A method for identifying magnetizing inrush current based on zero-sequence current

Abstract

The invention discloses a zero-sequence current-based excitation surge current recognition method. The excitation surge current recognition method comprises the steps of 1, sampling no-load-input side zero-sequence current I<0>; 2, calculating a fundamental wave value I<01> of the zero-sequence current I<0>, a zero-sequence current secondary harmonic value I<02> and a secondary harmonic content K, wherein the secondary harmonic content K is a ratio of the secondary harmonic value I<02> to the fundamental wave value I<01>; and calculating waveform asymmetry number of points N in a half cycle of the zero-sequence current I<0>; and 3, performing excitation surge current recognition: when the secondary harmonic content K is higher than a set threshold value K<set> or the waveform asymmetry number of points N is higher than a set threshold value N<set>, determining as excitation surge current, and closing differential protection; and when the secondary harmonic content K is lower than the set threshold value K<set> and the waveform asymmetry number of points N is lower than the set threshold value N<set>, determining as a failure, and opening differential protection. The excitation surge current recognition is more reliable and can more effectively prevent from misoperation of differential protection in no-load input of a transformer.

Description

technical field [0001] The invention relates to a method for identifying excitation inrush current based on zero-sequence current. Background technique [0002] As long as the system voltage changes and the excitation voltage is affected, an excitation inrush current will be generated. The differential is to calculate the differential current by using the current of the primary side and the secondary side of the transformer. When the transformer is in normal operation, the excitation current is very small. When the excitation inrush current occurs, the influence of the excitation current should not be ignored. The usual practice is Rely on various discrimination conditions to discriminate the excitation inrush current. [0003] At present, the identification of inrush current for transformer protection is calculated and judged based on the differential current after filtering out the zero-sequence current, and the second harmonic content or waveform symmetry in the differen...

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Problems solved by technology

[0003] At present, the identification of inrush current for transformer protection is calculated and judged based on the differential current after filtering out the zero-sequence current, and the second harmonic content or waveform symmetry in the differential current after filtering out the zero-sequence current is judged. Current, it is easy to cause the differential current to be a symmetrical waveform after filtering out the zero-sequence current, the second harmonic content is reduced, and it is lower than the second harmonic braking threshold, which will cause the transformer differential protection to malfunction due to the excitation inrush current

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