., St. Louis,

MO, and Cynthia Nyberg, Technical Support Special-

ist, Electrical Apparatus Service Association, Inc., St.

Louis, MO. Presented to the EPRI-sponsored National

Motors & Drives Steering Committee, Montreal, Que-

bec, Canada, June 29, 2000.

• A Survey of Faults on Induction Motors in Offshore Oil Industry, Petrochemical Industry, Gas Terminals

and Oil Refineries . Olav Vaag Thorsen, Senior Mem-

ber IEEE and Magnus Dalva, Member IEEE. IEEE

Transactions on Industry Applications, Vol. 31, No. 5,

Sept./Oct. 1995.

• Root Cause Failure Analysis for Large AC Induction

Motors. Austin Bonnett, Education and Technology

Consultant, Electrical Apparatus Service Association,

Inc., St. Louis, MO. Presented at EASA Convention

1999, Toronto, Ontario, Canada.

REFERENCES





APPENDIX A • Application Checklist

Voltage

• What is the nominal voltage?

• How much voltage variation is present?

• Is there voltage drop when starting under load?

• Is there nuisance tripping?

• Are there transient peaks?Environmental factors

• What is the frequency of moisture ingression?

• What is the frequency of condensation?

• What is the ambient temperature range?

• What other contaminants are present?

Load conditions

• Are there load swings? If so, how wide?

• What is the hp required versus rated hp?

• What is the load – pump, fan, compressor, conveyor?

How is the motor mounted / coupled?

• Direct coupled • What are the thrust conditions?

• Overhung load • Describe the motor’s mounting.

Starting method

• Across-the-line • Part-winding start

• Wye start, Delta run • Soft-start

Frequency of starting

• What is the running time between starts?

• How many starts per hour / 8-hours / 24-hours?

• Is it a demand system?

• Is it a constant or variable load?

• Describe the cycling.• Are there load-shedding opportunities?

Describe unusual service conditions

• See Appendix B, NEMA MG 1-1998, 14.3

Describe the application

• How critical is the operation?

• Is it a dedicated or redundant system?

• What is the availability of spares or backups?

• What are the consequences of shutdown?

History of failures or repairs

• Has the motor been rewound? If so, how many

times?

• What is the mean time between failures?

Root cause failure analysis

• What is the cause of failure?

• What can be done to eliminate the cause?

• What is the best method to detect the condition?

Are there similar motors and applications?

APPENDIX B • Unusual Service Factors, NEMA MG 1-1998, 14.3

14.3 UNUSUAL SERVICE CONDITIONS

The manufacturer should be consulted if any unusual ser-

vice conditions exist which may affect the construction or

operation of the motor. Among such conditions are:

a. Exposure to:

1. Combustible, explosive, abrasive, or conducting dusts

2. Lint or very dirty operating conditions where the accu-

mulation of dirt may interfere with normal ventilation

3. Chemical fumes, flammable or explosive gases

4. Nuclear radiation

5. Steam, salt-laden air, or oil vapor

6. Damp or very dry locations, radiant heat, vermin in-

festation, or atmospheres conducive to the growth of

fungus

7. Abnormal shock, vibration, or mechanical loading from

external sources

8. Abnormal axial or side thrust imposed on the motorshaft

b. Operation where:

1. There is excessive departure from rated voltage or

frequency, or both (see 12.45 for alternating-current

motors and 12.68 for direct-current motors)

2. The deviation factor of the alternating-current supply

voltage exceeds 10 percent

3. The alternating-current supply voltage is unbalanced

by more than 1 percent (see 12.46 and 14.36)

4. The rectifier output supplying a direct-current motor is

unbalanced so that the difference between the highest

and lowest peak amplitudes of the current pulses over

one cycle exceed

10 percent of the highest pulse amplitude at rated arma-

ture current

5. Low noise levels are required

6. The power system is not grounded (see 14.31)

c. Operation at speeds above the highest rated speed

d. Operation in a poorly ventilated room, in a pit, or in an

inclined position

e. Operation where subjected to:

1. Torsional impact loads

2. Repetitive abnormal overloads

3. Reversing or electric braking

4. Frequent starting (see 12.55)

5. Out-of-phase bus transfer (see 14.45)6. Frequent short circuits

f. Operation of machine at standstill with any winding con-

tinuously energized or of short-time-rated machine with any

winding continuously energized

g. Operation of direct-current machine where the average

armature current is less than 50 percent of the rated full-

load amperes over a 24-hour period, or continuous

operation at armature current less than 50 percent of rated

current for more than 4 hours





At the time of the motor repair, in addition to the task of

restoring the motor to its original condition, it is possible to

make modifications and upgrades. During the repair it may

become evident that the motor will fail again if returned to its

existing environment without modification. It may also be ex-

pedient to implement certian “upgrades” to enhance motor

performance, reliability and life.

