A Fast Identification Method of Exciting Inrush Current Based on Differential Current Discrete Cosine Transform

A technology of discrete cosine transform and excitation inrush current, which is applied in the directions of measuring electrical variables, measuring current/voltage, and measuring electricity, can solve problems such as protection misoperation, uncertain diversity, and complex shape of initial fault current, and reduce the impact Effect

Active Publication Date: 2018-07-24
KUNMING UNIV OF SCI & TECH
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  • Claims
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Problems solved by technology

However, the second harmonic braking method has the following disadvantages: because the current transformer core is usually made of high-permeability cold-rolled grain silicon steel material, which is very easy to saturate, so that the second harmonic of some phases in the excitation inrush current The wave component ratio is greatly reduced, resulting in protection misoperation
However, the inrush waveform is related to many factors, and it has uncertainty and diversity. At the initial fault, the current shape is complex, and simply extracting local feature quantities will often cause misjudgment. In the actual system, the diversity of fault conditions and the fault waveform must be considered Complexity

Method used

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  • A Fast Identification Method of Exciting Inrush Current Based on Differential Current Discrete Cosine Transform
  • A Fast Identification Method of Exciting Inrush Current Based on Differential Current Discrete Cosine Transform
  • A Fast Identification Method of Exciting Inrush Current Based on Differential Current Discrete Cosine Transform

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Embodiment 1

[0058] Example 1: Establish as figure 1 The simulation system model of transformer failure and excitation inrush current is shown, in which the transformers are three single-phase three-winding transformers, which adopt Yd11 connection method, connect its high-voltage windings to the 110kV system as the primary side of the transformer, and cascade the medium-voltage windings and low-voltage windings The secondary side of the transformer is formed, and the parameters of the equivalent double-winding transformer are as follows: the rated capacity is 250MVA, the rated transformation ratio is 110kV / 10.5kV, the equivalent resistance is 0.002pu, and the equivalent reactance is 0.08pu. Its magnetization parameters are shown in Table 1:

[0059]

[0060] Table 1

[0061] Now assume that the secondary winding of the transformer is single-phase grounded at 28.5% of the A-phase winding, the grounding resistance is 1 ohm, and the sampling frequency is 20kHz. Under this model, the samp...

Embodiment 2

[0066] Example 2: Establish as figure 1 The parameters of the transformer fault and excitation inrush simulation system model shown are described in detail in Embodiment 1, and will not be repeated here. Assume now that the transformer in the system produces an inrush current, and the sampling frequency is 20kHz. Under this model, the sampling data of each phase difference flow is as follows: Figure 4 shown.

[0067] Similarly, the corresponding phases can be obtained from the data of the sampling points sequence, such as Figure 5 shown. because σ A =4840, σ B =9341, σ C =9792, so log(σ max )=3.9909<4, it is judged as excitation inrush current according to the criterion. Consistent with the hypothesis, the judgment is correct.

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Abstract

The invention, which belongs to the technical field of relay protection of the power system, relates to a quick transformer excitation inrush current identification method based on differential current discrete cosine transform. When an internal short-circuit phenomenon occurs or an excitation inrush current is generated in the transformer, a measurement terminal detects and records three-phase differential current data. Transformation is carried out on all phases of differential current data based on discrete cosine transform; standard differences of the top ten items of real number sequences of all phases after discrete cosine transform can be obtained and a logarithmic value of a maximum value sigma max is used as a criterion feature quantity; the criterion feature quantity and a preset threshold value Th are compared to determine an internal short circuit and an excitation inrush current of the transformer; if the log (sigma max) is larger than Th, an internal short circuit phenomenon is determined to occur in the transformer; and if the log (sigma max) is less than or equal to Th, occurrence of the excitation inrush current is determined. The theoretical analysis and lots of simulation demonstrate that the method is correct and effective.

Description

technical field [0001] The invention relates to a fast identification method for excitation inrush current based on differential current discrete cosine transform, and belongs to the technical field of electric power system relay protection. Background technique [0002] As an essential primary device connected between different voltage levels, the transformer's safe operation is of great significance to the stability of the entire system. At present, the main protection of the transformer is based on the harmonic braking differential protection, that is, the protection of the transformer is completed by the second harmonic, differential snap action, and ratio differential. It uses the current difference between the primary and secondary sides of the transformer to perform a series of processing to obtain the criterion of the inrush current. However, since the transformer excitation inrush current is often as high as several times the rated current, the waveform is a sharp ...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01R31/02G01R19/165
Inventor 束洪春魏萌高利曹璞璘
Owner KUNMING UNIV OF SCI & TECH
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