If all the windings of one or two phases of a three-phase motor are burned, they are usually caused by phase failure operation. The appearance of the fault is as follows: the regular overheating of the winding is burning black, and the normal phase adjacent to the fault is intact. After the phase is missing, the motor can continue to run, but the single phase running speed caused by the lack of phase is obviously reduced.
The motor is a delta connection. If the B phase input line is disconnected (lacking B phase), the motor is converted to B and C, and the series branches are parallel to the A phase branch. When the load is constant, the A phase branch current is too large, and the A phase winding will inevitably burn out due to overheating.
The motor is Y connection, and it is also assumed that the B input line is disconnected (B phase). The two phase winding of A and C is actually a single phase winding, and the rotating magnetic field is an elliptical magnetic field. Therefore, under the same load, the load current will increase, which will cause the two phase winding to burn at the same time.