Patent ID: 8207742

Claim:
A method of operating a circuit breaker in an electric circuit, said method comprising: identifying a first circuit breaker as a reference circuit breaker; determining when said identified reference circuit breaker is in reverse current pick-up; and when not, determining when a second circuit breaker is in short-time pick-up, indicative of a fault on the electric circuit; and when not; comparing a third direction of current flow through a third circuit breaker with a first direction of current flow through said identified reference circuit breaker; determining if said third circuit breaker is carrying current in a forward direction with respect to said identified reference circuit breaker and when said third circuit breaker is not in short-time pick-up, executing the steps of: comparing a first direction of current flow through a first circuit breaker other than said identified reference circuit breaker with said first direction of current flow through said identified reference circuit breaker; determining when said first main circuit breaker other than said identified reference circuit breaker is in reverse current pick-up; and when said first main circuit breaker other than said identified reference circuit breaker is in reverse current pick-up, tripping said first main circuit breaker determined to be in reverse current pickup; when the first circuit breaker other than said identified reference circuit breaker is not in reverse current pick-up executing the steps of: calculating a partial differential current for each of a plurality of zones in said electrical system; and identifying one of said zones in said electrical system as carrying a maximum partial differential current; and tripping said circuit breaker in said identified one zone identified as carrying said maximum partial differential current; and increasing by a predetermined amount a trip time delay of said first and said second circuit breaker upstream of said third circuit breaker.