Motor Insulation Resistance Test Results

Usually either 30 and 60 sec or 60 sec and 10 min.

Motor insulation resistance test results.

Insulation resistance should be approximately one megohm for each 1 000 volts of operating voltage with a minimum value of one megohm. Maximum insulation resistance should be measured with 500 v dc with the windings at a operating temperature of 80 120 c depending on the motor type and efficiency. A general rule of thumb is 10 megohm or more. The winding temperature should be 25 c 15 c.

The insulation system of an electrical motor is said to be in good condition if. A common rule of thumb is insulation resistance changes by a factor of two for each 10 degrc change. So to compare new readings with previous ones you ll have to correct your readings to some base temperature. Minimum insulation resistance of the winding to ground is measured with 500 v dc.

Winding dc resistance test follow usace procedure three sets of results total a to b phase b to c phase c to a phase correct values to 40 c using the formula in step 8. All values obtained from winding dc resistance test should be below 1 megohm and similar in value. For example suppose you measured 100 megohms with an insulation temperature of 30 degrc. For example a motor rated at 2 400 volts should have a minimum insulation resistance of 2 4 megohms.

This test recognizes the fact that good insulation will show a gradually increasing ir after the test voltage is applied.