How to use a multimeter to judge the number of explosion-proof motor poles

All kinds of information of explosion-proof motor can be clearly seen on the nameplate of explosion-proof motor. For example, the form of explosion-proof motor, model, series, rated power, rated voltage and so on. However, if the nameplate is lost, the number of explosion-proof motor poles cannot be seen. In this case, the current μA of the multimeter can be used to test and judge.

Use a multimeter to determine the number of poles of the explosion-proof motor

First, open the junction box of the explosion-proof motor, remove the original power cord and the star or triangle connection, and find two leads of any phase winding from the six leads of the explosion-proof motor by using R×100Ω of the multimeter. Then the range switch of the multimeter to the current μA, and the pen into the crocodile clamp firmly clamp the above found winding two leads. Turn the belt wheel or shaft of the explosion-proof motor slowly and evenly for a circle by hand, and carefully observe the number of times the pointer of the multimeter swings. Every time the multimeter pointer swings, the current in this phase winding changes positively and negatively, so as to determine how many pairs of poles the explosion-proof motor has.

This method uses the asynchronous explosion-proof motor when the rotor rotates at a uniform speed, the remanent magnetic flux of the rotor cuts the stator winding and induces a tiny induced electromotive force, which generates a current and makes the multimeter pointer swing. It is worth mentioning that the explosion-proof motor that has not been used for a long time is tested by the above method, and the multimeter pointer may have no response. This is because the remanence of the explosion-proof motor has disappeared. At this time, as long as the explosion-proof motor is connected to the power line according to the normal method, the explosion-proof motor is energized for a few minutes, and the stator windings of the explosion-proof motor will obtain residual magnetism after power failure, and then the number of poles can be identified by the above method.