TYPE OF TESLA SINGLE-PHASE MOTOR.
Up to this point, two principal types of Tesla motors have been
described: First, those containing two or more energizing circuits
through which are caused to pass alternating currents differing from one
another in phase to an extent sufficient to produce a continuous
progression or shifting of the poles or points of greatest magnetic
effect, in obedience to which the movable element of the motor is
maintained in rotation; second, those containing poles, or parts of
different magnetic susceptibility, which under the energizing influence
of the same current or two currents coinciding in phase will exhibit
differences in their magnetic periods or phases. In the first class of
motors the torque is due to the magnetism established in different
portions of the motor by currents from the same or from independent
sources, and exhibiting time differences in phase. In the second class
the torque results from the energizing effects of a current upon
different parts of the motor which differ in magnetic susceptibility--in
other words, parts which respond in the same relative degree to the
action of a current, not simultaneously, but after different intervals
of time.
In another Tesla motor, however, the torque, instead of being solely the
result of a time difference in the magnetic periods or phases of the
poles or attractive parts to whatever cause due, is produced by an
angular displacement of the parts which, though movable with respect to
one another, are magnetized simultaneously, or approximately so, by the
same currents. This principle of operation has been embodied practically
in a motor in which the necessary angular displacement between the
points of greatest magnetic attraction in the two elements of the
motor--the armature and field--is obtained by the direction of the
lamination of the magnetic cores of the elements.
Fig. 62 is a side view of such a motor with a portion of its armature
core exposed. Fig. 63 is an end or edge view of the same. Fig. 64 is a
central cross-section of the same, the armature being shown mainly in
elevation.
[Illustration: FIG. 62.]
[Illustration: FIG. 63.]
[Illustration: FIG. 64.]
Let A A designate two plates built up of thin sections or laminae of soft
iron insulated more or less from one another and held together by bolts
_a_ and secured to a base B. The inner faces of these plates contain
recesses or grooves in which a coil or coils D are secured obliquely to
the direction of the laminations. Within the coils D is a disc E,
preferably composed of a spirally-wound iron wire or ribbon or a series
of concentric rings and mounted on a shaft F, having bearings in the
plates A A. Such a device when acted upon by an alternating current is
capable of rotation and constitutes a motor, the operation of which may
be explained in the following manner: A current or current-impulse
traversing the coils D tends to magnetize the cores A A and E, all of
which are within the influence of the field of the coils. The poles thus
established would naturally lie in the same line at right angles to the
coils D, but in the plates A they are deflected by reason of the
direction of the laminations, and appear at or near the extremities of
these plates. In the disc, however, where these conditions are not
present, the poles or points of greatest attraction are on a line at
right angles to the plane of the coils; hence there will be a torque
established by this angular displacement of the poles or magnetic lines,
which starts the disc in rotation, the magnetic lines of the armature
and field tending toward a position of parallelism. This rotation is
continued and maintained by the reversals of the current in coils D D,
which change alternately the polarity of the field-cores A A. This
rotary tendency or effect will be greatly increased by winding the disc
with conductors G, closed upon themselves and having a radial direction,
whereby the magnetic intensity of the poles of the disc will be greatly
increased by the energizing effect of the currents induced in the coils
G by the alternating currents in coils D.
The cores of the disc and field may or may not be of different magnetic
susceptibility--that is to say, they may both be of the same kind of
iron, so as to be magnetized at approximately the same instant by the
coils D; or one may be of soft iron and the other of hard, in order that
a certain time may elapse between the periods of their magnetization. In
either case rotation will be produced; but unless the disc is provided
with the closed energizing coils it is desirable that the
above-described difference of magnetic susceptibility be utilized to
assist in its rotation.
The cores of the field and armature may be made in various ways, as will
be well understood, it being only requisite that the laminations in each
be in such direction as to secure the necessary angular displacement of
the points of greatest attraction. Moreover, since the disc may be
considered as made up of an infinite number of radial arms, it is
obvious that what is true of a disc holds for many other forms of
armature.