Adaptive fault type fault line detection method for non-effectively earthed system

Abstract

The invention discloses an adaptive transient characteristic fault line detection algorithm for a non-effectively earthed system by utilizing wavelet packet frequency division characteristics. The method comprises the following steps of: (1) monitoring a waveform of a bus zero sequence voltage, and when an instantaneous value of the bus zero sequence voltage exceeds a setting value, starting a fault line detection device and recording, and acquiring transient zero sequence current of each line; (2) calculating the selected frequency band of the system according to the grid structure and line parameters of a power distribution network; (3) decomposing and reconstructing the zero sequence current of the line by employing a wavelet packet, and taking three lines with the highest zero sequence current envelope line area as alternative fault lines; (4) calculating a scaling factor r and a transient factor h, and judging the earthing fault generation type; and (5) calculating a first amplitude value comparison criterion and a second polarity comparison criterion according to the earthing fault type, introducing a third criterion when the two criterion results are inconsistent, and selecting the earthing line. The method is accurate in line selection, and the earth line selection reliability of the power distribution network can be improved.

Description

technical field [0001] The invention relates to a fault type line selection method for an ineffective grounding system, in particular to a fault type adaptive grounding line selection method for an ineffective grounding system. Background technique [0002] At present, the neutral point of my country's 6-35kV medium and low-voltage distribution network widely adopts two ineffective grounding methods: ungrounded and grounded through arc suppression coils (also called resonance grounding), which are called ineffective grounding systems. [1] . When a single-phase ground fault occurs in a non-effectively grounded system, no short-circuit loop is formed, only a small zero-sequence current is generated in the system, and the line voltage between the three phases remains basically unchanged, which does not affect the power supply to the load, so it is not necessary to immediately trip. my country's electric power regulations stipulate that the non-effectively grounded system can ...

AI Technical Summary

Problems solved by technology

This method not only consumes a lot of time and manpower, but also needs to interrupt the power supply of non-faulty lines for a short time, which reduces the reliability of power supply and causes unnecessary economic losses to the society.

In addition, the opening and closing of the switch during the manual route selection process will not only cause impact on the power grid, but also easily generate operating overvoltage and resonance overvoltage. Frequent switching operations will inevitably reduce the service life of the switch and greatly increase The burden of unattended substation equipment that requires remote remote operation

Therefore, in order to improve the automation level of fault line selection, many scholars at home and abroad have proposed a variety of line selection methods for line selection problems, and have launched several generations of line selection devices based on different line selection theories, but the actual application effect is not ideal. [5-6] , so that some on-site personnel give up using the line selection device, and still use the traditional manual method to find the faulty line

[0004] In the resonant grounding system, the reasons for the grounding fault are diverse, the transient process is complex, and due to the compensation effect of the arc suppression coil, the transient fault current is weak or even smaller than the steady-state fault current. These reasons cause the difficulty of line selection in the resonant grounding system

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