Improvements in Electrical Transmission of Power.
Year: 1891

page_text: Date of Application, 27th Aug., 1891
Complete Specification Left, 26th Apr. 1892-Accepted, 4th June, 1892
PROVISIONAL SPECIFICATION.
Improvements in Electrical Transmission of Power.
I, BENJAMIN JOSEPH BARNARD MILLS, of 23 Southampton Buildings, in the
County of Middlesex, Patent Agent, do hereby declare the nature of this inven-
tion, a communication to me from Harry Ward Leonard, of the City, County and
State of New York, in the United States of America, Electrical Engineer, to be
as follows:
The invention relates mainly to the use of electric motors for performing
mechanical operations, and especially to the use of motors for purposes in which
it is necessary to run at different speeds, and at the same time maintain a
constant torque, and also where it is necessary to change both the torque and 'the
speed of the motor.
The main object of the invention is to enable an electric motor to be run at
different speeds and also with different torques, and to enable the speed to be
changed with practically no variation of the torque, and also to keep the work done
by the motor constant under variations in the speed and torque required. In the
use of motors for electric railways, for example, it is often desirable that the
armature should exert a stronger torque or greater pull, as, for instance, where it is
desired to run with a heavier load, or ascend a grade, and it is also sometimes
desirable to alter the speed without varying the torque, so that a car may be
slowed down without detracting from the rotary effort of its motor. With such
electric motors as have heretofore been employed, the arrangements for changing
the speed have been such as to produce a variation in the field strength, which has
resulted in varying the torque, the torque being dependent on two factors, namely,
strength of field, and amperes of current in armature. By the present invention I
am enabled to vary the speed without affecting the strength of the field magnet or
the current traversing the armature coils, and therefore without changing the
torque, and also without materially altering the non-sparking points on the
commutator.
The main feature of the invention consists in energizing the field magnet of the
motor by a constant source of current separate from the source which supplies
the armature, and regulating the speed of the motor by varying the electro-motive
force of the source of current which supplies the motor armature. With a motor
so arranged, if the load is increased, there is a tendency to slowing down of the
armature, which results in a tendency to a decrease of counter electro-motive
force of the motor which causes a greater number of amperes of current to flow
through the motor armature and increases the torque or pull on the armature so as
to enable it to overcome the increased load without altering its speed but slightly;
and on the other hand, if it is desired to have the motor run at an increased speed,
the electro motive force of the source of supplying current for the armature
is raised, so that the voltage of the armature supplying current is increased
and the armature runs faster, though as this action increases its counter-electro-
motive force, there is no increase in the amperes traversing its armature. and
consequently no increase in the torque.
To explain this in a different way, it may be said that measuring the work done
by an electric motor in foot-pounds, the time element represents the speed of the
motor and the weight element the pull or torque. Each of these elemente corre-
sponds to one of the electrical conditions of the armature supplying circuit as
arranged according to the present invention, that is to say, the speed is dependent.
on the volts on the circuit, and the pull or torque on the amperes and by the

page_text: present invention the amperes alone are varied in order to change the torque, or
the volts alone are varied in order to change the speed.
By another feature of the present invention I am enabled to perform both the
operations above described without varying the power drawn from the main source
of supply, and this is accomplished by connecting the armature of the working
motor with an intermediate generator whose potential is capable of being varied,
which generator is run by a motor supplied by the main source. The field of the
working motor is preferably supplied from the main source, as are also the fields
of the intermediate motor and generator. Then if the element of "pounds pull"
in the foot-pounds of the work being done by the motor, is varied, the speed is
varied inversely as this variation in torque or pull by varying the volts supplied to
the motor armature inversely as the variation in the armature current resultant
upon such altered pull, so that the energy supplied to the motor and represented
by the product of the volts and amperes and the energy produced by the motor and
represented by the product of the speed and the pull, remain constant. Hence to
allow for the varying conditions required of the working motor, variations are
made only in the conditions of the circuit extending from the intermediate
generator to the working motor and the same power is drawn from the main source
of supply. In applying this feature of the invention to electric railways, I place
the intermediate motor and generator, as well as the working motor, on the car,
and cause the travelling contact with the line to supply the intermediate motor
armature by a multiple arc branch circuit, and the fields of all three of the
machines, the fields of the intermediate generator boing variable, without affecting
either of the other machines. Thus when a number of cars are running upon the
railroad, all in connection with the same supplying line, each one is regulated
within itself without affecting any of the others and always drawing the same
current from the line; that is, the operator will regulate the electro-motive force
of the intermediate generator so as to keep a constant current flowing from the liue
to the intermediate motor, and whenever the working motor is called upon for a
change of current on account of a change in the pull due to a grade or a curve or
to an increased weight, the speed of the car will automatically adjust itself to that
necessary to keep the work done by the motor constant.
