Transient directional protection method for AC line of high-voltage AC/DC compound system

Abstract

The invention discloses a transient directional protection method for an AC line of a high-voltage AC/DC compound system. The transient directional protection method specifically comprises the following steps of detecting electric signals at two ends of the protected AC line through current transformers at two ends of the line of the compound system separately; preprocessing the detected electricsignals to obtain current break variables at two ends of the protected AC line, switching sampling of a protection system into a high data acquisition frequency and extracting corresponding voltage and current according to the width of a data window; calculating a front travelling wave and back travelling wave total of the current; calculating wavelet coefficients; adaptively eliminating interference values of the obtained wavelet coefficients and obtaining a synchronously extruded wavelet coefficient through extrusion processing of the wavelet coefficients, wherein the synchronously extrudedwavelet coefficient represents the energy of a transient current wave; calculating the transient energy ratio of the front travelling wave to a back travelling wave of the current; and comparing the sizes of the energy ratio and a setting value to distinguish an internal fault from an external fault. According to the transient directional protection method, the AC line of the high-voltage AC/DC compound system is provided with relay protection.

Description

technical field [0001] The invention belongs to the technical field of electric power system relay protection, and relates to a transient direction protection method for an AC line of a high-voltage AC-DC hybrid system. Background technique [0002] Issues such as resource shortage and environmental pollution have become thorny issues for countries around the world, and green and low-carbon will also become the main direction of energy production and consumption. For this reason, countries around the world have formulated corresponding development goals and plans. EHV / UHV power transmission is the medium that must be relied upon to solve the large-scale development and long-distance transmission of clean energy. The "global interconnection" of the power grid also promotes the vigorous development of high-voltage AC-DC hybrid systems in various countries. By 2020, the 16-circuit DC transmission line and the flexible DC ring network with the highest voltage level in the world ...

AI Technical Summary

Problems solved by technology

Some scholars have proposed the direction protection of high-voltage transmission system based on the polarity of current traveling waves. However, judging the polarity is very dependent on the detection and transformation of the initial part of the traveling wave data, which is easily disturbed by data acquisition reliability and threshold problems.

Furthermore, the contradiction between the hybrid power grid's demand for ultra-high-speed protection action and the high-reliability requirement of the protection action needs to be coordinated through the ultra-high-speed and high reliability of the relay protection action performance. Problems with extraction and information processing methods make it difficult for protection to achieve rapid action

In summary, in view of the more stringent relay protection requirements of the high-voltage AC-DC hybrid power grid, a fast and reliable fault removal scheme for AC lines needs to be proposed urgently

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