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

A technology of excitation inrush current and transformer, which is applied in the direction of instruments, measuring electric variables, measuring current/voltage, etc., can solve the problem of second harmonic braking criterion error blocking differential protection, failure of second harmonic braking criterion, Low second harmonic content and other problems, to achieve the effect of strong anti-data loss ability

CN109038492BActive Publication Date: 2019-12-27CHINA THREE GORGES UNIV
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Patent Information

Authority / Receiving Office
CN · China
Patent Type
Patents(China)
Current Assignee / Owner
Publication Date
2019-12-27

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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.
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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...

Examples

Embodiment Construction

[0030] The transformer excitation inrush current identification method based on the discrete Fréchet distance algorithm includes the following steps:

[0031] Step 1: At a sampling frequency of 4kHz, collect the secondary current of the current transformers on both sides of the differential protection of the transformer, and form a differential current sequence I. According to N (N=80) points per cycle, the differential current signal sequence I={I(1),I(2),...I(i),...I(N)}, i=1,2,...N;

[0032] Step 2: Determine whether the value of the differential current signal sequence I in step 1 exceeds the setting value of the differential protection starting element, if exceeded, then start the criterion proposed by the present invention and carry out the discrimination of the fault differential current and the excitation inrush current;

[0033] Step 3: Use the 1 / 2 cycle data window to judge the extreme value of the differential current signal. If the extreme value is less than the th...