The circle diagram of the three-phase series commutator motor

The characteristics of a 3-phase series commutator motor may satisfactorily be predicted for normal brush positions by determining each loss in the motor separately. Owing to the high saturation of the iron the circle diagram has no real existence as a circle at all, but fictitious values for the magnitude and direction of a ¿short-circuit vector¿ may be deduced, giving a circle which represents the characteristics of the motor within the working range.