Method for single-phase earth fault line selection of small current grounding system

Abstract

The invention relates to the field of power systems and the automation of the power systems, in particular to a method for single-phase earth fault line selection of a small current grounding system. According to the method, the zero sequence circuit of a single-phase earth fault is analyzed, the frequency characteristic of the transient state characteristic quantity of the fault is obtained, an optimal FIR filter is designed according to the frequency characteristic to extract the components of transient state capacitive zero sequence currents with obvious fault characteristics, and the interference of noise and the interference of the unbalanced operation condition of a power grid are eliminated. A hierarchical clustering algorithm is used, the polarity and the amplitude characteristics of the transient state capacitive zero sequence currents of the initial ends of all feed lines are integrated to carry out classification on the feed lines, and a single feed line with the change trend of the transient state capacitive zero sequence current easier than the transient state capacitive zero sequence currents of other feed lines is selected as a fault line. The method improves the reliability of the line selection, lowers signal sampling frequency needs, avoids multi-layer signal decomposition, saves computing resources, and is easy to achieve.

Description

technical field [0001] The invention relates to the field of electric power system and automation thereof, in particular to a single-phase grounding fault line selection method of a small current grounding system. Background technique [0002] Although the line selection method for single-phase grounding faults in small current grounding systems has been studied extensively for a long time, due to problems such as inconspicuous fault characteristics, noise interference, and the influence of distribution network operating conditions (such as asymmetry), the existing There are still deficiencies in the reliability and universality of the fault line selection method. [0003] Based on different characteristic quantities, at present, single-phase ground fault line selection methods can be divided into three categories: signal injection method, steady-state line selection method and transient line selection method. Among them, both the signal injection method and the steady-stat...

AI Technical Summary

Problems solved by technology

Wavelet transform, as a powerful tool for time-frequency localization and multi-resolution analysis, has been widely used in the extraction of single-phase-to-ground fault transient feature quantities in simulation experiments, which effectively improves the reliability of fault line selection, but there are still deficiencies : First, the characteristic frequency band is determined according to the principle of maximum energy. Under severe noise interference or unbalanced operation of the power grid, the generated characteristic frequency band may not be an effective fault transient characteristic frequency band, causing misjudgment; in addition, the characteristic frequency band The frequency band is determined based on the analysis of the collected signals and cannot be known in advance. According to Shannon’s sampling law, the sampling frequency can only be increased as much as possible to meet the needs of unknown characteristic frequency bands and increase the requirements for hardware equipment; at the same time, the sampling data needs to be A large number of layer-by-layer extraction and separation, the amount of multiplication is huge, which is not conducive to the realization of embedded systems; in addition, according to the signal polarity to qualitatively distinguish faulty and non-faulty lines, only relying on human judgment, lack of quantitative scientific description, will also lead to misjudgment

Therefore, at present, the practical degree of single-phase ground fault line selection method based on wavelet transform is not high

Images