Bhattacharyya-distance-algorithm-based excitation inrush current and fault differential current identification method of transformer

Abstract

The invention relates to a Bhattacharyya-distance-algorithm-based excitation inrush current and fault differential current identification method of a transformer. The method comprises: collecting secondary currents of current transformers arranged at two sides under differential protection of a transformer according to N points of each cycle and forming a differential current signal sequence I; determining whether the value of the differential current signal sequence I exceeds a setting value of a differential protection starting component; if so, starting a provided criterion to carry out fault differential current and excitation inrush current determination; processing the differential current signal sequence by using a 1 / 2 cycle data window and predicting a corresponding sinusoidal wave, converting the differential current and a predicted sinusoidal sequence into a probability distribution function of sampled values similar to the image grayscale in the data window, and then carrying out matching calculation based on a Bhattacharyya distance; comparing a calculated Bhattacharyya coefficient Bc with a set threshold value Bcset and taking a protection action under the condition ofbeing higher than the threshold by the Bhattacharyya coefficient; and otherwise, locking protection. With the method, the in-zone fault, inrush current, the in-zone and out-zone fault CT saturation and the like can be determined accurately; and thus the reliability of the differential protection is ensured.

Description

technical field [0001] The invention relates to a transformer excitation inrush current and fault differential current identification method based on the Bhattacharyachian distance algorithm, which relates to the field of transformer differential protection. Background technique [0002] The transformer is one of the most important equipment in the power system, and its safe and stable operation is related to the stability of the entire power system. The excitation inrush current is the most important reason affecting the reliability of transformer differential protection. At present, researchers have proposed many identification methods, which can be divided into two categories. The first type is based on the pure current as the identification method, such as the second harmonic braking principle, discontinuity angle principle, waveform symmetry principle, waveform correlation principle, etc.; the second type is the comprehensive current and voltage as the judgment method. ...

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Problems solved by technology

The above situation makes it difficult to set the threshold value in the second harmonic braking method

[0004] Although the protection of the discontinuous angle measurement method does not have this problem, the measurement of the discontinuous angle requires a higher sampling rate, which requires higher protection hardware, and due to the high amplitude of the primary inrush and the presence of residual magnetism in the CT, etc. Influence, CT is easy to be saturated, in the discontinuous part of the primary inrush current, due to the saturation of CT, a reverse secondary current will be generated, resulting in the disappearance of the discontinuity angle in the secondary inrush current waveform

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