A differential protection method for negative sequence current of large power transformer

Abstract

The disclosed protection method for internal fault of large power transformer comprises: the protector samples the secondary current of current transformers on power transformer sides to obtain current instantaneous value and calculate complex number form of electric values by Fourier algorithm, corrects phase of connection form, and balances amplitude of transformation ratio; then, it calculates the complex number form of negative sequence current according to three-phase ac complex form, and computes negative sequence differential current and break current as the negative sequence differential protection principle to decide asymmetric inside and outside fault and drop out all breakers. This invention also contains exactly the negative sequence differential rate breaking feature and protection criterion, the adjusting means for protection values, the positive sequence current breaking criterion, and the block function for error action protection.

Description

technical field [0001] The invention relates to the field of power systems, in particular to a method for relay protection of the power system. Background technique [0002] First, the related art of the present invention is briefly described based on the following references. [0003] 1 He Jiali, Song Congju Editor-in-Chief. Power System Relay Protection. Updated Edition. Beijing: China Electric Power Publishing House, 2004 [0004] 2 Edited by Yang Qixun and Huang Shaofeng. Fundamentals of Microcomputer Relay Protection. Second Edition. Beijing: China Electric Power Press, 2005 [0005] 3 Edited by Wang Weijian. Principles and Applications of Electrical Main Equipment Relay Protection. Second Edition. Beijing: China Electric Power Press, 2002 [0006] Power transformers are important electrical equipment in power systems and are widely used in substations of different voltage levels. Transformer protection plays an extremely important role in the safe operation of power...

AI Technical Summary

Problems solved by technology

[0010] Aiming at the problem that the longitudinal differential protection of transformer phase current needs to overcome the influence of various unbalanced currents, which reduces the sensitivity of protecting the internal fault of the transformer, etc., on the basis of theoretical analysis and fault simulation of the internal and external faults of the transformer, the present invention proposes a A method for internal fault protection of large power transformers based on the principle of negative-sequence current differential, and discloses the specific implementation of the negative-sequence current differential protection of transformers. The protection uses the negative-sequence currents on each side of the transformer to form a negative Sequence current differential protection, which uses ratio brake negative sequence current differential protection as the main fault discrimination element, and cooperates with positive sequence current braking criterion, excitation inrush current blocking and current transformer secondary circuit disconnection blocking, etc. Together they form a relatively complete transformer negative-sequence current differential protection that can clearly distinguish asymmetrical faults inside and outside the transformer

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