Method for identifying transformer inner echo surge current

Abstract

A method for identifying inrush current in a transformer belongs to the technical field of relay protection for main equipment in a power system. According to the transformer and the cause of the inrush current, use a computer to collect the phase current and phase voltage of the primary and secondary windings of the running transformer, and calculate the difference between the primary and secondary phase currents, that is, the differential current; In the calculation period, the unsaturated operating area is determined according to the maximum value of the absolute value of the differential current; then the equivalent instantaneous inductance in the unsaturated operating area is calculated, and the operation transformer is judged by the average value of the equivalent instantaneous inductance in the unsaturated area. Should surge current, block the differential protection to prevent its malfunction. Compared with the second harmonic ratio excitation inrush blocking criterion and the third harmonic ratio current transformer saturation criterion, this method has the advantages of high reliability and strong anti-current transformer saturation ability in identifying and responding to inrush current.

Description

technical field [0001] The invention belongs to the technical field of relay protection for main equipment of a power system, and in particular relates to a method for identifying transformers and inrush currents that should be excited. Background technique [0002] Transformer relay protection is the guarantee for its safe and stable operation, but in actual operation, due to the influence of many external conditions and its own principles, the correct action rate of the differential protection as the main protection has always been low. Among the many influencing factors, due to the no-load closing of a transformer, an inrush current is generated in an adjacent operating transformer, which leads to many instances of misoperation of the differential protection of the operating transformer. The misoperation phenomenon of differential protection is attracting the attention of the relay protection circle because of its harmfulness, complexity and concealment. [0003] Aiming ...

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Problems solved by technology

However, the former will lower the sensitivity of differential protection, especially not conducive to the action of short-circuit fault protection between small turns; the latter has been researched and shown that it cannot eliminate the path of inrush current, and cannot avoid the generation of inrush current and the failure of differential protection of transformers. Misuse

According to the phenomenon that the current transformer saturation is more likely to cause the differential protection to malfunction when the inrush current is generated, it has been proposed to increase the current transformer saturation criterion to prevent the differential protection from malfunctioning, which improves the reliability of the differential protection to a certain extent. However, the third harmonic current transformer saturation criterion currently used has unreliable shortcomings. In practice, the third harmonic content may be low when the differential protection malfunctions, and it cannot play a braking role on the differential protection.

[0004] At present, there is no specific detection criterion for inrush current and corresponding differential protection anti-maloperation measures, but the excitation inrush current (mainly for the initial inrush current generated by transformer no-load closing) criterion and the current transformer saturation criterion are used. According to data, when the inrush current is generated, the blocking differential protection is not very effective in practice.

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