THE TESLA KOTATING MAGNETIC FIELD. MOTORS WITH CLOSED CONDUCTORS. SYNCHRONIZING MOTORS. KOTATING FIELD TRANSFORMERS
THE TESLA KOTATING MAGNETIC FIELD. MOTORS WITH CLOSED
CONDUCTORS. SYNCHRONIZING MOTORS. KOTATING FIELD
TRANSFORMERS.
THE best description that can be given
of what he attempted,
and succeeded in doing, with the rotating magnetic field,
is to be
found in Mr. Tesla's brief paper explanatory
of his rotary
cur-
rent, polyphase system, read before the American Institute of
Electrical Engineers, in New York, in May, 1888, under the
title
" A New System of Alternate Current Motors and Trans-
formers." As a matter of fact, which a perusal
of the paper
will establish, Mr. Tesla made no attempt
in that paper
to de-
scribe all his work. It dealt in reality with the few topics enu-
merated in the caption of this chapter. Mr. Tesla's reticence
was no doubt due largely to the fact that his action was gov-
erned by the wishes of others with whom lie was associated, but
it may be worth mention that the compiler
of this volume who
had seen the motors running, and who was then chairman of the
Institute Committee on Papers and Meetings had great
diffi-
culty in inducing Mr. Tesla to give the Institute any paper
at all.
Mr. Tesla was overworked and ill, and manifested the greatest
reluctance to an exhibition of his motors, but his objections were
at last overcome. The paper was written the night previous
to
the meeting, in pencil, very hastily, and under the pressure
just mentioned.
In this paper casual reference was made to two special forms
of motors not within the group to be considered. These two
forms were : 1. A motor with one of its circuits in series with a
transformer, and the other in the secondary
of the transformer.
2. A motor having its armature circuit connected to the gener-
ator, and the field coils closed upon themselves. The paper
in
its essence is as follows, dealing witli a few leading
features of
the Tesla system, namely, the rotating magnetic field, motorswith closed conductors, synchronizing motors, and rotating
field
transformers :
The subject which I now have the pleasure
of bringing
to
your notice is a novel system of electric distribution and trans-
mission of power by means of alternate currents, affording pecu-
liar advantages, particularly in the way of motors, which I am
confident will at once establish the superior adaptability of these
currents to the transmission of power
and will show that many
results heretofore unattainable can be reached by their use
results which are very much desired in the practical operation
of
such systems, and which cannot be accomplished by means of
continuous currents.
Before going into a detailed description of this system,
I think
it necessary to make a few remarks with reference to certain con-
ditions existing in continuous current generators and motors,
which, although generally known, are frequently disregarded.
In our dynamo machines, it is well known, we generate
alter-
nate currents which we direct by means of a commutator, a com-
plicated device and, it may be justly said, the source of most of
the troubles experienced in the operation
of the machines. Now,
the currents so directed cannot be utilized in the motor, but
they must again by means of a similar unreliable device
be reconverted into their original
state of alternate
currents.
The function of the commutator is entirely external, and in no
way does it affect the internal working
of the machines. In
reality, therefore, all machines are alternate current machines,
the currents appearing as continuous only
in the external circuit
during their transit from generator
to motor. In view simply
of
this fact, alternate currents would commend themselves as a more
direct application of electrical energy, and the employment of
continuous currents would only be justified
if we had dynamos
which would primarily generate, and motors which would be
directly actuated by, such currents.
But the operation of the commutator on a motor is twofold
;
first, it reverses the currents through
the motor, and secondly,
it effects automatically, a progressive shifting of the poles of one
of its magnetic constituents. Assuming, therefore, that both of
the useless operations in the systems, that is to say, the directing
of the alternate currents on the generator and reversing
the direct
currents on the motor, be eliminated,
it would still be necessary,
in order to cause a rotation of the motor, to produce a progressive.
shifting of the poles of one of its elements, and the question
presented itself How to perform this operation by the direct
action of alternate currents ? I will now proceed
to show how
this result was accomplished.
In the first experiment a drum-armature was provided
with
Fie.
two coils at right angles to each other, and the ends of these coils
were connected to two pairs of insulated contact-rings
as usual.
A ring was then made of thin insulated plates of sheet-iron and
wound with four coils, each two opposite
coils being
connected
together so as to produce free poles on diametrically opposite
sides of the ring. The remaining free ends of the coils were then
connected to the contact-rings of the generator armature so as
to form two independent circuits, as indicated It
may now be seen what results were secured in this combination,
and witli this view I would refer to the diagrams, Fig
The field of the generator being independently excited, the rota-
tion of the armature sets up currents in the coils c c l5 varying
in.
For instance, noting the direction outside of the ring
it will he found that inside the ring
it turns in an opposite
direc-
tion, while it is unaffected if placed
in a position symmetrical
to
the ring. This is easily explained. Each time that a pole ap-
proaches, it induces an opposite pole
in the nearest point on the
disc, and an attraction is produced upon
that point; owing
to this,
as the pole is shifted further away
from the disc a tangential pull
is exerted upon the same, and the action being constantly repeat-
ed, a more or less rapid rotation of the disc is the result. As the
pull is exerted mainly upon that part which is nearest to the
ring, the rotation outside and inside, or right and left, respectively,
is in opposite directions, Fig. 9. When placed symmetrically
to the ring, the pull on the opposite
sides of the disc being equal,
no rotation results. The action is based on the magnetic
inertia
of iron
; for this reason a disc of hard steel is much more af-
fected than a disc of soft iron, the latter being capable
of very
rapid variations of magnetism. Such a disc has proved to be a
very useful instrument in all these investigations,
as it has en-
abled me to detect any irregularity
in the action. A curious ef-
fect is also produced upon iron tilings.
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