Motor Insulation Resistance Test Procedure

The insulation resistance tester generally known by its trade name megger is capable of providing critical information regarding the condition of motor insulation.

Motor insulation resistance test procedure.

The measurement of insulation resistance is carried out by means of a megohmmeter high resistance range ohmmeter this is how the test works. Regular checks of motor insulation resistance the key to prolonging the life of any electrical device is periodic checks maintenance the insulation resistance of stored and active motors should be checked regularly. Ground insulation test of a motor. At a the insulation resistance decreases due to aging and dust accumulation.

Z 5 date of test r eading in megohms the graph below shows an example of the insulation resistance readings on an electric motor. The insulation resistance test consists in measuring the insulation resistance of a. For a three phase motor insulation resistance is usually measured between each motor winding or phase and between each motor phase and motor frame earth using an insulation tester or megger. The insulation resistance test is the second test required by the electrical safety testing standards.

Insulation resistance test insulation resistance failure of an electric motor is one of the first signs that the motor is about to fail. Developed early in the 20th century the insulation resistance ir test is the oldest and most widely used test for assessing the quality of insulation. In an industrial facility the recommended procedure is to perform periodic tests and record the results so that damaging trends can be detected and corrected to prevent an outage. Figure 3 typical scale on the megger insulation tester.

Curve b shows same values corrected to 20 c see page 22 giving a definite downward trend toward an unsafe condition. For a three phase motor the isolation resistance can usually be measured between each motor winding or phase and between each motor stage and motor frame earth by an insulation tester or megger 4. Curve a shows test values as measured. Set the voltage.

During the measurement and immediately afterwards some of the terminals carry dangerous voltages and must not be touched. Also acceptable values of insulation resistance depend upon the equipment you re testing. A if the insulation resistance of a new cleaned or repaired motor that has been stored for some time is less then 10 mω the reason might be that the windings are humid and. Historically many field electricians use the somewhat arbitrary standard of 1 megohm per kv.

Loss of insulation resistance of an electric motor is one of the first signs of motor failure. Reverse side of card at right is used to record the test data. Figure 4 typical record of insulation resistance of a mill motor. Since 80 of electrical maintenance and testing.