IMPROVEMENTS IN " ELECTRO-DYNAMIC MOTORS
Year: 1884

page_text: I THOMAS JOHN HANDFORD of 42 Southampton Buildings in the County of
Middlesex Patent Agent do hereby declare the nature of this invention for
IMPROVEMENTS IN
"
ELECTRO-DYNAMIC MOTORS a communication to me from
abroad by Frank Julian Sprague of New York in the County and State of
New York, United States of America Electrician to be as follows:-
This Invention relates to electro-dynamic motors of that class in which the main
field coils, that is to say those which determine the polarity of the field, are in
shunt relation to the armature, and the Invention consists in a new method of
regulation for such motors as hereinafter set forth whereby the speed or the power
of a motor may be varied or the speed may be maintained constant under varying
loads or under varying conditions of the circuit. The method of regulation is
therefore adapted to all the different conditions and situations in which such
motors may be used-whether they are stationary motors connected with a system
of electrical distribution in which case it is usually desirable to maintain a constant
speed under different loads and usually with a constant potential circuit or used
upon moving vehicles for railway purposes in which case the speed must necessarily
be often changed, and, also the power as for differing grades and where the initial
potential changes on account of the moving of the motor to different parts of the
circuit and from other causes.
The main features of the invention depend upon the following principles:-
In an electric motor with armature and field circuits independent, the total
power which can be developed and the economy and efficiency of the motor are
entirely independent of the strength of the field but depend within practical limits
alone upon the initial and counter electro motive forces, and the resistance of the
armature if the speed be not limited.
The strength of the field determines the speed at which the motor must run to
get a required efficiency.
With a given initial potential at the armature terminals, the speed may be
maintained constant no matter how the load varies from the maximum allowed, by
changing the strength of the field, such strength being diminished as the load is
increased, and vice versâ increased as the load is diminished.
In carrying the Invention into effect I weaken the field by decreasing the
magnetizing effect of the field magnet coils to produce an increase of the mechanical
effects-that is of the speed or power or both of the motor-and I strengthen the
field by increasing the magnetizing effect of its coils to decrease the said mechanical
effects. Thus in all the different conditions and uses I vary the magnetizing effect

page_text: of the field coils to vary mechanical effects in the motor. The different conditions
and purposes for which I make use of this method are as follows:-
To change the speed or power of a motor on a circuit of constant potential.
The speed or power is increased by weakening the field which produces a decreased
counter electro motive and an increased armature current and consequently the
increased mechanical effect desired; and such mechanical effect is decreased by
strengthening the field and thus increasing the counter electro-motive force.
To maintain the speed constant with a current of constant potential under
varying loads. When the load increases so that the speed would naturally decline,
the field is weakened, the counter-electro-motive force diminished and armature
current increased, the tendency to reduced speed is counteracted and there is
an increase in the mechanical effect-power. For a decreased load, the field is
strengthened, the counter electro-motive force increases, the current decreases, the
speed remains the same and the power is decreased.
To maintain speed or power constant under varying initial potential. If the
potential at the motor terminals increases, these mechanical effects increase or tend
to increase. By strengthening the field I produce an increased counter electro-
motive force so that the increased power or speed or the tendency thereto is
counteracted, and this counteracting may evidently itself be considered a decrease
in mechanical effect whether the regulation is performed simultaneously with the
increase of potential or before or after such increase. If the regulation is performed
simultaneously with a gradual change of potential, there may be less change in
counter electro-motive force or armature current, but there is still the counteracting
of the tendency to increased mechanical effect, which counteracting is, as before
stated, itself a decrease of mechanical effect. For a decreased or decreasing initial
potential the field is weakened, to counteract the decrease in mechanical effect
which would otherwise occur and therefore to produce an increased nrechanical
effect.
In any of the above cases, I may at the same time that I vary the magnetizing
effect of the field magnet coils vary also the armature current whereby an additional
effect is produced. In the complete specification to my application for Letters
patent dated the 28th January 1884 N° 2266 there is set forth a method of
varying the field of a motor by the use of adjustable independent field coils.
This is shewn in connection with means for varying the relation between the
number of field coils in series and those in shunt relation with the armature to
vary the armature current. The present invention, however, relates to other and
preferable modes of field regulation by varying the magnetizing effect of the field
coils which also may be used in connection with the above mentioned armature
regulation.
