PURPOSE: To locate fault section in a substation from a ground station side on the outside of the substation by partitioning buses in the substation into a plurality of sections through a plurality of radio CTs while furthermore providing a plurality of ground stations corresponding to the radio CTs and a decision section connected with the ground sections.

CONSTITUTION: A bus 1 is partitioned through a plurality of radio CTs 2 into a plurality of sections and a plurality of corresponding ground stations 15 are connected with a decision section 19. At the radio CT 2, a CT 4 detects current flowing through the bus 1 and then detects phase information and an effective value thereof which are temporarily stored 10, while furthermore a call command is high voltage received from the ground station 15 and current information is transmitted on wave 12 in response to the call command. The ground station 15, 15 transmits the call command on wave 17 in response to a command fed from the decision section 19 and a ground receiving section 18 receives the current information which is subsequently transmitted to the decision section 19. The decision section 19 comprises a control section 21 for taking in operational information of a bus protective relay and delivering the call command, and a detector 20 for detecting a fault section based on the current information. According to the constitution, fault section is located from the outside and emergency countermeasure is taken quickly.