Inductive current transformer accuracy of transformation for the PQ measurements

Inductive current transformer made of magnetic cores with high permeability are used for accurate wideband transformation of distorted current required by the power quality (PQ) measurements. However, such solutions are often characterized by not acceptable additional secondary current distortion in condition of variation of primary current rms value. The problem presented in this paper concerns determination and analysis of mutually exclusive magnetic requirements on inductive current transformer accuracy for transformation of current in both mentioned conditions. To show relevant considerations and support drawn conclusions about source of deterioration of inductive current transformers accuracy of transformation simple and effective procedure for designing inductive current transformer is discussed. The usage of the composited axially magnetic core from the magnetic cores made of permalloy and transformer steel ensured acceptable composite error for transformation of a given harmonic of distorted current and high accuracy in condition of variation of primary current rms value. Obtained resultant magnetization curve, regardless the rms value of primary current and its distortion level, provides proper magnetic permeability to prevent decrease of transformation accuracy for distorted current. The novelty of the paper concerns presentation of designing process and requirement that ensure such operation of inductive current transformer not obtainable without usage of the composited axially magnetic core.