Circuit breaker magnetic trip device with time delay

Abstract

A tripping device for a circuit breaker combines the functions of a current transformer and trip actuator. The device comprises a core member, and an armature disposed in relationship to the core member to establish first and second magnetic circuits. A primary winding carrying load current of an associated circuit interrupter is coupled to the first magnetic circuit and a secondary winding is coupled to the second magnetic circuit, the secondary winding having a temperature dependent switching resistor connected across its output. The armature is movable between normal and trip positions. Low to moderate overloads cause the resistor to heat and switch to a lower resistance, thereby permitting increased current to flow in the secondary winding. This generates magnetic flux opposing the flux produced by the primary winding to lower the net flux in the second magnetic circuit. Magnetic forces on the armature thereby become unbalanced, allowing the armature to move to the trip position. The switching resistor has a switching characteristic such that an inverse time-current delayed trip operation is provided. A spring and stop screw are provided to act upon the armature to allow the armature to immediately move to the trip position upon large overcurrent conditions, thereby providing an instantaneous trip capability.

Dependencies are inferred from the claim text.