Circuit breaker reactive to three time-overcurrent characteristics

Claim 1

A circuit breaker for use with a multiphase A.C. power line, said circuit breaker comprising: at least one disconnectable contact provided in series with said A.C. power line; current sensor means provided for each of the respective phases of said A.C. power line for detecting values of current in said respective phases and, in response, outputting corresponding sensed alternating current signals; means for rectifying said sensed alternating current signals to produce full wave rectified alternating current signals predominant phase selecting means for selecting the sensed alternating current signal having the largest amplitude among said sensed alternating current signals of said current sensor means and for outputting at least a half-cycle of said sensed alternating current signal; largest value detecting means for detecting the largest amplitude value among said full wave rectified alternating current signals of said current sensor means and outputting a pulsating DC current signal; peak holding means for storing a peak value of said pulsating D.C. current signal; signal conversion means for converting said sensed alternating current signal selected by said predominant phase selecting means to obtain a mean or effective value thereof; first level discriminating means for detecting when a level of said largest value detected by said largest value detecting means is, instantaneously, above a first predetermined value; first time-current operating means for outputting a trip signal when said first level discriminating means detects that the level of said largest value is above said first predetermined level; second level discriminating means for detecting when the peak value in said peak holding means is above a second predetermined value; second time-current operating means for timing a period during which said second level discriminating means continuously detects that said peak value is above said second predetermined value and, in response to expiration of a predetermined short time period, outputting said trip signal; third level discriminating means for detecting when said mean or effective value is greater than a third predetermined value; and third time-current operating means for timing a period during which said mean or effective value is greater than said third predetermined value and, in response to continuously detecting said mean or effective value of a predetermined long time period greater than said predetermined short time period, outputting said trip signal.