Single-phase ground fault detection method based on line equivalent impedance value

Abstract

The invention relates to the technical field of distribution network relay protection and more particularly relates to a single-phase ground fault detection method based on a line equivalent impedancevalue. With a condition that a ratio of a zero sequence voltage power frequency effective value to a zero sequence current power frequency effective value of a fault line is much smaller than that ofa non-faulty line as a basis, by collecting the zero sequence voltage of a bus and the zero sequence current of a feeder, the ratio of the zero sequence voltage power frequency effective value to thezero sequence current power frequency effective value of the line is calculated, and whether the line has a single-phase ground fault is judged according to the size of the ratio. According to the method, the fault line and the non-faulty line can be correctly judged, the influence of a transition resistance is small, the method has good applicability to linear fault resistance and nonlinear fault resistance and is not affected by the polarity of a transformer, the sensitivity of protection to a single-phase high-impedance ground fault can be improved, the safety and stability of a power distribution network are improved, and the probability of a safety accident caused by the high-resistance ground fault is reduced.

Description

technical field [0001] The invention relates to the technical field of distribution network relay protection, and more specifically, to a single-phase ground fault detection method based on line equivalent impedance values. Background technique [0002] Compared with the neutral point non-grounding method and the arc-suppression coil grounding method, the neutral point grounding method through a small resistance is more suitable for large and medium-sized urban distribution networks dominated by cable lines, which can effectively limit various overvoltages and The advantages of fast removal of faulty lines have been widely used in large and medium-sized city distribution networks. The environment of distribution network feeders is complex, and single-phase high-resistance grounding faults often occur. The main reasons include disconnection of overhead lines, tree branch hanging, aging and breakdown of insulators or arresters, and moisture in the cable insulation. The enviro...

AI Technical Summary

Problems solved by technology

At the same time, the grounded overhead line will generate a high step voltage, and the arc accompanied by the high-resistance fault will generate high temperature, which will cause a huge threat to the lives of pedestrians around.

[0003] Although the phase-based zero-sequence current protection scheme widely used in small-resistance grounding systems requires it to have certain sensitivity to single-phase transition resistance grounding faults, the capacitive current of the line to ground needs to avoid the fault outside the area. Its protection setting is relatively high, and its sensitivity to high-resistance ground faults is very low, which cannot meet the needs of high-resistance ground faults; some substations also adopt zero-sequence protection schemes, but due to the difficulty of polarity verification of transformers, coupled with The difference between the zero-sequence power direction of the faulty line and the non-faulty line is only about 90 degrees. When the current is small, it is easy to generate a large calculation error, resulting in misjudgment

Images