Flux Distribution in DC Machines On-Load and Overloads

In this paper, a method is provided for finding the magnetic fields in dc machines on-load and overloads. Mathematically, the problem is that of solving a quasi-Poissonian equation through use of a modified relaxation method. The differential equations are first replaced by difference equations; this constitutes a set of algebraic equations which are solved by a procedure consisting of relaxation and block relaxation of the potentials, and of underrelaxing the reluctivities. Currents and nonlinearities caused by the saturation of the iron are fully considered. A flow chart of a computer program is given, and the procedure is applied for finding the fields in a 500-hp, 4-pole dc motor at rated load, at twice rated load, and at six-times rated load with a high-speed computer. Flux plots in the region between the commutating pole and the armature show the spread of the main pole flux into the commutating region at overloads.