Transformer differential protection method based on virtual magnetic flux-differential current characteristics

Abstract

The invention is a transformer differential-protecting method based on virtual magnetic flux-differential current property, and its characteristic: it advances a concept of virtual magnetic flux, i.e. it converts leakage flux to primary side to become a main magnetic flux with fixed number of winding turns, then according to the character that the virtual magnetic flux-differential current curve is approximately elliptical and has good central symmetry, simultaneously defines a nonsymmetrical degree to reflect the central symmetric degree of figure so as to under the control of computer, use the nonsymmetricl degree average of several continuously-sampling points in the front two main frequency cycles to compare with a preset braking threshold value after the differential current is over action threshold value, as soon as the nonsymmetrical degree average of any one phase is greater than or equal to the braking threshold value, judge this is surge current and otherwise judge this is internal failure, and the computer send corresponding control instruction by this, and the invention has the advantages f simplicity, convenience, high flexibility, etc.

Description

technical field [0001] The invention relates to a differential protection method for a transformer. The method judges an excitation inrush current and an internal fault according to the central symmetry of a virtual magnetic flux-differential current curve of a transformer, and belongs to the technical field of transformer relay protection. Background technique [0002] In the field of transformer relay protection, the main protection usually adopts differential protection. Differential protection is based on comparing the amplitude and phase of the current on each side of the transformer and applying the principle of Kirchhoff’s current law. The differential current on both sides of the transformer It refers to the difference between the primary side current and the converted secondary side current. The differential current of a transformer in normal operation is zero, while the excitation inrush current and internal fault current correspond to a large differential current. ...

AI Technical Summary

Problems solved by technology

[0004] Judging from practical experience, there are still many problems to be solved in various schemes. As far as the principle of magnetic flux characteristics is concerned, although the characteristics of the main magnetic flux of the transformer can fundamentally distinguish the inrush current from the internal fault, it is often difficult to accurately obtain the leakage current of the transformer. Difficulties are encountered in key parameters such as inductance, especially in the case of internal faults, the leakage magnetic field of the transformer still needs to be further studied, so the practical application is limited

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