Identification method of transformer excitation inrush current based on discrete fréchet distance algorithm

Abstract

An identification method of transformer magnetizing inrush current based on a discrete Frechet distance algorithm. The method includes the following steps: for N points in each cycle, collecting secondary current of current transformers on both sides of transformer differential protection, and forming a differential current signal sequence I ; Judging whether the value of the differential currentsignal sequence I exceeds the setting value of the differential protection start-up element, and if so, starting the criterion provided by the invention for judging the fault differential current andthe excitation inrush current; The data window of 1 / 2 cyclic wave is used to judge the extreme value of the sampled differential current sequence. If the data window is lower than the threshold value,it is considered as inrush current and blocking protection. If the threshold is higher than the extreme value, the standard sine wave sequence with amplitude of 1 is generated synchronously by normalizing the extreme value as a standard; The normalized difference flow sequence I and the standard sine wave sequence I (i) s ( / i) are used as points of a discrete curve to calculate a discrete Frechetdistance, and the distance value F is obtained, the F value is compared with a set threshold value F (i) set ( / i), and the threshold value is lower than the threshold value, and the protection actionis performed; Above this threshold, the protection is latched. The method of the invention can identify the similarity between the waveform curve of the fault and the inrush current, including the symmetrical inrush current and the standard sine wave curve, so as to ensure the correct operation of the differential protection of the transformer.

Description

technical field [0001] The invention relates to a transformer excitation inrush current identification method based on a discrete Fréchet distance algorithm, and relates to the field of transformer differential protection. Background technique [0002] The theoretical basis of differential protection is Kirchhoff's current law. Because differential protection itself has good selectivity and sensitivity, it is more suitable for power transformers. However, according to statistics, the differential protection in power transformers has a high rate of malfunctions. The most direct and extremely important reason is the malfunctions caused by the excitation inrush current generated during the operation of the transformer. [0003] The principle of second harmonic braking and discontinuity angle belongs to the traditional identification method. These two methods have defects in practical application: for example, when the differential current is a symmetrical inrush current, its s...

AI Technical Summary

Problems solved by technology

These two methods have defects in practical application: for example, when the differential current is a symmetrical inrush current, its second harmonic content is low, which will cause the second harmonic braking criterion to fail and differential protection to malfunction; When the transformer is switched on without load with a high-impedance internal fault, the differential current contains an obvious inrush current in addition to the fault current, which will increase the content of the second harmonic, resulting in the second harmonic braking criterion falsely blocking the differential protection

However, these methods may be difficult to implement in engineering because of high hardware requirements, or the need to obtain voltage leads to complicated wiring, or the identification accuracy is not high in actual engineering, or there are other reasons, and ultimately fail to completely solve the identification of excitation inrush current. question

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