Due to small grounding current and unstable electric arc at fault position

it is difficult to obtain the zerocurrent of fault circuit and to tune the parameters of equipments in a small current grounding system with arc suppression coils. Hence the fault circuit selection in this system has always been a complex and difficult problem. This paper presents an adaptive fault circuit selection method based on the principle that the difference of transient energy of normal circuits and that of fault circuit is minimal. The proposed method can erase the influence of small fault current and unstable electric arc. With great adaptability to various faults happened in the system with arc suppression coils and considerable immunity to noises and no requirements of presetting

the overall performance of the protection has been upgraded by using the proposed algorithm. Large amount of digital simulation results show that the proposed method is effective and reliable.