Improved Magnetic Circuit Model for Magnetic Shielding Effectiveness in Rogowski Coil

The magnetic circuit approach is commonly used as a powerful analysis and design tool for magnetic devices because of its computational simplicity and comparable accuracy. Currently, magnetic circuit solutions for magnetic shielding effectiveness assume a rectangular shell structure of shielding under vertical external magnetic fields, leading to inaccuracies in parametric analysis. In this article, an improved magnetic circuit model is proposed by considering the hollow cylindrical structure of shielding to investigate magnetic shielding effectiveness in Rogowski coils. The proposed model is verified by simulation studies based on the finite-element method (FEM) for a wide range of design parameters. It is shown that magnetic shielding effectiveness of magnetic circuit models has no more than 27% error for horizontal air gaps and 17% for vertical air gaps when the shielding thicknesses and the shielding distances from non-magnetic former are varied from 5 to 30 mm. The proposed magnetic circuit approach has also been confirmed by magnetic shielding of a hollow toroidal structure. It is found that the maximum percentage error in the magnetic shielding effectiveness does not exceed 18% for the same parameter range. The method is also validated for the changes in air gaps, permeability of shielding materials, and the major radius of the non-magnetic former.

I. Introduction

Rogowski coils (RCs) are well recognized as primary current sensors. They are exceptionally well suited for high-voltage applications and have been used for current measurements for several decades. Since RCs have no ferromagnetic materials as core, they exhibit linear characteristics for a wide range of measured current with no saturation.