Influence of the interaction of voltage and current parts of a combined instrument transformer on its measurement properties

A method of avoidance of mutual influences in a designed combined instrument transformer is presented. The combined instrument transformer comprises a current and voltage transformer in the same housing. Because of a low rated frequency, the main influences are: the current transformer on the voltage transformer through the magnetic field and inversely through the electric field. The mutual reactance and capacitance were determined based on 3D field distributions obtained by the numerical field method.