Improvements in Indirect Regulation of Dynamo-electric Machinery.
Year: 1897

page_text: PROVISIONAL SPECIFICATION.
Improvements in Indirect Regulation of Dynamo-electric Machinery.
I, WALLACE FAIRWEATHER, C.E., of 62, Saint Vincent Street, in the City of
Glasgow, Chartered Patent Agent, do hereby declare the nature of this invention
(as communicated to me by the Crocker-Wheeler Electric Company, Manufacturers,
a corporation organized under the laws of the State of New Jersey, U.S.A., and
having its principal office at 39, Cortlandt Street, New York, State of New York,
United States of America) to be as follows:-
:―
The systems herein described are applicable to the regulation of dynamo-electric
machinery generally, whether the machinery to be regulated is used as a generator
or as a motor. The broad purpose is to regulate motors which are to be connected
with their armatures in a constant-current circuit in series, and with their fields
in a constant-potential circuit in multiple. There is provided means for regulat-
ing each motor independently of the others, so as to maintain a constant or
regulatable speed under varying load, by controlling the field of the motor to be
regulated. It is intended to claim the specific arrangements hereinafter described
for effecting the regulation of the motors, and also for producing a constant
current under a varying load, and a constant-potential under a varying load. But
it must be understood that the system described as being intended to produce a
constant-potential under varying load is not limited to use with a generator, nor
is the system for producing a constant current under varying load limited to use with
a generator, nor is the system for securing constant speed under varying load limited
to a motor. The various applications of the different features of the system will be
explained in the course of the specification.
Referring now to the drawings, which form a part of this specification,
Figure 1 illustrates a system of regulation of a motor to secure constant or
controllable speed under varying load;
Figure 2 illustrates a modification of the system of Fig. 1;
Figure 3 illustrates a system for regulating a generator to secure a constant
current under a varying load;
Figure 4 illustrates a system for regulating a generator to secure a constant or
controllable potential under a varying load.
Figure 1 shows the armatures of the working motors, which are to be regulated,
connected in series in a circuit supplied from a constant-current source, and their
fields, only one of which is illustrated, connected in multiple in a circuit supplied
from a constant-potential source. According to the present invention, the working
motors are connected in the constant-current and constant-potential circuits, as
stated, and there is added to the apparatus a regulating dynamo-electric machine,
the armature of which is connected in series with the field-coils, or a part of the
field-coils, of the working motor, and is driven in a constant field at a rate which
varies proportionately and simultaneously with the variations in the speed of the
working motor. The strength of the field of the working motor will thus depend
on the balance between a constant electromotive force and the electromotive force

page_text: developed in the armature of the regulating machine, which latter varies with the
speed of the motor armature. Thus the speed of the working-motor armature
remains approximately constant under varying load. All of the circuits of the
working motors may be supplied from a common constant-potential source, or
each may have a local field circuit, as preferred. The expression "working
motor is used above, because one examining the drawing without having read
the full description will readily see which machine this expression refers to. But
hereafter the more accurate term, "the machine to be regulated," will be used
to designate that machine the speed of which it is the object of the invention to
maintain constant under a varying load.
The armatures of the machines to be regulated connected in series in the
constant-current circuit C, as shown, are supplied with a constant current by a
suitable generator G. In the figure under discussion, this generator is indicated
. by a conventional illustration of a constant-current generator. The specific
arrangement for producing. a constant current will be described more fully in
connection with Figure 3, and is not illustrated in Figure 1, because while
applicable to supply the constant current in that figure, it is not strictly limited
to supplying a constant current, and is, moreover, more complex and less readily
understood than the more conventional representation of the constant current
generator. The field C of each of the machines to be regulated is connected in
a local field-circuit, which includes the armature B of the regulating machine
and the generator armature H of the motor-dynamo I H J K, the armatures of
which are mounted rigidly on the same shaft. Normally the armature of the
regulating machine is connected by a belt or other suitable connection to the
armature of the machine to be regulated, and normally opposes a counter-electro-
motive force to the current generated by the generator-armature of the motor-
dynamo. The field of the regulating machine E and the fields I J of the motor-
dynamo and the motor-armature K of the motor-dynamo are all connected in
multiple to a suitable constant-potential generator C, through the constant-potential
circuit CP. In series with the field I of the motor-dynamo is a double rheostat I) D,
and a reversing switch bbdd. The purpose of the rheostat is to control the-speed
which the armature of the machine to be regulated shall maintain, and the revers-
ing switch is for reversing the armature of the machine to be regulated. The
two rheostats D D, are connected with one of the terminals of the field-coil I.
The other terminal is connected with two plates dd. The other plates bb are
connected, each respectively with one of the leads of the constant-potential
circuit CP. The parts DD ddbb are insulated, and the switch is provided with
an insulating switch-arm a, which has two contact plates, one positioned to
connect one of the rheostats I) with one of the plates b and the other positioned
to connect one of the plates 6 with one of the plates d, as shown.
The operation is as follows: The constant-current generator & supplies the
circuit C. This supplies energy to the armature A of the machine to be regulated.
The constant-potential generator P supplies the circuit CP, which supplies energy
to run the motor-dynamo and to charge the field I and the field E. The speed
of the generator-armature H is constant under these conditions, and the electro-
motive force developed in it depends upon the direction and strength of its field I,
which is controlled by the rheostat and reversing switch. The armature B of
the regulating machine runs at a speed which varies with that of the armature A
of the machine to be regulated, which it normally helps to drive, and developes an
electromotive force which varies with the speed. The strength of the field C,
and hence the speed of the armature. A of the machine to be regulated, is
determined by the balancing of the electromotive forces developed in the generator-
armature of the motor-dynamo and the armature of the regulating machine.
Should the speed of the machine to be regulated rise above the predetermined
speed, the electromotive force generated in the armature of the regulating machine
would be increased. In like manner, should the speed in the armature of the
machine to be regulated be diminished, the electromotive force in the armature

