Fast and Complete Mitigation of Residual Flux in Current Transformers Suitable for Auto-Reclosing Schemes Using Jiles-Atherton Modeling

Abstract

Accurate measurement of electrical currents cannot be done when the core of current transformers (CTs) is saturated. One of the reasons that causes saturation of a CT is the activation of the auto-reclose function for the circuit breaker. When the circuit breaker is switched off, a residual flux will remain in the CT core, and when the circuit breaker is reconnected, this residual flux may cause saturation of the CT core. It is necessary to remove the residual flux in an auto-reclosing scheme. In the auto-reclosing scheme, due to the short time interval between each reclosing shot of the circuit breaker, only methods that have a high-speed operation should be used to mitigate the residual flux to prevent CT core saturation. This paper introduces a fast and complete demagnetization method based on Jiles-Atherton magnetic modeling to mitigate the residual flux in the CT core. The advantages of this method are high-speed performance, independent of the CT characteristics, high accuracy and high reliability against the secondary open circuit. To evaluate the efficacy of the proposed method, software simulations and laboratory experiments are performed on a 63kV, 300A/5A CT. The results are presented and analyzed.