Computation of magnetic fields in saturated iron structures with special reference to the computation of short circuit performance of induction machines with wound rotors

The thesis is principally concerned with the solution of non- linear field problems with particular reference to the computation of the magnetostatic field in magnetically saturated electrical machines. The field is divided into a core region for which a two- dimensional solution is obtained and an end region, the analysis of which takes account of the three-dimensional geometry using the method of images. The influence of saturation in the core region is explored by solving the non—linear partial differential equation in terms of vector potential-. The magnetic field in the core region can therefore be described by a two—dimensional mildly non—linear elliptic partial differential equation. This equation can be solved approximately by different discretization techniques in which the problem is transformed into one of solving a set of non—linear equations. Different possibilities for discretization have been compared and it has been found that the discretization mesh consisting of triangles and having free topology has advantages over some other types of discretization. The necessary number of mesh nodes for given accuracy has been found by numerical experimentation. Several methods for the solution of the set of non—linear algebraic equations arising from discretization are compared.