Transformer protection method based on equivalent excitation impedance characteristics

Abstract

The invention discloses a transformer protection method based on equivalent excitation impedance characteristics. The transformer protection method comprises the following steps of after a transformerdifferential protection device is started, calculating a voltage at two sides of a transformer and the power frequency quantity of differential current by using a semi-cycle Fourier algorithm, and calculating transformer equivalent excitation impedance Z (1) at a protection starting moment according to the voltage and the power frequency quantity; calculating an average value of the equivalent excitation impedance of a transformer and Z (1) within a period of time t after the protection is started to obtain an average value sequence Zav of the equivalent excitation impedance of the transformer; if the average value of the equivalent excitation impedance of the transformer is always smaller than the setting value Zset within the time t, considering that the transformer has an internal fault, and sending out a protection tripping signal; otherwise, determining that the transformer operates normally or has an external fault, and protecting against action. The transformer protection method is advantaged in that internal faults and normal operation / external faults can be correctly distinguished, correct locking is achieved when magnetizing inrush current is generated, moreover the method has good adaptability to complex conditions such as transformer saturation or CT saturation caused by residual magnetism and direct-current magnetic bias.

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 equivalent excitation impedance characteristics. Background technique [0002] As the core equipment in the power system, the power transformer has a vital impact on the safe and stable operation of the entire power system. Among them, the operation reliability of relay protection is the key element to ensure the safety of power transformer equipment. However, the statistical data about the protection operation of power transformers shows that the correct action rate of differential protection as the main protection of large power transformers has been at a relatively low level, which does not match the actual safety requirements and development level of the current power grid. In recent years, with the increasing complexity of the power system structure, the probability of unexplained errors an...

AI Technical Summary

Problems solved by technology

However, field data show that with the increasingly complex power system, transformer misoperation accidents often occur in situations that are far more complex than transformer no-load closing, and the traditional excitation inrush current identification algorithm based on the research and development of the typical waveform of the excitation inrush current is not effective.

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