Adjustable flux transfer shunt trip actuator and electric power switch incorporating same

Abstract

A flux transfer shunt trip actuator has an elongated seat member extending between the legs of a U-shaped magnetically permeable frame member. A plunger is magnetically latched against the seat formed by the seat member in a retracted position by permanent magnets positioned adjacent the seat. The field generated by permanent magnets produces a latching force which exceeds a bias force generated by a helical compression spring extending along the elongated seat member and biasing the plunger toward an actuated position spaced from the seat. A coil surrounding the elongated seat member and the spring, generates an electromagnetic field when energized which bucks the permanent magnet field so that the plunger is driven to the actuated position by the spring. Preload on the spring is adjusted by an adjusting member positioned along a threaded shaft coaxial with the spring and extending from the bight of the U-shaped frame in the opposite direction from the pair of legs of the frame. A pair of opposed cylindrical sections project from the adjusting member through the bight and bear against the spring.