page_text: of the regulating machine would be diminished. Since the electromotive force
developed in the armature of the regulating machine, while the machine to be
regulated is run at normal speed, is a counter-electromotive force, any increase
or diminution therein will result in diminution or increase in the strength of the
field of the machine to be regulated, with consequent diminution or increase of
the torque of the armature of the machine to be regulated, resulting in the main-
tenance of practically constant speed. Should the increase in the electromotive
force developed in the regulating machine be so great as to reverse the field of
the machine to be regulated, the armature thereof would tend to reverse and its
speed would be checked.
Small changes in the speed of the armature of the machine to be regulated,
and hence of the regulating machine, may, by the arrangement, make large
changes in the difference between the electromotive force developed in the armature
of the regulating machine and in the generator-armature of the motor-dynamo,
and hence make large changes in the strength of the field of the
machine to be regulated. This principle is of the utmost importance
in securing constant speed with large variations in the load. The
speed of the machine to be regulated will be approximately constant, even with
considerable variations in the strength of the current in the constant-current
circuit. And changes in the potential on the constant-potential circuit produce
two effects in the system which oppose and tend to neutralize each other. Suppose,
for instance, that the potential in the constant-potential circuit falls. This tends
to cause a decrease in the current developed by the generator armature but it is
accompanied by a decrease in the field-strength of the regulating machine, which
diminishes the counter-electromotive force developed in the regulating machine,
and tends to increase the strength of the current in the field-circuit of the machine
to be regulated. On the other hand, should the potential rise in the constant-
potential circuit, the resulting tendency to increase the current in the field-circuit
of the machine to be regulated will be opposed by the resulting increase in the
counter-electromotive force generated in the armature of the regulating machine.
Thus the system secures constant speed with varying load, in spite of changes in
the constant-current and constant-potential circuits.
In starting up the system described, the proper method is, first to close the
circuit through the armature of the machine to be regulated, then to close the
circuit of the field and armature of the motor part of the motor-dynamo, and then
to close the circuit of the field of the dynamo part of the motor-dynamo, and
gradually cut out the resistance therein, until the switch is adjusted for the desired
speed of the machine to be regulated. The switches are generally omitted.
The following modifications may be made in the system described, without
departing from the invention:
1st. Figure 2 illustrates one modification, which differs from the system of
Figure 1 in the omission of the motor-dynamo, the field of the machine to be
regulated and the armature of the regulating machine being connected up in
series with the constant-potential circuit. The construction of the switch is as
follows: The contact strips 123 and 6 are insulated from each other and arranged
in concentric circles or ares of circles. The outer strip 1 is the are of a circle, the
ends of which terminate in sets of resistance coils R. The strip is connected
to one lead of the constant-potential circuit CP. A strip 3, which embraces an
entire circle, is connected to the other lead of this constant-potential circuit.
Between strips 1 and 3 are two strips 2, each extending through less than a semi-
circle of arc. These two strips are the terminals of a conductor which includes
the field-coils C of the machine to be regulated and the armature B of the
regulating machine in series with each other. Two brushes 4 and 5 at either
end of the insulated arm, pivoted in the centre of the switch complete the reversing
and starting part of the switch, and constitute a complete switch for the field or
the working inotor. There are also two sets of resistance coils r r connected to a
terminal of the field-coils of the regulating machine and an inner ring 6 connected

page_text: to one of the leads of the constant-potential circuit, or to the plate 1. These.
with contact plate 7 which is mounted on the same arm with plates 4 and 5, form
the circuit-closing and regulating switch for the field f of the regulating machine.
The contact strips of these two switches and their contact plates are so set relatively
to each other that the two switches shall be opened and closed together. These
sets of resistance coils are for starting and stopping, and for obtaining extremely
low speeds of the armature of the working motor, for various purposes. The speeds
obtained when these coils are called into requisition are not so constant as the
speeds obtained in other positions of the apparatus. Usually the resistance
coils R will not be used concurrently with the coils r, since double regulation of
the field F by resistance and indirectly through the regulating machine is not
desirable. A certain speed corresponds to each button of the resistance coils 7
which the working motor will attain and maintain approximately under varying
load.
The constant-potential field-circuit being open at the switch, is closed through
the field-coils C and f by moving the switch arm to the left or right of the zero
position, according to the direction in which the working motor is to be driven.
The current passes from the common constant-potential source P through the
switch, through the field-coils C of the machine to be regulated, and the armia-
ture B of the regulating machine; also the current passes from the common
constant-potential source through the regulator 67 r, and the field f of the regulat-
ing machine.
As soon as there is any field established for the machine to be
regulated, its armature begins to revolve under the influence of the current in the
constant-current circuit. The armature B of the regulating machine is thereby
also driven, being, as is shown, coupled to the armature of the machine to be
regulated. The field C of the machine to be regulated is then further strengthened
by cutting out the resistance coils R, and when these are passed, the switch-arm
of the regulator 67 r, has reached the set of buttons connected with the resistance
coils, and is set on any desired button. This determines the speed at which the
machine to be regulated shall run. The regulating machine is driven by the
current from the constant-potential circuit, and opposes to the current through
the field-coils C a counter-electromotive force which regulates the strength of the
field of the machine to be regulated. If the load on the machine be lessened and
this machine in consequence speeds up, the regulating machine will also speed up
and its counter-electromotive force will be increased, whereby the field of the
machine to be regulated will be cut down, and vice versa, if the load is increased,
the field strength of the machine to be regulated will be increased. Increase in
the field strength of the machine to be regulated prevents decrease in the speed of
its armature, and diminution of its field strength prevents increase in the speed
of its armature. Small changes in the speed of the armature of the machine to
be regulated, and nence of the regulating machine, make large changes in the strength
of the field of the machine to be regulated. Therefore, the speed of the machine
to be regulated can be kept nearly constant, even with large variations in the
load. The energy consumed at the regulating machine helps to drive the machine
to be regulated. Should the speed be so increased as to cause the regulating
machine to generate current, the field of the machine to be regulated will be
reversed, and its armature will be checked. The armature of the regulating
machine now acts as a drag, as does also the field of the machine to be regulated.
The speed will therefore quickly fall to normal. Since the energy required by the
field of any machine is exceedingly small, compared with the energy required by
the armature, the regulating machine in the system may be small, compared with
a controller which controls the energy supplied to the armature, though not so
small in the system of Figure 2 as in the system of Figure 1.
2nd. In the arrangement of Figures 1 or 2 the field-coil E can be connected
in and energized from the constant-current circuit instead of being supplied from
the constant-potential circuit. This is obvious, since either circuit gives a con-
stant excitation, and that is all that is required.
3rd. The elaborate switch shown in the arrangement of Figure 2 may be

