MODIFICATIONS AND EXPANSIONS OF THE TESLA POLYPHASE SYSTEMS.
In his earlier papers and patents relative to polyphase currents, Mr.
Tesla devoted himself chiefly to an enunciation of the broad lines and
ideas lying at the basis of this new work; but he supplemented this
immediately by a series of other striking inventions which may be
regarded as modifications and expansions of certain features of the
Tesla systems. These we shall now proceed to deal with.
In the preceding chapters we have thus shown and described the Tesla
electrical systems for the transmission of power and the conversion and
distribution of electrical energy, in which the motors and the
transformers contain two or more coils or sets of coils, which were
connected up in independent circuits with corresponding coils of an
alternating current generator, the operation of the system being brought
about by the co-operation of the alternating currents in the independent
circuits in progressively moving or shifting the poles or points of
maximum magnetic effect of the motors or converters. In these systems
two independent conductors are employed for each of the independent
circuits connecting the generator with the devices for converting the
transmitted currents into mechanical energy or into electric currents of
another character. This, however, is not always necessary. The two or
more circuits may have a single return path or wire in common, with a
loss, if any, which is so extremely slight that it may be disregarded
entirely. For the sake of illustration, if the generator have two
independent coils and the motor two coils or two sets of coils in
corresponding relations to its operative elements one terminal of each
generator coil is connected to the corresponding terminals of the motor
coils through two independent conductors, while the opposite terminals
of the respective coils are both connected to one return wire. The
following description deals with the modification. Fig. 22 is a
diagrammatic illustration of a generator and single motor constructed
and electrically connected in accordance with the invention. Fig. 23 is
a diagram of the system as it is used in operating motors or converters,
or both, in parallel, while Fig. 24 illustrates diagrammatically the
manner of operating two or more motors or converters, or both, in
series. Referring to Fig. 22, A A designate the poles of the field
magnets of an alternating-current generator, the armature of which,
being in this case cylindrical in form and mounted on a shaft, C, is
wound longitudinally with coils B B'. The shaft C carries three
insulated contact-rings, _a b c_, to two of which, as _b c_, one
terminal of each coil, as _e d_, is connected. The remaining terminals,
_f g_, are both connected to the third ring, _a_.
[Illustration: FIG. 22.]
[Illustration: FIG. 24.]
A motor in this case is shown as composed of a ring, H, wound with four
coils, I I J J, electrically connected, so as to co-operate in pairs,
with a tendency to fix the poles of the ring at four points ninety
degrees apart. Within the magnetic ring H is a disc or cylindrical core
wound with two coils, G G', which may be connected to form two closed
circuits. The terminals _j k_ of the two sets or pairs of coils are
connected, respectively, to the binding-posts E' F', and the other
terminals, _h i_, are connected to a single binding-post, D'. To operate
the motor, three line-wires are used to connect the terminals of the
generator with those of the motor.
[Illustration: FIG. 23.]
So far as the apparent action or mode of operation of this arrangement
is concerned, the single wire D, which is, so to speak, a common
return-wire for both circuits, may be regarded as two independent wires.
In the illustration, with the order of connection shown, coil B' of the
generator is producing its maximum current and coil B its minimum; hence
the current which passes through wire e, ring b, brush b', line-wire E,
terminal E', wire j, coils I I, wire or terminal D', line-wire D, brush
_a'_, ring _a_, and wire _f_, fixes the polar line of the motor midway
between the two coils I I; but as the coil B' moves from the position
indicated it generates less current, while coil B, moving into the
field, generates more. The current from coil B passes through the
devices and wires designated by the letters _d_, _c_, C' F, F' _k_, J J,
_i_, D', D, _a'_, _a_, and _g_, and the position of the poles of the
motor will be due to the resultant effect of the currents in the two
sets of coils--that is, it will be advanced in proportion to the advance
or forward movement of the armature coils. The movement of the
generator-armature through one-quarter of a revolution will obviously
bring coil B' into its neutral position and coil B into its position of
maximum effect, and this shifts the poles ninety degrees, as they are
fixed solely by coils B. This action is repeated for each quarter of a
complete revolution.
When more than one motor or other device is employed, they may be run
either in parallel or series. In Fig. 23 the former arrangement is
shown. The electrical device is shown as a converter, L, of which the
two sets of primary coils _p r_ are connected, respectively, to the
mains F E, which are electrically connected with the two coils of the
generator. The cross-circuit wires _l m_, making these connections, are
then connected to the common return-wire D. The secondary coils _p' p''_
are in circuits _n o_, including, for example, incandescent lamps. Only
one converter is shown entire in this figure, the others being
illustrated diagrammatically.
When motors or converters are to be run in series, the two wires E F are
led from the generator to the coils of the first motor or converter,
then continued on to the next, and so on through the whole series, and
are then joined to the single wire D, which completes both circuits
through the generator. This is shown in Fig. 24, in which J I represent
the two coils or sets of coils of the motors.
There are, of course, other conditions under which the same idea may be
carried out. For example, in case the motor and generator each has three
independent circuits, one terminal of each circuit is connected to a
line-wire, and the other three terminals to a common return-conductor.
This arrangement will secure similar results to those attained with a
generator and motor having but two independent circuits, as above
described.
When applied to such machines and motors as have three or more induced
circuits with a common electrical joint, the three or more terminals of
the generator would be simply connected to those of the motor. Mr.
Tesla states, however, that the results obtained in this manner show a
lower efficiency than do the forms dwelt upon more fully above.