How to use a multimeter to quickly judge the quality of a three-phase asynchronous AC motor

For some three-phase asynchronous AC motors that have not been used for a long time or are old, an insulation resistance meter and a multimeter can be used to quickly and comprehensively judge whether they are good or bad.

(1) Use an insulation resistance meter to test the insulation condition. A 500V insulation resistance meter can be used to test the insulation resistance of the three-phase asynchronous AC motor being tested. It mainly tests the insulation resistance between the motor stator winding and the housing. Under normal circumstances, the resistance value should be greater than 0.5MΩ, and the larger the value, the better. If it is less than 0.5MΩ, it means that the insulation resistance is poor.

(2) Use a multimeter to test the condition of each phase winding. If the insulation condition of the motor is good when tested with a clamp ammeter, use a pointer multimeter to test the windings of each phase of the three-phase asynchronous motor.

1) Y-connected motor: The specific method of using a multimeter to detect the quality of each phase coil winding of a Y-connected motor is as follows.

① Before testing the phase windings of a three-phase asynchronous AC motor with Y-connection, first set the multimeter to the milliampere range at the lowest range.

② Connect the two probes of the multimeter to the connection terminals of any two phases in the junction box of the motor to be tested, and do not remove the connecting piece. Then, turn the motor by hand to make it idle, and observe whether the pointer of the multimeter swings left and right.

a-If it can swing left and right, then change the two test leads of the multimeter to the connection terminals of the other two phases in the junction box, and use the same method to observe whether the pointer of the multimeter swings left and right. Repeat this until all three phases are measured in pairs. If the test results are the same (that is, the pointer of the multimeter can swing left and right), it means that the motor being tested is good and can continue to be used.

b. If the multimeter pointer does not swing left and right during one or more tests, it means that there is a problem with the motor being tested and it cannot be used any further.

2) Delta-connected motors: The specific method of using a multimeter to detect the quality of each phase winding of a delta-connected motor is as follows.

For motors with △ connection, before using a pointer multimeter to test each phase of the winding, the three connecting pieces in the terminal box of the motor under test should be removed (when removing, the connection positions of the three connecting pieces should be recorded first to facilitate restoration). After using a multimeter to measure the three-phase winding, temporarily connect them in a Y manner, and then determine the quality of the motor according to the above-mentioned test method.