Phase-splitting zero-sequence brake method for preventing multiple-branch voltage transformer differential protection unwanted operation

Abstract

The invention discloses a phase-splitting zero-sequence brake method for preventing multiple-branch voltage transformer differential protection unwanted operation, wherein the three-phase difference currents in the transformer differential protection constitute ratio braking element with the maximum value of zero-sequence current on each of the neutral point earthing end (or branches), when the ratio value is less than a setting value K, the corresponding differential current is judged to be the error current caused by the faults outside the area, brake the corresponding phase ratio differential protection, thus preventing the differential protection accidental operation of the transformer. The transformer differential protection accidental operation resulted from ground fault outside the lateral area when the errors of the three-phase current transformer are in inconformity.

Description

technical field [0001] The invention relates to a transformer protection method, in particular to a phase-separated zero-sequence braking method for preventing maloperation of multi-branch transformer differential protection. Background technique [0002] The existing power transformer differential protection device uses a ratio brake element, that is, the ratio of the differential current to the through current, to identify the fault outside the zone and the fault in the zone; The waveform or harmonic content of the differential current is used to identify the excitation inrush current and over-excitation current to achieve the purpose of identifying internal faults. For power transformers with neutral points directly grounded on two or more sides, when an external ground fault occurs on one neutral point grounding side, a large ground fault zero-sequence current may occur on multiple grounding sides. In order to prevent the zero-sequence current from causing differential ...

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 of the differential current, the ratio braking element and the inrush braking element cannot perform reliable braking, especially when the transformer load current is small or even zero, the ratio braking element and the inrush braking element cannot perform reliable braking. Braking cannot be performed, as long as the error current exceeds the threshold, the transformer differential protection will malfunction

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