page_text: omitted, the field-coils of the regulating machine and the machine to be regulated
being connected in multiple to the constant-potential circuit, each in series through
a rheostat.
4th. The field magnet of the machine to be regulated may be provided with two
opposing coils.
It will be seen that the essence of the invention is the method of regulating
electric motors, which consists in supplying the armature with a constant current.
supplying the field from a source of energy which is separate from that which
supplies the armature, and which is preferably a constant-potential source, and
varying the field-strength of the machine to be regulated by varying the effective
electromotive force in the field-circuit with the speed of the armature of the
machine to be regulated. This is preferably accomplished by balancing a constant
electromotive force against a variable electromotive force, the latter in the arrange-
ment shown being developed in the armtaure of a regulating machine which is
mechanically connected to the armature of the machine to be regulated, and the
speed of which is varied proportionately and simultaneously with the speed of
the arinature of the machine to be regulated. And provision is made also for con-
trolling the direction of the motion of the armature of the machine to be regulated,
as well as its speed. No attempt is made to indicate all the different combina-
tions which can be adopted to produce the desired effect, but merely to show a
number of the general forms, with a view to indicating that the specific arrange-
ment may be widely varied.
Figure 3 illustrates the preferred form for producing a constant-current under
varying load. The generator G F of this figure might take the place of the
generator G of Figure 1, and supply the circuit C of that figure, which is the
equivalent of the circuit C° of Figure 3, with the constant-current. By a varying
load in this case is meant variations in the amount of energy which the generator
is called upon to supply. The same expression has heretofore been used to denote
variation in the amount of work which a motor is called upon to do, in the
arrangement, for instance, of Figure 1.
The field-coil F of the machine F G to be regulated is supplied by the armature L
of a regulating machine L M N, the field-coil F and armature L being connected
in series. The armature of the regulating machine is preferably connected to
the armature of the machine to be regulated by a belt or other suitable device.
so that the two are run together. The field of the regulating machine is provided
with two coils, one of which M is a branch from the circuit CP and is supplied
from the constant-potential source P, represented conventionally, and is constant
in strength, and the other of which N is connected in circuit C in series with the
armature G. These two coils M and N are wound so as to oppose each other; and
the field strength of the regulating machine is due to the difference between the
two. The excitation due to the coil N is normally less than that due to the coil M.
Thus the field of the machine to be regulated is normally excited by the constant-
potential circuit. The means controlled by the constant-current circuit acts merely
in opposition. The armature of the machine to be regulated and of the regulating
machine are both driven at a practically constant speed, and the energy developed
in them will depend upon their fields. When the machine G is developing the
normal amount of current, the balance between the excitation of the field-coils M
and N will be such as to give to the regulating machine the strength of the field
which will cause it to develop at the normal speed an electromotive force just
sufficient to permit what may be called the normal current to flow through the
field-coils F. If the current falls in the armature of the machine to be regulated,
this will result in a decrease in the excitation of the coil N, and a consequent
increase in the strength of the field of the regulating machine, and also, of
course, in the field of the machine to be regulated. If, on the other hand, the
strength of the current generated by the machine to be regulated should increase
beyond the normal strength, the field-strength of the regulating machine will be
diminished, and thereby the field-strength of the machine to be regulated will
be diminished. These variations in the field-strength of the machine to be regulated

page_text: will result, of course, in the corresponding variations of the current generated
Since the field of the regulating machine is the resultant of two excitations which
are opposed to each other, small changes in the current may, by the. arrangement,
result in comparatively large changes in the strength of the regulating machine,
the therefore of the machine to be regulated, and the current generated by the
machine to be regulated is thus kept constant.
The arrangement illustrated in Figure 3, may be modified as follows:
1. As a suitable means for driving the armature of the machine to be regulated
with a constant speed, it may be connected up mechanically with the armature
of a shunt-wound motor, which is connected in the constant-potential circuit in
multiple with the field of the regulating machine connected to that circuit. It
is well known that a shunt-wound motor connected with a constant-potential
circuit runs at a uniform speed, and hence the armature of the machine to be
regulated and of the regulating machine, will be driven at a constant speed.
2. The field-coil of the regulating machine which is connected with the constant-
potential circuit may be omitted, so that the field-strength of the regulating
machine will depend entirely upon the excitation due to the coil which is in the
constant current circuit, and the field-circuit of the machine to be regulated,
instead of being closed upon the armature of the regulating machine, may be
connected through that armature to the leads of the constant-potential circuit. In
this case the armature of the regulating machine may, by arrangement, oppose a
counter-electromotive force to that of the constant potential-circuit, which counter-
electromotive force will be increased by increase in the current developed in the
machine to be regulated, and will be diminished by diminution in the current
developed in the machine to be regulated. Increase in the counter-electromotive
force of the regulating machine will result in the diminution in the field-strength
of the machine to be regulated, and consequently in the diminution in the counter-
electromotive force developed in the regulating machine will result in increase in
the field-strength of the machine to be regulated, and consequently in increase
in the current generated by the machine to be regulated. Here again a small
change in the field-strength of the regulating machine, and consequently of the
counter-electromotive force developed by the regulating machine, may, by arrange-
ment result in large change in the field-strength of the machine to be regulated,
whereby the current will be kept constant. It will be seen that this arrangement
is fundamentally identical with that of Figure 2, if, as above suggested, in the
system of Figure 2 the field of the regulating machine be supplied from the
constant-current circuit.
3. In the arrangement of Figure 3, the constant-current circuit, instead of
being, as there shown, independent of the constant-potential circuit, may be a
branch of the constant-potential circuit. In such an arrangement the machine to
be regulated may, according to the direction of its field, run as a motor, consum-
ing part of the energy supplied from the constant-potential circuit, in which case
the energy consumed in it is used in driving the machinery to which its armature
is coupled, or it may be driven by this machine and generate volts which are added
to those of the constant-potential source. In the latter case field-coils of the
regulating machine should be so related to each other that they will
neutralize each other when the normal current is flowing in the main
circuit. If the current falls off, the excitation of the constant field coil
of the regulating machine will predominate, and the direction of the
winding should be such that the field developed for the machine to
be regulated will cause it to generate volts which are added to those of the
constant-potential source. If, on the other hand, the current in the main
circuit should rise above the normal current, the excitation pro-
duced by the variable field-coil of the regulating machine will predominate. The
machine to be regulated will then run as a motor, and consume a part of the
energy of the constant-potential source, opposing a counter-electromotive force
which cuts down the voltage thereof. For reasons above explained, a small
change in the field-coil of the regulating machine produces a large change in

page_text: the resultant field, and the armature of the regulating machine being short-circuited, a
disproportionately large current will be developed by it, even in a weak field,
hence small changes in the current in the main circuit effect large changes in
the field of the machine to be regulated, and in the voltage developed in its
armature.
Figure 4 illustrates an arrangement for producing a constant-potential or a
potential which can be regulated under a varying load, by which is meant
variation in the amount of energy which the machine is called upon to generate.
The system, however, is applicable to the regulation of dynamo-electric machinery
whether the machinery is used as a dynamo or as a motor. If it is to be used as
a dynamo, it will supply to the leads a constant-potential current, or, in certain
cases, a current the potential of which is maintained more constant than it would
be if the regulating machine was not used; or, as is often desirable, the machine
to be regulated is used to supply a current the potential of which rises as the
load increases, or by a reversal of the operation, may supply a current the potential
of which decreases as the current itself increases. If the machine to be regulated
is to be used as a motor, it will be connected between the leads of a constant-
potential circuit, and except as hereinafter stated, it will run at a constant speed
with a varying load. The system will be described as it operates as a generator,
and as such it may be used in place of the constant-potential source in Figures 1
and 3. It is not, however, shown in either of those figures because of its being
complicated and to avoid the implication that it is intended only for use as a
generator.
The machine to be regulated should be shunt-wound, or separately excited. Its
armature is connected to the leads of the system, and all or a part of the field-
coils of the regulating machine are also connected with the leads in series with
the armature of the machine to be regulated. The armature of the regulating
machine is placed in series with all or part of the field-coils of the machine to
be regulated. The regulating machine is geared to other apparatus so that it shall
run at a constant speed. It is shown as a part of a motor-dynamo UTSW V.
While the machine to be regulated may be separately excited, ordinarily a shunt-
wound machine will be employed. In this case, the armature of the regulating
machine is placed in the shunt with the field-coils of the machine to be regulated,
the two being connected across or in multiple with the line and in series with
each other. In this arrangement it will be seen that the field-coil of the regulating
machine, which is in series with the armature of the machine to be regulated,
is supplied by, and its field-strength is dependent upon the current in the armature
of the machine to be regulated, and is independent of the current in its own
armature, except that there will be some reaction by reason of the current in its
own armature, which, however, is not relied upon for effecting regulation. On
the other hand the field of the machine to be regulated is in series with its own
armature, as well as that of the regulating machine, and the field-strength of the
machine to be regulated is, therefore, dependent upon the algebraic sum of the
voltages of both machines. If the current in the armature of the machine to be
regulated increases, for instance, upon reduction of the resistance of the circuit,
the potential tends to fall, in which case the field-strength of the machine to be
regulated should be increased. Conversely, if the current diminishes, for instance,
upon increase of resistance in the circuit, the potential tends to rise and the field-
strength should be aiminished. The regulating machine will either be run as a
motor by the current in the field-circuit, and help drive the machinery to which
it is geared, in which case it will act as a retard, developing a counter-electromotive
force which cuts down the effective electromotive force of this circuit, and diminish
the field-strength of the machine to be regulated, or, the regulating machine
will be run by the machinery to which it is geared, in which case it will act as a
boost, generating an electromotive force which will he added to the electromotive
force in the field-circuit, thereby increasing the effective electromotive force
therein and increasing the field-strength of the machine to be regulated. It may

