Small current grounding system fault line selection method using power frequency component wavelet coefficients to carry out linear fitting detection

Abstract

The invention relates to a small current grounding system fault line selection method using power frequency component wavelet coefficients to carry out linear fitting detection, and belongs to the field of a power system relay protection technology. The small current grounding system fault line selection method includes the steps of being capable of obtaining fault zero sequence current according to measured three-phase current at a protection installing position after a single-phase earth fault of a small current grounding system occurs, carrying out wavelet decomposition on the zero sequence current of each feeder line of a 5-millisecond short time window after the fault occurs, extracting the wavelet coefficients containing power frequency bands, carrying out linear fitting on the wavelet coefficients, representing variation trend of the power frequency bands of the zero sequence current of the feeder lines by using polarity of obtained fitting straight slope, and constructing feeder line selection sign functions according to the rule that the variation trend polarity of the power frequency bands of the fault feeder lines is opposite to the variation trend polarity of the power frequency bands of the faultless feeder lines, and variation trends of the power frequency bands of the faultless feeder lines are same. If a sign function value of one of the feeder lines is minus one, then the feeder line is the fault feeder line, on the contrary, if the sign function value of one of the feeder lines is one, then the feeder line is the faultless feeder line, and if the sign function values of all the feeder lines are one, then faults happen to buses. The small current grounding system fault line selection method is simple in principle, low in sampling frequency, and capable of achieving correct line selection when the faults happen on the conditions of initial fault current angles of the small faults.

Description

technical field [0001] The invention relates to a faulty line selection method for a small current grounding system, in particular to a faulty line selection method for a small current grounding system using power frequency component straight line fitting detection. Background technique [0002] When a single-phase ground fault occurs in a small-current grounding system in which the neutral point is grounded through an arc-suppression coil, the fault transient current amplitude is much larger than the steady-state current and is not affected by the arc-suppression coil. Compared with the steady-state component, the transient component after the fault has great advantages, making the line selection method based on the transient quantity the first choice for fault line selection. [0003] Most of the line selection methods based on transient quantities are based on the differences between the faulty line and the healthy line in terms of the sudden change direction and amplitud...

AI Technical Summary

Problems solved by technology

Most of the faults in the small current grounding system are single-phase grounding faults, and the problem of line selection has been difficult to solve. The main reasons are: 1. The fault boundary is complex and random, such as the initial phase angle of the fault, the fault distance, the transition resistance, and different fault conditions. Transient zero-sequence signal frequency components, attenuation characteristics, and spectrum energy distribution are quite different; 2. When a single-phase ground fault occurs near the voltage zero-crossing point,...

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