Microcomputer based electronic trip system for circuit breakers

Claim 1

A tripping system for interrupting a three phase current path having a ground path coincident therewith, comprising: a set of current sensors, each situated adjacent the current path for sensing a respective phase of current therein and each providing a respective current signal therefrom; summation means, coupled to the set of current sensors, for adding the current signals from the set of current sensors and for producing an output current signal therefrom in the presence of a ground fault; a set of gain circuits, each responsive to a respective one of the current signals and each having: a first gain section for amplifying the respective current signal by a first predetermined gain factor, and a second gain section for amplifying the respective current signal by a second predetermined gain factor; a processor, responsive to the output current signal and the set of gain circuits, for analyzing the three phase current path by selectively receiving the respective current signal from either the first gain section or the second gain section at each gain circuit according to a predetermined resolution criteria, and for engaging the interruption means to interrupt the current path; and data memory means coupled to said processor for storing data representative of tripping characteristics, wherein the processor compares the rectified signal to the data and engages the interruption means if the rectified signal exceeds a threshold data level.