MOTOR WITH "CURRENT LAG" ARTIFICIALLY SECURED.
One of the general ways followed by Mr. Tesla in developing his rotary
phase motors is to produce practically independent currents differing
primarily in phase and to pass these through the motor-circuits. Another
way is to produce a single alternating current, to divide it between the
motor-circuits, and to effect artificially a lag in one of these
circuits or branches, as by giving to the circuits different
self-inductive capacity, and in other ways. In the former case, in which
the necessary difference of phase is primarily effected in the
generation of currents, in some instances, the currents are passed
through the energizing coils of both elements of the motor--the field
and armature; but a further result or modification may be obtained by
doing this under the conditions hereinafter specified in the case of
motors in which the lag, as above stated, is artificially secured.
Figs. 42 to 47, inclusive, are diagrams of different ways in which the
invention is carried out; and Fig. 48, a side view of a form of motor
used by Mr. Tesla for this purpose.
[Illustration: FIGS. 42, 43 and 44.]
A B in Fig. 42 indicate the two energizing circuits of a motor, and C D
two circuits on the armature. Circuit or coil A is connected in series
with circuit or coil C, and the two circuits B D are similarly
connected. Between coils A and C is a contact-ring _e_, forming one
terminal of the latter, and a brush _a_, forming one terminal of the
former. A ring _d_ and brush _c_ similarly connect coils B and D. The
opposite terminals of the field-coils connect to one binding post _h_ of
the motor, and those of the armature coils are similarly connected to
the opposite binding post _i_ through a contact-ring _f_ and brush _g_.
Thus each motor-circuit while in derivation to the other includes one
armature and one field coil. These circuits are of different
self-induction, and may be made so in various ways. For the sake
of clearness, an artificial resistance R is shown in one of these
circuits, and in the other a self-induction coil S. When an alternating
current is passed through this motor it divides between its two
energizing-circuits. The higher self-induction of one circuit produces a
greater retardation or lag in the current therein than in the other. The
difference of phase between the two currents effects the rotation or
shifting of the points of maximum magnetic effect that secures the
rotation of the armature. In certain respects this plan of including
both armature and field coils in circuit is a marked improvement. Such a
motor has a good torque at starting; yet it has also considerable
tendency to synchronism, owing to the fact that when properly
constructed the maximum magnetic effects in both armature and field
coincide--a condition which in the usual construction of these motors
with closed armature coils is not readily attained. The motor thus
constructed exhibits too, a better regulation of current from no load to
load, and there is less difference between the apparent and real energy
expended in running it. The true synchronous speed of this form of motor
is that of the generator when both are alike--that is to say, if the
number of the coils on the armature and on the field is _x_, the motor
will run normally at the same speed as a generator driving it if the
number of field magnets or poles of the same be also _x_.
[Illustration: FIGS. 45, 46 and 47.]
Fig. 43 shows a somewhat modified arrangement of circuits. There is in
this case but one armature coil E, the winding of which maintains
effects corresponding to the resultant poles produced by the two
field-circuits.
Fig. 44 represents a disposition in which both armature and field are
wound with two sets of coils, all in multiple arc to the line or main
circuit. The armature coils are wound to correspond with the field-coils
with respect to their self-induction. A modification of this plan is
shown in Fig. 45--that is to say, the two field coils and two armature
coils are in derivation to themselves and in series with one another.
The armature coils in this case, as in the previous figure, are wound
for different self-induction to correspond with the field coils.
Another modification is shown in Fig. 46. In this case only one
armature-coil, as D, is included in the line-circuit, while the other,
as C, is short-circuited.
In such a disposition as that shown in Fig. 43, or where only one
armature-coil is employed, the torque on the start is somewhat reduced,
while the tendency to synchronism is somewhat increased. In such a
disposition as shown in Fig. 46, the opposite conditions would exist. In
both instances, however, there is the advantage of dispensing with one
contact-ring.
[Illustration: FIG. 48.]
In Fig. 46 the two field-coils and the armature-coil D are in multiple
arc. In Fig. 47 this disposition is modified, coil D being shown in
series with the two field-coils.
Fig. 48 is an outline of the general form of motor in which this
invention is embodied. The circuit connections between the armature and
field coils are made, as indicated in the previous figures, through
brushes and rings, which are not shown.