At present it is necessary in electric railways to provide at the generating point
an amount of power largely in excess of that which is required to normally run
all the cars, in consequence of the great amount of pull which is required in
going around curves and up grades, but since by the present invention no more
energy is required from the line in these cases than at other times, the current
required by the working motor to give it the necessary torque being given by
increasing the amperes on the circuit from the intermediate generator with corre-
sponding reduction in the volts, the power plant may be largely reduced from what
is required at present, and the prime power, either water or steam-power, much
more easily governed and the operation of the generators much simplified because
of the nearly constant load, the current on the line being maintained at a suitable
average.
The present invention also includes the use of alternating currents for supplying
continuous current motors through the medium of an alternating current motor
running an intermediate generator. Since the speed of this alternating current
motor never has to be changed, any suitable form of alternating current dynamo
machine may be used for the purpose.
This arrangement may be used either for stationary or locomotive electric
motors: The intermediate alternating current, motor and continuous current
generator may be made separate machines mechanically connected together, or
instead a combined machine may be made in which there are two windings upon
the armature, one of which receives the alternating current and so rotates the
armature synchronously with the supplying generator, while the other set of coils
produces a continuous current. The field magnet of this transformer excited
from a separate source, and variations of the strength of such magnet will not,

page_text: affect the speed of rotation due to the alternating current, but will affect the
electro-motive force of the continuous generating winding. This makes an effective
arrangement by means of which alternating currents of high tension may be con-
veyed to a distance.and continuous regulable currents of lower tension supplied to
consumers.
In applying the invention to elevators, the device for controlling the electro-
motive force of the generator which supplies current to the arinature of the motor
which operates the elevator is placed in the elevator car itself, and there is also
included a reversing device so that by reversing the generator, the operating motor
and the direction of movement of the elevator car are reversed.
L 1001
B. J. B. MILLS,
By Harris & Mills,
23, Southampton Buildings, London, W.C., Agents.
COMPLETE SPECIFICATION.
Improvements in Electrical Transmission of Power.
I, BENJAMIN JOSEPH BARNARD MILLS, of 23 Southampton Buildings, in the
County of Middlesex, Patent Agent, do hereby declare the nature of this inven-
tion, (a communication to me from Harry Ward Leonard, of the City,
County and State of New York in the United States of America, Electrical
Engineer) and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :—
The invention relates mainly to the use of electric motors for performing
mechanical oporations, and ospecially to the use of motors for purposes in which
it is necessary to run at different speeds and at the same time maintain a constant
torque, and also where it is necessary to change both the torque and the speel of
the motor.
The main object of the invention is to enable an electric motor to be run at
different speeds and also with different torques, and to enable the speed to be changed
with practically no variation of the torque, and also to keep the work done by the
inotor constant under variations in the speed and torque required. In the use of
motors for electric railways, for example, it is often desirable that the armaturo
should exert a stronger torque or greater pull, as, for instance, where it is desired
to run with a heavier load, or ascend a grade, and it is also sometimes desirable to
alter the speed without varying the torque, so that a car may be slowed down
without detracting from the rotary effort of its motor. With such electric motors
as have heretofore been employed, the arrangements for changing the speed have
been such as to produce a variation in the field strength, which has resulted in
varying the torque, the torque being dependent on two factors, namely, strength
of field, and amperes of current in armature. By the present invention I am
enabled to vary the speed without affecting the strength of the field magnet
or the current traversing the armature coils, and therefore without changing
the torque, and also without materially altering the non-sparking points on the
commutator.