The following is a list of possible options that may be con-

sidered by the repair facility.

Bearings

• Enclosure — sealed, shielded or open

• Roller or ball (for direct couple or radial load)

External seals

• Non-contact bearing isolator

• Lip seal

Lubrication

• Synthetic grease• Automatic grease applicators

• Oil-mist systems

• Forced-lube oil systems

• Mineral oil for food service or potable water applica-

tions

Severe starting conditions

• Increase rigidity of winding blocking

• Redesign to wye start, delta run to reduce torque and

inrush current

• Increase slot fill

Environmental protection

• Abrasion resistance

Special coatings

Full-length slot wedges for form coil machines

• Corrosion resistance

Special epoxy paints

Stainless steel shafting

Lead potting compound

Filters

Screens, baffles or covers

Power considerations

• Power factor correction capacitors

• Surge protection or lightning arrestors

Increase motor cooling

• Directional fans

• Special fans to increase air flow

• Heat exchanger

• Auxiliary blower (especially for VFD-fed motors)

• Maximize slot fill

Special accessories

• Winding temperature detectors

• Bearing temperature detectors

• Vibration monitoring: accelerometers or non-contact

shaft probes

• Oil chamber heater and thermostat for cold climates

Leads

• Bring out minimum number of leads

• Seal the lead opening against moisture and chemicals

• Increase the lead size

• Other special considerations such as bus bar, special

lugs, etc.Noise reduction

• Add soundproofing material

• Add exterior shrouding

• Utilize special fan configurations

• Special balance requirements

Outlet box

• Size

• Better enclosure for weather protection

Efficiency considerations

• Voltage optimization

• Upgrade insulation class

• Concentric to lap conversion

• Optimize span

• Maximize slot fill (copper and insulation)

• Connection options (wye start, delta run; part-winding

start)

