Flux-transfer trip device for a circuit breaker

In an electromagnetic trip device,

• A. a frame of highly permeable magnetic material comprising a back wall, a front wall, and a pair of spaced side walls extending between said front and back walls;
• B. a plunger of highly permeable magnetic material supported for straight line reciprocal movement through a close-fitting hole in said front wall;
• C. a permanent magnet of cobalt-rare earth material having a pair of opposed poles one of which is located adjacent said back wall;
• D. a pole piece of highly permeable magnetic material located between the other pole of said permanent magnet and said plunger and providing a surface against which said plunger is held in a withdrawn position by holding flux from said permanent magnet passing through the interface between said pole piece and said plunger;
• E. a tripping coil supported within said frame and surrounding a portion of said plunger for developing, upon energization, tripping flux passing through said interface that opposes the holding flux from said permanent magnet passing through said interface, thereby effecting release of said plunger from its withdrawn position upon energization of said tripping coil;
• F. spring means for moving said plunger out of said withdrawn position upon release of said plunger;
• G. flux-diverting structure of highly permeable magnetic material located between said tripping coil and said permanent magnet for shunting a portion of said tripping flux through a shunt path that bypasses said permanent magnet and said back wall;
• 1. said shunt path containing a relatively large non-magnetic gap for limiting the tripping flux through said shunt path sufficiently to cause about 30 percent or more of said tripping flux to pass through said permanent magnet in a direction opposite to the direction of said holding flux, and
• 2. said non-magnetic gap acting when said coil is de-energized to limit the holding flux passing through said shunt path sufficiently to cause about 90 percent or more of the total holding flux developed by said permanent magnet to pass through said interface,
• H. a shaft;
• I. a tripping member mounted on said shaft;
• J. a lever also mounted on said shaft and having two spaced-apart ends, one of which is pivotally connected to said plunger and the other of which is connected to said apring means, and
• K. means for adjusting the force developed by said spring means while said plunger is held in said withdrawn position.