Theory and equivalent circuits of the stator-fed polyphase shunt commutator motor

Tensor analysis is used to develop a comprehensive theory of the stator-fed 3-phase shunt commutator motor. Before proceeding with the general analysis, the simple case of a machine where all the phase shift between the secondary standstill induced voltage and the secondary impressed voltage is either in the motor or the regulator is considered. From the equations of performance of the simple machine, the existing equivalent circuit proposed by Coulthard is derived. The limitations of this circuit are discussed and better circuits are proposed. For the general analysis, the machine has an auxiliary winding on the stator displaced from the main winding for power-factor improvement, a shift of the brushes from the neutral position, and a biased double regulator with completely dissimilar-component single regulators for speed and power-factor control. An equivalent circuit for the general machine is proposed and a method of measuring its parameters is indicated. Certain modifications to the theory to overcome inherent limitations are discussed.