Insulation test for three phase motor. Please Help!

[nazoom]

Hi

I need to know the steps for insulation testing of three phase motor?Please do you have a detailed explanation? Also I have one question, what do we do with the 400 V Coil in the Contactor? Do we disconnect them, or short links them? How? OR do we leave them?

I know that I have to disconnect the star/delta links in the terminal box!

Any help is much appreciated.

 

[telectrix]

disconnect links as you say. then IR each phase of the motor phase to phase and to casing. you can leave the coil connected

 

[nazoom]

Sorry, so I disconnect the Contactor links as well as the Star delta links?

Just to make sure. Thanx a million

 

[telectrix]

if you are just testing the motor, when you dis the links , also dis the feeds from the contactor.

 

[jpmiff]

Hi

to do a quick IR test on a motor wired in star no need to remove the links in the Tbox, just disconnect the supply at the motor and test, all the windings are connected together, this will show any insulation problems on motor.
If we have any problems with motors and suspect the IR we always do a test in the panel first, on the out going terminals to the motor, this tests all the circuit including cable. then depending on the results what we do next

 

[sparkspark]

Label the cores if not labelled! Remove cable from motor j box- 3 or 6 cores depending on if run in star or delta OR star and delta!
If using links, remove links noting positioning
Identify the three coils using cont tester (typically 0.6 ohm/ winding)
Then IR test between the coils, and each coil to the chassis of the motor.
Disconnect control box end of cable. IR test between cores, and between each core and SWA if used.

Hope this is of help.

if using IR tests in control box, remember to isolate first! disconnect electronic stuff! check continuity thru contactor when bar pushed in, and IR between poles to check not breaking down. Low IR can be moisture in industrial env, dry out and retest B4 condemnation.

 

[Marvo]

I would disconnect the wiring at the terminal box on the motor and test as suggested above. If you leave wiring connected or test from the contactors at the star/delta starter then the results are for the cabling as well as the motor, if you test at the motor then the results accurately reflect the condition of the motor.

 

[jpmiff]

Hi

you are correct , but in a production plant and you have a motor tripping you are under a lot of pressure to diagnose faults as soon as pos, my way determines if there is a fault due to IR pretty quick. if the test shows IR is ok then look for other reasons.
nothing disconected at the motor no time wasted

 

[nazoom]

Thanx for all the help and advise.