A Study of the 3-Phase Commutator Armature With Six Adjustable Brushes

This paper attempts a detailed study of the characteristics of a three phase commutator armature with six adjustable brushes per pole pair. As the brushes are being shifted, the effective number of turns per phase, phase resistance, phase leakage reactance and flux shape, change considerably. These values are being derived as a function of the brush spacing angle and, with the help of the Goerges diagram, the resulting flux shapes are being determined. Furthermore, the change of leakage reactance with varying armature speed is being discussed. The principles of the derivations are general and may be applied to any similar problems.