The aim of this thesis is to implement the method μPEEC to assess, without using simulations or measurements, the reluctance of magnetic circuits and simple 2D to predict their behavior from electromagnetic design phases . It's just asking the field created by a blade straight conductor placed in a round window or rectangular magnetic circuit with or without an air gap. This study is part of a larger research aimed at developing the equivalent circuit of transformers, before prototyping to optimize these components in their applications. Before reaching this goal, several steps were taken gradually, with the help of analytical solutions and finite element simulations to validate our approaches.