Improved Gapped-Core CT Dimensioning Algorithm Considering Relay and System Requirements

Current-transformer (CT) core saturation leads to relay maloperation. Meanwhile, the increment of core area and subsequently the total weight of cores not only leads to a heavy and expensive CT, but also it is one of the most important restrictions in manufacturing CTs. Gapped-core CTs, especially the TPY-type CT, are used to decrease the core area and weight, and to reduce the core remanent flux and possibility of CT saturation. Designing a TPY-type CT includes proper determination of influencing parameters and the utilization of an appropriate analytical approach. For this purpose, a new algorithm to design the TPY-type CT, and some analytical methods to compute the required parameters of gapped-core CTs are proposed in this paper. It is indicated that the CT dimensioning based on the proposed approach results in a much lower expense CT while it satisfies the IEC standard and relay requirements.