Transformer excitation inrush current identification method based on improved symbolic sequence entropy method

Abstract

The transformer excitation inrush current identification method based on the improved symbol sequence entropy method collects the secondary current of the current transformers on both sides of the differential protection of the transformer at a certain sampling frequency, forms a differential current signal sequence, and judges the amplitude of the differential current sequence at the same time Whether it exceeds the setting value of the differential protection starting element, if it exceeds, the starting criterion is used to judge the fault differential current and the excitation inrush current. First, normalize the initial signal sequence of the differential flow to form a normalized differential current signal sequence, compare the direction of size change between two adjacent sampling points in a cycle data window, and form a new symbol sequence. The window constructs a vector symbol sequence with a width of 2. Only three modes of 00, 11 and 22 are reserved to calculate the symbol entropy value and compare it with the set threshold value. If it is lower than the threshold value, it will be judged as an internal fault and a protection action will be taken; If it is higher than the threshold value, it will be judged as excitation inrush current or non-internal fault, and the protection will be blocked.

Description

technical field [0001] The invention belongs to the technical field of transformer differential protection, in particular to a transformer excitation inrush current identification method based on an improved symbol sequence entropy method. Background technique [0002] In recent years, the power industry has made great progress. With the continuous production of ultra-high voltage, ultra-high voltage and large-capacity power transformers in my country, more and more long-distance power transmission systems are built and operated, so the requirements for the safety, stability and reliability of power systems are getting higher and higher. The power transformer is one of the most critical power equipment in the power system, especially the large power transformer is not only expensive, but also has serious failure losses, and its normal operation will affect the safe and stable operation of the entire power system. [0003] In the field work, most of the transformers in opera...

AI Technical Summary

Problems solved by technology

However, with the improvement of voltage level, the expansion of power grid scale, and the increase of transformer unit capacity, when a serious fault occurs inside a large transformer, the second harmonic content in the short-circuit current will increase significantly due to resonance, which may cause Delayed action of differential protection for second harmonic braking, especially for the case where the end of the transformer is connected to a long line

And with the improvement of the transformer core material, its magnetic saturation point is reduced. When the residual magnetism is high and the closing angle meets certain conditions, the content of the second harmonic in the three-phase inrush current may be less than 15%. The minimum second harmonic content of a certain phase may be below 7%, and the corresponding discontinuity angle will be less than 30°~60°

At this time, no matter whether the second harmonic braking is used or the discontinuous angle principle of phase braking is adopted, the transformer longitudinal differential protection cannot avoid malfunction. Therefore, it is necessary to find a new method to solve the problem.

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