Direct acting overcurrent system for high voltage circuit breakers

Claim 1

A direct acting overcurrent sensing system for operating high voltage circuit breakers and the like comprising: a first current sensor inductively coupled to a power line being protected; said first sensor comprising a saturable core adapted to saturate at a point below the upper end of the operating current range of said system; a second current sensor coupled to the output of said first current sensor, said second sensor having inductively coupled primary and secondary windings; at least one of said windings having a plurality of taps; means adjustably coupled to said taps for controlling the output level of the signal developed by said second sensor to be compatible with the operating characteristics of the overcurrent sensing system; bridge means for converting the output of said second sensor into a D.C. signal; means coupled to said bridge means for developing a predetermined reference level; a static time delay circuit; circuit means coupled to said bridge means and said reference level generating means for enabling said time delay circuit when the output of said bridge means reaches said reference level; said time delay circuit including means for generating a delayed triggering signal whereby said delay is inversely proportional to the magnitude of the output of said bridge means; a branch circuit coupled to said bridge means comprising series connected switch means and a trip coil, said switch meAns having a control input coupled to the output of said time delay circuit for energizing said coil by said bridge means upon the occurrence of said triggering signal; a circuit breaker coupled to said line being protected, said circuit breaker comprising magnetic latch means for including said trip coil for tripping said circuit breaker when said tripping coil is energized, said second sensor adjustable means being settable to provide the requisite operating power to said magnetic latch.