page_text: be changed from one of these forms to the other by merely changing the
polarity of the field of the regulating machine without changing the direction
of rotation of its armature. The regulating machine may also be so arranged
that without change in the connections, it shall under some conditions be run as
a motor by the current in the field-circuit, acting as a retard to the electromotive
force in the circuit, and under other conditions be run as a generator by the
machinery to which it is geared, acting as a boost to the electromotive force in the
circuit. These three methods are called respectively the retard, the boost, and the
retard-and-boost methods. In each of the three methods the speed of the armature
of the regulating machine should be kept constant, and the field of the regulating
machine be varied with the current in the main machine.
In the figure under consideration the system is shown for practising the retard,
boost, and retard-and-boost methods. If the system is used to practise a retard
or a boost method, the effects may vary in either direction from maximum to
zero; and if it is used to practise a retard-and-boost method, the regulating
machine may pass gradually from maximum retard to maximum boost, or, from
maximum boost to maximum retard, with increase of current in either direction in
the armature of the machine to be regulated. This is controiled by the direction
of the field of the regulating machine. The field-coils of the regulating machine
are connected to line through a reversing switch. If used as a retard-and-boost,
the regulating machine need not be so large as where it is used always as a retard
or always as a boost. For a one-hundred kilowatt main machine, a regulating
machine of about one-half horsepower capacity could do the work when acting as
a retard-and-boost. There is on the field of the regulating machine, in addition
to the coils T, which are connected to the line in series with the armature of the
main machine, a constant excitation, which may be in the form of coils U,
supplied from a storage battery, or the like. But these coils are shown as
supplied from leads taken from the mains, and where the system is a constant-
potential system, the excitation will, of course, be practically constant. Where
it is specified that one of the coils of the regulating machine has an excitation that
is constant, the meaning is that it is supplied from some independent source, or
from the main machine in the manner stated. The two field-coils of the regulating
machine always oppose each other; and may be so wound as to be balanced while
there is an assumed mean or normal current in the armature of the machine to be
regulated. The machine to be regulated is then by assumption supplying the
line with current of the desired potential, and is supplying its own field from
the regulating machine. If the current in the line changes the regulating
machine will act as a retard or boost, either increasing or diminishing the
effective electromotive force in the field circuit of the machine to be regulated,
as the current in that machine increases or diminishes. To effect this the field-
coils UT, should be so wound that it will run as a motor when the magnetization
due to the coil U exceeds that of the coil T, and will run as a dynamo when the
magnetization due to the coil T exceeds that of the coil U. The regulating
machine will then start as a motor when the current in the machine to be regulated
is low, and act as a diminishing retard as that current rises toward the mean
strength, and as an increasing boost as that current increases beyond the mean
strength. This is only a particular case. The system is very flexible. For
example, the regulating machine may start as a generator when the current in
the armature of the machine is low, and become a motor when this current rises
beyond the mean strength. The connections of the field-coils of the regulating
machine may be such that the effect of the regulating machine will be either to
increase or to diminish the field of the machine to be regulated, when the latter
is acting as a dynamo, and the current in the armature of the machine to be
regulated increases, or, conversely, the regulating machine may operate to diminish
or increase the field of the machine to be regulated when the latter is acting as
a motor, and the current in the armature of the machine to be regulated
increases.

page_text: An advantage of the system herein described when the machine to be regulated
is running in multiple with other machines, or is used in charging storage
batteries, is that it can never be reversed by a momentary back-current, because the
demagnetizing effect of the back-current is checked by the saturation of the field
of the regulating machine. This may be explained as follows: A series-wound
dynamo cannot be used in multiple with other similar generators, or in multiple
with constant-potential shunt-wound generators, or to charge storage batteries.
This is because its voltage varies with its load, and a slight decrement in the
current delivered, due to accidental reduction in speed, or some other minor cause,
would produce a decrease of voltage which would cause a further decrease of
delivered current, resulting in a still further decrease of voltage, and so on, until
the electromotive force of the dynamo has entirely vanished, and has even been
reversed and carried to a maximum in the opposite direction. An ordinary
compound-wound generator the field-magnets of which are partly series-wound,
has the same characteristics, it being possible to reverse its potential by a
momentary reversed current in the series coils. In this system this is impossible,
because the demagnetizing action due to a reversed current never acts directly upon
the field of the machine to be regulated, but only indirectly through the regulating
machine. It is therefore limited by the saturation of the field of the regulating
machine. Up to the point of reversing and saturating the field of the regulat-
ing machine a reverse current will tend to modify the field of the machine to be
regulated, but this effect will not be increased by any increase in the reverse current
however great.
The system of Figure 4 may be modified by omitting the coil U from the field
of the regulating machine. Other means than that shown may be adopted for
driving the armature of the regulating machine.
Improvements in Indirect Regulation of Dynamo-electric Machinery.
I, WALLACE FAIRWEATHER, C.E., of 62, Saint Vincent Street, in the City of
Glasgow, Chartered Patent Agent, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement: —
The systems herein described are applicable to the regulation of dynamo-electric
machinery generally, whether the machinery to be regulated is used as a generator
or as a motor. The broad purpose is to regulate motors which are to be connected
with their armatures in a constant-current circuit in series, and with their fields
in a constant-potential circuit in multiple. There is provided means for regulat
ing each motor independently of the others, so as to maintain a constant or
regulatable speed under varying load, by controlling the field of the motor to be
regulated. It is intended to claim the specific arrangements hereinafter described
for effecting the regulation of the motors, and also for producing a constant
current under a varying load, and a constant-potential under a varying load. But
it must be understood that the system described as being intended to produce a
constant-potential under varying load is not limited to use with a generator, nor
is the system for producing a constant current under varying load limited to use with
a generator, nor is the system for securing constant speed under varying load limited
to a motor. The various applications of the different features of the system will be
explained in the course of the specification.