According to one modification I wind the field coils in two sets or ranges each
connected with the supplying circuit at one end and having the other end free.
By connecting the free end of each range to different points of the opposite range
more or less of the coils are placed in parallel circuit with each other and the
resistance of the field and consequently. the current and magnetizing effect of the
field coils are varied. Thus the field coils may be considered as broken at their
free terininals, and by a suitable commutator which will be presently described
greater or less portions of the coils are progressively thrown into multiple arc with
each other to decrease the resistance strengthen the field and diminish the speed;
and progressively removed from such relation to produce a contrary effect. This
arrangement may be used with the armature terminals fixed or with the armature
capable of being shunted around a greater or less number of the field coils, the
present mode of regulation admitting of being used in connection with that set
forth in the said former specification as before mentioned. Incidentally this
regulation of the field has an increased effect by the increase or diminution of the
armature current due to the increase or diminution of the resistance around which
it is shunted. But by using the field and arinature regulation together a great
effect may be produced on the speed of the armature; by a very slight change the

page_text: r
racing" of the armature, even if the whole load is suddenly thrown off is
prevented. However the regulation of the field alone gives complete control of the
motor for all practical purposes.
The commutator and connections employed with the new method of regulating
the field, are constructed and arranged in the following manner.
The commutator is composed of a circle of metal blocks two of which are
extended into arcs or quadrants.
The connections froin the field sections are made-the first and last to single and
opposite blocks of the commutator and each of the others to two blocks. The
commutator arm which is pivotted consists of an insulating central portion and
metal extensions. These ends each bear on one of the arcs or quadrants and upon
the range of contacts.
By moving the commutator arm in one direction or the other, more or less of*
the sections of field coils in which the magnet is wound are multiple-arced upon
each other, the magnetizing effect of such coils is varied, and the strength of the
magnet is increased or diminished.
In applying this commutator in connection with the arrangement for changing
the relation between the sections of field coils in series and those in shunt relation
to the armature, set forth in the said former specification, additional arms insulated
from each other, and bearing on the contact blocks are employed and the terminals
of the armature are connected respectively with these arms.
As these arms are moved, the armature is shunted around a greater or less
number of the field coils, remaining in series with the remainder. Both sets of
arms may work simultaneously if desired.
By the use of the commutator so arranged the armaturo current or the strength
of the field or both may be regulated, the circuits never being broken, no adjustable
resistances being employed and all the field coils being constantly in circuit while
their magnetizing effect is varied.
The field regulation or both field and armature regulation may be accomplished
automatically by devices controlled by variations in the speed of the motor. Thus
a constant speed is maintained. For example a centrifugal governor may be
employed connected with the motor shaft so as to be affected by variations in
speed. Its moving collar carries two contact arms insulated from each other
and connected respectively with the conductors. These arms enter between three
arms which also are insulated from one another. A small electric motor has one
of its terminals connected with two of the arms and the other terminal with
the other arm.
The motor shaft is connected by a worm gearing or other slowing down gearing
with the arm of the commutator. An adjustable weight is employed so that the
governor can be set to hold the contact arms centrally at the normal speed of the
motor to be regulated, for its proper efficiency. Should a variation in the load
cause the speed to slightly decrease, the governor balls fall, and the arins make
their lower contacts, closing circuits to the motor and causing it to revolve in
a direction to shift the commutator arm to decrease the field strength and so keep
the speed at its normal point. When on the contrary the speed, slightly increases
circuit is closed to the motor in the opposite direction and the movement of the
commutator arm causes an increase in the field strength which keeps the speed still
at the normal.
In some cases the field may be wound with two sets of coils, one of which is
divided into sections and the other which may be termed an independent field coil
is provided with movable terminals making contacts at the bights of the divided or
sectional field coils, by means of which the potential existing at these terminals,
and hence the current in the independent field coils, may be varied or reversed at
will. By such variation, the variable magnetic moment of the independent field
coil may be cumulative differential or nil with reference to the magnetic moment of
the divided coil, and if the resistances and turns are properly proportioned, the

page_text: resultant magnetic moment or free field may be progressively varied from saturation
'to zero.