The main feature of the invention consists in energizing the field magnet of the
motor by a constant source of current separate from the source which supplies the
armature, and regulating the speed of the motor by varying the electro-motive
With a notor
force of the source of current which supplies the motor armature.
so arranged, if the load is increased, there is a tendency to slowing down of the
armature, which results in a tendency to a decrease of counter electro motive force
of the motor, which causes a greater number of amperes of current to flow through
the motor armature and increases the torque or pull on the armature so as to enable
it to overcome the increased load without altering its speed but slightly, aud, on
the other hand, if it is desired to have the motor run at an increased speed, the
.

page_text: electro motive force of the source of supplying current for the armature is raised
so that the voltage of the armature supplying current is increased and the armature
runs faster, though, as this action increases its counter clectro motive force, there
is no increase in the amperes traversing its armature, and consequently no increase
in the torque.
To explain this in a different way it may be said that measuring the power
exerted by an electric motor in foot-pounds per second, the time element
represents the speed of the motor, and the weight element, the pull or torque
Each of these elements corresponds to one of the electrical conditions of the
armature supplying circuit as arranged according to the present. invention, that
is to say, the speed is dependent on the volts on the circuit; and the pull or
torque on the amperes, and by the present invention the amperes alone are
varied in order to change the torque, or the volts alone are varied in order to
change the speed.
By another feature of the present invention I am enabled to vary both the speed
and torque in any reciprocal relation desired without varying the power drawn
from the main source of supply, and this is accomplished by connecting the
armature of the working motor with an intermediate generator, whose potential is
capable of being varied, which generator is run by a motor supplied by the main
source. The field of the working motor is preferably supplied from the main
source, as are also the fields of the intermediate motor and generator. Then if
the element of "pounds pull" in the foot-pounds of the work being done by the
motor is varied, the speed is varied inversely, as this variation in torque or pull by
varying the volts supplied to the motor armature inversely as the variation in the
armature current resultant upon such altered pull, so that the energy supplied to
the motor and represented by the product of the volts and amperes, and the energy
produced by the motor and represented by the product of the speed and the pull,
remain constant. Hence, to allow for the varying conditions required of the
working motor, variations are made only in the conditions of the circuit extending
from the intermediate generator to the working motor, and practically the same
power is drawn from the main source of supply. In applying this feature of the
invention to electric railways, I place the intermediate motor and generator, as well
as the working motor, on the car, and cause the travelling contact with the line
to supply the intermedi.ste motor armature by a multiple are branch circuit, and
the fields of all three of the machines, the field of the intermediate generator being
variable, without affecting either of the other machines. Thus when a number of
cars are running upon the railroad, all in connection with the same supplying line,
each one is regulated within itself without affecting any of the others, and
always drawing the same current from the line, that is, the operator will regulate
the electro-motive force of the intermediate generator so as to keep a constant current
flowing from the line to the intermediate motor, and whenever the working
motor requires a change of current ou account of a change in the pull due
to a grade or a curve, or to an increased weight, the speed of the car will
automatically adjust itself to that necessary to keep the work done by the motor
constant.
At present it is necessary, in electric railways, to provide at the generating
point an amount of power 'largely in excess of that which is required to normally
run all the cars, in consequence of the great amount of pull which is required in
going around curves and up grades, but since by the present invention no more
energy is required from the line in these cases than at other times, because of the
reduction of speed as already set forth, the current required by the working motor
to give it the necessary torque being given by increasing the amperes on the circuit
from the intermediate generator with corresponding reduction in the volts, the power
plant may be largely reduced from what is required at present, and the prime power,
either water power or steam power, much more easily governed, and the operation of
the generators much simplified because of the nearly constant load, the current on
the line being maintained at a suitable average,

page_text: The present invention also includes the use of alternating currents for supplying
continuous current motors through the medium of an alternating current motor
running an intermediate generator. Since the speed of this alternating current
motor never has to be changed, any suitable form of alternating current dynamo
machine may be used for the purpose.
The invention may be better understood by reference to the accompanying
drawings, in which :-
Figure 1 is a diagram of an arrangement for a stationary motor embodying a simple
form of the 'invention.
