An Alternative Method for Determining the Magnetic Field in the Air-gap of Rotating Electrical Machines

Knowing how to calculate the magnetic field created in the air-gap of rotating electrical machines (REM) represents an essential step in understanding their operating principle. The approach followed by many manuals and classical text-books on REM involves first determining the magnetic field created by a full pitch coil (using Ampère’s Law) and next calculating the magnetic field created by the distributed winding making use of the superposition principle. However, in the authors’ opinion this method presents severe shortcomings. On the one hand it lacks generality: transferring this method to coils that span less than 180 degrees demands the application of additional laws (e.g.: zero divergence of the induction). On the other hand, it requires unrealistic simplifications such as assuming an infinite permeability of iron. In this work we present an alternative approach that aims at overcoming these difficulties. It only requires the application of the Ampère’s Law, does not rely on unnecessary simplifications, and has a greater generality.