Automatic Out-of-step Protection of Synchronous Motor Supplied by Converter

The paper deals with out-of-step protection of synchronous motor. Synchronous motor supplied by converter works in wide range of speed, and faces disturbance and acute change of load torque. The out-of step is frequently occurs, and damages the motor, affects on related process. The problem can be solved by adjusting supplied voltage according to the calculated load angle. The load angle can not be measured in working condition. But it can be calculated from stator voltage, current, and power factor which can be easily measured. The research discloses the inherent relations among the stator voltage, current, power factor, and load angle using phase graph under steady state adjustable voltage. Based on the relationship of the quantities, it proposes a scheme of automatic out-of-step protection. The scheme bas been simulated on a synchronous motor. The simulation results verify the validity and feasibility of the proposition.