Testing Motor Repairs

I run an electric motor rewind shop and to answer your question correctly, I would need you to answer a question for me. Are you looking to test the electrical functionality/integrity of the motor or the mechanical functionality or both?

There are quite a few different ways to test the electrical integrity of a motor. Most tests are done before the work is done to determine the scope of work needed to bring the motor back to full capability. The two most important tests are the meggar and the surge test. Megging the motor will look for shorts from phase to ground, while surge testing will compare phase to phase and likely catch turn to turn faults. You can combine this with hi pot tests( possibly destructive if not done correctly) and of course a good visual of the stator, laminations, windings, end strings.

Motors that have experienced any type of damage to the lamination stack(rotor dragging on stator, ground short in the slot) must be core loss tested to determine if any hot spots will be present and how much efficiency will be lost. Some of the problems can be rectified. A bar to bar test can also be performed to test the integrity of the rotor. An open bar in the rotor can also be detected via vibrational analsis.

Mechanical damage to rotor journals, bearing housings, laminations, and balancing of the rotor must all be rectified at the time of the rewind

After the motor is rewound and all mechanical work performed it can be assembled and further tested. A full dyno load test can be performed and balanced three phase load. In addition, megging and surging the motor again can be performed again to further validate the work performed. It is also a good idea to perform vibrational analysis when dyno load testing to check vibration levels.

Of course all this work is not usually carried out on smaller motors due the point of diminishing returns, but on larger motors any and all testing must be thoroughly performed. the latest on the technology front for motor testing is MCA(motor circuit analysis) which can test air gap eccentricity among other things which i am not very familiar with, yet.