SINGLE-PHASE COMMUTATOR MOTORS 367

and i", and using the lagging component for field excitation.
This is done most conveniently by shunting the field by a non-
inductive resistance. Let r0 be the non-inductive resistance in
shunt with the field winding, of reactance, XQ + xi9 where a?i is

FIG. 177.—Single-phase commutator-motor improvement of power-factor
by introduction of lagging e.m.f. of rotation.

that part of the self-inductive reactance, x, due to the field coils.
The current, i*', in the field is lagging 90° behind the current, i",

in a non-inductive resistance, and the two currents have the
•/

ratio -.>, =

-; hence, dividing the total current, 01, in this
proportion into the two quadrature components, 01' and 01",

+

FIG. 178.—Single-phase commutator motor. Unity power-factor produced
by lagging e.m.f. of rotation.

in Fig. 177, gives the magnetic flux, 0$, in phase with OP', and
so lagging behind 01, and then the e.m.f. of rotation is OEi, the
e.m.f. of alternation OEQ, and combining OEi, OE^ and OE'

it