Losses and Efficiency of Series-Excited DC Motors

An analysis of technical and educational literature has shown that the issues of losses and efficiency of DC machines and their analysis are carried out in relation only to parallel and independent excitation machines. Losses and efficiency of series-excited motors are not considered. The analysis of the components of total losses in series excitation motors and their dependence on the load showed that all losses can be divided into three groups: losses depending on the square of the load factor, losses whose values are inversely proportional to the load factor and losses, the values of which are inversely proportional to the square load factor. The indicated dependence of losses on load is typical only for the type of engine under consideration. The study of the dependence of the efficiency of series-excited motors on the load made it possible to formulate a condition that determines the value of the load at which the efficiency of the motors will take its maximum value. The resulting condition is radically different from the similar one given in the general theory of electrical machines.