Patent ID: 8908780

Claim:
A protective relay provided at one end of a protective section for performing data transmission with another protective relay provided at an opposite end of the protected section via a transmission path to make a fault judgment on the inside and outside of the protected section, the protective relay comprising: a transmitting and receiving circuit transmitting data to the another protective relay and receiving data from the another protective relay; a receiving level detection block detecting a receiving level of the protective relay that is a receiving level of the data from the another protective relay at the transmitting and receiving circuit; and a transmission level control block comparing the receiving level of the protective relay detected within a definite period of time with a predetermined level, the definite period of time being a period just after the data transmission has been established between the protective relay and the another protective relay and in which the receiving level and the transmission level of the protective relay become the same as a receiving level and a transmission level of the another protective relay, and when the receiving level of the protective relay within the definite period of time is larger than the predetermined level, the transmission level control block performing a transmission level reduction control that reduces the transmission level of the transmitting and receiving circuit.