Non-linear alternating current transducer

A current transformer core, comprising:

• a yoke for receiving primary and secondary windings, said yoke having a graded air gap defined by a plurality of legs extending between opposite side arms of said yoke, a first air gap segment being situated in a first leg, a second slightly longer air gap segment being situated in a second leg, and so on to an Nth air gap segment that is longer than the previous air gap segment and is situated in an Nth leg extending between said opposite side arms of said yoke,
• whereby said air gap provides a non-linear magnetic circuit response for changes in current flowing through said primary winding.

A control circuit for sending, monitoring, and interrupting current in a line conductor, said control circuit being coupled to a circuit breaker electrically connected to said line conductor, said circuit breaker having a trip coil for interrupting the current through said line conductor when said trip coil is energized, comprising:

• a current transformer having a core including a yoke with the line conductor passing through said yoke to define a primary winding, and having a secondary winding mounted on said yoke, said yoke having a graded air gap defined by a plurality of legs extending between opposite side arms of said yoke, a first air gap segment being situated in a first leg, a second and slightly longer air gap segment being situated in a second leg, and so on to an Nth air gap segment that is longer than the previous air gap segment and is situated in an Nth leg extending between said opposite side arms of said yoke, whereby said air gaps provides a non-linear magnetic circuit response including a non-linear voltage across said secondary winding for changes in current through said line conductor.