Figure 2, a diagram showing the arrangement of the stationary motor supplied
by an intermediate variable generator.
Figure 3, a diagram showing the same arrangement applied to an electric
railway car.
Figure 4, a diagram showing the use of alternating currents in connection with
a stationary motor.
Figure 5, a diagram illustrating the alternating current arrangement in connection
with an electric railway.
Figure 6 is a diagram illustrating an alternating current system in which the
intermediate generator and motor are combined into a single machine.
Figures 7 and 8 are diagrams showing an application of the invention to elevators
or lifte, and also illustrating the method of reversing the motion of electric motors
which I employ.
Referring first to Figure 1; A is a suitable dynamo electric machine, and 1, 2 is
a circuit extending from its armature and including the armature of au electric
motor B, which may be considered as one intended to do work which requires it to
run at different speeds and also with different torques while performing either a
constant work or a variable work. C is a constant potential dynamo, whose
circuit 3, 4 includes the field magnet of motor B, whereby the said field magnet
is maintained at a constant strength. A multiple are branch 4, 5 from the
circuit 3, 4 includes the field magnet of the generator A, although if desired the
magnet of the generator may be energized from another exciting machine.or from
the circuit of the generator itself. In any case however I prefer to have the field
circuit of the generator A extend into proximity with the motor B or the point
where its work is to be performed, and at the location of said motor or work I
provide an adjustable resistance D or other means for regulating the potential of
the generator A. The resistance D is used to vary the speed of the motor B by.
varying the electro-motive force of the generator A, and since this is done without
affecting the field magnet of the motor B, it is accomplished, when the pull element
of the work is constant, without any change in the torque of the motor, so that
it runs with the same torque although at different speed. When the pull element
of the work does vary, the current required to produce.the necessary torque to take
care of the altered pull will automatically flow and the speed will remain practically
the same.
Since the armature of the motor B is always in a strong and constant
magnetic field, the neutral point on the commutator is kept constant even if
the work varies, provided the torque is kept constant, and oven when the torque
varies the distortion of the neutral point is very slight, and therefore there is.
no detrimental sparking at the commutator brushes even in reversing the rotation
of the armature, and it will further be seen that the efficiency of the 'apparatus
is practically the same at low speed as at full speed. Qis a circuit controller
and reverser by which the. working motor B may be started, stopped,, aud
reversed.
Referring now to Figure 2; the working motor B has its armature connected
in circuit with the armature of the generator A, whose armature is placed on
the saine shaft with, or otherwise geared to, the armature of an intermediate
motor E, this being a shunt wound motor whose field and armature are both
supplied from the main circuit 6, 7 extending from the armaturo terminals of a

page_text: '
constant potential generator F which forms. the main source of supply. The
field magnet of the working motor B, and that of the intermedinte generator A,
are each supplied by a multiple arc circuit from the main line 6, 7, the field
circuit of the intermediate generator A having included in it an adjustable
resistance D, or the magnet being provided with other suitable means for
varying its strength so as to change the electro motive force of the machine.
It will be seen that in this case, as in the one previously described, the
working motor B has its field supplied from a separate source from that which
supplies its armature, and the field magnet is therefore kept at a constant
strength independent of any changes which occur in the conditions of the
armature circuit. If it is desired to change the speed of the motor B without
varying its torque, that is, when the pull of the load is not changed, the
resistance D is adjusted so as to increase the strength of the field magnet of
the intermediate generator A and raise the electro motive force of said
generator, whereby the voltage of the circuit 8, 9 is raised, and the armature
of the motor B is made to run at an increased speed, but, there being no
change in the amperes flowing in the motor armature because the counter electro
motive force will increase in proportion to the speed, and no change in the
strength of the motor field magnet, the torque of the motor remains the same
as before.
When the pull clement of the load on the motor is increased, the
tendency to decline in speed causes the amperes on the circuit 8, 9 to increase,
and the torque of the motor is therefore raised so that the. motor runs under the
increased pull at practically the same speed as before.
It will be seen that the motor can be operated at a constant speed, the rate of
such speed being variable at will, and at any one speed it will supply automatically
the necessary torque for the load.