page_text: Referring now to the drawings left with the Provisional Specification, which form a
part of this specification,
Figure 1 illustrates a system of regulation of a motor to secure constant or
controllable speed under varying load.
Figure 2 illustrates a modification of the system of Fig. 1;
Figure 3 illustrates a system for regulating a generator to secure a constant
current under a varying load;
Figure 4 illustrates a system for regulating a generator to secure a constant or
controllable potential under a varying load.
Figure 1 shows the armatures of the working motors, which are to be regulated,
connected in series in a circuit supplied from a constant-current source, and their
fields, only one of which is illustrated, connected in multiple in a circuit supplied
from a constant-potential source. According to the present invention, the working
motors are connected in the constant-current and constant-potential circuits, as
stated, and there is added to the apparatus a regulating dynamo-electric machine,
the armature of which is connected in series with the field-coils, or a part of the
field-coils, of the working motor, and is driven in a constant field at a rate which
varies proportionately and simultaneously with the variations in the speed of the
working motor. The strength of the field of the working motor will thus depend
on the balance between a constant electromotive force and the electromotive force
developed in the armature of the regulating machine, which latter varies with the
speed of the motor armature. Thus the speed of the working-motor armature
remains approximately constant under varying load. All of the circuits of the
working motors may be supplied from a common constant-potential source, or
each may have a local field circuit, as preferred. The expression "working
motor" is used above, because one examining the drawing without having read
the full description will readily see which machine this expression refers to. But
hereafter the more accurate term, "the machine to be regulated," will be used
to designate that machine the speed of which it is the object of the invention to
maintain constant under a varying load.
The armatures of the machines to be regulated connected in series in the
constant-current circuit C, as shown, are supplied with a constant current by a
suitable generator G. In the figure under discussion, this generator is indicated
by a conventional illustration of a constant-current generator. The specific
arrangement for producing a constant current will be described more fully in
connection with Figure 3, and is not illustrated in Figure 1, because while
applicable to supply the constant current in that figure, it is not strictly limited
to supplying a constant current, and is moreover, more complex and less readily
understood than the more conventional representation of the constant current
generator. The field C of each of the machines to be regulated is connected in
a local field-circuit, which includes the armature B of the regulating machine
and the generator armature H of the motor-dynamo I H J K, the armatures of
which are mounted rigidly on the same shaft. Normally the armature of the
regulating machine is connected by a belt or other suitable connection to the
arinature of the machine to be regulated, and normally opposes a counter-electro-
motive force to the current generated by the generator-armature of the motor-
dynamo. The field of the regulating machine E and the fields I J of the motor-
dynamo and the motor-armature K of the motor-dynamo are all connected in
multiple to a suitable constant-potential generator C, through the constant potential
circuit CP. In series with the field I of the motor-dynamo is a double rheostat D D,
and a reversing switch bbdd. The purpose of the rheostat is to control the speed
which the armature of the machine to be regulated shall maintain, and the revers-
ing switch is for reversing the armature of the machine to be regulated. The
two rheostats D D, are connected with one of the terminals of the field-coil I.
The other terminal is connected with two plates Dd. The other plates b b are
connected, each respectively with one of the leads of the constant-potential
circuit CP. The parts DD ddbb are insulated, and the switch is provided with

page_text: an insulating switch-arm a, which has two contact plates, one positioned to
connect one of the rheostats 1) with one of the plates and the other positioned
to connect one of the plates b with one of the plates d, as shown.
The operation is as follows: The constant-current generator G supplies the
circuit C. This supplies energy to the armature A of the machine to be regulated.
The constant-potential generator P supplies the circuit CP, which supplies energy
to run the motor-dynamo and to charge the field I and the field E. The speed
of the generator-armature H is constant under these conditions, and the electro-
motive force developed in it depends upon the direction and strength of its field I,
which is controlled by the rheostat and reversing switch. The armature B of
the regulating machine runs at a speed which varies with that of the armature A
of the machine to be regulated, which it normally helps to drive, and developes an
electromotive force which varies with the speed. The strength of the field C,
and hence the speed of the armature A of the machine to be regulated, is
determined by the balancing of the electromotive forces developed in the generator-
armature of the motor-dynamo and the armature of the regulating machine.
Should the speed of the machine to be regulated rise above the predetermined
speed, the electromotive force generated in the armature of the regulating machine
would be increased. In like manner, should the speed in the armature of the
machine to be regulated be diminished, the electromotive force in the armature
of the regulating machine would be diminished. Since the electromotive force
developed in the armature of the regulating machine, while the machine to be
regulated is run at normal speed, is a counter-electromotive force, any increase
or diminution therein will result in diminution or increase in the strength of the
field of the machine to be regulated, with consequent diminution or increase of
the torque of the armature of the machine to be regulated, resulting in the main-
tenance of practically constant speed. Should the increase in the electromotive
force developed in the regulating machine be so great as to reverse the field of
the machine to be regulated, the armature thereof would tend to reverse and its
speed would be checked.
Small changes in the speed of the armature of the machine to be regulated,
and hence of the regulating machine, may, by the arrangement, make large
changes in the difference between the electromotive force developed in the armature
of the regulating machine and in the generator-armature of the motor-dynamo,
and hence fake large changes in the strength of the field of the
machine to be regulated. This principle is of the utmost importance.
the load. The
in securing constant speed with large variations in
speed of the machine to be regulated will be approximately constant, even with
considerable variations in the strength of the current in the constant-current
circuit. And changes in the potential on the constant-potential circuit produce
two effects in the system which oppose and tend to neutralize each other. Suppose,
for instance, that the potential in the constant-potential circuit falls. This tends
to cause a decrease in the current developed by the generator armature but it is
accompanied by a decrease in the field-strength of the regulating machine, which
diminishes the counter electromotive force developed in the regulating machine,
and tends to increase the strength of the current in the field-circuit of the machine
to be regulated. On the other hand, should the potential rise in the constant-
potential circuit, the resulting tendency to increase the current in the field-circuit
of the machine to be regulated will be opposed by the resulting increase in the
counter-electromotive force generated in the armature of the regulating machine.
Thus the system secures constant speed with varying load, in spite of changes in
the constant-current and constant-potential circuits.
In starting up the system described, the proper method is, first to close the
circuit through the armature of the machine to be regulated, then to close the
circuit of the field and armature of the motor part of the motor-dynamo, and then
to close the circuit of the field of the dynamo part of the motor-dynamo, and

