Differential protection method based on adaptive ratio braking curve

Abstract

The invention provides a differential protection method based on an adaptive ratio braking curve. The method comprises the following steps: sampling three-phase current on each side of a transformer; calculating a differential current phasor value and a braking current phasor value; performing phase current break variable calculation on each sampled phase current instantaneous value, and judging whether a phase current break variable criterion is satisfied; after the break variable criterion is satisfied, starting a timer to start timing, and inputting two-broken-line braking characteristics within a set time T1; and logging out the two-broken-line braking characteristics after the time T1, and inputting three-broken-line braking characteristics with stronger braking property. By adoption of the differential protection method provided by the invention, the objective of preventing maloperation by the three-broken-line braking characteristics with stronger braking property after removing an internal fault by using the two-broken-line braking characteristics with higher sensitivity and removing an external fault is achieved, the defect that both of the sensitivity and the safety of the protection cannot be achieved resulting from that a single braking curve is adopted in conventional differential protection is overcome, and the protection action performance is improved, therefore the differential protection method has a great engineering application value.

Description

technical field [0001] The invention belongs to the field of relay protection of electric power system, and more specifically relates to a differential protection method of an adaptive ratio braking curve suitable for microcomputer protection. Background technique [0002] The principle of current differential protection is based on Kirchhoff's current law, and it acts on the difference between the inflow current and outflow current of the protected element. Delayed removal of various short-circuit faults in the area, so it is widely used as the main protection of various components. [0003] In differential protection, the ratio braking characteristic with broken line is usually used, the most basic is the two broken line braking characteristic. The braking characteristic of the two-fold line is composed of a non-braking horizontal section and a braking oblique section. The setting of the horizontal section is to prevent the protection from malfunctioning when the measured...

AI Technical Summary

Problems solved by technology

[0004] Practice shows that the application of two-fold line characteristic differential protection on generators, transmission lines and other components has achieved good results, but there are some problems when it is applied to transformers: it is affected by restorative inrush current and current transformer (CT ) due to the influence of the transmission error, the misoperation phenomenon of the two-fold line characteristic differential protection after the external fault is removed occurs from time to time

[0005] The three-fold line braking characteristic can well solve the problem of misoperation of the protection after the external fault is removed, but it brings the side effect of low sensitivity when there is a slight inter-turn fault inside the transformer.

The horizontal section of the two-fold line characteristic ensures the sensitivity of the slight turn-to-turn fault inside the transformer, but it makes the protection prone to misoperation when the external fault is removed; although the three-fold line characteristic makes the protection have higher safety, it reduces the sensitivity.

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