Study On Fault Line Selection Of Single - Phase Earth Fault In Resonant Grounding Of Small Current Grounding System

At present, neutral point ineffectively grounded power system, which divided into isolated, arc suppression coil and the effective resistance grounding, is widely used in 3～ 66 kV power distribution system in many countries, including China. In the distribution network, there are more than 80% of the failures are single-phase-to-earth fault. Early ways to eliminate this kind of failure is manual switch, which was replaced by lots of fault line selection methods since 1980s for causing great losses to both the user and the power grid. However, in actual situation, the low accuracy and reliability of the line selection devices may cut the power supply reliability and increase the outage cost. Therefore, it is significance to study how to improve the accuracy and reliability of line selection methods in the neutral point ineffectively grounded power system.This paper introduces the single-phase-to-earth fault line selection methods in neutral point ineffectively grounded power system, and analyzes the situations of steady and transient state in different grounding modes. Fault line selection method in resonance system is finally chosen as the research subject in this paperWavelet packet decomposition is used to decompose fault signals because it can divide frequency multi-levelly. Also, this paper presents detailed introduction in how to choose wavelet function. Then structure nodes and the relationship between the first modulus maxima corresponding to the figure, to determine the correlation coefficient of line selection method based on the diagram for this article adopted by the transient component of line selection method, the steady-state line selection method, zero sequence active power method is adopted, this paper combines steady-state criterion with transient-state criterion based on fuzzy theory, the two criterion of information fusion, calculate the final fault credibility, namely the possibility of every line fault.Finally, this paper builds an arc suppression coil system resonant grounding model based on MATLAB, whose parameters such as the length of the line and failure location can change. Applying research method proposed in this paper to the models which have different parameters, the final test results show that the proposed method to select the arc suppression coil can improve the accuracy of fault line selection to a certain extent.