Small current grounding system single-phase earth fault direction detecting method utilizing linearity between line zero sequence current and voltage derivative

Abstract

The invention provides a small current grounding system single-phase earth fault direction detecting method utilizing the linearity relation between a line zero sequence current and a voltage derivative and belongs to the field of relay protection of power distribution networks. The linearity relation between upstream and downstream voltages and currents of a fault point is analyzed when a single-phase earth fault occurs in an unearthed and arc suppression coil grounded system, a method for fault direction detection by utilizing the linearity relation between the line zero sequence current andthe voltage derivative at a detection point is provided. The zero-sequence voltage and zero-sequence current at each detection point are acquired, linear fitting is conducted on a zero-sequence current sample value sequence and a corresponding zero-sequence voltage difference value sequence, it is judged whether the detection points having the fit goodness greater than a threshold value and the fitting function slope greater than 0 are located at the downstream of fault points or not, if not, the detection points are located at the upstream of the fault points. The method can be simultaneously suitable for low-resistance and high-resistance earth faults of a small current grounding system, improves the adaptability of a fault direction detection algorithm and has a wide actual applicationvalue.

Description

technical field [0001] The invention proposes a method for detecting the direction of a single-phase grounding fault in a small current grounding system using the linearity relationship between the zero-sequence current and the zero-sequence voltage derivative, which can be reliably used for both low and high-resistance grounding faults in an ungrounded system and a resonant grounding system detection. Background technique [0002] my country's medium-voltage distribution network mostly adopts low-current grounding methods, including neutral point ungrounded and neutral point grounded through arc suppression coils (resonant grounding). Reliable detection of single-phase ground faults has always been difficult due to weak fault currents and unstable arcs. Among the existing ground fault direction detection methods, the detection method based on steady-state information needs to use the signal of a long time after the fault, the detection speed is low, and the effect is not i...

AI Technical Summary

Problems solved by technology

Reliable detection of single-phase ground faults has always been difficult due to weak fault currents, unstable arcs, etc.

Among the existing ground fault direction detection methods, the detection method based on steady-state information needs to use the signal of a long time after the fault, the detection speed is low, and the effect is not ideal; while the high frequency (hundreds of Hz) based on ground fault The direction detection method of the transient electrical quantity needs to filter out the power frequency component during detection, which may easily cause information omission, especially when the high-impedance grounding is used, because the frequency of the fault transient signal is close to the power frequency and the amplitude is small, The direction detection method based on high-frequency transient electrical quantities is not applicable; in addition, the patent "A method for locating high-resistance ground faults in small current grounding systems based on the amplitude comparison of transient current projection components" proposes a method based on transient current projection components. The direction detection method of amplitude comparison, which has high line selection accuracy for high-resistance ground faults of resonant grounding systems, but is not suitable for low-resistance ground faults

[0003] It can be seen that most methods cannot adapt to different fault situations at the same time, and different algorithms need to be selected according to the system grounding method and fault type, which increases the complexity of the algorithm

In addition, for the method of using the attenuation transient component of the fault electrical quantity, because the power frequency component has the same rule in the upstream and downstream of the fault point, it cannot be used for positioning. Therefore, it is regarded as an interference quantity in practical applications and often needs to be filtered. In addition, the digital filter is generally used in the device to filter out the power frequency component, which not only increases the amount of calculation, but also when the frequency of the transient signal is relatively close to the power frequency, the filtering effect will not be obvious

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