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Electric motors are the backbone of industry. The U.S. Departmentof Energy estimates that in the U.S. alone there are 40 million motorsoperating in industry, and the fact that those motors use 70 % of theelectricity consumed by industry indicates their importance.

A program to avert costly failuresin your facility will benefit fromincluding thermal imaging as acondition-monitoring techniquefor electric motors. Using ahandheld thermal imager, youcan capture infrared temperaturemeasurements of a motorstemperature profile as a two-dimensional image.

Thermal images of electricmotors reveal their operatingconditions as reflected by theirsurfact temperature. Such condi-tion monitoring is important as away to avert many unexpectedmotor malfunctions in systemsthat are critical to manufacturing,commercial and institutionalprocesses. Such preventiveactions are important becausewhen a critical system fails, itinevitably increases costs,requires the reallocation ofworkers and material, reducesproductivity and, if not corrected,can threaten corporate profit-ability and, possibly, the wellbeing of employees, customersand/or clients.

What to check?

Ideally, you should check motorswhen they are running undernormal operating conditions.Unlike an infrared thermometerthat only captures temperature ata single point, a thermal imagercan capture temperatures atthousands of points at once, for

Inspecting

electric motors

For more information on Thermal Imagersgo to www.fluke.com/thermography

Application Note

Applications forThermal Imagers

all of the critical components: themotor, shaft coupling, motor andshaft bearings, and the gearbox.Remember: each motor isdesigned to operate at a specificinternal temperature. The othercomponents should not be as hotas the motor housing.

What to look for?

All motors should list the normaloperating temperature on thenameplate. While the infraredcamera can not see the inside of

the motor, the exterior surfacetemperature is an indicator of theinternal temperature. As the motorgets hotter inside, it also getshotter outside. Thus, an experi-enced thermographer who is alsoknowledgeable about motors canuse thermal imaging to identifyconditions such as inadequateairflow, impending bearing failure,shaft coupling problems, andinsulation degradation in therotor or stator in a motor.

In general, it is a good idea to

create a regular inspection routethat includes all critical motor/drive combinations. Then, save athermal image of each one on acomputer and track measure-ments over time. That way, youllhave baseline images to compareto, that will help you determinewhether a hotspot is unusual ornot, and, following repairs, tohelp you verify if the repairswere successful.

Properly functioning bearings shouldshow cool temperatures.

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What represents ared alert?

Equipment conditions that posea safety risk should take thehighest repair priority. After that,consider that each motor has amaximum operating temperaturethat usually appears on itsnameplate and represents the

maximum allowable rise in tem-perature of the motor aboveambient. (Most motors aredesigned to operate in ambienttemperatures that do not exceed40 C.) Generally speaking, each10 C rise above its rated temper-ature cuts a motors life in half.Regularly scheduled infraredinspections of electric motorsidentify motors which are startingto overheat. Even an initial ther-mal image will reveal whether amotor is running hotter than a

similar motor doing a similar job.

Whats the potential costof failure?

For a specific motor, you could doan analysis based on the cost ofthe motor, the average amount oftime a line is down from a motorfailure, the labor required tochange out a motor, etc.

Of course, productivity lossesfrom downtime vary from indus-try to industry. For example, lostproduction from a papermakingmachine can be as much as$3,000 per hour while in thesteel casting industry losses canbe as high as $1,000 per minute.

Follow-up actionsIf you suspect overheating is theresult of one of the following,consider the action described:a. Inadequate airflow. If a brief

shutdown is possible withoutaffecting the plant process,shut off the motor long enoughto perform minor cleaning onthe air intake grills. Schedulea thorough motor cleaningduring the next planned plantshutdown.

b. Unbalanced voltage or an

overload. The usual cause, ahigh-resistance connection inthe switchgear, disconnect, ormotor connection box, canusually be pinpointed by athermographic inspection andconfirmed using a multimeter,clamp meter or a power qual-ity analyzer.

This thermal image shows a cool motor on the left and a hot gearbox on the right, with anespecially white-hot anomaly.

c. Impending bearing failure.When the thermal imagesindicate an overheating bear-ing, generate a maintenanceorder to either replace the

bearing or lubricate the bear-ing. While somewhat expen-sive and requiring an expert,vibration analysis can oftenhelp you determine the bestcourse of action.

d. Insulation failure. If it will nottoo greatly impact production,de-rate the motor in accor-dance with NEMA standards.Generate a work order toreplace the motor as soon aspossible.

e. Shaft misalignment. In most

cases, vibration analysis willconfirm a misaligned coupling.If a shutdown is possible, dialindicators of laser-alignmentdevices can be used and themisalignment can be correctedthen and there.

Whenever you discover a prob-lem using a thermal imager, usethe associated software to docu-ment your findings in a reportthat includes a thermal imageand a digital image of the equip-ment. Its the best way to com-

municate the problems you foundand the suggested repairs.

2 Fluke Corporation Thermal Applications: Inspecting electric motors

Fluke CorporationPO Box 9090, Everett, WA USA 98206

Fluke Europe B.V.PO Box 1186, 5602 BDEindhoven, The Netherlands

For more information call:In the U.S.A. (800) 443-5853 orFax (425) 446-5116In Europe/M-East/Africa (31 40) 2 675 200 orFax (31 40) 2 675 222In Canada (800) 36-FLUKE orFax (905) 890-6866From other countries +1 (425) 446-5500 orFax +1 (425) 446-5116Web access: http://www.fluke.com

2005 Fluke Corporation. All rights reserved.Printed in U.S.A. 8/2005 2519596 A-EN-N Rev A

Fluke.Keeping your worldup and running.

An imaging tip:Sometimes it is difficult to get a direct view of the component youwant to inspect, such as a motor or gearbox mounted high up on thetop of a machine. Try using a thermal mirror to see the reflection ofthe component. An aluminum sheet (1/8-in. thick) works very well.Either carefully slip it temporarily into place or mount it perma-nently in a location that facilitates your inspection. The aluminumdoes not have to be highly polished to be effective. However, if youare trying to secure true (as opposed to comparative) temperaturereadings, you must learn how to characterize the mirror and adjustyour emissivity readings accordingly. For this technique to work, thesurface of the mirror needs to be clean, since oil and other coatingswill alter the reflective properties of the mirror.