The stator coils of three-phase motor are symmetrically arranged at 120 degree electric angles to each other. When three-phase alternating current is introduced, a circular electromagnetic field is generated. The closed conductor on the rotor cuts alternating electromagnetic field to produce rotating electromagnetic force, which drives the motor rotor to rotate.
When the motor is running with a failure phase, we can analyze it in two case: the stop state and the run state.
In the stop state, due to the absence of a phase power supply, the magnetic field induced by the motor stator will become an approximately elliptical magnetic field rather than a circular magnetic field, so that it will not have the starting moment, so it can not rotate, but can only emit buzz. Because of the magnetic field attraction, the rotor core and the stator core of the motor attract each other, forming the motor blocking state. At the same time, the electric current of the motor is very large, so it can be heated and burned in a very short time.
In the run state, because the motor is rotating at this time, there is a lack of a phase of electricity, which makes the electromagnetic field change from a round to an oval shape, but at this time the motor's rotational inertia can make the motor's stator continue to rotate; however, because of the lack of phase, the output of the motor is greatly reduced, the speed of the-bit motor is obviously decreased, the current of the motor is increased, and the motor can be burnt out in a few minutes.
How to judge the cause of Motor burn-out, we open the motor end cover and take a look at the Coil burn-out situation, as we know: Overload burn-out motor its stator coil because it is uniform heat, usually three-phase coil burn-out at the same time, and phase missing burn-out For the star connection is burning two-phase Coil, for the triangle connection is burning a phase coil, this can be seen through the motor coil wiring diagram.