page_text: '
gradually cut out the resistance therein, until the switch is adjusted for the desired
speed of the machine to be regulated. The switches are generally omitted.
The following modifications may be made in the system described, without
departing from the invention:
1st. Figure 2 illustrates one modification, which differs from the system of
Figure 1 in the omission of the motor-dynamo, the field of the machine to be
regulated and the armature of the regulating machine being connected up in
series with the constant-potential circuit. The construction of the switch is as
follows: The contact strips 1 2 3 and 6 are insulated from each other and arranged
in concentric circles or arcs of circles. The outer strip 1 is the arc of a circle, the
ends of which terminate in sets of resistance coils R. The strip is connected
to one lead of the constant-potential circuit OP. A strip 3, which embraces an
entire circle, is connected to the other lead of this constant-potential circuit.
Between strips 1 and 3 are two strips 2, each extending through less than a semi-
circle of arc.
These two strips are the terminals of a conductor which includes
the field-coils C of the machine to be regulated and the armature B of the
regulating machine in series with each other. Two brushes 4 and 5 at either
end of the insulated arm, pivoted in the centre of the switch complete the reversing
and starting part of the switch, and constitute a complete switch for the field of
the working-motor. There are also two sets of resistance coils connected to a
terminal of the field-coils of the regulating machine and an inner ring 6 connected
to one of the leads of the constant-potential circuit, or to the plate 1. These,
with contact plate 7 which is mounted on the same arm with plates 4 and 5, form
the circuit-closing and regulating switch for the field f of the regulating machine.
The contact strips of these two switches and their contact plates are so set relatively
to each other that the two switches shall be opened and closed together. These
sets of resistance coils are for starting and stopping, and for obtaining extremely
low speeds of the armature of the working motor, for various purposes. The speeds
obtained when these coils are called into requisition are not so constant as the
speeds obtained in other positions of the apparatus. Usually the resistance
coils R will not be used concurrently with the coils r, since double regulation of
the field F by resistance and indirectly through the regulating machine is not
desirable. A certain speed corresponds to each button of the resistance coils r
which the working motor will attain and maintain approximately under varying
load.
The constant-potential field-circuit being open at the switch, is closed through
the field-coils C and f by moving the switch arm to the left or right of the zero
position, according to the direction in which the working motor is to be driven.
The current passes from the common constant-potential source P through the
switch, through the field-coils C of the machine to be regulated, and the arma-
ture B of the regulating machine; also the current passes from the common
constant-potential source through the regulator 67r, and the field f of the regulat-
ing machine.
As soon as there is any field established for the machine to he
regulated, its armature begins to revolve under the influence of the current in the
constant-potential circuit. The armature B of the regulating machine is thereby
also driven, being, as is shown, coupled to the armature of the machine to be
regulated. The field C of the machine to be regulated is then further strengthened
by cutting out the resistance coils R, and when these are passed, the switch arın
of the regulator 67 r, has reached the set of buttons connected with the resistance
coils, and is set on any desired button. This determines the speed at which the
machine to be regulated shall run. The regulating machine is driven by the
current from the constant-potential circuit, and opposes to the current through
the field-coils C a counter-electromotive force which regulates the strength of the
field of the machine to be regulated. If the load on the machine be lessened and
this machine in consequence speeds up, the regulating machine will also speed up
and its counter-electromotive force will be increased, whereby the field of the
machine to be regulated will be cut down, and vice versa, if the load is increased

page_text: the field strength of the machine to be regulated will be increased. Increase
in the field strength of the machine to be regulated prevents decrease in the
speed of its armature, and diminution of its field strength prevents increase in
the speed of its armature. Small changes in the speed of the armature of the
machine to be regulated, and hence of the regulating machine, make large changes
in the strength of the field of the machine to be regulated. Therefore, the speed
of the machine to be regulated can be kept nearly constant, even with large
variations in the load. The energy consumed at the regulating machine helps
to drive the machine to be regulated. Should the speed be so increased as to
cause the regulating machine to generate current, the field of the machine to
be regulated will be reversed, and its armature will be checked. The armature
of the regulating machine now acts as a drag, as does also the field of the
machine to be regulated. The speed will therefore quickly fall to normal. Since
the energy required by the field of any machine is exceedingly small, compared
with the energy required by the armature, the regulating machine in the
system may be small, compared with a controller which controls the energy sup-
plied to the armature, though not so small in the system of Figure 2 as in the
system of Figure 1.
2nd. In the arrangement of Figures 1 or 2 the field-coil E can be connected
in and energized from the constant-current circuit instead of being supplied
from the constant-potential circuit. This is obvious, since either circuit gives a
constant excitation, and that is all that is required.
3rd. The elaborate switch shown in the arrangement of Figure 2
omitted, the field-coils of the regulating machine and the machine to be regulated
may be
being connected in multiple to the constant-potential circuit, each in series
through a rheostat.
4th. The field magnet of the machine to be regulated may be provided with two
opposing coils.
It will be seen that the essence of the invention is the method of regulating
electric motors, which consists in supplying the armature with a constant current,
supplying the field from a source of energy which is separate from that which
supplies the armature, and which is preferably a constant-potential source, and
varying the field-strength of the machine to be regulated by varying the effective
electromotive force in the field circuit with the speed of the armature of the
machine to be regulated. This is preferably accomplished by balancing a constant
electromotive force against a variable electromotive force, the latter in the arrange-
ment shown being developed in the armature of a regulating machine which is
mechanically connected to the armature of the machine to be regulated, and the
speed of which is varied proportionately and simultaneously with the speed of
the armature of the machine to be regulated. And provision is made also for con-
trolling the direction of the motion of the armature of the machine to be regulated,
as well as its speed. No attempt is made to indicate all the different combina-
tions which can be adopted to produce the desired effect, but merely to show, a
number of the general forms, with a view to indicating that the specific arrange-
ment may be widely varied.
Figure 3 illustrates the preferred form for producing a constant-current under
varying load. The generator G F of this figure might take the place of the
generator G of Figure 1, and supply the circuit C of that figure, which is the
equivalent of the circuit C of Figure 3, with the constant-current. By a varying
load in this case is meant variations in the amount of energy which the generator
is called upon to supply. The same expression has heretofore been used to
denote variation in the amount of work which a motor is called upon to do, in the
arrangement, for instance, of Figure 1.
The field-coil F of the machine F G to be regulated is supplied by the arma-
ture L of a regulating machine L M N, the field-coil F and armature L being
connected in series. The armature of the regulating machine is preferably
connected to the armature of the machine to be regulated by a belt or other

