Dc Motor Insulation Resistance Test

To measure insulation resistance a dc voltage of 500v or 1000v is applied between the windings and the ground of the motor as shown below.

Dc motor insulation resistance test.

Electrical motor insulation conditions dc testing. How to measure insulation resistance of a motor the measurement of insulation resistance is carried out by means of a mega ohmmeter a high resistance range ohmmeter. Step 1 remove all electrical power from the dc motor. The health of the winding is best indicated by its resistance and not its impedance.

The megger tester uses a high voltage generally in the 1000 to 10 000 volt range to identify insulation leakage in motor coils and adjacent wiring. By following a basic setup you can test a dc motor using this high voltage testing device. If we use ac to conduct the insulation test we will be measuring impedance instead of the resistance as the insulation has a substantial capacitive reactance. Minimum insulation resistance of the winding to ground is measured with 500 v dc.

B kv is the rated machine terminal to terminal voltage. Insulation resistance maintenance test values for motor windings 1 minute 40 c a rated line to line voltage for three phase ac machines line to ground voltage for single phase machines and rated direct voltage for dc machines or field windings. The winding temperature should be 25 c 15 c. Dc alone is used because we need to measure only the resistance of the winding insulation.

Testing and data processing were carried out on site using a pc. These electrical standards apply to testing cables generators circuit breakers and many other electrical systems where insulation quality around the conductors must be at its best. The test may be non destructive for in service equipment. 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.

This test may take place on installing or on the reel cable tools appliances transformers power distribution subsystems capacitors motors and any type of electrical equipment or wiring.