1. The motor does not start torque, or can not start when no-load, and emits abnormal sound.
Reason: (l) Three-phase power supply circuit (including the knife switch, lead stator winding) has a phase of power failure, resulting in single-phase start.
(2) The power supply voltage is too low.
(3) Excessive wear of the bearing, so that the rotor near the stator side, resulting in the stator and rotor different heart, uneven air gap.
2. The motor start torque is small, can not start when loading, the motor stops when the load increases, sometimes emits strong noise, local fever.
Reason: The power grid voltage is low, windings have turn short circuit, the rotor windings have broken or off welding phenomenon, after starting a phase of disconnection caused single-phase operation.
3. The starting current is large, unbalanced and loud, which causes the protective device to cut off the power.
Reason: Stator winding wiring method may be incorrect, winding to ground insulation aging.