page_text: suitable device, so that the two are run together. The field of the regulating
machine is provided with two coils, one of which is a branch from the
circuit CP and is supplied from the constant-potential source P, represented
conventionally, and is constant in strength, and the other of which N is con-
nected in circuit C° in series with the armature G. These two coils M and N are
wound so as to oppose each other; and the field-strength of the regulating
machine is due to the difference between the two. The excitation due to the coil N
is normally less than due to the coil M. Thus the field of the machine to be
regulated is normally excited by the constant-potential circuit. The means con-
trolled by the constant-current circuit acts merely in opposition. The armatures
of the machine to be regulated and of the regulating machine are both driven
at a practically constant speed, and the energy developed in them will depend
upon their fields. When the machine G is developing the normal amount of
the current, the balance between the excitation of the field-coils M and N will
be such as to give to the regulating machine the strength of the field which
will cause it to develop at the normal speed an electromotive force just sufficient
to permit what may be called the normal current to flow through the field-
coils F. If the current falls in the armature of the machine to be regulated,
this will result in a decrease in the excitation of the coil N, and a consequent
increase in the strength of the field of the regulating machine, and also, of
course, in the field of the machine to be regulated. If, on the other hand, the
strength of the current generated by the machine to be regulated should increase
beyond the normal strength the field-strength of the regulating machine will be
diminished, and thereby the field-strength of the machine to be regulated will
be diminished. These variations in the field-strength of the machine to be
regulated will result, of course, in the corresponding variations of the current
generated. Since the field of the regulating machine is the resultant of two
excitations which are opposed to each other, small changes in the current may,
by the arrangement, result in comparatively large changes in the strength of
the regulating machine, and therefore of the machine to be regulated, and the
current generated by the machine to be regulated is thus kept constant.
.
The arrangement illustrated in Figure 3, may be modified as follows:
1. As a suitable means for driving the armature of the machine to be regulated
with a constant speed, it may be connected up mechanically with the armature
of a shunt-wound motor, which is connected in the constant-potential circuit in
multiple with the field of the regulating machine connected to that circuit. It
is well known that a shunt-wound motor connected with a constant-potential
circuit runs at a uniform speed, and hence. the armature of the machine to be
regulated and of the regulating machine, will be driven at a constant speed.
2. The field-coil of the regulating machine which is connected with the con-
stant-potential circuit may be omitted, so that the field-strength of the regulating
machine will depend entirely upon the excitation due to the coil which is in the
constant-current circuit, and the field-circuit of the machine to be regulated,
instead of being closed upon the armature of the regulating machine, may be
connected through that armature to the leads of the constant-potential circuit. In
this case the armature of the regulating machine may, by arrangement, oppose a
counter-electromotive force to that of the constant-potential circuit, which counter-
electromotive force will be increased by increase in the current developed in the
machine to be regulated, and will be diminished by diminution in the current
developed in the machine to be regulated. Increase in the counter-electromotive
force of the regulating machine will result in the diminution in the field-strength
of the machine to be regulated, and consequently in the diminution in the counter-
electromotive force developed in the regulating machine will result in increase in
the field-strength of the machine to be regulated, and consequently in increase
in the current generated by the machine to be regulated. Here again a small
change in the field-strength of the regulating machine, and consequently of the
counter-electromotive force developed by the regulating machine, may, by arrange-

page_text: ment result in large change in the field-strength of the machine to be regulated,
whereby the current will be kept constant. It will be sean that this arrangement
is fundamentally identical with that of Figure 2, if, as above suggested, in the
system of Figure 2 the field of the regulating machine be supplied from the
constant-current circuit.
3. In the arrangement of Figure 3, the constant-current circuit, instead of
being, as there shown, independent of the constant-potential circuit, may be a
branch of the constant-potential circuit. In such an arrangement the machine to
be regulated may, according to the direction of its field, run as a motor, consum-
ing part of the energy supplied from the constant-potential circuit, in which case
the energy consumed in it is used in driving the machinery to which its armature
is coupled, or it may be driven by this machine and generate volts which are added
to those of the constant-potential source. In the latter case field-coils of the
regulating machine should be so related to each other that they will
neutralize each other when the normal current is flowing in the main
circuit. If the current falls off, the excitation of the constant field-coil
of the regulating machine will predominate, and the direction of the
winding should be such that the field developed for the machine to
be regulated will cause it to generate volts which are added to those of the
constant-potential source. If, on the other hand, the current in the main
circuit should rise above the normal current, the excitation
pro-
duced by the variable field-coil of the regulating machine will predominate. The
machine to be regulated will then run as a motor, and consume a part of the
energy of the constant-potential source, opposing a counter-electromotive force
which cuts down the voltage thereof. For reasons above explained, a small
change in the field-coil of the regulating machine produces a large change in
the resultant field, and the armature of the regulating machine being short-circuited, a
disproportionately large current will be developed by it, even in a weak field,
hence small changes in the current in the main circuit effect large changes in
the field of the machine to be regulated, and in the voltage developed in its
armature.
Figure 4 illustrates an arrangement for producing a constant-potential or a
potential which can be regulated under a varying load, by which is meant
variation in the amount of energy which the machine is called upon to generate.
The system, however, is applicable to the regulation of dynamo-electric machinery
whether the machinery is used as a dynamo or as a motor. If it is to be used as
a dynamo, it will supply to the leads a constant-potential current, or, in certain
cases, a current the potential of which is maintained more constant that it would
be if the regulating machine was not used; or, as is often desirable, the machine
to be regulated is used to supply a current the potential of which rises as the
load increases, or, by a reversal of the operation, may supply a current the potential.
of which decreases as the current itself increases. If the machine to be regulated
is to be used as a motor, it will be connected between the leads of a constant-
potential circuit, and except as hereinafter stated, it will run at a constant speed
with a varying load. The system will be described as it operates as a generator,
and as such it may be used in place of the constant-potential source in Figures 1
and 3. It is not, however, shown in either of those figures because of its being
complicated and to avoid the implication that it is intended only for use as a
generator.
The machine to be regulated should be shunt-wound, or separately excited. Its
armature is connected to the leads of the system, and all or a part of the field-
coils of the regulating machine, are also connected with the leads in series with
the armature of the machine to be regulated. The armature of the regulating
machine is placed in series with all or part of the field-coils of the machine to
be regulated. The regulating machine is geared to other apparatus so that it shall
run at a constant speed. It is shown as a part of a motor-dynamo U T S W V.
While the machine to be regulated may be separately excited, ordinarily a shunt-

