Simple null-drift filtering method based on zero-offset bus protection differential current

Abstract

The invention discloses a simple null-drift filtering method based on a zero-offset bus protection differential current. The method comprises the following steps of (1) calculating an instantaneous value of the differential current when no started protection and no mutated braking current exist; (2) calculating the average null-drift value of every circuit branch of a differential loop according to the instantaneous value of the differential current; (3) deducting the null-drift value from the instantaneous current value of every circuit branch; (4) calculating the instantaneous value of the braking current. The method is capable of fully utilizing the existing calculated differential current in the bus differential protection to calculate the null-drift value of the A / D channel of every circuit branch in the differential loop in real time without dependence on the frequency and adequate sampling data windows in the prior art; the method has the advantages of being simple, reliable and fast in algorithm and free of calculation of every circuit branch, reduces consumption of program resources, and improves the program efficiency.

Description

technical field [0001] The invention relates to the field of busbar protection in relay protection, in particular to a simple zero-drift filtering method based on the busbar protection differential current bias being zero. Background technique [0002] The A / D zero drift of the sampling circuit will have a certain impact on the algorithm of the power system protection device, especially the bus differential protection connected in multiple intervals. There is zero drift in multiple interval sampling loops. If the bus differential current and braking current are not filtered out, they will deviate from the time axis under normal operating conditions, which will affect the instantaneous value protection algorithm of bus protection and the CT saturation algorithm of external faults. . [0003] The differential current and braking current formulas in the busbar protection algorithm are: [0004] [0005] [0006] In formula (1) and formula (2), i d is the sum of the ins...

AI Technical Summary

Problems solved by technology

When leaving the factory, the initial zero drift needs to be solidified into the protection device, which not only increases the workload of the factory inspection personnel, but also has an impact on the later calculation of the zero drift change step.

For the busbar protection with a large number of access intervals, the hardware of the current protection device can meet the access of multiple intervals, but the number of intervals connected in the actual project is less than the maximum number of branches supported by the hardware. The zero drift of the sampling channel used is also calculated in real time, which affects the efficiency of the protection program

Images