Demagnetization circuit and method for online elimination of residual magnetism of electromagnetic current transformer

Abstract

The present invention relates to the electric power automation technology, and aims to provide a demagnetizing circuit and method for removing residual magnetism of an electromagnetic current transformer on line. The demagnetizing circuit comprises a series connection structure formed by a third resistor and an inductor, a third switch is also connected in parallel at two ends of the inductor, the series connection structure is connected in parallel at two ends of a secondary side of a current transformer with a second resistor and a first switch, an outer end of the third resistor is earthed, an outer end of the inductor is connected to one end of a direct current power supply through a second switch, the other end of the direct current power supply is earthed, and a first resistor is disposed between the second resistor and a non-earthing end of the first switch. With adoption of the circuit and the method, the residual magnetism inside the current transformer is removed within a very short time when the switches are disconnected, and the accuracy of relay protection setting calculation and the reliability of relay protection actions are raised. The residual magnetism can be removed on line, and the current transformer does not need to be out of service. No complicated signal detection circuits or control circuits are required, and the circuit is easy to realize. The error of residual magnetism of an iron core after demagnetizing is small, and the demagnetizing speed is high.

Description

Technical field [0001] The invention relates to a circuit and method for online elimination of residual magnetism of an electromagnetic current transformer, and belongs to electric power automation technology. Background technique [0002] Electromagnetic current transformers are widely used standard measurement and protection test equipment in power systems. In the case of line-switching operation in the power system or in the case of a short-circuit fault, the line current will have a considerable DC component during the transient process, which will cause the core to appear remanent magnetism, which will cause the core’s magnetic permeability to drop and affect the transformer’s performance. performance. [0003] For protective current transformers, the existence of a large amount of residual magnetism will increase the saturation of the iron core and shorten the saturation time, which is an important reason for the unbalanced current and the misoperation of the differential pr...

AI Technical Summary

Problems solved by technology

At present, people have carried out research on this issue, for example, if the iron core of the protective transformer has an air gap, the residual magnetism can be limited to less than 10%, and the transient characteristics are greatly improved, but the magnetic resistance is large and the magnetic circuit efficiency is high. Reduction will also increase magnetic flux leakage and reduce measurement accuracy, and it is inconvenient to manufacture; for metering current transformers, closed-circuit or open-circuit demagnetization methods can be used for demagnetization to reduce errors, but generally cannot be processed online, and need to increase current The whole set of facilities is relatively heavy and the wiring and operation of the demagnetization process are relatively complicated; the transformer winding core made of laminated iron core or amorphous or permalloy material can reduce the influence of residual magnetism, However, the higher price of such materials will increase the manufacturing cost of the transformer exponentially

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