Zone protective directional relay scheme

Claim 1

A protective system for protecting elements of an electric power system of the type having at least first and second circuit elements which are to be selectively isolated from each other and from a remainder of said power system, said elements being isolatable by at least first, second and third circuit breakers, said protective system comprising: a first transmitter/actuator unit associated with said first circuit breaker, at least one second transmitter/actuator unit associated with said second circuit breaker, at least one third transmitter/actuator unit associated with said third circuit breaker; at least one first data link for connecting said first and said second transmitter/actuator units; at least one second data link for connecting said first and said third transmitter/actuator units; each one of said transmitter/actuator units including: means for measuring a fault current flowing through its respective circuit breaker; fault-direction detecting means for detecting direction of said fault current with respect to a first protection zone which protection zone is defined by selected ones of said circuit breakers of said protection system which are associated with said first element, or with respect to a second protection zone defined by another group of selected ones of said circuit breakers which are associated with said second element; first and second evaluation units; a first branched data link for transmitting output signals from said fault-direction detecting means to said first and second evaluation units; a second branched data link for transmitting command signals for opening and closing said circuit breakers; said first evaluation unit of said first and said second transmitter/actuator units being connected to one another by said first data link, said evaluation units including means for logically relating outputs from said fault-direction detecting means and for decoding whether a fault condition is occurring inside or outside said first protection zone; and said second evaluation unit of said first transmitter/actuator unit being connected to one of said evaluation units of said third transmitter/actuator unit through said second data link; said evaluation units receiving output signals from said fault-direction means and further including means for logically relating said output signals to determine if a fault has occurred inside or outside said second protection zone and means for generating and transmitting signals for opening said circuit breakers associated with said second protection zone when said fault is determined to occur inside said second protection zone.