Field Method for Verifying Stator Short Circuits
Field Method for Verifying Stator Short Circuits
(OP)
What is a good quick and dirty field method of determining if the stator of a 3-phase induction motor has shorted phase-phase (preferably at the motor "T" leads)? The motor trips on instantaneous overcurrent during start, but DC resistance tests to ground show very good results. The feeder cables test good also. I do not want to close back in on a suspected fault to capture current magnitude during the overcurrent protection operation.





RE: Field Method for Verifying Stator Short Circuits
No inductance bridge or meter available? Then check the inductive voltage drop across each winding. Connect a suitable wattage lamp in series with the winding and feed the combination with AC. Measure the ac voltage drop across the winding. Repeat for all windings. The voltage drop shall be the same (+/-5% again) if the windings are healthy.
Please note that the motor windings shall be isolated from ground (they usually are) and that you are using lethal voltages. This test shall not be performed by non-electric people and the motor shall not be left without supervision during the test.
RE: Field Method for Verifying Stator Short Circuits
A surge ringing pulse is applied to each phase and the trace of each phase circuit is compared. Turn to turn, phase to phase or wrong connections are detected. The test voltage level must be high enough to bridge weak or defective insulation.
RE: Field Method for Verifying Stator Short Circuits
RE: Field Method for Verifying Stator Short Circuits
RE: Field Method for Verifying Stator Short Circuits
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Field Method for Verifying Stator Short Circuits
RE: Field Method for Verifying Stator Short Circuits
Digital low-resistance ohmmeter... up to 10 amperes of test current {and still reasonably portable} with Kelvin test leads.
RE: Field Method for Verifying Stator Short Circuits
RE: Field Method for Verifying Stator Short Circuits
http://www.eng-tips.com/viewthread.cfm?qid=17776
http://www.eng-tips.com/viewthread.cfm?qid=97804
RE: Field Method for Verifying Stator Short Circuits
Repeat the test twice using the other possible phase to phase connections treating the motor as 3 single phase inductances.
Also works for transformers and just about ANY inductive device that does NOT have shading poles such as an AC only relay coil or a shaded pole motor but those are throw away items anyways.
Mike Cole, mc5w@earthlink.net