Patent ID: 7301743

Claim:
A device for advanced protection from a short circuit current comprising: means for providing signals representative of the current in a supply feeder for all phases; means for providing signals representative of the current in a load which is supplied from said supply feeder for all phases; means for processing said signals representative of the current in the supply feeder separately for each phase to determine the rate-of-change of current in all phases of the supply feeder; means for processing said signals representative of the current in the supply feeder and said signals representative of the current in the load by subtraction of said signal representative of the current in the supply feeder from signal representative of the current in the load and producing the differential signals for all phases; means for comparing said rate-of-change of current in the supply feeder to a protective device first setting for each phase and producing a first conditional signal when the magnitude of said rate-of-change of current exceeds the protective device first setting; means for comparing said differential signal to a protective device second setting for each phase and producing a second conditional signal when the magnitude of said differential signal exceeds the protective device second setting; means of producing a tripping signal when the first and the second conditional signals are present simultaneously in one or more phases; and a means for opening a circuit in response to said tripping signal.