Motor Insulation Resistance Test Results

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

Motor insulation resistance test results.

The insulation system of an electrical motor is said to be in good condition if. This test recognizes the fact that good insulation will show a gradually increasing ir after the test voltage is applied. After the connections are made the test voltage is applied and the ir is read at two different times. So to compare new readings with previous ones you ll have to correct your readings to some base temperature.

Determine rules for the actual minimum insulation resistance value of an electric motor because resistance varies according to method of construction condition of insulation material used rated voltage size and type. A common rule of thumb is insulation resistance changes by a factor of two for each 10 degrc change. 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. Minimum insulation resistance of the winding to ground is measured with 500 v dc.

For example a motor rated at 2 400 volts should have a minimum insulation resistance of 2 4 megohms. All values obtained from winding dc resistance test should be below 1 megohm and similar in value. 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. Record initial and corrected values on motor testing record sheet.

Insulation resistance should be approximately one megohm for each 1 000 volts of operating voltage with a minimum value of one megohm.