Three-phase brake device for preventing multiple-branch voltage transformer differential protection unwanted operation

Abstract

The invention discloses a three-phase brake device 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, the comparator outputs 0, the signal is outputted through an OR gate 5, or when the OR gate 5 outputs 0, the three-phase differential protection exit is locked, or when the OR gate 5 outputs 1, and the corresponding differential protection actuations are allowed. The advantage of the invention is, 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, and without influencing the correct actuation of the differential protection under the circumstance of in-area faults.

Description

technical field [0001] The invention relates to a transformer protection device, in particular to a three-phase brake device 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 a power transformer with neutral points directly grounded on two or more sides, when an external ground fault occurs on one grounding side, a large ground fault zero-sequence current may occur on multiple sides. In order to prevent the zero-sequence current from causing differential protection misoperation, the method of tran...

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 on the neutral point grounding side where an external fault occurs, the traditional method cannot eliminate the zero-sequence current caused by the external grounding fault on the neutral point grounding side. Influenced, there will be a large differential unbalanced current, and the ratio braking element and inrush braking element cannot perform reliable braking, especially when the transformer load current is small or even zero. The inrush braking element cannot brake this, as long as the error current exceeds the threshold, the transformer differential protection will malfunction

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