Insulation Resistance Test Results For Motors

Loss of insulation resistance of an electric motor is one of the first signs of motor failure.

Insulation resistance test results for motors.

Leaking is a term associated with something bad occurring. If the value returned is. 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. Also acceptable values of insulation resistance depend upon the equipment you re testing.

The international electrical testing association neta specification maintenance testing specifications for electrical power distribution equipment and. Reverse side of card at right is used to record the test data. Figure 3 typical scale on the megger insulation tester. Dc voltage of 500 or 1000 v is applied between the windings and the ground of the motor.

Insulation resistance test insulation resistance failure of an electric motor is one of the first signs that the motor is about to fail. Hands down without a doubt one of the most universally searched topics on ec m s website from a historical perspective is insulation resistance testing as a result some of our most popular evergreen articles like understanding insulation resistance testing continue to top the charts when it comes to most popular content. Figure 4 typical record of insulation resistance of a mill motor. The measurement of insulation resistance is carried out by means of a megohmmeter high resistance range ohmmeter this is how the test works.

During the measurement and immediately afterwards some of the terminals carry dangerous voltages and must not be touched. When insulation deteriorates or has been damaged current will leak into parts of the motor it shouldn t causing undo wear. Curve a shows test values as measured. In the case of wire insulation in motors leaks are not only bad but potentially dangerous and costly.

Curve b shows same values corrected to 20 c see page 22 giving a definite downward trend toward an unsafe condition. Historically many field electricians use the somewhat arbitrary standard of 1 megohm per kv. Set the voltage. Since 80 of electrical maintenance and testing.

What we learn from insulation resistance testing. Ground insulation test of a motor. 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. The insulation resistance tester generally known by its trade name megger is capable of providing critical information regarding the condition of motor insulation.

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.