Field support

• Startup

• Predictive maintenance

Vibration monitoring

Current analysis

Thermography

Tribology

APPENDIX C • Repair Options





APPENDIX D • Motor Repair Guidelines and Resources

EASA AR100-1998 Recommended Practice - Rev. January 1998

TABLE OF CONTENTS

SECTION 1: GENERAL1. 1 P U RP OS E

1.2 S COP E

1 .3 I D E N TI F I C ATI O N

1.3.1 Serv ice Center Labeling

1 .3 .2 R ec or ds

1 .3 .3 N a me pl a t e

1 .4 C L EAN IN G

1 .5 TE R M I NA L L E AD S

1.6 TERMINAL CONNECTORS

1 .7 TE R M I NA L B OX E S

1 .8 C O OL I N G S YS TE M

1 .9 E X TE R I OR F I NI S H

1.10 PACKAGING AND TRANSPORTATION

SECTION 2: MECHANICAL REPAIR

2 .1 S H AF TS

2 .1 .1 S h a f t E xt e n si on s

2 .1.1 .1 Diameter Tolerances

2 .1.1 .2 Permissible Runout

2 .1.1 .3 Keyseat (Keyway) Width

Tolerances

2. 2 B E AR IN GS

2 .2 .1 B a l l o r R ol l er B e ar i n gs

2 .2 .2 S l ee v e B e ar i ng s

2 .2.2 .1 Sleeve Bear ing E nd-Thrust

2 .2.2 .2 Oil R ings

2 .2 .2 .3 S e a l s

2 .3 L UB R I C ATI O N

2. 3. 1 G r ea s e

2. 3. 2 O il

2 .4 F R AM E A ND B E A R I NG H O US I N G S

2 .4 .1 G e ne ra l

2 .4.2 Mounting Sur face Tolerances ,

Eccentricity and Face Runout

2 .5 L AM I NA TI O NS

2 .6 B AL AN CI N G

2. 7 S LI P R IN GS

2.8 COMMUTATORS

2 .8 .1 M a ch in in g

2 .8 .2 Un d e rc u tt i n g

2 .9 B R U SH H OL D ER S

2 .1 0 B R US H E S

2.11 BRUSH SETTING FOR DC MACHINES

2.12 AIR GAP MEASUREMENTOF DC

MACHINES

2.13 ACCESSORIESTABLE S

2 -1 S h a f t E x t e n si o n D i ame t e r To l er an c e s—

NEMA Frame Size Machines

2-2 Shaft Extension Diameter Tolerances—IEC

Frame Size Machines

2-3 Permissible Shaft Extension Runout—NEMA

Frame Size Machines

2-4 Permissible Shaft Extension Runout—IEC

Frame Size Machines

2-5 Shaft E xtension Keyseat Width Tolerances—

NEMA Frame Size Machines

2-6 Shaft Extension Keyseat (Keyway) Width

Tolerances—IEC Fra me Size Machines

2-7 Sleeve Bear ing Diametral Clearance Guide—

Horizontal Mounting

2-8 Labyr inth Seal Diametral Clearance Guide

2-9 Mounting Surface Tolerances, Eccentricity,

and Face Runout—NEMA Type C Face-

Mounting Motors and Type D Flange-Mount-

ing Motors

2-10 Mounting Surface Tolerances, Eccentricity,

and Face Runout—NEMA Type P Flange-

Mounting Motors

2-11 Mounting Rabbet (Spigot) Diameter Toler-

ances—IEC Flange-Mounted Machines

2-12 Mounting Sur face Eccentr ici ty and Face

Runout—IEC Flang e-Mounted Machines

2-13 Brush-to-Brushholder Cleara nce

SECTION 3: REWINDING

3. 1 I N SP E C TI O N

3 .1 .1 Wi n d in g s

3 .1 .2 C o re L ami na t i on s

3 .1.3 Thermal Protectors or Sensors

3 .2 R E WI N D I NG S P E C I F I C ATI O N

3 .3 S TR I P P I N G O F WI N D I NG S

3.4 INSULATION SYSTEM

3 .5 C O ND UC TO R S

3.6 STATOR, ROTOR, AND ARMATURE

COILS

3 .6.1 Random-Wound Coils

3 .6.2 Form-Wound Coils

3. 7 F I E LD CO I LS

3 .7 .1 S t a t i on ar y Co il s

3 .7 .2 R ot a t i n g C o il s

3 .8 AMORTISSEUR AND SQUIRREL CAGE

WINDINGS

Table of Contents, Page 1 EASA AR100-1998 Recommended Practice - Rev. January 1998