For an illustration, suppose the working motor B to have an armature with a
capacity to stand 200' amperes, and a field magnet wound for and excited by
500 volts; the intermediate motor armature will stand 40 amperes, and the inter-
mediate generator armature 200 amperes, the fields of the intermediate motor and
generator being wound for and excited by 500 volts each; suppose also that to
operate at full speed with an average load, the working motor requires for its
armature, 500 volts and 40 amperes; in this case the inter.nedinte generator A is
operated with its strongest field so that it supplies the working motor with the
required 500 volts and 40 amperes, it being understood that for simplicity of
explanation the losses in conversion are disregarded.
In
Now if the load is increased to an extent requiring five times the pull which was
required before, this will involve having five times the torque, which requires five
times the current in the armature, the field of the motor remaining the same.
consequence of the increased torque of the motor, the generator supplies 200 amperes
to its armature, and in order to keep the power constant the field of the generator A
is weakened so as to reduce the potential to 100 volts. The motor will now run at
one fifth of its full speed and its torque or pull will be five times as great as before,
but the power supplied by the main line 6, 7 will be no greater than before. It
will be seen that by this arrangement a number of motors may be operated on the
Bame line, each under varying conditions of pull and epeed, and the same current
maintained on the line 6, 7, so that the generating plant at F may be made much
smaller than has heretofore been necessary because of the increased power called
for by increased loads.
Figure 3 shows the arrangement of Figure 2 applied to a car.
The drawing
shows a portion of the car with the working motor B geared to the driving axle,
the intermediate generator A mounted on the car and connected with the armature
of the motor B, and the intermediate motor E also on the car and having its
armature shaft connected with the armature shaft of the generator A. One
travelling contact is shown at G, the other being formed by the car wheels as
shown. The fields of the three machines are all shown as connected in multiple
arc with the line, the armature of the intermediate motor E being also in a multiple

page_text: arc branch, and the field circuit of the generator A being provided with a resistance
box D. The operation is the same as described with reference to Figure 2, and it
will be seen that by the use of this arrangement the street car can if desired be
propelled up grades or around curves without requiring any more current from the
line than is necessary on a level straight track, the speed of the propelling motor
being varied at will by the regulation of the generator A, and the torque being
automatically determined by the pull of the lond. Preferably the current on the
circuit 6, 7 is, as stated, of much higher potential than that on circuit 8, 9, the
motor E and generator A being, as described, constructed to reduce the tension of
the current. An ampere meter V is shown to enable the operator to observe the
current taken from the line by the motor E.
For the transmission of current to a great distance the use of alternating currents
is desirable, so that a high electro-motive force or tension can be obtained without
the necessity of conveying such high tension currents through moving parts or
contacts, and because such currents can be converted or transformed by devices
having no moving parts; on the other hand, in order to enable a motor to run
efficiently with variable speed and variable torque, it is necessary to employ con-
tinuous currents. This is provided for in connection with the invention by the
arrangement shown in Figure 4, which shows this feature in connection with
stationary motor apparatus. L is an alternating current generator situated at the
source of power, and M is a tension raising converter at the station, by menus of
which a current of very high potential is delivered to the line 10, 11, which is
supposed to extend a considerable distance from the generator L. At any point
where it is desired to do work I place a tension reducing converter N to reduce the
tension of the current to the desired point, the secondary of said converter being
connected to the armature circuit of an alternating current motor 0, which, as its
speed is never changed, may be any efficient type of alternating current machine
running synchronously with the generator L. I employ the alternating current
motor O to operate the continuous current generator A, the armature of the
generator A being in circuit with the armature of the working motor B. P is a
continuous current exciter, which is used to excite the field of the main generator L,
that of the alternating current motor O, that of the continuous current generator A,
and that of the working motor B, all these field circuits, as well as that of the
exciting machine itself, being in multiple arc to each other. The multiple arc
circuit, which includes the field magnet coils of the continuous current generator A,
is provided with an adjustable resistance D, or other suitable means may be
employed for regulating the strength of the field magnet. The method of altering
the speed and torque of the working motor B, is the same as has already been
described with reference to Figures 2 and 3. The variations of work done by the
intermediate motor B may be made so gradual as not to affect the synchronous
operation of the alternating current inotor O.
