Quick distinguishing method for zero-sequence directional elements of alternating-current and direct-current serial-parallel power grid

Abstract

The invention relates to a quick distinguishing method for zero-sequence directional elements of an alternating-current and direct-current serial-parallel power grid. The quick distinguishing method includes computing sampling values of zero-sequence voltage and zero-sequence current according to sampling values of three-phase voltage and three-phase current at a protection mounting position; establishing a time-domain differential equation based on instantaneous sampling values of the zero-sequence voltage and the zero-sequence current; computing weights of zero-sequence resistance and zero-sequence inductance by the aid of the time-domain differential equation and a least square method; converting the weight of zero-sequence resistance and the zero-sequence inductance of a system to frequency domain, and computing power-frequency zero-sequence impedance; and judging whether forward or reverse grounding faults occur or not by means of judging whether an area of an impedance plane with the zero-sequence impedance is in a positive-direction action area or a negative-direction action area. The method is not affected by low-frequency weights, fractional harmonic waves or the fact that positive-sequence impedance is unequal to negative-sequence impedance after the alternating-current and direct-current serial-parallel power grid fails, reliability of computation results is guaranteed, action performances of the zero-sequence directional elements are far superior to those of various power-frequency directional elements based on full-period Fourier algorithm and semi-period Fourier algorithm, and the quick distinguishing method has an extremely important application value.

Description

technical field [0001] The invention relates to the technical field of relay protection automation in the field of electric power engineering, in particular to a fast zero-sequence directional element discrimination method suitable for an AC / DC hybrid power grid. Background technique [0002] Compared with the AC transmission mode, HVDC transmission has the characteristics of large transmission capacity, small active power loss, can be used for asynchronous networking, can limit the short-circuit current level of the power system, and has no stability problems in the AC transmission system. The AC-DC hybrid power grid has become the development direction of my country's power grid. [0003] The characteristic of HVDC transmission is that its inverter side converter will fail in commutation when the AC system fails. The main features of commutation failure are: if the commutation failure lasts for more than two cycles, the waveform of commutation failure will appear as a pul...

AI Technical Summary

Problems solved by technology

[0018] The purpose of the present invention is to provide a fast zero-sequence directional element discrimination method for AC / DC hybrid power grids to solve the large calculation errors in the phasor algorithm using Fourier filtering in the relay protection of AC / DC hybrid power grids. Problems that adversely affect relay protection performance

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