Motor Insulation Resistance Test Results

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.

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. 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. The insulation system of an electrical motor is said to be in good condition if.

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. For example a motor rated at 2 400 volts should have a minimum insulation resistance of 2 4 megohms. After the connections are made the test voltage is applied and the ir is read at two different times. The winding temperature should be 25 c 15 c.

So to compare new readings with previous ones you ll have to correct your readings to some base temperature. Record initial and corrected values on motor testing record sheet. This test recognizes the fact that good insulation will show a gradually increasing ir after the test voltage is applied. For example suppose you measured 100 megohms with an insulation temperature of 30 degrc.

A general rule of thumb is 10 megohm or more.