Ground fault protective apparatus and method

Claim 2

Apparatus for detecting ground faults on an associated alternating current network, comprising: a plurality of groups of zero sequence current monitors, the monitors of each group being electrically isolated from every other group and surrounding conductors of the associated network which define a portion of the associated network as a zone of protection, the monitors of each group being connected to produce a current output signal whenever current flow through the conductors of the associated network into the zone of protection differs from current flow through the conductors of the associated network out of the zone of protection by more than a predetermined amount; and a plurality of current-sensitive ground fault sensors, each sensor being connected to the output of a current monitor group and being adapted to actuate an associated circuit interrupter device upon receipt of an output current signal from its connected current monitor group.

Claim 3

Apparatus for protecting a power distribution network from damage due to ground faults, comprising: a plurality of groups of current transformer means for detecting differential current flow, each group being electrically isolated from every other group being associated with a zone of the network being protected, each of said current transformer means surrounding phase and neutral conductors of a network branch entering the associated zone and measuring differential current through all of said conductors, the current transformer means of each group being connected so as to measure net differential current through all branches entering the associated zone; circuit interrupter means operable upon actuation to isolate a portion of the distribution network being protected from the remainder of the network; and a plurality of current-sensitive switch means, each of said switch means being connected to one of said groups of current transformer means, each of said switch means being connected to said circuit interrupter means and operable upon detection of net differential current through all branches crossing a zone boundary above a predetermined level to actuate said circuit interrupter means and isolate the associated zone from the remainder of the network.

Claim 4

Apparatus for protecting a power distribution network from damage due to ground faults, comprising: a plurality of groups of current transformer means for detecting differential current flow, each group being electrically isolated from every other group being associated with a zone of the network being protected, each of said current transformer means surrounding phase and neutral conductors of a network branch entering the associated zone and measuring differential current through all of said conductors, the current transformer means of each group being connected so as to measure net differential current through all branches entering the associated zone; circuit interrupter means operable upon actuation to isolate a portion of the distribution network being protected from the remainder of the network; and a plurality of current-sensitive switch means, each of said switch means being connected to one of said groups of current transformer means, each of said switch means being connected to said circuit interrupter means and operable upon detection of net differential current through all branches crossing a zone boundary above a predetermined level to actuate said circuit interrupter means and isolate the associated zone from the remainder of the network.

Claim 5

Apparatus as recited in claim 2, wherein said current transformers comprise zero sequence current monitors.

Claim 6

Apparatus as recited in claim 3, wherein said switch means comprise ground fault sensors.

Claim 7

Apparatus as recited in claim 4, wherein said ground fault sensors comprise relays.