OVER-SPEED PREVENTING APPARATUS FOR DC MOTOR

摘要

OVER-SPEED PREVENTING APPARATUS FOR DC MOTOR An over-speed preventing apparatus for a DC motor comprises a DC motor the speed of which is controlled by the adjustment of the armature voltage thereof. A rectifier circuit supplies power to the separately-excited field winding of the motor. A predetermined field current command is generated and the actual field current is detected. A constant current control system controls the rectifier circuit in accordance with the error between the field current command and the detected value of the field current. The apparatus further comprises a unidirectional element connected in parallel to the field winding in the direction in which the field current is made to flow back. A current decrease detector is inserted between the rectifier circuit and the parallel circuit including the field winding and the unidirectional element. A protecting device is energized by the current decrease detector.