Induction motor short circuit

[Trika]

Hey guys I really need some help,few weeks ago I came across a shocking ground fault short circuit on 2.2KW motor. I did all the necessary tests on the motor but I didn't pick up any problems with it,but as soon as we started the motor it kept on tripping with ground fault short circuit. The motor resistance,windings and phase to earth were all ok,the fault only came when we were starting the motor. The motor cable was also ok, we decided to change the motor and the problem disappeared. So please if anyone knows what was wrong with the motor please assist me with this problem,or anyone who knows how to test such. All the motor readings were ok.

 

[Alec_t]

Welcome to EP!

The motor resistance,windings and phase to earth were all ok

What was the resistance test voltage?

 

[Bluejets]

The motor resistance,windings and phase to earth were all ok

How were these tested?
What test meter was used?

as soon as we started the motor it kept on tripping with ground fault short circuit.

Sure it was ground fault and not overload?
If ground fault, not necessarily short circuit.

 

[Minder]

You have to use a 'Megger' instrument to test the insulation.
An ordinary meter does not always show leakage, it does not take much to affect a GFI breaker.

 

[Trika]

How were these tested? Phase to earth and phase to phase test
What test meter was used? Megger test



Sure it was ground fault and not overload?
If ground fault, not necessarily short circuit.

 

[Trika]

How were these tested?
What test meter was used?



Sure it was ground fault and not overload? The VSD indicated that it was ground short circuit.
If ground fault, not necessarily short circuit.

 

[Trika]

Welcome to EP!

What was the resistance test voltage?

Yes it was,using a megger

 

[Minder]

If you have the motor off, place it on something insulated, remove the earth GND conductor and see if it runs OK, if it does, test voltage from frame to earth GND.
If it runs up to speed, place the earth to the motor frame and see if it trips when up to speed.

 

[Bluejets]

Yes it was,using a megger

You did not answer all the requested queries.
Show results of the tests.
Without these, help is not possible.

 

[ivak245]

Capacitor start motor? Centrifugal start/run switch? more info needed.