366

ELECTRICAL APPARATUS

the increased loss of power, but is far greater than corresponding
thereto. It is the result of the lag of the e.m.f. of rotation, which
produces a lagging e.m.f. component partially compensating for
the leading e.m.f. consumed by self-inductance, a lag of the e.m.f.
being equivalent to a lead of the current.

Er

FIG. 175.—Single-phase commutator-motor vector diagram.

As the result of this feature of a lag of the magnetic flux, $,
by producing a lagging e.m.f. of rotation and thus compensating
for the lag of current by self-inductance, single-phase motors
having poor commutation usually have better power-factors, and

FIG. 176.—Single-phase commutator-motor diagram with phase displace-
ment between flux and current.
improvement in commutation, by eliminating or reducing the
short-circuit current under the brush, usually causes a slight de-
crease in the power-factor, by bringing the magnetic flux, $, more
nearly in phase with the current, 7.
204. Inversely, by increasing the lag of the magnetic flux,r<i>,
the phase angle can be decreased and the power-factor improved.
Such a shift of the magnetic flux, $, behind the supply current, i,
can be produced by dividing the current, i, into components, V