Electric Motor Winding Imbalance testing

[kitosepa]

I have a maintenance question to ask of all my learned colleagues out there.
Is it worthwile to perform Predictive Winding Imbalance testing on Low Voltage motors on a set frequency?

No online systems installed. Specific motors: 280kW, 380 V. Monitoring will be by shutting down the motor, isolating it and then measuring the winding resistances, possibly using a ductor.

Cheers

 

[edison123]

A surge comparison test is the only one that will detect winding turn shorts effectively. Google Baker surge tester.

Muthu

http://www.edison.co.in

 

[electricpete]

From pure reliability standpoint, I agree with Muthu. Surge test is the best you can do to ensure a motor that passes will operate without turn failure.

It is a specialized test that requires some expertise to perform and interpret, also potentially destructive (so don't test unless you have a sparet on time).

For the above reason, a typical practice for field test centers around megger testing and various other "easier" tests that include winding resistance balance, and if you buy a box it may have inductive imbalance, capacitance measurements etc. I said typical practice - I didn't say it was smart... open to discussion.

I'm not sure if a ductor is a good device for winding resistance testing because there are some issues with building up the current and interrupting the current in an inductive circuit. Kelvin or similar bridge test is typically used for this purpose and bridge is incorporated into the motor testers like pdma, bjm etc.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[esee135]

Winding resistance down to fine decimals is an indicator, similar to performing transformer resistance tests. Taking a baseline from original commissioning will also allow you to determine if you have bad brazing. The baker test set is fairly standard.

Also running amps and volts can help.

I agree with electricpete, a ductor/welder tripping or disconnecting will cause a large inductive voltage from the di/dt break. It's similar to a surge application.

Also insulation resistance testing likely won't pick up the imbalance. IR will detect polarization/leakage currents of your insulation system.