Unbalanced three-phase voltage, heavy load, improper operation and maintenance will affect the three-phase current imbalance of the motor. In addition, stator and rotor winding fault is also one of the important factors.

The stator winding has inter turn short circuit, local grounding, open circuit, etc., which will cause excessive current in one or both phases of the stator winding, resulting in serious imbalance of three-phase current. The faults of runner and rotor winding are shown as follows:

1. there are dust, sundries and hard trauma in the inner chamber, resulting in inter turn short circuit.

2. one phase of stator winding is open circuit.

3. the stator winding is damp and has leakage current.

4. the bearing and rotor are damaged and deformed, and the rotor rubs against the runner winding.

5. the broken bar of squirrel cage rotor winding is welded and cracked, resulting in unstable current.