Research On Technology Of Line Detection And Fault Location For Single-Phase-To-Earth Fault In Neutral Point Non-Effectively Grounded Systems

The non-effectively grounded system is used in the distribution net of 6-66KV. It has the virtue of proving power supply's reliability. But fault selection and fault location are not solved when single-phase permanent earthing appears. This paper studies single-phase earthing fault selection and fault location in the non-effectively grounded system.It defines the concept of single fault degree and continuous fault degree. The former shows quantificationally the fault sign degree of every line in some fault, and the latter shows quantificationally the fault sign degree of every line in the fault process.It brings a new method of fault selection on the base of wavelet packet transform and Wiener filter. The method uses wavelet packet transform in quadrature to zero-sequence steady state current after fault, choosing wavelet coefficient according to different earthing mode. It filters noise blending the wavelet coefficient throughout Wiener filter and analyzes the information without noise and calculates the fault probability of every line.It is a development of fault selection that synthesizing all kinds of fault selection methods. The premise of methods fusion is confirming the applicability of all kinds of methods, which calls validity of methods. The paper determines the validity of methods through data mining on large numbers of local data based on rough set theory. It deals with decision rules out of line by the form of probability effectively and expands rules continually with the increase of fault sample intelligently. Then realizing integrating fault selection methods by fuzzy theory based on the validity. Then realizing integrating fault selection methods by fuzzy theory based on the validity.Since it can run for a while when fault appears in the non-effectively grounded system, the paper brings forward continuous selection strategy for using fault information as much as possible. It fuses single fault degree by D-S evidence theory and calculates continuous fault degree. The line of maximum degree is the fault line. On the base of introducing evidence theory, it can change fault information fusion problem into evidential reasoning problem, so the result is supported by information in the farthest degree and restrains the influence of disturbed poor data. This method makes the best of fault information and reduces the request of memory capacity.The character of low current earthing system is blowing out of arc automatically and has no use for fault location. When permanent earth happens, the system cuts off the line then finds fault point. This paper brings forward fault location method based on C-type...