Phase-sequence synthetic brake method for preventing multi-branch transformer differentical protection malfunction

Abstract

A phase sequence combination braking method for preventing multibranch transformer differential protection misoperation is to make up of ratio brake elements by the maximum value of the zero sequence current of each neutral point earth (or branch) and the positive or the negative sequence currents of the three phase differential current in the transformer differential protection. When the ratio value is smaller than that of the setting K, then it is decided that the earth out of the neutral point earth is fault and a three-phase brake signal is output to brake the three phase ratio differential protection which can prevent transformer differential protection misoperation resulted from the earth fault out of the neutral point earth when errors of three phase current inductors are different.

Description

technical field [0001] The invention relates to a transformer protection method, in particular to a phase sequence synthesis braking method for preventing misoperation of differential protection of multi-branch transformers. Background technique [0002] The existing differential protection device for power transformers can identify external faults and internal faults through the ratio braking criterion, that is, the ratio of differential current to ride-through current; By analyzing the waveform or harmonic content of the differential current, the excitation inrush current and the overexcitation current can be identified to achieve the purpose of judging internal faults. For power transformers with two or more neutral points directly grounded, when an out-of-area ground fault occurs on one neutral point grounding side, there may be large ground fault zero-sequence currents on multiple grounding sides. In order to prevent the zero-sequence current from causing the different...

AI Technical Summary

Problems solved by technology

However, when the errors of the three-phase current transformers on the grounding side are inconsistent, and the transformer only has power supply on the grounding side where an external fault occurs, the traditional method cannot eliminate the influence of the zero-sequence current caused by the external grounding fault on the grounding side, and there will be a large The differential unbalanced current, the ratio braking criterion and the inrush braking criterion cannot perform reliable braking, especially when the transformer load current is small or even zero, the ratio braking criterion, the inrush braking criterion Criterion can not brake for this, as long as the error current exceeds the threshold, the transformer differential protection will malfunction

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