Research On Fault Detection And Location Method In Power Distribution Network

Most medium voltage distribution networks in China adopt small current grounding mode,that is,neutral ungrounded mode or resonant grounded mode.After single-phase grounding fault(i.e.small current grounding fault)occurs,the fault current is small and unstable,and it is difficult to be detected and removed effectively,which poses a potential threat to the safe and reliable operation of distribution network.To solve this problem,this paper presented a new method of fault line selection and section fault location for small current grounding fau lt,after discussing the characteristics of small current grounding fault.The mechanism of small current grounding fault and zero sequence current characteristics are studied.After the zero sequence equivalent circuit and simulation model of small current grounding fault are established,the transient process and resonance mechanism of small current grounding fault are analyzed,and the distribution characteristics of zero sequence current under fault and its time-frequency domain characteristics are also investigated.And then,the time-frequency domain characteristics differences of transient zero sequence current between fault lines and sound lines are explored,which provides theoretical support for fault line selection and location.A fault line selection method for small current grounding based on admittance characteristic coefficient is proposed.According to the distribution characteristics of zero sequence fault current under small current grounding fault and zero-sequence voltage of network,the equivalent admittance characteristics at the head of distribution network under transient oscillation frequency are analyzed,and the admittance characteristic coefficient is used to select the fault line.A simulation model of small current grounding fault in distribution network is established.Through this simulation model,a lot of simulation tests are carried out to verify the correctness and reliability of the proposed method.An improved relative entropy based fault location method for small current grounding is proposed.This paper expounds the basic principle of relative entropy of signal,and the relative entropy characteristics of transient zero-sequence current on both sides of fault line section of distribution network with small current grounding neutral point.On this basis,the improved relative entropy is used to locate the fault section.By improving the traditional relative entropy algorithm,it does not need to transmit the full sampled data of the signal,and only needs to transmit a relat ively small array of characteristic probability distribution of the data,which reduces the requirement of the communication channel.The simulation results show that the proposed fault location method is reliable,and it can operate correctly in different fault locations,fault resistance and fault instant.