Novel scheme based on flux restraint theory used in distinguishing inrush currents for UHV transformers

As to differential protection for ultra-high voltage (UHV) three-phase divided tank transformer, this paper provides a novel fast magnetizing inrush currents distinguishing scheme based on magnetizing character. With sufficient consideration to realistic application factor of UHV transformer end connecting with long-distance transmission line, and with corresponding calculation for transformer equivalent instantaneous reluctance using adaptive digital low-pass filter, this scheme is good for solving problems of calculation error rising from transformer model simplification. According to different characteristics in variation during internal fault and magnetizing inrush, it can be accomplished to identify magnetizing inrush in just 10ms, at the same time it also gives the consideration to the influence of TA saturation during internal fault in guarantee of correct judgement even TA is in serious saturation. This scheme is with following virtues including real time response, small calculation workload, high reliability, and promising engineering applications. It is proved its real time capability and reliability through test.