fluke test tools keep your motors and motor drives up and running

7/29/2019 Fluke Test Tools Keep Your Motors and Motor Drives Up and Running

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Application Note

Most facilities need to get maxi-mum life out of their motors,because they are expensive toreplace in terms of both moneyand labor. Electrical, insulationresistance and thermal measure-

ment are three tests that cantroubleshoot motors, drives, andassociated electrical panels andprolong their operational lifetime.Used together, thermal imagerscan detect potential problemsand insulation resistance andelectrical tests can determine thecause.

Handheld thermal imagerssuch as the Fluke Ti30 can col-lect heat signatures from a rangeof motors, from 1000 hp down to5. A thermal imager is good forspot checks, to see if motors and

associated panels and controlsare operating too hot, and fortroubleshooting, to track downthe specific failed component atfault. It can also check for phaseimbalance, bad connections, andabnormal heating on the electri-cal supply.

Electrical, insulation andthermal measurements

for motors and drivesInsulation multimeters and thermal imagers:

Two testers that go great together.

An insulation multimeter likethe Fluke 1587 canperform most of the other testsyou need to troubleshoot andmaintain motors. When a motoris having problems, check the

supply voltage and then useinsulation testing to check thestarter and control contacts,measure the insulation resistanceof the line and load circuits toground, and winding resistancephase to phase and phase toground.


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2 Fluke Corporation Electrical, insulation and thermal measurements for motors and drives

About thermal measurements

A motors heat signature will tellyou a lot about its quality and

condition. If a motor is overheat-ing, the windings will rapidlydeteriorate. In fact, everyincrease of 10C on a motorswindings above its design oper-ating temperature cuts the life ofits windings insulation by 50percent, even if the overheatingis only temporary.

If a temperature reading in themiddle of a motor housing comesup abnormally high, take a ther-mal image of the motor and findout more precisely where the

high temperature is coming from,i.e. windings, bearings or cou-pling. (If a coupling is runningwarm it is an indicator of mis-alignment.)

There are three primarycauses for abnormal thermal pat-terns; typically most are theresult of a high-resistance con-tact surface, either a connectionor a switch contact. These willusually appear warmest at thespot of high-resistance, coolingoff the further away from the

spot. This thermal image showsa classic pattern in the centerphase connection on the line-side of a breaker; note how theconductor cools off at the top ofthe image.

Load imbalances, whethernormal or out of specification,appear equally warm throughoutthe phase or part of the circuitthat is undersized/overloaded.Harmonic imbalances create asimilar pattern. If the entire con-ductor is warm, it could be

undersized or overloaded; checkthe rating and the actual load todetermine which.

Failed components typicallylook cooler than similar, normallyfunctioning ones. The most com-mon example is probably ablown fuse. In a motor circuitthis can result in a single phasecondition and, possibly, costlydamage to the motor.

Examples

This thermal image shows a drive cabinet with hot connections on both Aand B phases. The exact cause cant be determined solely from the image,although it may be a load or balance issue.

This image shows another bearing prob-lem with heat also transferring into thecoupling on the right side.

This image shows a warm bearing (or seal) on the pump. Clearly the accessis tight but we can still compare the bearing to the housing around it.

This image shows the motor itselfheating up, due to reduced airflowor, more probably, to misalignment.


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1. Visual inspection

First, look for a reason NOTto energize. Remove powerfrom the motor and starter(or drive), following lockout/tagout procedures, and dis-engage the motor from theload.

Conduct a visual, smell,and heat inspection,interview the client andcheck the nameplate.

Look for loose connec-tions at the starter andcheck all fasteners.

Use a DMM to check thesupply voltage, then thevoltage starter contacts.

Dont risk a fire from a pos-sibly shorted motor. If thesupply is good, then theresa motor problem.

