Finite Element Analysis of the Asymmetric Field Distribution Effect on the Operation of a Current Transformer

Current transformers (CTs) are important in power grids because they feed the protection relays with current signals. So the accuracy of their output signals should beensured in various conditions. Different factors affect the accuracy of the CT output current. Some of them such as thestray flux produced by the adjacent bus bars current and theeccentricity of the primary conductor with respect to the CT cause the magnetic field distribution of the current transformerto be asymmetric. So they can result in the current transformer local saturation in specific conditions which can lead to theundesirable operation of the protection relays. In this paper, the operation of a typical current transformer with protection coreis analyzed in the presence of these factors. The conditions considered in this paper include the operation under the adjacent bus bar overload and when there is an eccentricity in the primary conductor with respect to the CT core. These conditions are analyzed using 2D FEM.

Keywords:

Current Transformer , stray flux , Over-current condition , Finite Element Method