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.

The measurement of insulation resistance is carried out by means of a megohmmeter high resistance range ohmmeter this is how the test works. 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. Historically many field electricians use the somewhat arbitrary standard of 1 megohm per kv. Ground insulation test of a motor.

Winding insulation test primarily for non submersible type pump motors prep determine testing voltages determine minimum acceptable resistance at 40 c short all three phases together at terminals use a multimeter to measure resistance between the leads and grounded motor frame. 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. In the case of wire insulation in motors leaks are not only bad but potentially dangerous and costly. Curve a shows test values as measured.

The international electrical testing association neta specification maintenance testing specifications for electrical power distribution equipment and. Leaking is a term associated with something bad occurring. When insulation deteriorates or has been damaged current will leak into parts of the motor it shouldn t causing undo wear. 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.

Set the voltage. The insulation resistance tester generally known by its trade name megger is capable of providing critical information regarding the condition of motor insulation. What we learn from insulation resistance testing. Figure 3 typical scale on the megger insulation tester.

Figure 4 typical record of insulation resistance of a mill motor. If the value returned is. 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.

Since 80 of electrical maintenance and testing. 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 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. Also acceptable values of insulation resistance depend upon the equipment you re testing.

During the measurement and immediately afterwards some of the terminals carry dangerous voltages and must not be touched.