Transformer protection method based on characteristics of excitation impedance fluctuation

Abstract

The invention discloses a transformer protection method based on characteristics of excitation impedance fluctuation. The method comprises the following steps of firstly, when a differential protection device is started, extracting primary and secondary side voltages and a differential current power frequency of the transformer by using the semi-cycle Fourier algorithm, and calculating the excitation impedance of the transformer; studying the volatility of the excitation impedance in one cycle, and calculating a variance k1 and an impedance mean k2 of the excitation impedance in one cycle; setting fixed values kset1 and kset2 according to a large number of simulation and field experiences; considering that the transformer generates an excitation inrush current when k1 is greater than or equal to kset1; considering that the transformer has an internal fault or the faulty transformer is closed if k1 is less than kset1 and k2 is less than or equal to kset2; and considering that the transformer is running normally/has external fault if k1 is less than kset1 and k2 is greater than kset2. The method provided by the invention can correctly distinguish the excitation inrush current and theinternal fault of the transformer, avoid the incorrect operation caused by the false start of the transformer when no-load closing, and effectively improve the reliability of the protection action ofthe transformer.

Description

technical field [0001] The invention belongs to the field of power systems, relates to the field of transformer protection, in particular to a transformer protection method based on excitation impedance fluctuation characteristics. Background technique [0002] The power transformer is one of the most important electrical equipment in the power system, and its safe operation is of great significance to ensure the reliable transmission, distribution and application of electric energy. Power transformers are key electrical equipment for large-capacity and long-distance transmission of electric energy. After a fault occurs, quickly, sensitively and reliably isolating the fault is of great significance to the safety of the transformer, and it can also effectively ensure the reliable transmission of electric energy and the safe operation of the power grid. . Relay protection is the first line of defense for the safe operation of the power grid. For transformer protection, a seri...

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Problems solved by technology

[0003] With the increasing scale of the power system, the use of large-capacity capacitors, long transmission lines and a large number of power electronic components, the complex electromagnetic transient environment makes the threshold value of waveform characteristics such as transformer differential current harmonics and discontinuity angle more and more If the experience value is not satisfied, the phenomenon of protection refusal and malfunction occurs from time to time

In response to this phenomenon, a large number of expert

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