Split-phase differential protection method based on scalar product brake criterion normalization

Abstract

The invention belongs to the field of relay protection of a power system, and relates to a split-phase differential protection method based on scalar product brake criterion normalization. The method comprises the following steps of: acquiring the currents on the two sides of a transmission line by utilizing current transformers (CTs) on the two sides of the transmission line; calculating the amplitude values, the phase angles and the phase angle difference between the currents on the two sides by utilizing a full-wave Fourier algorithm; if the phase angle difference between the currents on the two sides is less than 120 degrees, determining that an internal fault exists, performing the protection action of tripping; and if the phase angle difference between the currents on the two sides is more than 120 degrees, turning to the amplitude value judgment below: first, judging whether the amplitude values of the currents on the two sides are both greater than three times the rated current of the primary side of the CT, wherein if the amplitude values are both greater than three times the rated current of the primary side of the CT, the proportionality factor K=2, and if the amplitude values are not greater than three times the rated current of the primary side of the CT, the proportionality factor K=0.8; and then calculating the ratio of the smaller amplitude value to the greater amplitude value of the currents on the two sides, wherein if the ratio is less than the K, determining that an internal fault exists, and performing the protection action of tripping. According to the split-phase current differential protection method of the transmission line provided by the invention, the sensitivity of the internal fault and the selectivity of an external fault are taken into consideration.

Description

technical field [0001] The invention relates to the field of relay protection of electric power systems, in particular to a new criterion of phase-separated current differential of transmission lines. Background technique [0002] The principle of split-phase current differential is based on Kirchhoff's current law. It can realize full-line quick movement without considering the distributed capacitance of the transmission line and the CT saturation of the current transformer. It has a phase selection function. The principle is simple. The large-scale popularization of communication engineering and the advancement of digital signal processing technology have become an ideal protection method for transmission lines. The new differential criterion proposed by many literatures is manifested in the use of fault current (including power frequency variation, zero-sequence current component, etc.) and adaptive criterion [1～7] etc., all aim to improve the sensitivity of faults insid...

AI Technical Summary

Problems solved by technology

However, there are problems in the existing criterion of current split-phase current differential protection: the criterion is affected by factors such as load current, current transformer saturation, distributed capacitive current and transition resistance, and its braking performance is not ideal when an external fault occurs. And the action sensitivity is not high enough when the internal failure occurs

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