Research On Single-phase To Ground Fault Line Detection And Location Method In Distribution Networks

Small current grounding is used in medium voltage distribution network of ourcountry which refer to arc suppression coil grounding system and neutral pointungrounded system, but the problem of fault line selection and location have notsolved due to tiny fault current of single phase to ground in small current groundingsystem, arc of instability and other influence factor exist. In order to shorten poweroutage time, reduce outage area, improve power supply reliability and ensure gridsecurity and stability, efficient, accurate and reliable research of single-phase faultline selection and fault location methods is urgent.The paper aims to solve the problem of fault line selection and location indistribution network system that the main research includes the following work.Firstly, recent research about fault line selection and location in distributionnetwork system is introduced. Advantage, disadvantage and applicable scope areanalyzed. Passive methods and active methods as well as their difficult technicalproblems are discussed. By separately analyzing characteristics of transient zerosequence current component and steady-state zero-sequence current component ofsingle-phase ground fault in arc suppression coil grounding system and neutral pointungrounded system, fault characteristic quantity of possible extraction in lineselection and location is confirmed.Secondly, wavelet energy comparison line selection and wavelet packet energycomparison line selection method are put forward. Wavelet energy comparison lineselection method is to use wavelet transformation sub-frequency characteristics todecompose wavelet energy in frequency cycle zero-sequence current signals afterfault, then seek the wavelet energy of coefficients after wavelet decomposition, andline selection is based on principle of maximum of wavelet energy in fault line.Wavelet packet energy line selection is to put transient current in each feeder intoMATLAB, and then quarter cycle short window data in fault line is taken to waveletpacket decomposition, and calculate transient energy of sub-band. Defining featureband as maximum transient energy in the sub-band, feature band energy is improvedwith calculation, and then according to the principle of maximum energy to selecetdthe fault line.Finally, based on the short window energy of zero-mode current, a short window energy fault location method is proposed. By defining square of thezero-mode current and the short window energy of quarter cycle in checked fault linepoint, the short window energy is calculated at each detection point,and thenchanged to per-unit value. Finally the fault position can be determined by comparingthe per-unit values in test points.