Adaptive-slope transformer zero-sequence differential protection method and device

Abstract

The invention discloses an adaptive-slope transformer zero-sequence differential protection method comprising the following steps: the zero-sequence current at the output end of a Y winding side of a transformer and the grounding zero-sequence current at a neutral point side of the transformer are compared to calculate the zero-sequence differential current and the brake current of the transformer; the size and direction of obtained zero-sequence power are calculated based on the zero-sequence voltage and the zero-sequence current at the output end of the Y winding side of the transformer, and the zero-sequence differential braking slope of the transformer is dynamically adjusted; when an external fault occurs, dynamically adjusted high slope is adopted in zero-sequence differential protection to prevent external metallic grounding and prevent transformer zero-sequence differential protection malfunction caused by CT saturation of the grounding zero-sequence current at the neutral point side; and when an internal fault occurs, low slope is adopted in zero-sequence differential protection. The invention further provides a corresponding device. The method and the device are used to monitor to-ground insulation of a power transformer in real time. An external grounding fault and an internal grounding fault of a transformer can be distinguished quickly and accurately. High sensitivity to internal faults is realized. Reliable braking can be achieved with use of high slope for an external fault.

Description

technical field [0001] The invention belongs to the field of power system protection, in particular to a method and device for zero-sequence differential protection of a transformer. Background technique [0002] When a power transformer has a weak fault in the Y side area, the sensitivity of the ratio differential is generally low, and the zero-sequence differential protection can greatly improve the sensitivity of this type of fault. And because the zero-sequence differential protection fully satisfies Kirchhoff's law, the inrush current presents as a through current, which has little influence on the zero-sequence differential protection. [0003] In practical applications, the CTs on both sides of the zero-sequence differential protection of the transformer do not strictly implement the requirements of the same model and the same transformation ratio. The current adopts P-class CT with small transformer ratio. According to years of operating experience, the correct act...

AI Technical Summary

Problems solved by technology

[0006] The purpose of the present invention is to provide a transformer zero-sequence differential protection method with adaptive slope, which is specially used to solve the problem that the correct action rate of the transformer zero-sequence differential protection is not high. The method uses the output terminal of the Y winding side of the power transformer The magnitude and direction of the zero-sequence power calculated by the zero-sequence voltage and zero-sequence current dynamically adjust the slope of the zero-sequence differential braking of the transformer to meet the operating requirements of high sensitivity to internal faults and reliable braking of external faults

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