Over-speed preventing apparatus for DC motor

Abstract

An over-speed preventing apparatus for the DC motor comprises a DC motor the speed of which is controlled by the adjustment of the armature voltage thereof, controlled-rectifier means for supplying power to the separately excited field winding of the motor, means for generating a predetermined field current command, means for detecting the field current, and a constant current control system for controlling the rectifier means 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, current decrease detector means inserted between the rectifier circuit and the parallel circuit including the field winding and the unidirectional element, and protecting means energized by the current decrease detector means.

Dependencies are inferred from the claim text.