BUS SHORTING PROTECTIVE DEVICE

PURPOSE: To judge failure in buses by using for a first fault detection relay a distance relay wherein its mho element is a circle containing the origin on an impedance plane, and wherein its blinder element is placed almost in parallel with the reactance axis. CONSTITUTION: The mho element of a first fault detection relay, or short-circuit distance relay 44S (IFT) that makes judgment according to the sum current (IFT) of currents IF1 IF2 flowing from higher level transmission lines F1 , F2 , is constituted as a circle containing the origin. In addition, a blinder element is placed along the reactance axis (vertical axis). If any fault occurs in a bus, the sum current IFT input to the 44S (IFT) relay is increased and reaches a relay operating region, which operates the 44S (IFT) relay; the currents IL1 , IL2 input to a 44S (IL1 ) relay and a 44S (IL2 ) relay is not increased, and thus neither the 44S (I$L1 ) relay nor the 44S (IL2 ) relay operates. Therefore, it is judged that the fault is located in buses.