Circuit interrupter circuit including improved control

摘要

A relatively simple trip or control circuit for a circuit breaker in which the time constant for an input signal related to the amount of current flowing in the lines to be protected is purposely made relatively large so that tripping is slightly delayed for approximately three-half cycles of line current for overload currents in the range of 500 to 1000% of rated current. A Zener diode resistive network is used in combination therewith for providing near instantaneous tripping in the range of overload current above 1000%. The short delay is useful for preventing circuit breaker tripping when overloads of the spurious or transient type are impressed occasionally on the electrical conductors of the circuit being protected. The delay characteristic is not purposely related to any function of the overload current but is rather arbitrarily chosen to be greater than approximately 25 milliseconds because most spurious or transient signals have a duration of less time.