The Studies On The Novel Method Of Non-direct-ground System Single Line-to-earth Fault Location

Small current earth at neutral point is popular in power distribution networks. This kind of earth is advantageous to reliability of power supply, but presents a objectionable problem that when single-phase grounding fault occurs, it is difficult to implement fault circuit selection and protection. The raison is that single-phase grounding fault does not form a short circuit, the fault component is small, on influence of interference and measurement error thc correct judgment is hard to be made. This thesis deals with this problem, aims to find the deficiency of existing method, to probe for new selection method and improve selection strategy. As a basis, mechanisms and features in single-phase fault that occurs on neutral non-grounded networks are discussed in this thesis, and di tinctions of fault component between fault circuit and health circuit are listed. Effect of Peterson coil on single-phase fault is also discussed. With deeply studying on wavelet transform, and with considering the characteristics of small current fault, wavelet transform is applied in this thesis to analyze the fault and select the fault circuit. According to practical situation, idea of integrated method for fault circuit selection is put forward and expounded. And in order to suit this idea, energy method and magnitude & ohase comparison method as well as its extended form are investigated and improved further more. Field data is important to solve fault circuit selecting problem. This thesis contributes some fault data recorded from field in case of man-made single-phase grounding fault. Some methods are examined utilizing these data.