Instantaneous current characteristic based current transformer saturation recognition improvement method

Abstract

The invention discloses an instantaneous current characteristic based current transformer (CT) saturation recognition improvement method. On the basis of a combination of the conventional time-difference method and a virtual braking current method for recognizing the current transformer saturation, the alternating current / direct current component condition of the fault current before CT saturation is fitted according to the instantaneous sampling value of the fault current before saturation through a discrete sliding-window iterative Fourier algorithm; then an implicit expression relation between the fault current and the virtual braking current threshold value D is fitted by a BP neutral network which is trained by a genetic algorithm (GA); and finally, the instantaneous sampling value of the fault current which is measured in real time is input into an algorithm program to adaptively select the virtual braking current threshold value D. By adoption of the instantaneous current characteristic based current transformer (CT) saturation recognition improvement method, the problem of overlong locking differential protection time when a fixed threshold value is chosen by the conventional virtual braking current method under severe saturation is effectively solved; and in addition, the openness of differential protection can be accelerated under a condition of fault transferring from an extra-region to an intra-region.

Description

technical field [0001] The patent of the invention belongs to the field of electric power system relay protection, and in particular relates to an improved identification method for current transformer protection based on instantaneous current characteristics. technical background [0002] The principle of current differential protection is simple, with high sensitivity and quick action. It has been widely used in the main protection of lines and electrical equipment. Whether it can reliably identify faults in the area mainly depends on whether the corresponding current transformer can Correct transfer of fault and non-fault currents. When the iron core of the current transformer is saturated, it will distort the secondary current and affect the correct operation of the differential protection. Accurately identify the saturation and non-saturation state of the current transformer and actually block and open the differential protection, which is very important for ensuring th...

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Problems solved by technology

[0004] The purpose of the present invention is to solve the problem that the threshold value setting of the traditional virtual braking current transformer saturation identification method is fixed, which leads to the opening delay and low sensitivity of the differential protection when the fault is transferred from outside the zone to the zone. Adapt to the method of adjusting the threshold value

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