MOTOR WITH CONDENSER IN ONE OF THE FIELD CIRCUITS.
If the field or energizing circuits of a rotary phase motor be both
derived from the same source of alternating currents and a condenser of
proper capacity be included in one of the same, approximately, the
desired difference of phase may be obtained between the currents flowing
directly from the source and those flowing through the condenser; but
the great size and expense of condensers for this purpose that would
meet the requirements of the ordinary systems of comparatively low
potential are particularly prohibitory to their employment.
Another, now well-known, method or plan of securing a difference of
phase between the energizing currents of motors of this kind is to
induce by the currents in one circuit those in the other circuit or
circuits; but as no means had been proposed that would secure in this
way between the phases of the primary or inducing and the secondary or
induced currents that difference--theoretically ninety degrees--that is
best adapted for practical and economical working, Mr. Tesla devised a
means which renders practicable both the above described plans or
methods, and by which he is enabled to obtain an economical and
efficient alternating current motor. His invention consists in placing a
condenser in the secondary or induced circuit of the motor above
described and raising the potential of the secondary currents to such a
degree that the capacity of the condenser, which is in part dependent on
the potential, need be quite small. The value of this condenser is
determined in a well-understood manner with reference to the
self-induction and other conditions of the circuit, so as to cause the
currents which pass through it to differ from the primary currents by a
quarter phase.
Fig. 91 illustrates the invention as embodied in a motor in which the
inductive relation of the primary and secondary circuits is secured by
winding them inside the motor partly upon the same cores; but the
invention applies, generally, to other forms of motor in which one of
the energizing currents is induced in any way from the other.
Let A B represent the poles of an alternating current motor, of which C
is the armature wound with coils D, closed upon themselves, as is now
the general practice in motors of this kind. The poles A, which
alternate with poles B, are wound with coils of ordinary or coarse wire
E in such direction as to make them of alternate north and south
polarity, as indicated in the diagram by the characters N S. Over these
coils, or in other inductive relation to the same, are wound long
fine-wire coils F F, and in the same direction throughout as the coils
E. These coils are secondaries, in which currents of very high potential
are induced. All the coils E in one series are connected, and all the
secondaries F in another.
[Illustration: FIG. 91.]
On the intermediate poles B are wound fine-wire energizing coils G,
which are connected in series with one another, and also with the series
of secondary coils F, the direction of winding being such that a
current-impulse induced from the primary coils E imparts the same
magnetism to the poles B as that produced in poles A by the primary
impulse. This condition is indicated by the characters N' S'.
In the circuit formed by the two sets of coils F and G is introduced a
condenser H; otherwise this circuit is closed upon itself, while the
free ends of the circuit of coils E are connected to a source of
alternating currents. As the condenser capacity which is needed in any
particular motor of this kind is dependent upon the rate of alternation
or the potential, or both, its size or cost, as before explained, may be
brought within economical limits for use with the ordinary circuits if
the potential of the secondary circuit in the motor be sufficiently
high. By giving to the condenser proper values, any desired difference
of phase between the primary and secondary energizing circuits may be
obtained.