'
Figure 5 shows the alternating current arrangement applied to a railway car, a
portion of the car being shown in the drawing in plan view running upon rails Q.Q.
The circuit 10, 11 extends from the secondary of the tension raising convertor M
supplied by the alternating current dynamo L as before. The primaries of the
tension reducing converters N N, are connected in multiple arc with the
circuit 10, 11, the secondaries of these converters, which have a current of lower.
tension, being connected with the working conductors R R of the railway, which
working conductors may he the traffic rails themselves, or of any other suitable
character, current being taken from them by travelling contacts ss, or by the car
wheels if the rails form the conductors. To avoid the necessity of using the con-
verters with their secondaries in multiple arc, the working conductors R R may be
divided into sections in any suitable manner, so that a car running on the railway
will receive the current of only a single couverter at one time. Upon the car is
shown the alternating current motor O connected directly with the travelling
contacts 8, and having its armature shaft joined by a belt r with the arinature.
shaft of the continuous current generator, A, whose armature circuit extends to the

page_text: armature of the motor B, which is suitably connected with the running gear of the
car to propel the same. The exciter P is preferably placed on the car in this case
and connected by a belt t with the shaft of the alternating current motor O. The
armature of the exciting generator P is connected with the field magnets of the
generator A and motors B and O, these field magnets being all in multiple arc to
each other. In order to start the apparatus, in case the motor O be of a type
such that it is not able to start itself under conditions of no load, it is preferred to
provide a storage battery S connected so as to be charged by the exciter P', and so
that by opening the switch and closing the switch ", the battery may bo used to
excite all the fields until the car is under way, when the switch u may be closed
and the switch opened and the field excited by the dynamo P. Or in order to
start the alternating current motor gradually, the dynamo P may be run as a motor
by the storage battery until the synchronizing speed is reached, and the alternating
current motor will then be connected with the line.
I have shown in Figures 4 and 5 an alternating current motor connected
mechanically with a continuous current generator, the two machines being separate
ODC8. I may however employ a transformer in which an alternating current is
supplied to the primary and a continuous current is produced in the secondary,
the latter being capable of having its electro-motive force varied, so that the
device is in all respects suitable to be substituted for the separate motor and
generator herein before described. By this arrangement I combine the intermediate
generator and motor into a single machine. Such an arrangement is illustrated
in Figure 6, a form of transformer which I may employ being shown moroly in
diagram.
The source of alternating current supplies, through the tension reducing
converter N, the motor coils of the rotating transformer X, which coils are
connected with rings on the armature shaft, so that the armature is revolved
synchronously with that of the supplying generator. The transformer armature
has also upon it a continuous winding, which is connected at intervals with the
segments of a commutator y. In practice the number of segments and connections
thereto will of course be much greater than is shown in the drawing, which is
intended merely for illustration. The brushes z z take off a continuous current
from the commutator y, which is supplied to the working motor B, or to other
translating devices, as shown.
The exciting machine supplies a continuous current to the field magnets of the
transformer, and in the circuit thereof is the adjustable resistance, or other suitable
means are provided for varying the electro-motive force of the exciting machine.
The alteration of the strength of the field magnet of the transformer produced by
such variation of the electro-motive force supplied thereto, does not affect the
speed of the revolution of the armature produced by the alternating current, but
does affect the generation of the continuous secondary current, and so varies
the electro-motive force supplied to the working motor or other translating
device.
I do not claim herein specifically the transformer just described by the use
of which the intermediate motor and generator are combined into a single
machine, since I intend to make this arrangement the subject of another
application.
It is to be understood that in referring in this Specification to "alternating'
currents, I do not intend to confine myself to currents whose alternate phases
are opposite in direction, but to include all pulsating and intermittent currents,
and all other currents of a character adapted to produce other currents by
induction.
In applying the invention to lifts or elevators, I mechanically connect the
operating motor with the elevator car in any suitable manner, and I place the device
by means of which the electro-motive force of the supplying generator is controlled,
upon the said moving elevator car. I have shown in Figures 7 and 8 this system,
the controlling device being one which also controls and reverses the direction of

page_text: rotation of the motor. The use of such reversing device is however evidently not
confined to elevators alone, but it may be employed with motors for other purposes
as well.
