Principles of power-frequency magnetic field shielding with flat sheets in a source of long conductors

This paper presents a theoretical analysis of a two dimensional (2-D) model of power-frequency magnetic field shielding. It consists of multiple linear and conducting layers, as well as multiple current-carrying conductors. Explicit expressions for magnetic field and power loss are deduced by solving diffusion equations using the method of variable separation. They are verified by experimental results of magnetic field shielding with both aluminum and magnetic material shields. Shielding principles taking into account geometric and material parameters (e.g., relative permeability, conductivity, thickness, etc.) are presented based on the simplification of closed-form expressions. Those general shielding principles are applicable when the shield is sufficiently large. The derived shielding principles are used to address practical design issues of power-frequency magnetic field shielding. Conclusions regarding material selection, location, and current circulation are obtained. They can be applied in practical shielding design if sources are lines, bus bars, cables, or any other long current-carrying conductors in power systems