What we learn from insulation resistance testing.
Insulation resistance test results for motors.
Figure 4 typical record of insulation resistance of a mill motor.
If the value returned is.
Since 80 of electrical maintenance and testing.
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.
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.
Dc voltage of 500 or 1000 v is applied between the windings and the ground of the motor.
During the measurement and immediately afterwards some of the terminals carry dangerous voltages and must not be touched.
Insulation resistance test insulation resistance failure of an electric motor is one of the first signs that the motor is about to fail.
Figure 3 typical scale on the megger insulation tester.
In the case of wire insulation in motors leaks are not only bad but potentially dangerous and costly.
Reverse side of card at right is used to record the test data.
Leaking is a term associated with something bad occurring.
The international electrical testing association neta specification maintenance testing specifications for electrical power distribution equipment and.
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.
Ground insulation test of a motor.
When insulation deteriorates or has been damaged current will leak into parts of the motor it shouldn t causing undo wear.
Also acceptable values of insulation resistance depend upon the equipment you re testing.
Loss of insulation resistance of an electric motor is one of the first signs of motor failure.
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.
The insulation resistance tester generally known by its trade name megger is capable of providing critical information regarding the condition of motor insulation.
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.
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.
Set the voltage.
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.
