Distribution circuit single-phase grounding protection control method based on software frequency measurement and harmonic wave analysis

Abstract

The invention provides a distribution circuit single-phase grounding protection control method based on software frequency measurement and harmonic wave analysis. First, at least 2 cycle wave discrete digital sequences of zero sequence current and voltage are obtained by a constant time interval fixed sampling system, then a high accuracy software frequency measurement method put forward in the method is used for obtaining a frequency measuring value, and an interceptive discrete sampling sequence length and a sequence value can be modified by use of a discrete sampling sequence length modifier formula, and finally, fundamental current amplitude and phase calculation of the zero sequence current and voltage and harmonic analysis are performed to realize single-phase grounding protection control of a faulty line. When the zero sequence current and fundamental wave voltage are greater than a fixed value, phase angle of the fault current starts, in a set zone of action, relay protection to isolate the fault line.

Description

technical field [0001] The invention relates to a power system distribution network fault detection analysis and control technology, in particular to a distribution line single-phase grounding protection control method based on high-precision software frequency measurement and harmonic analysis. Background technique [0002] The main fault form of distribution lines is single-phase grounding, and about 80% of the faults in the entire power distribution system are caused by single-phase grounding. At present, most of the main power distribution lines in our country adopt the neutral point ungrounded, the neutral point through the arc suppressing coil or the high resistance grounding system, also known as the small current system. The biggest advantage of using the low-current grounding method for the power distribution network is that the system can still supply power normally after a single-phase grounding occurs. However, the small current system will not form a short circ...

AI Technical Summary

Problems solved by technology

However, the small current system will not form a short circuit when a single-phase ground fault occurs, so the fault characteristics are not obvious, and the existing ground protection control method cannot quickly and accurately control the distribution network terminal to isolate the fault line

For example, currently used power distribution terminals (such as FTU, DTU, RTU, etc.) often use the amplitude limit method. When the fault zero-sequence current exceeds the threshold, it is determined as the fault line, but this method has low detection sensitivity; there is also a group ratio Amplitude-to-phase method, by comparing the amplitude of the fault current of all lines, selecting the line with larger amplitude and then judging its polarity to determine the faulty line, this method is compared with the simple amplitude comparison method and polarity comparison method The effect is good, but the reliability is still low; and the current (power) direction method: compare the phase relationship between the line fault power frequency zero-sequence current and zero-sequence voltage, and determine the fault line when the current (power) flows to the bus. Because it does not need other line information to be self-identified, the detection sensitivity is high, and the effect is better than the former, so it has wide applicability

However, the power frequency of the distribution line often has a frequency offset, so the direct calculation of the traditional method without high-precision measurement of the frequency often leads to misjudgment, so the reliability of this method is not high

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