Abstract: In a power receiving system, a network transformer, a protector breaker and a current detector are connected between the load side of each of a plurality of network lines and a network bus, a breaker is connected to the primary side of the network transformer, the current detector being operative to detect an accident current on the secondary side of the network transformer, and relays or an operation controller is provided which is responsive to the detection signal to open the breaker and protector breaker to switch off accident currents on the primary and secondary sides of the network transformer, whereby the protective range is so expanded as to cover a line section between the network transformer and the protector breaker and the scale of the overall power receiving system is reduced.

Abstract: A device which protects a spot network type power receiving and transforming system when, while the system and an electric generator are operating in parallel, overall interruption of power supplied to the primary side of network transformers occurs suddenly. In the spot network type power receiving and transforming system, protector circuit breakers are provided on several branch buses connected to a common bus and a generator circuit breaker is connected to the electric generator; a link circuit breaker is connected to the common bus between the spot network type power receiving and transforming system and the electric generator; and network relays are connected in parallel with the protector circuit breakers respectively.