A Fault Line Selection Method for Distribution Networks Considering Secondary Faults

Abstract

A distribution network fault line selection method considering secondary faults, the steps are mainly: A. Sampling to obtain the effective value of the zero-sequence voltage of the busbar at the current sampling moment; B. Obtaining the value of the feeder n within one cycle after the fault Zero-sequence current value sequence; C. Get the wavelet singular entropy measurement value sequence of feeder n; D. Secondary fault judgment; E. Construct the wavelet time-spectrum matrix of the first fault interval; G. Establish the matrix similarity of the first fault interval degree criterion; H, find the fault feeder for the first time; I, division of secondary fault intervals; J, repeat E-H steps to get the first fault feeder; K, construct wavelet time-spectrum matrix of secondary fault intervals ; L, establishing the matrix similarity criterion of the secondary fault interval; M, finding the secondary fault feeder. The method can timely determine whether there is a secondary fault and identify the secondary fault feeder, so that the line fault can be completely and timely processed, and the distribution network has high safety and reliability.

Description

technical field [0001] The invention belongs to the field of grounding protection of a resonant grounding system of a power system. Background technique [0002] Since the neutral point of the medium and low voltage distribution network in my country usually adopts a resonant grounding system through the arc suppression coil, its characteristic is that after a single-phase ground fault occurs, the system is allowed to operate with a fault for 1-2 hours. However, long-term operation with faults may cause line insulation problems, especially in lines where cables are widely used, due to the large capacitive current of cables, it is easy to cause secondary multi-point faults. Secondary faults mean that multiple faults do not occur at the same time, there is a time difference between the two faults, and after the previous fault occurs, the system has not been adjusted from the fault state to the normal state, and suffers a new disturbance fault working conditions. Therefore, i...

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Problems solved by technology

[0003] With the expansion of the power network, the number of outgoing lines in the small-current grounding system continues to increase, and the probability of two-point grounding in the system or the same-phase grounding of other lines before removing the single-point grounding fault also increases. It is difficult to use the traditional single-phase line selection criterion

This is because the current method only considers a single fault on the line, but ignores the possibility of secondary faults in the line, even if the secondary fault exists

For the resonant grounding system of the distribution network, when a single-phase ground fault occurs somewhere in the line, due to the compensation effect of the neutral point arc suppression coil in the zero sequence circuit, the fault current is very weak, and the sensitivity of fault detection line selection is low

If a secondary fault occurs on the phase with the same name of another line at this time, since a large fault current cannot be formed, the secondary fault process will be submerged in the transient process of the first fault, making it impossible to extract the secondary fault during the fault feature extraction process. The electrical information of the fault, so that the feeder of the secondary fault cannot be determined in time, resulting in the missed selection of the fault feeder, resulting in the failure of the distribution line to be completely and timely processed, and the safety and reliability of the distribution network need to be further improved

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