At the same time by moving the armature terminals to the various bights of the
sectional field coils the potential existing at these terminals may be varied at will
as set forth in the said former specification.
A combination of these methods of varying the magnetic moment of the field and
the armature current or potential gives me great control over a motor working on
what is ordinarily known as a constant potential circuit and is especially adapted
for handling motors for electric railway purposes where high potentials must obtain,
motors must be worked in parallel circuit and there will be variation of potential
at different points along the line and under different circumstances and at different
times.
In order to prevent heating of the sectional coils they are wound of differently
sectioned wire, of variable number of turns and resistances because the coils nearest
the line terminals must ordinarily carry more current than those farthest removed,
three or more of such sections being by preference employed in a range or ranges.
The different coils may be wound on the main or different cores.
A better method of working is to wind the field with two sets of variable coils,
these sets being in parallel circuit. The armature and independent field coils may
now one or both have one or both terminals movable along either or both sets of
coils. If the terminals move on both sets of coils, these sets may be considered the
arms of a Wheatstone Bridge and the independent field coil or the armature or both
may be considered as taking the place of the galvanometer circuit but with movable
terminals. By putting the terminals of the armature on different sets of field coils
it is impossible to short circuit the armature in reversing the potential existing at
such terminals which short circuit if taking place when moving at a high speed
would endanger the brushes and armature.
As examples of the variations in detail which may be made whilst retaining the
same principle it should be observed that the sectional field coils may be employed
in combination with an independent field coil variably shunted on sectional field
coils and that the armature circuit may be similarly, but independently shunted on
sectional field coils. The field moment can be varied from saturation to zero and
armature potential varied at will. Two ranges of sectional field coils in parallel
circuit may be employed in combination with armature circuit, and independent
field circuit, each variably shunted on the two ranges of field coils or the armature
circuit may be variably shunted on one set of field coils, and the independent field
coil variably shunted on other set of field coils, or the armature circuit may be
variably shunted on one set of field coils and the independent field coil variably
shunted across both sets of field coils.
It is evident that any of the well known methods of automatically shifting the
contacts to provide for steady running under variable loads may be used-and it is
unnecessary to enter into detailed description of such.
As has been already explained modifications of these modes of regulation can be
applied to change the power or speed of the motor with a constant current or to
maintain speed or power constant in a varying potential circuit. The Invention
may also be otherwise varied in its details whilst still retaining the same principle
as for example-other methods of varying the magnetizing effects of the field coils
may be used such as reversing the current in some of the sections, cutting in or out
of circuit sections, shunting same, or using resistances.
Dated thio 20th day of November 1981.

page_text: Improvements in Electro-dynamic Motors.
I THOMAS JOHN HANDFORD of 42 Southampton Buildings in the County of
Middlesex Patent Agent do hereby declare the nature of this invention for
"IMPROVEMENTS IN ELECTRO-DYNAMIC MOTORS" and in what manner the same
is to be performed, to be particularly described and ascertained in and by the
following statement :—
This invention relates to electro-dynamic motors of that class in which the main
field coils,, that is to say those which determine the polarity of the field, are in
shunt relation to the armature, and the invention consists in a new method of
regulation for such motors, as hereinafter set forth, whereby the speed or the
power of a motor may be varied, or the speed may be maintained constant under
varying loads or under varying conditions of the circuit. This method of regulation
is therefore adapted to all the different conditions and situations, in which such
motors may be used,-whether they are stationary motors connected with a system
of electrical distribution, in which case it is usually desirable to maintain a constant
speed under different loads and usually with a constant potential circuit, or used
upon moving vehicles for railway purposes, in which case the speed must necessarily
be often changed, and, also the power as for different grades and where the initial
potential changes on account of the moving of the motor to different parts of the
circuit and from other causes.
The main features of the invention depend upon the following principles :-
In an electric motor, with armature and field circuits independent, the total
power which can be developed and the economy and efficiency of the motor are
entirely independent of the strength of the field, but depend within practical
limits alone upon the initial and counter electro-motive forces, and the resistance
of the armature, if the speed be not limited.
The strength of the field determines the speed at which the motor must run to
get a required efficiency.
