As per international standards, at the end of testing of HT motors, high voltage test is done on stator windings and subsequently Insulation-Resistance (IR) of winding is measured to ensure healthiness of winding.
But, really, this does not ensure healthiness of winding, as winding might have failed/punctured in the over hang portion of winding and does not get earthed and will not reveal in IR value. There are some such cases when IR was perfectly good but machine fail to start when first commissioned. On opening winding the machine, failure observed in over hang portion. To avoid this situation, it is recommended to measure the DC resistance of winding also, after HV test.
Tip Provided By: Dinesh Soni, Consultant
Kirloskar Brothers Ltd.