GROUND FAULT DETECTOR INCLUDING MAGNETIC AMPLIFIER BRIDGE MEANS

摘要

A protective device for detecting abnormal leakage current to ground in an electrical circuit energized through two or more conductors connected to an AC source, one of the conductors being grounded at the source. The device comprises a magnetic amplifier having a pair of reactor cores upon which a plurality of gate windings are arranged to form a balanced inductance bridge. An oscillator is connected across the bridge to apply a carrier signal at a frequency many times higher than the frequency of the AC source, and the bridge output is connected through a peak detector and amplifier to drive the solenoid of a circuit breaker. Each supply line conductor of the monitored circuit is wound about both the reactor cores with the sense of each windings being arranged to provide a net magnetic flux of zero when equal currents are flowing through each conductor. In this manner the magnetic amplifier provides at the bridge output a null signal during normal current conditions and an error signal voltage in the presence of a current imbalance between the conductors.