UTILIZING FAMILIAR TYPES OF GENERATOR OF THE CONTINUOUS CURRENT TYPE.
The preceding descriptions have assumed the use of alternating current
generators in which, in order to produce the progressive movement of the
magnetic poles, or of the resultant attraction of independent field
magnets, the current generating coils are independent or separate. The
ordinary forms of continuous current dynamos may, however, be employed
for the same work, in accordance with a method of adaptation devised by
Mr. Tesla. As will be seen, the modification involves but slight changes
in their construction, and presents other elements of economy.
On the shaft of a given generator, either in place of or in addition to
the regular commutator, are secured as many pairs of insulated
collecting-rings as there are circuits to be operated. Now, it will be
understood that in the operation of any dynamo electric generator the
currents in the coils in their movement through the field of force
undergo different phases--that is to say, at different positions of the
coils the currents have certain directions and certain strengths--and
that in the Tesla motors or transformers it is necessary that the
currents in the energizing coils should undergo a certain order of
variations in strength and direction. Hence, the further step--viz., the
connection between the induced or generating coils of the machine and
the contact-rings from which the currents are to be taken off--will be
determined solely by what order of variations of strength and direction
in the currents is desired for producing a given result in the
electrical translating device. This may be accomplished in various ways;
but in the drawings we give typical instances only of the best and most
practicable ways of applying the invention to three of the leading types
of machines in widespread use, in order to illustrate the principle.
Fig. 25 is a diagram illustrative of the mode of applying the invention
to the well-known type of "closed" or continuous circuit machines. Fig.
26 is a similar diagram embodying an armature with separate coils
connected diametrically, or what is generally called an "open-circuit"
machine. Fig. 27 is a diagram showing the application of the invention
to a machine the armature-coils of which have a common joint.
[Illustration: FIG. 25.]
Referring to Fig. 25, let A represent a Tesla motor or transformer
which, for convenience, we will designate as a "converter." It consists
of an annular core, B, wound with four independent coils, C and D, those
diametrically opposite being connected together so as to co-operate in
pairs in establishing free poles in the ring, the tendency of each pair
being to fix the poles at ninety degrees from the other. There may be an
armature, E, within the ring, which is wound with coils closed upon
themselves. The object is to pass through coils C D currents of such
relative strength and direction as to produce a progressive shifting or
movement of the points of maximum magnetic effect around the ring, and
to thereby maintain a rotary movement of the armature. There are
therefore secured to the shaft F of the generator, four insulated
contact-rings, _a b c d_, upon which bear the collecting-brushes
_a' b' c' d'_, connected by wires G G H H, respectively, with the
terminals of coils C and D.
Assume, for sake of illustration, that the coils D D are to receive the
maximum and coils C C at the same instant the minimum current, so that
the polar line may be midway between the coils D D. The rings _a b_
would therefore be connected to the continuous armature-coil at its
neutral points with respect to the field, or the point corresponding
with that of the ordinary commutator brushes, and between which exists
the greatest difference of potential; while rings _c d_ would be
connected to two points in the coil, between which exists no difference
of potential. The best results will be obtained by making these
connections at points equidistant from one another, as shown. These
connections are easiest made by using wires L between the rings and the
loops or wires J, connecting the coil I to the segments of the
commutator K. When the converters are made in this manner, it is evident
that the phases of the currents in the sections of the generator coil
will be reproduced in the converter coils. For example, after turning
through an arc of ninety degrees the conductors L L, which before
conveyed the maximum current, will receive the minimum current by reason
of the change in the position of their coils, and it is evident that for
the same reason the current in these coils has gradually fallen from the
maximum to the minimum in passing through the arc of ninety degrees. In
this special plan of connections, the rotation of the magnetic poles of
the converter will be synchronous with that of the armature coils of the
generator, and the result will be the same, whether the energizing
circuits are derivations from a continuous armature coil or from
independent coils, as in Mr. Tesla's other devices.
In Fig. 25, the brushes M M are shown in dotted lines in their proper
normal position. In practice these brushes may be removed from the
commutator and the field of the generator excited by an external source
of current; or the brushes may be allowed to remain on the commutator
and to take off a converted current to excite the field, or to be used
for other purposes.
In a certain well-known class of machines known as the "open circuit,"
the armature contains a number of coils the terminals of which connect
to commutator segments, the coils being connected across the armature in
pairs. This type of machine is represented in Fig. 26. In this machine
each pair of coils goes through the same phases as the coils in some of
the generators already shown, and it is obviously only necessary to
utilize them in pairs or sets to operate a Tesla converter by extending
the segments of the commutators belonging to each pair of coils and
causing a collecting brush to bear on the continuous portion of each
segment. In this way two or more circuits may be taken off from the
generator, each including one or more pairs or sets of coils as may be
desired.
[Illustration: FIG. 26.]
[Illustration: FIG. 27.]
In Fig. 26 I I represent the armature coils, T T the poles of the field
magnet, and F the shaft carrying the commutators, which are extended to
form continuous portions _a b c d_. The brushes bearing on the
continuous portions for taking off the alternating currents are
represented by _a' b' c' d'_. The collecting brushes, or those which may
be used to take off the direct current, are designated by M M. Two pairs
of the armature coils and their commutators are shown in the figure as
being utilized; but all may be utilized in a similar manner.
There is another well-known type of machine in which three or more
coils, A' B' C', on the armature have a common joint, the free ends
being connected to the segments of a commutator. This form of generator
is illustrated in Fig. 27. In this case each terminal of the generator
is connected directly or in derivation to a continuous ring, _a b c_,
and collecting brushes, _a' b' c'_, bearing thereon, take off the
alternating currents that operate the motor. It is preferable in this
case to employ a motor or transformer with three energizing coils, A''
B'' C'', placed symmetrically with those of the generator, and the
circuits from the latter are connected to the terminals of such coils
either directly--as when they are stationary--or by means of brushes
_e'_ and contact rings _e_. In this, as in the other cases, the ordinary
commutator may be used on the generator, and the current taken from it
utilized for exciting the generator field-magnets or for other
purposes.