Reduction of Leakage Magnetic Field in Electromagnetic Systems Based on Active Shielding Concept Verified by Eigenvalue Analysis

Leakage fields are one of the main issues in design of electromagnetic systems. Some of these fields close their paths through the core and air, giving rise to non-ideal behavior of the magnetic systems. This paper explains a novel concept of active shielding which consists of two compensation coils in series and generates a counter field opposite to the leakage fields leaking from an iron-core system. As the method is based on physical reasoning of electromagnetic coupled circuit theory, the design criterions for the compensating coils parameters, their number of turns and their adaptation to the systems, were considered. The state of the art is presented by a model which is verified by roots of system characteristic equations, using state equations. In a case study, this method was investigated in a 25 kA (125 kVA) current injection transformer (CIT) system delivering a secondary current as closely proportioned to the primary current as possible, using finite element method (FEM) simulation. This paper will also push the state of the art by reducing the age effect of the CIT through mechanical force reduction.