Insulation problems on motorsand drives are usually caused byimproper installation, environ-mental contamination, mechani-cal stress or age. Insulationtesting can easily be combined inwith regular motor maintenance,to identify degradation beforefailure, and during installationprocedures to verify system safetyand performance. When trouble-shooting, insulation resistancetesting can be the missing linkthat enables you to get a motor

back into operation the easy way,by simply replacing a cable.Insulation testers apply a dc

voltage across an insulation sys-tem and measure the resultingcurrent. This allows them to cal-culate and display the resistanceof the insulation. Typically, thetest verifies high insulation resis-tance between a conductor andground or high insulation resis-tance between adjacent conduc-tors. Two common examplesinclude testing motor windings

for insulation from the motorframe and checking phase con-ductors for resistance frombonded conduit and enclosures.

Insulation multimeters com-bine the insulation resistancefunctions above with the othertests needed to investigatemotor, drive, and electrical trou-ble, from basic supply measure-ments to contact temperature.The key difference is that insula-tion resistance tests are per-formed on de-energized systems,

while electrical tests (and ther-mal) are almost always per-formed on live, operatingsystems.

2. Control contactscheckNext, check the control con-tacts for quality of contact:

1. Lockout and tagout thedisconnect to the starter.

2. Manually engage thestarter, so the contactsclose.

3. Set the insulation testerto the low ohms range.

4. Measure the resistanceacross each set of con-tacts.

5. The reading should benearly zero. If its higherthan 0.1 ohms, that set ofcontacts needs to bereplaced.

About insulation resistance testing

Electrical and insulation resistance

tests on motors


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To pass these tests, the lineand load circuits need toshow high resistance.As a general rule, ACdevices need a minimum

2 megohms to ground andDC devices need 1megohm to ground toensure safe operation.

Note: Different companies have differ-ent threshold minimums for insulationresistance on used equipment, rangingfrom 1 to 10 megohms. Resistance onnew equipment should test muchhigherfrom 100 to 200 megohmsor more.

If the load side resistancevalues are acceptable thenproceed to the next test. Ifthey arent, then start trac-

ing the problem: is the insu-lation breakdown in theload side of the starter, thecables, or the motor?

3. Resistance of line andload circuits to ground

Then, measure the insulationresistance of the line andload circuits to ground.However, before doing ANYinsulation resistance test-ing, you MUST isolate anyelectronic controls andother devices from the cir-cuit under test. Then:

1. Lockout and tagout thedisconnect to the starter.

2. Set the insulation testerto the appropriate testvoltage (250, 500 or1000 V).

3. Identify the resistance

between these points:

Line side of starterto ground

Load side of starterto ground

4. Winding resistancephase to phase andphase to ground

Take insulation resistance

measurements phase tophase and phase to ground.

Good results: Balanced comparative

low resistance values onall three stator phases

High resistance valueson the phase to groundinsulation test

Problems: Gross resistance deficien-

cies, such as a phase onphase short.

Any winding to windingresistance imbalance. Ifthe readings differ bymore than a few percent,the motor is probablyunsafe to energize.

Fluke CorporationPO Box 9090Everett, WA USA 98206

Fluke Europe B.V.PO Box 11865602 BD EindhovenThe Netherlands

For more information call:

In the U.S.A. (800) 443-5853or Fax (425) 446 -5116In Europe/M-East/Africa +31 (0)40 2 675 200or Fax +31 (0)40 2 675 222In Canada (905) 890-7600or Fax (905) 890-6866From other countries +1 (425) 446 -5500or Fax +1 (425) 446 5116

Visit us on the world wide web at:

http://www.fluke.com

Fluke (UK) Ltd.52 Hurricane WayNorwichNorfolkNR6 6JBUnited KingdomTel.: (020) 7942 0700Fax: (020) 7942 0701E-mail: [email protected]

Visit us on the world wide web at:

http://www.fluke.co.uk

2005 Fluke Corporation. All rights reserved.Printed in U.S.A. 6/2005 2517897 A-EN-N Rev APub_ID: 10987-eng

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