With a given initial potential at the armature terminals, the speed may be
maintained constant, no matter how the load varies from the maximum allowed,
by changing the strength of the field, such strength being diminished as the load
is increased, and vice versa increased as the load is diminished.
These principles may be illustrated as follows:
Consider the motor current as derived from mains having a fixed difference of
potential, and the motor with its field and armature in shunt relation.
In this case, the armature, runs with a velocity dependent upon the strength of
field, the initial potential, the number of turns, resistance, et cetera of the armature,
and the load; and a counter electro-motive force is set up which diminishes the
armature current. The higher the speed, the greater this counter electro-motive
force.

page_text: E-e
Let E be the initial and e the counter electro-motive force, and r the resistance
of the armature, the current flowing in the armature is then With a given
armature and given field e varies with the speed. Now the power at any given
speed and strength of field varies with the current, and with any given current
varies with the strongth of field. The total work done is the product of the speed
by the work per turn, and since the speed is as e, and the work per turn as the
current, the total work done is expressed by C (E-c). The efficiency is the
ratio It will be seen that both these expressions-the total work done and the
efficiency are independent of any function of the field, but depend only on the
initial and counter electro-motive forces and the resistance of the armature, and
any given value of e can be attained with any strength of field by attaining proper
speed.
Suppose the motor doing a certain amount of work at a certain speed.
If c =
E
2'
E
2 T
armature current is and work done is
E2
3 E
Now let the speed be increased one half by diminishing the mechanical work
per turn the field remaining the same-e now equals, current is and work
3 E'
done which is less than before-with the same field.
16 r
3 E
E
3 E3
16 r'
4 1
Let the original field be strengthened one half, the speed remaining the same.
e now equals current is and work done
this diminished work is with a stronger field.
same as in last case. But
Suppose now that this last field be decreased one ninth and speed increased one
seventh.
7 E
12'
e now equals current is
although with a weaker field.
5 E
127'
and work done
35 E
144 F
more than in the last case
Or we may consider the speed of a machine constant, its field alone being varied,-
and differentiating the expression for work done
c(E
T
de
we have (E-2 e) as
the rate of variation of work with variation of e, that is, of field.
It will be noticed however that this increase of work with a diminished field
follows only when the electrical efficiency is above fifty per cent, that is, when c
E
e
E
is greater than for with de negative, the expression has a positive value only
when this relation holds. If working with e less than 1, the field must be
strengthened to increase the work done, but except in starting a machine, this is
the worst possible way of working it and being uneconomical is of course
objectionable.
In carrying this invention into effect I weaken the field by decreasing the
magnetizing effect of the field magnet coils to produce an increase of the
mechanical effects-that is, of the speed or power, or both, of the motor-and I
strengthen the field by increasing the magnetizing effect of its coils to decrease
the said mechanical effects.
While in the above mathematical demonstration, I have for convenience
considered the motor as in circuit with mains having a constant difference of
potential, as if for instance it were connected with a multiple arc system of
electrical distribution, it will be evident that the same method is applicable to the
regulation of the motor under changes of potential in the circuit for if an increased
difference of potential occurs, the field is strengthened to counteract it; and for a 4
decreased difference of potential the field is correspondingly weakened..
In all the different conditions and uses, as I have already stated, I vary the
magnetizing effect of the field coils to vary mechanical effects in the motor. The-
4

page_text: different conditions and purposes for which I make use of this method are as
follows:-
To change the speed or power of a motor on a circuit of constant potential.
The speed or power is increased by weakening the field, which produces a
decreased counter electro-motive and an increased armature current and conse-
quently the increased mechanical effect desired; and such mechanical effect is
decreased by strengthening the field, and thus increasing the counter electro-
motive force.
To maintain the speed constant with a current of constant potential under
varying loads. When the load increases so that the speed would naturally
decline, the field is weakened, the counter electro-motive force diminished and
armature current increased, the tendency to reduced speed is counteracted and
there is an increase in the mechanical effect-power. For a decreased load, the
field is strengthened, the counter electro-motive force increases, the current
decreases, the speed remains the same and the power is decreased.
