This chapter describes the important properties of the harmonic functions that are needed in the present application. Simple geometries are often possible to obtain a good estimation of the electric field in a certain region of a transformer by idealizing the geometry to such an extent that the field can be calculated analytically. This has the advantage of exhibiting the field as a function of several parameters so that the effect of changing these and how this affects the field can be appreciated. A computer program was written to implement this procedure for calculating the electric field. According to the given formulas, the field is infinite at the corners of the conductors. Finite element methods permit the calculation of electric potentials and fields for complicated geometries. Modern commercial finite element codes generally provide a set of drawing tools, which allow the user to input the geometry in as much detail as desired.