Three-Phase Asynchronous Motors: Prevention Tips For Starting Failures

A three-phase asynchronous motors' rotor speed lags behind its rotating magnetic field, generating induced current and electromagnetic torque for energy conversion. Classified by rotor structure into squirrel-cage and wound-rotor types, it outperforms single-phase motors in efficiency and material savings. Squirrel-cage motors are cost-effective and reliable but hard to regulate, while wound-rotor variants use slip rings and external rheostats to optimize starting and speed control.

Its core principle relies on symmetrical three-phase AC supplied to stator windings, creating a rotating magnetic field. This field cuts stationary rotor conductors, inducing current via electromagnetic induction. The current-carrying rotor conductors then experience electromagnetic force, driving rotation in the magnetic field's direction.

Causes include poor sealing leading to corrosive ingress, bearing damage-induced stator-rotor friction (sweep), winding friction with end covers, long-term overload, and mechanical vibration-driven insulation aging.

Countermeasures: Eliminate leaks; ensure proper bearing heating (80–100℃) and cleaning during assembly; avoid shaft machining and maintain stator-rotor alignment; prohibit grease mixing; inspect idle motors thoroughly before use; prevent overload and frequent starts.

Single/Two-Phase Winding Burnout

Primarily caused by phase-loss operation. A running motor can continue operating but with reduced speed and unbalanced current, overheating windings. A stationary motor with phase loss will only hum and fail to start, as a pulsating magnetic field cannot generate starting torque.

Phase loss severely damages windings faster in static motors due to high locked-rotor current. Regular maintenance of three-phase asynchronous motors and their MCC units-especially checking switches, contacts, and cables-is critical to prevent phase loss and ensure safe operation.