Figure 7 shows the devices used in connection with a "three-wire" system of
electrical distribution, of which pn and c are the conductors.
A circuit 1, 2 from the outer conductors, supplies the field and armature of the
intermediate motor A, and which is mechanically connected with the armature of
the intermediate generator B, and which supplies the armature of the working
motor C, which is suitably geared to the elevator car D to operate the same.
The field of the motor is supplied by a multiple are circuit from the three wire
system.
Within the elevator car is the controlling device consisting of two sets of
adjustable resistance coils a and a!, and between them a switch handle b, to which is
permanently connected the wire 3 which passes to the field magnet of the
generator B and thence to the neutral wire of the three wire system. From the
extremity of the resistance coila a, wire 4 extends to the positive conductor of the
three wire circuit, and from resistance a¹ wire 5 extends to the negative three-wire
conductors.
'
To start the elevator, the switchi handle b is moved upon either resistance, a or a³,
whereupon the field magnet of generator Bis energized, and said generator supplies
the armature of motor C, so as to start the car, but the electro-motive force supplied
to the motor armature is low on account of the resistance a in the field circuit of
the intermediate generator. To increase the speed the switch arm is moved so as to
cut out resistance, which varies simply the electro-motive force supplied to the
armature of the working motor and does not affect the field magnet thereof, so that
variations in speed are produced for any given weight moved without varying the
torque or efficiency and without altering the non-sparking point. To run the motor
in the opposite direction, the switch arm is moved to the adjustable resistance a',
which reverses the field magnet of the generator B and so reverses the rotation of
the motor C.
In Figure 8 E is an engine or motor of any kind mechanically connected with
the armature of the generator B to run the same, Generator B supplies armature
of motor C which is connected with the elevator car. G is an exciting machine
run preferably by the same power as the generator B and supplying by separate
multiple arc circuits the fields of the generator B and motor C. The field circuit
of the generator B runs to the elevator car and is there connected with a suitable
reversing and resistanco controlling switch H by means of which the field magnet
of the generator B is strengthened, weakened, or reversed, to raise, lower, and
reverse the electro-motive force on the armature supplying circuit of the motor C
with the result hereinbefore described.
Having now particularly described and ascertained the nature of my Baid
invention, and in what manner the same is to be performed I declare that what I
claim is :-
1. The method herein described of operating and regulating an electric motor,
consisting in supplying its field magnet and its armature from separate sources
changing the amperes of current supplied to the armature to vary the torque
changing the volts or electro-motive force on the armature cironit to vary the speed,
and reversing the electro-motive force on the armature supplying circuit to reverse
the direction of rotation of the motor.
2. The method herein described of regulating and reversing the motion of an
electric motor, which consists in regulating the electro-motive force of the generator
supplying the armature of said motor to vary the speed, and reversing the electro-
motive force of such generator to reverse the motor.
3. The combination of a main source of electrical supply, an intermediate motor
having its armature and field magnet both connected with said source, an inter-

page_text: mediate electric generator operated by the said intermediate motor, and provided
with means for varying its clectro-motive force, and a working motor having its
armature supplied from said intermediate generator and its field magnet otherwise
supplied, substantially as hereinbefore described.
4. The combination of an electro-dynamic motor and a dynamo-electric generator,
having their armatures electrically connected together, and both having separately
excited field magnets, and means for varying the strength of the field magnet of the
generator, substantially as set forth..
5. The method of reversing the direction of rotation of a motor having a sepa-
rately excited field magnet, which consists in reversing the electro-motive force of
the generator supplying the arinature of the motor, substantially as set forth.
6. The combination of a moveable elevator car, a stationary electric motor
connected with said car to move it, a generator supplying the armature of said
motor, a separate source of supply for the field magnet of said motor, and a regulator
on the elevator car for varying and reversing the electro-motive force of the
generator, substantially as herein before described. -
B. J. B. MILLS,
By Harris & Mills,
23, Southampton Buildings, London, W.C., Agents.