Alternating-current power delivery system

Claim 1

An alternating-current power delivery system comprising: a. a main circuit controller comprising current-limiting interrupting means for carrying the current through said controller when the controller is closed and a resistor shunting said interrupting means to provide a resistive conductive path shunting said interrupting means when the interrupting means operates to interrupt the current therethrough, b. a plurality of branch circuit breakers connected in parallel with each other and in series with said main circuit controller, c. each of said branch circuit breakers comprising relatively movable contacts that are separable to effect opening of the branch circuit breaker and each having a maximum currentinterrupting capacity substantially lower than the prospective current of said system at the point in which said branch circuit breaker is connected, d. means responsive to the flow of fault current through said main circuit controller and any one of said branch circuit breakers for causing said interrupting means to operate with a current-limiting action that: (1) limits the peak let-through current through said interrupting means to a value substantially below the peak of the prospective current of said system at the point of said main circuit breaker and (2) diverts the main circuit-controller current from a path through said interrupting means into a path through said shunting resistor, e. means responsive to said fault current for normally causing the one branch circuit breaker through which said fault current flows to open within several cycles after the flow of fault current begins and while the main circuit-controller current is following a path through said shunting resistor, f. means for reclosing said main circuit-controller interrupting means immediately after said one branch circuit breaker opens and interrupts the current therethrough, g. and an additional normally-closed circuit breaker in series with said rsistor and said branch circuit breakers and operable in the event said one branch circuit breaker fails to interrupt for interrupting the current through said resistor, h. said resistor having an impedance no higher than about 18 percent of normal load impedance but sufficiently high to limit fault current through said branch circuit breakers and said additional circuit breaker under short circuit conditions to a value within the maximum current-interrupting capacity of said branch circuit breakers and said additional circuit breaker, i. said additional circuit breaker remaining closed during the period between opening and reclosing of said main circuitcontroller interrupting means if said one branch circuit breaker is successful in interrupting the fault current therethrough.