Deriving DC Machine Toeque by the Principle of Virtual Work

The purpose of this paper is to fill a gap which exists in the "textbook" theory of dc machines. The paper shows that the usual expression for dc machine torque can be obtained from the direct application of the principle of virtual work to the machine, making the traditional assumptions. The method provides additional benefits in that it demonstrates the reluctance torque which results from the saliency of the field structure and shows that compensating windings have no effect on the torque under the assumed linear conditions.