Research On Single-phase Grounding Fault Location In Medium-power Multi-branch Distribution Network

Medium-power distribution network is designed to complicated structure,numerous branches and short lines. There are a lot of cables, hybrid lines, cable distributive boxes and switchgear cupboards in distribution network, which would make fault location difficult. Through the analysis, most location algorithms can hardly apply in hybrid lines and branch lines, so it’s important for system stability and power supply reliability to make further research on fault location in branch network, especially the single-phase grounding fault.In this paper, the phase-mode matrices are used to decouple three-phase system and the effect of distribution transformers and their loads on modulus networks considering the practical situation are analyzed. This paper analyzes the steady and transient characteristics of single-phase grounding fault theoretically, and then the simulation data confirm it’s correct. The above content laid a theoretical foundation for the following research.The paper puts forward a single terminal fault location algorithm for direct distribution lines based on steady state information in consideration of characteristics of the transverse current at fault point. This algorithm consists of two fault criteria, in which the main criterion is not affected by transition resistance, and auxiliary criterion needs to use characteristics of transition resistance. According to the algorithm put forward above, the fault location in branch lines and hybrid lines can be realized. Finally, the algorithm applied in mixed lines and branch lines is validated by simulation and the example given.In view of the limit of steady location algorithm, a two-terminal fault location method using transient information is proposed based on steady algorithm. The algorithm criterion is modified considering the nonlinear characteristics of transition resistance, so the algorithm can not only realize the permanent fault location, but also the instantaneous fault location. The algorithm only uses two terminal current and single-ended voltage information, and gets time-domain discrete values of zero mode current after fault point by the distributed parameter line model and Stehfest inversion algorithm. Then combined with characteristics of single-phase grounding fault, the criterion of this algorithm is presented, and the method can be achieved on the fault location of branch lines and hybrid lines. Finally, the algorithm adopts search method to determine fault point and is verified through the simulation and some specific examples.