3.9 THERMAL PROTECTORS OR SENSORS

3.10 SHAPING AND LACING OF STATOR

WINDINGS

3.11 COIL CONNECTIONS

3.11 .1 Making Connections

3 .11 .2 Insulat ing Connections

3 .1 2 WE D G E S

3.13 BANDING OF ROTORS AND

ARMATURE S

3.14 IMPREGNATION OF WINDINGS

SECTION 4: TESTING

4.1 SAFETY CONSIDERATIONS

4.2 INSULATION CONDITION TESTS

4 .2 .1 I n s pe ct i on

4 .2.2 Insulat ion Resis tance Test

4 .2.3 Polar izat ion Index (P-I) Test

4 .2.4 Insulat ion Power Factor Tests

4 .2.5 Step Voltage Test

4 .2.6 Turn-to-Turn Test

4 .2.7 Inter laminar Insulat ion Test

4 .2.8 Bear ing Insulat ion Test

4 .3 RECOMMENDED WINDING TESTS

4.3.1 Stator and Wound-Rotor Windings

4 .3.2 Squirrel Cage Windings

4 .3 .3 Ar mat ur e W in d in g s

4 .3.4 Shunt, Ser ies , In terpole, Compen-

sating and Synchronous Rotor

Windings

4 .3.5 Interconnection of Windings

4 .4 HIGH-POTENTIAL TESTS

4 .4 .1 Wi n di n gs

4 .4.1 .1 New Windings

4.4.1.2 Reconditioned Windings

4.4.1.3 Windings Not Recondi-

tioned

4 .4.2 Accessor ies

4.4.2.1 New Accessories

4.4.2.2 Accessories of Machines

with Reconditioned

Windings

4.4.2.3 Accessories of Machines

with Windings Not

Reconditioned

4 .5 NO-LOAD TESTS

4. 5. 1 S pe ed

4. 5. 2 C u rr en t

4 .5 .3 C oo li n g S y st e m

4 .5 .4 S o un d Le v el

4 .5 .5 B e ar in g T e mper a t u r e

4 .5.6 Vibration Tests

4 .6 P E R F O RM AN C E T E S TS

4.7 INSTRUMENTCALIBRATION

TABLE S

4-1 High-Potential Test U sing AC—New

Windings

4-2 High-Potential Test Using DC—New

Windings

4-3 High-Potential Test U sing AC—New

Accessories

4-4 High-Potential Test Using DC—New

Accessories

4-5 Unfi l tered Vibration Limits—Resiliently

Mounted Machines

APPENDIX: ELECTRICAL TESTING

SAFETY CONSIDERATIONS

A.1 PERSONAL SAFETY

A. 1. 1 Tr a in in g

A. 1. 2 C lo th in g

A .1 .3 S uper v is i on

A. 1. 4 F i rs t Ai d

A. 2 TE S T A RE A

A .2 .1 E n c lo sur e

A. 2. 2 G a t es

A. 2. 3 S ig ns

A. 2. 4 L ig ht i ng

A .2 .5 S a fe t y E q u ipmen t

A .2 .6 Te s t Un it C l e a ran c e

A. 3 UN I T UN D E R TE S T

A.3 .1 Suitabi l i ty for Test

A.3 .2 Exclusive Attention

A. 3. 3 G r ou n di ng

A.3.4 B a se

A. 4 TE S T P A NE L S

A .4 .1 C o ns t r uct i on

A. 4. 2 V ol t a ge s

A .4 .3 War n i ng L ig h t s

A .4 .4 D i s co n ne ct

A. 4. 5 S a f et y S w i t ch

A. 4. 6 L ea d s

A.4 .7 High-Potential Ground Test

BIBLIOGRAPHY

STANDARDS ORGANIZATIONS &

OTHER RESOURCES

Note: Sections pertaining to the repa ir of l iquid-filled

and dry-type distribution transformers were withdrawn

from this edition of EASA Recommended Practice for the

Repair of Rotating Electr ical Apparatus .

Table of Contents, Page 2

EASA AR100-1998 Recommended Practice - Rev. January 1998

Standards Organizations & Other Resources

The following organizations produce documents

and standards, some of which are referenced in the

EASA Recommended Practi ce for th e Repair of Ro-

tat ing El ectr ical Apparatus .

ABMA—American Bearing

Manufacturers Association

1200 19th St., NW, Suite 300

Washin gton, DC 20036

(202) 429-5155

Fa x: (202) 223-4579

ANSI—American National

Standards Inst itute

11 West 42nd St., 13th Floor

New York, NY 10036

(212) 642-4900

Fa x: (212) 302-1286

IEC —Internat ional

Electrotechnical Commission *

3 rue de Varembe

CH 1211 Geneva 20, Switzerland

IEEE—Institute of Electrical and Electronics

Engineers, Inc.

345 East 47th St.

New York, NY 10017

(212) 705-7900

Fa x: (212) 752-4929

For Publications:

445 Hoes Lane

P. O. Box 1331Piscat awa y, NJ 08855-1331

(800) 678-4333

Fa x: (908) 981-9667

ISO—Internat ional Organizat ion

of Standardizat ion *

1 rue de Varembe

CH 1211 Geneva 20, Switzerland

MIL-STD—United Sta tes Government

Printing Office

710 North Capitol St.

Washin gton, DC 20420

(202) 512-1800

Fa x: (202) 512-2250

NEMA—National Electrical

Manufacturers Association

1300 N. 17th St., S uite 1847

Rossly n, VA 22209(703) 841-3200

For Publications:

(703) 841-3201

Fax: (703) 841-3300

NFPA—National Fire

Protection Association

One Bat terymarch Park

Quincy, MA 02269

(617) 770-3000

Fax: (617) 770-0700

For Publications:

P. O. Box 9146

Quincy, MA 02269

(800) 344-3555

Fax: (617) 984-7057

NIST—National Institute of

Stan dards a nd Technology

Route 270

Gaithersburg, MD 20899

(301) 975-2000

UL—Underwriters’ Laboratories, Inc.

