Dc Motor Insulation Resistance Test

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.

Dc motor insulation resistance test.

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. For each system megger has the product best suited to conducting a comprehensive diagnostic insulation test. Minimum insulation resistance of the winding to ground is measured with 500 v dc. The test may be non destructive for in service equipment.

The leakage current through insulation expressed as resistance is displayed so it can be graphed. 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. 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. 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.

Abstract this paper presents one of the maintenance test methods and the results of its application in the determination of the insulation condition of hv electric motors. 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 health of the winding is best indicated by its resistance and not its impedance.

Electrical motor insulation conditions dc testing. Step 1 remove all electrical power from the dc motor. Dc alone is used because we need to measure only the resistance of the winding insulation. 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.

The winding temperature should be 25 c 15 c.