1.College of New Energy, China University of Petroleum (East China), Qingdao 266580, China;2.Zhaoqing Power Supply Bureau, Guangdong Power Grid Co., Ltd., Zhaoqing 526000, China;3.Research Center for Smart Grid, Shandong University of Technology, Zibo 255049, China

In distribution networks, the probability of the line breaking and grounding fault is high, and it may cause electric shock, fire and other accidents. The differences of transient electric quantities between single-phase line breaking and grounding fault and normal single-line grounding fault and the applicability of existing transient line selection methods are not clear. The equivalent circuit of the single-phase line breaking and grounding fault in non-solidly grounded system is established by fault boundary conditions. The characteristics of transient zero-sequence voltage/current at the moment of line breaking and grounding in the ideal scenario are preliminarily analyzed. Also, the differences of transient electric quantities between single-phase line breaking and grounding fault and normal single-line grounding fault, and the applicabilities of the line selection methods of transient current amplitude/polarity comparison and transient power direction are analyzed. The results show that there is obvious transient process at the moment of line breaking and grounding, and the transient characteristics are different from normal single-line grounding fault. However, in the selected frequency band, the transient electric quantity constraint relationships at the moment of line breaking and grounding are consistent with that of normal single-line grounding fault. The existing line selection methods are still applicable, but the sensitivity of the line selection using the transient electric quantities generated at the moment of line breaking is low. Finally, the simulation is used to verify the applicabilities of line selection methods.