The distorted lines must be regarded as resultants of the two induced
polarities of the armature, one polarity due to the induction of the
field, the other to the induction from its own windings. The positions
of the brushes have much to do with determining the amount and degree of
distortion. In the case of the ring armature it will be seen that some
of the lines of force within the armature persist in their polarity and
direction, almost as induced by the armature windings alone, and leak
across without contributing their quota to the field. Two such lines are
shown in dotted lines.
In motors there is a similar but a reversed distortion.
Fig. 169. DISTORTION OF FIELD IN A RING ARMATURE OF AN ACTIVE DYNAMO.
Fig. 170. DISTORTION OF FIELD IN A RING ARMATURE OF AN ACTIVE MOTOR.