Abstract: A fault component current is obtained in response to a fault at a fault point within a protective section on a transmission line at one end of the protective section. Assuming that a phase difference between the fault component current and a fault point current flowing through the fault point is known, the fault point current is obtained on the basis of the fault component current and the phase difference. Then, a voltage at an assumed fault point is obtained by using voltage and current at the one end of the protective section and the line constants of the protective section. An assumed fault point is then obtained to permit the voltage at the assumed fault point to be in phase with the fault point current. The assumed fault point is assumed to be a true fault point.

Abstract: At an end (11) of a power transmission line (10), a fault detecting system monitors variations resulting from a fault in voltage and current being transmitted through the line and calculates the distance between the end and location (20) of the fault by the use of the variations and a line constant inherent to the line, such as that given by the characteristic impedance and the propagation constant, to thereby locate the fault with a sufficient accuracy by directly using the commercial frequency and without affected by the impedance that accompanies the fault. The system can calculate the fault impedance from the distance and those backward impedances seen at the end and an opposing end (12) of the line backwardly of the location of fault.