The aim of the paper is to present a mathematical model useful to analyze the different operating conditions of the different structures of rotating electrical machines. For this purpose it is first shown that the same mathematical expression describes the air gap m. m. f. generated by each kind of machine winding, if reference is made to a proper mathematical definition of the current distributions. The final mathematical model is expressed in a very general form and it enables us to simulate all different machine kinds only by introduction of proper assumption.