Examination of Eddy Current between Steel Sheets without Insulation and Criterion for Determining the Necessity of Insulation

Abstract

In the laminated core of transformers, motors, etc., each electrical steel sheet is usually insulated in order to reduce the eddy current loss. It has been reported that the insulation is not necessary in such a laminated core in some conditions. However, few studies have been performed in quantitative and systematic examination of the relationship between the insulation and eddy current. In this study, the eddy current losses of a core made of SPCC (colded rolled steel sheets) of different widths with and without insulation under various conditions are analyzed by using the finite element method (FEM) and considering the contact resistance. The equivalent circuit of a laminated core without insulation is presented, that can be used for determining the necessity of insulation. It is shown that the increase in the eddy current is affected by the ratio of the resistance of steel to the contact resistance. An experimental investigation is also carried out.