Magnetizing inrush current discrimination method based on equivalent excitation impedance frequency domain character of transformer

Abstract

The invention discloses a magnetizing inrush current discrimination method based on equivalent excitation impedance frequency domain character of a transformer, which discriminates magnetizing inrush current by the equivalent excitation impedance frequency domain character of the transformer. The discrimination method comprises the steps of: indicating the equivalent excitation impedance of the transformer as Z (n) after N point sampling discretization in one power frequency cycle, wherein the equivalent excitation impedance of the transformer changes along with time; carrying out frequency domain analysis on Z (n) and using the ratio of DC component amplitude absolute Z (0) to fundamental wave component absolute Z (1) and fixed-ratio threshold fixed value Kzd to carry out magnetizing inrush current discrimination. The discrimination method discriminates magnetizing inrush current and short circuit fault current according to the character of the excitation impedance of the transformerin the frequency domain when the magnetizing inrush current occurs to the transformer, which is simple and clear, does not need to consider system parameters and transformer parameters, can be automatically adapted to various types of transformers and the various connecting manners of the transformers , as well as the changes of system operation manner and system structure, reliably lock when inrush current occurs to the only transformer, and can act quickly when fault occurs to a region in which transformer fault and magnetizing inrush current exit simultaneously.

Description

technical field [0001] The invention relates to a novel identification method for excitation inrush current in differential protection of transformers, belongs to the technical field of relay protection for main equipment in power system automation, and is an identification method for excitation inrush current based on frequency-domain characteristics of transformer equivalent excitation impedance. Background technique [0002] How to distinguish magnetizing inrush current and fault current in transformer protection is a difficult problem. At present, the transformer protection configured in the actual system mainly uses the principle of second harmonic braking based on the characteristics of the inrush current waveform, the principle of discontinuity angle and the principle of waveform symmetry to distinguish the excitation inrush current, among which the second harmonic braking principle is the most widely used . Although this type of identification method based on the in...

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Problems solved by technology

[0003] The problem to be solved by the present invention is: the existing transformer excitation inrush current identification method based on the inrush current waveform characteristics is likely to cause misoperation of the transformer differential protection, and the identification effect is not ideal; the voltage and current are used to identify changes in transformer parameters, thereby identifying The method of transformer failure or not requires transformer parameters or system parameters, but it is difficult to accurately measure the parameters of the protected transformer or system parameters in practical applications, and the practical value is not high

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