Abstract: In overhaul and maintenance of motors of thermal power plant, some new problems were occurred due to the technical progress, the equipment upgrading and unit capacity increasing. The damage of shaft current of heavyduty asynchronous motor and preventive pretreatment measures were introduced, the problems occurred in variable frequency operation of common three phases asynchronous motors were discoursed. The changing direction problem of heavyduty motor was predetermined, and the correctness of changing direction of motor was ensured.

Key words: heavy-duty asynchronous motor, shaft current, shaft voltage, motor steering, predetermine, overhaul and maintenance, 330MW thermal power generation unit