(1) the motor winding open circuit, resulting in unbalanced three-phase current, the motor overheating;

(2) the motor winding short circuit, short circuit current is much larger than the normal operating current, the winding copper loss increase, leading to overheating winding, even burning;

(3) the motor connection errors, when a delta connected motor wrongly into the star shaped, motor still with full load, the stator winding current flowing to exceed the rated current, eventually lead to motor bicycle, if stopped for a long time and has not cut off power supply, winding is not only a serious overheating, will also be burned. When the motor is the wrong star connection into a triangle, the winding and core overheating, will be seriously burned winding;

(4) the motor windings reversed, will lead to serious unbalance of three-phase current, and the heating winding.

(5) the mechanical failures of motor, when the motor shaft bending, the assembly is not good, is there anything wrong with the bearing and so on, all can make the motor current increases, increasing the copper loss and mechanical friction loss, the motor overheating.