SINGLE-PHASE COMMUTATOR MOTORS 381

211. Theoretical Investigation.—In its most general form, the
single-phase commutator motor, as represented by Fig. 185,
comprises: two armature or rotor circuits in quadrature with
each other, the main, or energy, and the exciting circuit of the
armature where such exists, which by a multisegmental commu-
tator are connected to two sets of brushes in quadrature position
with each other. These give rise to two short-circuits, also in
quadrature position with each other and caused respectively by
the main and by the exciting brushes. • Two stator circuits, the

FIG. 185.

field, or exciting, and the cross, or compensating circuit, also in
quadrature with each other, and in line respectively with the
exciting and the main armature circuit.

These circuits may be separate, or may be parts or components
of the same circuit. They may be massed together in a single
nlot of the magnetic structure, or may be distributed over the
whole periphery, as frequently done with the armature windings,
and then as their effective number of turns must be considered
their vector resultant, that is:

2 ,

where n' = actual number of turns in series between the arma-
ture brushes, and distributed over the whole periphery, that is,
an arc of 180° electrical. Or the windings of the circuit may be
distributed only over an arc of the periphery of angle, co, as
frequently the case with the compensating winding distributed
in the pole face of pole arc, co ; or with fractional-pitch armature
windings of pitch, o>. In this case, the effective number of turns

is:

n = -n sm
co