page_text: wound machine will be employed. In this case, the armature of the regulating
machine is placed in the shunt with the field-coils of the machine to be regulated.
the two being connected across or in multiple with the line and in series with
each other. In this arrangement it will be seen that the field-coil of the regulating
machine, which is in series with the armature of the machine to be regulated,
is supplied by, and its field-strength is dependent upon the current in the armature
of the machine to be regulated, and is independent of the current in its own
armature, except that there will be some reaction of the current in its
own armature, which, however, is not relied upon for effecting regulation. On
the other hand the field of the machine to be regulated is in series with its own
armature, as well as that of the regulating machine, and the field-strength of the
machine to be regulated, is, therefore, dependent upon the algebraic sum of the
voltages of both machines. If the current in the armature of the machine to be
regulated increases, for instance, upon reduction of the resistance of the circuit,
the potential tends to fall, in which case the field-strength of the machine to be
regulated should be increased. Conversely, if the current diminishes, for instance,
upon increase of resistance in the circuit, the potential tends to rise and the field-
strength should be diminished. The regulating machine will either be run as a
motor by the current in the field-circuit, and help drive the machinery to which
it is geared, in which case it will act as a retard, developing a counter-electromotive
force which cuts down the effective electromotive force of this circuit, and diminish
the field-strength of the machine to be regulated, or, the regulating machine
will be run by the machinery to which it is geared, in which case it will act as a
boost, generating an electromotive force which will be added to the electromotive
force in the field-circuit, thereby increasing the effective electromotive force
therein and increasing the field-strength of the machine to be regulated. It may
be changed from one of these forms to the other by merely changing the polarity
of the field of the regulating machine without changing the direction
of rotation of its armature. The regulating machine may also be so arranged
that without change in the connections, it shall under some conditions be run as
a motor by the current in the field-current, acting as a retard to the electromotive
force in the circuit, and under other conditions be run as a generator by the
machinery to which it is geared, acting as a boost to the electromotive force in the
circuit. These three methods are called respectively the retard, the boost, and the
retard-and-boost methods. In each of the three methods the speed of the armature
of the regulating machine should be kept constant, and the field of the regulating
machine be varied with the current in the main machine.
In the figure under consideration the system is shown for practising the retard,
boost, and retard-and-boost methods. If the system is used to practise a retard
or a boost method, the effects may vary in either direction from maximum to
zero; and if it is used to practise a retard-and-boost method the regulating
machine may pass gradually from maximum retard to maximum boost, or, from
maximum boost to maximum retard, with increase of current in either direction in
the armature of the machine to be regulated. This is controlled by the direction
of the field of the regulating machine. The field-coils of the regulating machine
are connected to line through a reversing switch. If used as a retard-and-boost,
the regulating machine need not be so large as where it is used always as a retard
or always as a boost. For one hundred kilowatt main machine a regulating
machine of about one-half horsepower capacity could do the work when acting as
a retard-and-boost. There is on the field of the regulating machine, in addition
to the coils T, which are connected to the line in series with the armature of the
main machine, a constant excitation, which may be in the form of coils U,
supplied from a storage battery, or the like. But these coils are shown as
supplied from leads taken from the mains, and where the system is a constant-
potential system, the excitation will, of course, be practically constant. Where
it is specified that one of the coils of the regulating machine has an excitation that
is constant, the meaning is that it is supplied from some independent source, or
from the main machine in the manner stated. The two field-coils of the regulating

page_text: machine always oppose each other; and may be so wound as to be balanced while
there is an assumed mean or normal current in the armature of the machine to be
regulated. The machine to be regulated is then by assumption supplying the
line with current of the desired potential, and is supplying its own field without
let or hindrance from the regulating machine. If the current in the line changes,
the regulating machine will act as a retard or boost, either increasing or diminishing
the effective electromotive force in the field circuit of the machine to be regulated,
as the current in that machine increases or diminishes. To effect this the field-
coils U T, should be so wound that it will run as a motor when the magnetization
due to the coil U exceeds that of the coil T', and will run as dynamo when the
magnetization due to the coil T exceeds that of the coil U. The regulating
machine will then start as a motor when the current in the machine to be regulated
is low, and act as a diminishing retard as that current rises toward the mean
strength, and as an increasing boost as that current increases beyond the mean
strength. This is only a particular case. The system is very flexible. For
example, the regulating machine may start as a generator when the current in
the armature of the machine is low, and become a motor when this current rises
beyond the mean strength. The connections of the field-coils of the regulating
imachine may be such that the effect of the regulating machine will be either to
increase or to diminish the field of the machine to be regulated, when the latter
is acting as a dynamo, and the current in the armature of the machine to be
regulated increases, or, conversely, the regulating machine may operate to diminish
or increase the field of the machine to be regulated when the latter is acting as
a motor, and the current in the armature of the machine to be regulated
increases.
An advantage of the system herein described when the machine to be regulated
is running in multiple with other machines, or is used in charging storage
batteries is that it can never be reversed by a momentary back-current, because the
demagnetizing effect of the back-current is checked by the saturation of the field
of the regulating machine. This may be explained as follows: A series-wound
dynamo cannot be used in multiple with other similar generators, or in multiple
with constant-potential shunt-wound generators, or to charge storage batteries.
This is because its voltage varies with its load, and a slight decrement in the
current delivered, due to accidental reduction in speed, or some other minor cause,
would produce a decrease of voltage which would cause a further decrease of
delivered current, resulting in a still further decrease of voltage, and so on, until
the electromotive force of the dynamo has entirely vanished, and has even been
reversed and carried to a maximum in the opposite direction. An ordinary
compound-wound generator the field-magnets of which are partly series-wound,
has the same characteristics, it being possible to reverse its potential by a
momentary reversed current in the series coils. In this system this is impossible,
because the demagnetizing action due to a reversed current never acts directly upon
the field of the machine to be regulated, but only indirectly through the regulating
machine. It is therefore limited by the saturation of the field of the regulating
machine. Up to the point of reversing and saturating the field of the regulat-
ing machine a reverse current will tend to modify the field of the machine to be
regulated, but this effect will not be increased by any increase in the reverse current
however great.
.
The system of Figure 4 may be modified by omitting the coil U from the field
of the regulating machine. Other means than that shown may be adopted for
driving the armature of the regulating machine.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:-
1. The method of regulating electric motors which consists in supplying the

page_text: armature with a constant current, supplying the field from a source of energy
separate from that which supplies the armature, and varying the field by varying
the effective electromotive force in the field circuit simultaneously with the speed
of the armature of the machine to be regulated, substantially as described.
2. The combination of a machine to be regulated, a constant-potential machine
and a regulating-machine connected with the field of the machine to be regulated,
and means for varying the speed of the armature of the regulating-machine
proportionately and simultaneously with the speed of the armature to be regulated,
substantially as described,
3. The method of obtaining a constant current upon a main circuit which
consists in connecting the said circuit to a constant-potential source through the
armature of a regulated machine, energizing the field-magnet of the main regulated
machine from a source which is controlled by the current in the main circuit, and
varying and reversing the current supplied to the field-coils of the regulated
machine, whereby the current on the main circuit is kept constant, substantially
as described.
4. The combination of a regulated machine, a main circuit to be supplied with
constant current, the armature of the regulated machine being connected in the
main circuit, a field-circuit for the regulated machine, a regulating-
machine the armature of which is connected in this field-circuit, a
constant-potential source, means dependent upon the constant-potential
source for exciting the field of the regulated machine, a field-coil for
the regulating-machine which is connected in the main circuit, the elements
being so arranged that the effect of the current from the constant-potential
source and the effect of the current in the main-circuit oppose each other in the
field-circuit of the regulated machine so that its field is a resultant due to the
difference between their effects, and varies with changes in the strength of
the current in the main circuit, substantially as described.
5. The method of regulating one dynamo-electric machine by another such
machine, which consists in making variations in the field strength of the regulating-
machine dependent upon the current in the armature of the machine to be
regulated, and independent of the current in its own armature and making
variations in the field strength of the machine to be regulated dependent upon
the algebraic sum of the voltages of the line and the regulating-machine, sub-
stantially as described.
6. The combination of a line, a main machine connected to the line, and a
regulating machine, with a field-coil of the regulating-machine connected to the
line in series with the armature of the main machine, and with the armature of
the regulating-machine and a field-coil of the main machine, connected across or
in multiple with the line and in series with each other, whereby the field strength
of the regulating-machine is dependent upon the current in the armature of the
main machine, and the field strength of the main machine is dependent upon the
algebraic sum of the voltages of the line and the regulating-machine, substantially
as described.