333 Pfingsten Rd.

Northbrook, IL 60062

(847) 272-8800, Ext . 42612

Fax: (708) 272-8129

Standards Organizations

* IEC and ISO standards are available through ANSI, which

is the American representative to all international stan-

dards groups.





A Guid e T o A C M oto r R epa ir And Rep lac eme nt

Table Of Contents

Introduction ............................................................................................................................1

Plan Ahead............................................................................................................................. 2

Why Motors Fail ..................................................................................................................... 2

Making The Decision To Repair Or Replace .............................................................................. 3

Obtaining Quality Motor Repairs .............................................................................................. 8

Specifying A Motor Rewind......................................................................................................11

Evaluating And Selecting A Motor Service Center ..................................................................... 13

Obtaining Motor Repairs Of The Highest Quality...................................................................... 15

EASA’s Quality Initiatives........................................................................................................ 16

About EASA.......................................................................................................................... 17

Appendix: Motor Repair Procedures ........................................................................................18

References............................................................................................................................. 21

Prepared by Electrical Apparatus Service Association, Inc. in cooperation with the U.S. Department of Energy’s Motor Challenge Program.

Copyright©1999 Electrical Apparatus Service Association, Inc.1331 Baur Blvd., St. Louis, MO 63132, 3 14-993-2220.

APPENDIX D • Motor Repair Guidelines and Resources (continued)

CONTENTS

P a g e

Introduction ........................................... ................................................. .... 1

Energy Losses in Induction Motors .............................................. ......... 4

The Motor Repair P rocess .......................................... ............................. 7Prelimina ry Inspection ................................................. .................... 7

Repair or Replacement of P arts . . . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . . . 9

Repairs to the Rotor Assembly ............................................... .........11

Recording the Winding Deta ils ............................................. ......... 13

Stripping the Stat or Winding.. . . . . . . . . .. . . . . . .. . . . . . .. . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . 14

Specifying the Replacement Winding ............................................ 17

Cleaning and Inspecting the St r ipped S tator . . . . . .. . . . . . .. . . . . . .. . . . . . .. . . . . 21

Rewindin g ............................................. ........................................... 22

Testing the Wound St ator ............................................. .................. 23

Impregnating and Cleaning the Rewound Stat or . . . . . . .. . . . . . .. . . . . . .. . . . 24

Re-assembly .................................................. ................................... 25

Testing the Assembled Motor ................................................ ......... 28

Appendix 1 ............................................. .................................................. .. 30

Winding Variations; Their Effect on Performance

Appendix 2 ............................................. .................................................. .. 34

Burn-out Ovens and Their Effect on St ator Core Losses

Appendix 3 ............................................. .................................................. .. 38

Calcula tion of Losses and Efficiency From Test Da ta

Appendix 4 ............................................. .................................................. .. 40

Glossa ry of Terms

Appendix 5 ............................................. .................................................. .. 42Check List of Best P ractices to Mainta in Energy E fficiency

AEMT

Association of Electrical and Mechanical Trades

G OOD P RACTICE G U IDE

THE REPAIR OF

INDU CTION MOTORSBest Practices

to Mainta in Energy E ff iciency

© Crown Copyright 1998

All rights reserved. No part of the publication may be produced or transmit ted in

any form or by any means, including photocopying and recording, without the

written permission of the copyright holder, application for which should be addressed

to the publishers. Such writt en permission must a lso be obtained before any part

of this publication is stored in a retrieval system of any nature.

ISB N: AEMT 0 9509409 3 3

Published by t he Association of Electrical and Mechanical Trades

177 Bagnall Road, Basford, Nottingham, NG6 8SJ

Tel. 0115 978 0086 Fa x. 0115 942 4488

Reprinted with permission (1999) by


1331 Baur B lvd., St. Louis, MO 63132 U.S.A.

314-993-2220 • Fax: 314-993-1269 • ww w.easa .com

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