1

222 ELEMENTS OF ELECTRICAL ENGINEERING

the commutating machines thus can be made to give a lagg:
voltage, that is, to compensate for low power-factor due to lagg:
current. Thus, by inserting such a commutating machine ii
the secondary of an induction machine, the latter can be ms
to give unity power-factor or even leading current.

Such phase compensation is frequently used in alternatli
current commutator motors to get good power-factor. Thus
the series motor, by shunting the field by a non-inductive
sistance, and thereby lagging the field exciting component
the current and with it the field flux and the voltage indue
in the armature by its rotation, behind the main current, t
series motor can at higher speeds be made to give unity pow<
factor. At low speeds, such complete compensation is n
possible, as the compensating voltage is proportional to t
speed.