To maintain speed or power constant under varying initial potential. If the
potential at the motor terminals increases, these mechanical effects increase or tend
to increase. By strengthening the field I produce an increased counter electro-
motive force so that the increased power or speed or the tendency thereto is
counteracted; and this counteracting may evidently be itself considered a decrease
in mechanical effect, whether the regulation is performed simultaneously with the
increase of potential or before or after such increase. If the regulation is performed
simultaneously with a gradual change of potential, there may be less change in
counter electro motive force or armature current, but there is still the counter-
acting of the tendency to increased mechanical effect, which counteracting is, as I
have just said itself a decrease of mechanical effect. For a decreased or decreasing
initial potential the field is weakened, to counteract the decrease in mechanical
effect which would otherwise occur and therefore to produce an increased mechanical
effect.
In any of the above cases, I may at the same time that I vary the magnetizing
effect of the field magnet coils vary also the armature current whereby an
additional effect is produced.
In the complete specification to Letters patent granted to me dated the
28th January 1884 N° 226684 there is set forth a method of varying the field of a
motor by the use of adjustable independent field coils. This is shown in connection
with means for varying the relation between the number of field coils in series
and those in shunt relation with the armature to vary the armature current. My
foreign correspondent has devised other and preferable modes of field regulation
by varying the magnetizing effect of the field coils which also may be used in
connection with the above-mentioned armature regulation.
According to one of these methods I wind the field coils in two sets or ranges
each connected with the supplying circuit at one end and having the other end free.
By connecting the free end of each range to different points of the opposite range,
more or less of the coils are placed in parallel circuit with each other and the
resistance of the field and consequently the current and magnetizing effect of the
field coils are varied.
If the armature is in shunt relation with a part of the field coils as described
in the specification to the said former patent, this also incidentally affects the
armature circuit.
The same commutator may be employed for varying the field and for varying
the armature current in the manner set forth in the said former specification.
The different coils may be wound on the main or different cores.
The field regulation or both field and armature regulation may be accomplished
automatically by devices controlled by variations in the speed of the motor. Thus
a constant speed is maintained.

page_text: And in order that the said Invention may be perfectly understood I shall now
proceed more particularly to describe the same and for that purpose shall refer to
the several figures on the accompanying sheet of drawings which illustrate
diagrammatically the principles and features of this Invention and the mode of
carrying out the same.
Figures 1 and 2 represent an arrangement described in the said former specifica-
tion. C, C are main conductors, a, a¹ is the field circuit, and a a¹¹ a¹ the armature
shunt. In figure 2, the armature is shunted around a less number of field coils,
the difference of potential at its circuit terminals is lessened and it receives less
current, and the speed or power is diminished. According to my present Inven-
tion, however, I may accomplish this regulation without changing the armature
terminals.
According to one modification which is illustrated in Figures 3 and 4 the field
coils are broken at terminals p p¹ and by a suitable commutator which will be
presently described, greater or less portions of the coils are progressively thrown
into multiple are with each other to decrease the resistance, strengthen the field
and diminish the speed; and progressively removed from such relation to produce a
contrary effect. In this arrangement the armature terminals are considered as fixed.
Figures 5, and 6 show the same arrangement of field, with the armature capable
of being shunted around a greater or less number of the field coils, illustrating
the fact that the present mode of regulation may be used in connection with
that set forth in the said former specification as before mentioned. Incidentally
this regulation of the field has an increased effect, by the increase or diminution
of the armature current, due to the increase or diminution of the resistance
around which it is shunted. But by using the field and armature regulation
together a greater effect may be produced on the speed of the armature; by a
very slight change, the "racing" of the armature, even if the whole load is suddenly
thrown off is prevented. However, the regulation of the field alone gives complete
control of the motor for all practical purposes.
Figure 7, illustrates the commutator.and connections employed with this method
of regulating the 'field.
CC are the main conductors and c c' c¹¹ et cetera, are sections of field coils.
The commutator is composed of a circle of metal blocks d d¹ d¹¹ d¹ two of
which are extended into the arcs c. The connections from the field sections are
made the first and last to single and opposite blocks d of the commutator and
each of the others to two blocks d¹ d¹ d" and d¹¹.
The pivoted commutator arm consists of an insulating central portion B and
metal extensions ff'. These ends each bear on one of the arcs and upon the
range of contacts.
•
The field current from C passes to h where (in the present position of the arm)
it divides, part passing to contact du, extension f, are e and coils c¹ to the reuniting
point h¹.
