Differential protection restraining procedures for objects with more than two supply ends

Problem of application of the biased differential protection for multi-circuit differential scheme is discussed in this paper. Efficiency of six various methods of the restraining current determination was examined and the method that reveals the best performance is recommended. Additionally, supporting criterion signal to solve the problem of identification of low current internal faults incepted during external faults is proposed. Considered restraining principles were analysed by simulative tests. Simulation signals were obtained with use of EMTP software, whereupon wide scope of normal as well as abnormal operating conditions of the modelled power system were taken into account.