REGULATOR FOR ROTARY CURRENT MOTORS.
An interesting device for regulating and reversing has been devised by
Mr. Tesla for the purpose of varying the speed of polyphase motors. It
consists of a form of converter or transformer with one element capable
of movement with respect to the other, whereby the inductive relations
may be altered, either manually or automatically, for the purpose of
varying the strength of the induced current. Mr. Tesla prefers to
construct this device in such manner that the induced or secondary
element may be movable with respect to the other; and the invention, so
far as relates merely to the construction of the device itself,
consists, essentially, in the combination, with two opposite magnetic
poles, of an armature wound with an insulated coil and mounted on a
shaft, whereby it may be turned to the desired extent within the field
produced by the poles. The normal position of the core of the secondary
element is that in which it most completely closes the magnetic circuit
between the poles of the primary element, and in this position its coil
is in its most effective position for the inductive action upon it of
the primary coils; but by turning the movable core to either side, the
induced currents delivered by its coil become weaker until, by a
movement of the said core and coil through 90 deg., there will be no current
delivered.
Fig. 34 is a view in side elevation of the regulator. Fig. 35 is a
broken section on line _x x_ of Fig. 34. Fig. 36 is a diagram
illustrating the most convenient manner of applying the regulator to
ordinary forms of motors, and Fig. 37 is a similar diagram illustrating
the application of the device to the Tesla alternating-current motors.
The regulator may be constructed in many ways to secure the desired
result; but that which is, perhaps, its best form is shown in Figs. 34
and 35.
A represents a frame of iron. B B are the cores of the inducing or
primary coils C C. D is a shaft mounted on the side bars, D', and on
which is secured a sectional iron core, E, wound with an induced or
secondary coil, F, the convolutions of which are parallel with the axis
of the shaft. The ends of the core are rounded off so as to fit closely
in the space between the two poles and permit the core E to be turned to
and held at any desired point. A handle, G, secured to the projecting
end of the shaft D, is provided for this purpose.
[Illustration: FIG. 34.]
[Illustration: FIG. 35.]
In Fig. 36 let H represent an ordinary alternating current generator,
the field-magnets of which are excited by a suitable source of current,
I. Let J designate an ordinary form of electromagnetic motor provided
with an armature, K, commutator L, and field-magnets M. It is well known
that such a motor, if its field-magnet cores be divided up into
insulated sections, may be practically operated by an alternating
current; but in using this regulator with such a motor, Mr. Tesla
includes one element of the motor only--say the armature-coils--in the
main circuit of the generator, making the connections through the
brushes and the commutator in the usual way. He also includes one of the
elements of the regulator--say the stationary coils--in the same
circuit, and in the circuit with the secondary or movable coil of the
regulator he connects up the field-coils of the motor. He also prefers
to use flexible conductors to make the connections from the secondary
coil of the regulator, as he thereby avoids the use of sliding contacts
or rings without interfering with the requisite movement of the core E.
If the regulator be in its normal position, or that in which its
magnetic circuit is most nearly closed, it delivers its maximum induced
current, the phases of which so correspond with those of the primary
current that the motor will run as though both field and armature were
excited by the main current.
[Illustration: FIG. 36.]
To vary the speed of the motor to any rate between the minimum and
maximum rates, the core E and coils F are turned in either direction to
an extent which produces the desired result, for in its normal position
the convolutions of coil F embrace the maximum number of lines of force,
all of which act with the same effect upon the coil; hence it will
deliver its maximum current; but by turning the coil F out of its
position of maximum effect the number of lines of force embraced by it
is diminished. The inductive effect is therefore impaired, and the
current delivered by coil F will continue to diminish in proportion to
the angle at which the coil F is turned until, after passing through an
angle of ninety degrees, the convolutions of the coil will be at right
angles to those of coils C C, and the inductive effect reduced to a
minimum.
Incidentally to certain constructions, other causes may influence the
variation in the strength of the induced currents. For example, in the
present case it will be observed that by the first movement of coil F a
certain portion of its convolutions are carried beyond the line of the
direct influence of the lines of force, and that the magnetic path or
circuit for the lines is impaired; hence the inductive effect would be
reduced. Next, that after moving through a certain angle, which is
obviously determined by the relative dimensions of the bobbin or coil F,
diagonally opposite portions of the coil will be simultaneously included
in the field, but in such positions that the lines which produce a
current-impulse in one portion of the coil in a certain direction will
produce in the diagonally opposite portion a corresponding impulse in
the opposite direction; hence portions of the current will neutralize
one another.
As before stated, the mechanical construction of the device may be
greatly varied; but the essential conditions of the principle will be
fulfilled in any apparatus in which the movement of the elements with
respect to one another effects the same results by varying the inductive
relations of the two elements in a manner similar to that described.
[Illustration: FIG. 37.]
It may also be stated that the core E is not indispensable to the
operation of the regulator; but its presence is obviously beneficial.
This regulator, however, has another valuable property in its capability
of reversing the motor, for if the coil F be turned through a
half-revolution, the position of its convolutions relatively to the two
coils C C and to the lines of force is reversed, and consequently the
phases of the current will be reversed. This will produce a rotation of
the motor in an opposite direction. This form of regulator is also
applied with great advantage to Mr. Tesla's system of utilizing
alternating currents, in which the magnetic poles of the field of a
motor are progressively shifted by means of the combined effects upon
the field of magnetizing coils included in independent circuits, through
which pass alternating currents in proper order and relations to each
other.
In Fig. 37, let P represent a Tesla generator having two independent
coils, P' and P'', on the armature, and T a diagram of a motor having
two independent energizing coils or sets of coils, R R'. One of the
circuits from the generator, as S' S', includes one set, R' R', of the
energizing coils of the motor, while the other circuit, as S S, includes
the primary coils of the regulator. The secondary coil of the regulator
includes the other coils, R R, of the motor.
While the secondary coil of the regulator is in its normal position, it
produces its maximum current, and the maximum rotary effect is imparted
to the motor; but this effect will be diminished in proportion to the
angle at which the coil F of the regulator is turned. The motor will
also be reversed by reversing the position of the coil with reference to
the coils C C, and thereby reversing the phases of the current produced
by the generator. This changes the direction of the movement of the
shifting poles which the armature follows.
One of the main advantages of this plan of regulation is its economy of
power. When the induced coil is generating its maximum current, the
maximum amount of energy in the primary coils is absorbed; but as the
induced coil is turned from its normal position the self-induction of
the primary-coils reduces the expenditure of energy and saves power.
It is obvious that in practice either coils C C or coil F may be used as
primary or secondary, and it is well understood that their relative
proportions may be varied to produce any desired difference or
similarity in the inducing and induced currents.