Transformer excitation surge current identification method based on improved symbol sequence entropy method

Abstract

The invention discloses a transformer excitation surge current identification method based on an improved symbol sequence entropy method. The method comprises the steps: collecting the secondary current of current transformers at two differential protection sides of a transformer under a certain sampling frequency, forming a differential current signal sequence, judging whether the amplitude of the differential current sequence exceeds a setting value of a differential protection starting element or not, and if yes, starting a criterion to discriminate the fault differential current and the excitation surge current. The method performs normalization processing on a difference flow initial signal sequence to form a normalized difference flow signal sequence, compares the size change directions between two adjacent sampling points in a cyclic wave data window to form a new symbol sequence, and constructs a vector symbol sequence with the width of 2 by adopting a sliding window, only three modes of 00, 11 and 22 are reserved to calculate symbol entropies, the symbol entropies are compared with a set threshold value, if the symbol entropies are lower than the threshold value, an internal fault is judged, and a protection action is performed; and if the symbol entropies are higher than the threshold value, the excitation surge current or the non-internal fault is judged, and the protection is locked.

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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