:
The rest passes through coils c, to contacts d'1, arc e, extension f' and 'contacts
dd to h¹. It will be seen that coils c and c¹ are thus placed in multiple arc to
each other.
By moving the commutator arm in one direction or the other, more or less of
the sections of field coils in which the magnet is wound are multiple-arced upon
each other, the magnetizing effect of such coils is varied, and the strength of the
magnet is increased or diminished.
Figure 8 shows this arrangement in connection with that for changing the
relation between the sections of field coils in series and those in shunt relation
to the armature set forth in the said former specification.
Here the additional arms D D¹ insulated from each other and bearing on the
contact blocks are employed.
The terminals of the armature M are connected respectively with these arms.

page_text: As the arms D D¹ are moved, the armature is shunted around a greater or less
number of the field coils, remaining in series with the remainder. The arms B
and D D¹ may work simultaneously if desired.
By the use of the commutator shown in figure 8 the armature current or the
strength of the field or both may be regulated, the circuits never being broken, no
adjustable resistances being employed and all the field coils 'being constantly in
circuit while their magnetizing effect is varied.
Figure 9 illustrates an automatic arrangement which may be employed for
moving the arm B, to maintain a constant speed.
A centrifugal governor F is connected with the motor shaft so as to be affected
by variations in speed. Its moving collar carries two contact arms m m¹ insulated
from each other and connected respectively with the conductors C C¹. These arms
enter between the three arms n n¹ n11 which also are insulated from one another.
G is a small electric motor, one of whose terminals is connected with the two
arms n, n the other with arm n¹.
The motor shaft is connected by a worm gearing or other slowing down gearing
with the arm B. The connecting spindle is for convenience of illustration broken
off and laid out in dotted lines. An adjustable weight H is employed so that the
governor can be set to hold the contact arms centrally at the normal speed of
the motor to be regulated, for its proper efficiency. Should a variation in the load
cause the speed to slightly decrease, the governor balls fall, and the arms make
their lower contacts, closing circuits to motor G, and causing it to revolve in a
direction to shift the arm B to decrease the field strength and so keep the speed at
its normal point.
When, on the contrary the speed, slightly increases, circuit is closed to the
motor G in the opposite direction, and the movement of the arm B causes an
increase in the field strength which keeps the speed still at the normal.
.
As has been already explained, modifications of these modes of regulation can be
applied to change the power or speed of the motor with a constant current or to
maintain speed or power constant in a varying potential circuit.
I do not limit myself to the particular apparatus herein described, or to any
particular mode of construction set forth, but claim more especially the method of
regulation in its broadest sense.
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
1st The method of regulation for an electro-dynamic motor whose main field
coils are in shunt relation to its armature, which consists in strengthening the
magnetizing effect of the field magnet coils of the motor to decrease the mechanical
effects, as speed or power, or both, and vice versa, weakening such magnetizing
effect to increase the said mechanical effects, substantially as hereinbefore
described.
2nd The method of maintaining constant under varying loads the speed of an
electro-dynamic motor whose main field coils are in shunt relation to its armature,
which consists in strengthening the magnetizing effect of the field magnet coils as
the load is diminished, and vice versa, weakening the said magnetizing effect as the
load is increased, substantially as hereinbefore described.
3rd In an electro-dynamic motor, the combination of independent methods of
varying the effective magnetic moment, or magnetic intensity, of the field, with
means for varying or reversing the potential existing at the armature terminals,
substantially as hereinbefore described.
4th In an electro-dynamic motor whose main field coils are in shunt relation to
its armature, the employment of automatic devices dependent upon its speed,
operating to increase the strength of the field as the load is diminished or the
initial potential is increased, and vice-versa to decrease the strength of the field

page_text: as the load is increased or the initial potential decreases, to maintain a fairly
constant speed in the motor, substantially as herein before described.
5th An electro-dynamic motor having sectionally wound field coils and a com-
mutator or commutators constructed and arranged substantially as herein before
described with reference to Figures 7 and 8 for changing the relation between the
several sections of the field coils or for both changing the relation between
the several sections of the field coils and varying or reversing the potential
existing at the armature terminals, substantially as hereinbefore described.
n
11