Differential protection method for preventing false operation during current disappearance

Abstract

The invention relates to a differential protection method for preventing false operation during current disappearandce, which comprises the following steps: preparing to trip according to the differential protection action after a protection device starts for 60ms; then, using a waveform similarity criterion to compute waveform similarity coefficients computed in a short window data of a differential action element 20ms before; if the waveform similarity coefficient values in the data window are all less than 0.2, tripping immediately; and if the condition that the waveform similarity coefficient values in the data window are greater than 0.2 exists, delaying differential protection for 20ms, and triggering port if the fault does not disappear. The method is based on a least square filtering principle, compares whether a target alternating quantity is the normal system waveform or distorted waveform according to the waveform similarity coefficients, and does not differentiate the faultstarting time or the fault disappearing time. The method can reliably prevent the external fault from cutting off the current, and avoid the condition of internal differential protection malfunctioncaused by current distortion.

Description

technical field [0001] The invention belongs to the technical field of power system automation, and relates to a new criterion for preventing differential protection from malfunctioning when the current disappears. Background technique [0002] In the high-voltage power grid, after a fault occurs, current distortion and tailing will occasionally occur when the circuit breaker cuts off the fault current. This abnormality will affect the differential protection, and even cause malfunction in severe cases. [0003] One of the traditional methods is to directly add delay to prevent this kind of misoperation from happening; the other is to judge the saturation and block the differential protection through the saturation criterion; the third is to calculate the value greater than zero and less than The number of points of zero judges the symmetry of the waveform. [0004] Method 1: There are many saturation criterion algorithms, but most of them are based on the synchronous metho...

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Problems solved by technology

[0004] Method 1: There are many saturation criterion algorithms, but most of them are based on the synchronous method. The basis of the synchronous method is to distinguish the differential current from the braking current at different initial moments, but when the current is caused by the cut-off of the circuit breaker, the synchronous The saturation criterion does not apply in this case

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