Method for identifying transformer inner echo surge current

Abstract

The invention provides an identification method for sympathetic inrush in transformer which belongs to power system main equipment relay protection technology field. The identification method has characteristic in that: the method identifies transformer sympathetic inrush by using non-saturation area equivalent instantaneous inductance. Phase current winding around primary-secondary sides of operating transformer and primary side phase voltage are collected by computer according with transformer sympathetic inrush generating reason, and difference of primary-secondary sides phase current is calculated, namely different current; next, non-saturation operation region is ensured according with max of different current absolute value; then, equivalent instantaneous inductance in non-saturation operation region is calculated, and sympathetic inrush in transformer is judged according with equivalent instantaneous inductance average value in non-saturation operation region, differential protection is closed locked for preventing misoperation. The method has merits of high reliability, strong saturability of anti-current transformer in comparison with secondary harmonic ratio inrush current locking criterion and third harmonic ratio current transformer saturation criterion.

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 ...

AI Technical Summary

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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