A Saturation Suppression Approach for the Current Transformer-Part I: Fundamental Concepts and Design

The current transformer (CT) is prone to the magnetic core saturation during the power system faults. The CT saturation can prolong and/or miscoordinate operation of relays and thus may result in the system stability problems and equipment damage. This paper proposes a new hardware-based method to suppress or prevent the CT saturation. The proposed approach is based on adding a controllable resistor at the CT secondary circuit which dynamically generates a flux to oppose the time varying flux associated with the decaying dc component of the fault current. Part I of this two-part paper presents the concept, the controllable-switch operational strategy, the design steps, and the parameters of the controllable resistor. Part II provides a comprehensive evaluation of the controllable resistor based on offline digital time-domain simulation and control-hardware-in-the-loop studies.