Maximum differential flow brake device for preventing multiple-branch voltage transformer differential protection unwanted operation

Abstract

The invention discloses a maximum differential flow 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 comparator outputs 0, the lateral area outer ground fault is determined, the three-phase differential protection exit is locked, 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, without influencing the in-area breakdown, the correct actuation of differential protection can be guaranteed.

Description

technical field [0001] The invention relates to a transformer protection device, in particular to a maximum differential current 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, t...

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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