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Simultaneous single phase faults on different phases of parallel transmission lines may cause three phase trips on both lines although the faults in question do not warrant three phase trip. When such lines constitute the only link between a power plant and the remaining power system, misoperation of relays often leads to a loss of generators through loss of synchronism. This problem has been analyzed, and a new integrated relaying principle proposed which produces a secure decision to trip only the faulted phases in cases of complex simultaneous faults. Results of simulated relay performance are given. Also included are some preliminary considerations regarding computer implementation of the new relay.