Improvements in Continuous Current Electric Motors, and Method of Regulating the same.
Year: 1896

page_text: Date of Application, 25th Feb., 1896-Accepted, 4th Apr., 1896
COMPLETE SPECIFICATION.
Improvements in Continuous Current Electric Motors, and Method of
Regulating the same.
1, JAMES DEVONSHIRE, Secretary of The British Thomson-Houston, Limited,
of 38, Parliament Street, Westminster, London (a communication from abroad by
Elihu Thomson of Swampscott, in the State of Massachusetts, United States of
America), 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 present invention relates to the construction and manner of compounding or
regulating electric motors run from main or supply wires of constant or approxi-
mately constant potential. Motors of this kind have frequently been made with
a constant or approximately constant field excitation dependent generally upon the
magnetizing action of what is termed a shunt field coil or one which is in a branch
of the armature fed from the mains, which coil, being connected directly to the
mains, carries a current of approximately constant amount. When the motor is
thus provided with a constant field, there will be (unless the armature be extremely
small in magnetic power as compared with the field) a certain falling off in the speed
under heavy or increased load amounting sometimes to a few per cent. which, however,
may be made less or more according to the proportioning.
In case it is desired that the motor shall be self-regulating as to speed under
light and full load, that is shall maintain an even and constant speed whether
lightly or fully loaded, a condition not quite possible with the best forms of
shunt wound motors, it is necessary to compound the motor or so affect the
strength of the field megnetism that under load the magnetism shall be weaker
thereby diminishing the counter electro-motive force of the armature and permitting
more current to flow in the latter to increase the torque and bring the armature up
to speed.
Heretofore the compounding or regulating action has been obtained by the
application to the field magnet of the machine, of regulating coils which carry a
current varying with the load and which act directly upon such field magnet in
opposition or in a contrary way to the shunt field coils, or other magnetizing
influence, in a manner to cut down the field magnetism so that on an increase of
the current flowing in the armature from one of the constant potential mains or
wires to the other upon a loading which decreases the speed, the effect will be to
cut down the magnetism and therefore the counter electro-motive force of the
motor, upon which it speeds up to produce the same counter electro-motive force
or nearly that force which it had before. Such regulating or compounding coils
are usually, for the sake of simplicity and convenience, placed in the direct circuit
with the armature so as to carry current varying with the load or counter electro-
motive force, but might be coils in any circuit or deriving current from any
source if the current in them be made, in any of the various ways known in the
art, to carry the proper varying current. In this way indeed the motor may be
constructed so that it will not simply maintain constant speed during variations of
load but it may increase in speed with the load, but the great objection to this
method of compounding the motor or regulating its speed is, that should the
motor be greatly overloaded or should it be subjected to sudden gush of an
armature current through any cause the chances are, in fact the probabilities are,
that the field magnetism will be reversed, or at least so far weakened that the

page_text: motor will not turn at all, or will lose its torque, the field having been weakened to
an extent far below that which gives it a torque under the conditions. In fact the
sudden abnormal flow in the regulating circuit in the machine may sometimes even
reverse the magnetism of the field of the motor and tend to turn it in the other
direction. This weakening of the field magnetism is also attended by a destructive
burning and sparking at the commutator of the dynamo and with other irregularities
not necessary to mention.
While I have described, as a type of motor to which my invention is applicable,
one in which the field excitation is produced by shunt field coils which are supplied
from constant potential mains, I do not wish to be understood as limiting myself
in this respect since the difficulties before-mentioned would exist in whole or in part,
however, the normal field excitation is produced, whether from a separate exciting
source of energy, from permanent magnetism, or by other connections of the principal
cuils of the machine, and my principle of construction for regulation or compounding
is applicable to electric motors generally though for the sake of simplicity, I have
described the invention as carried out in connection with a motor having its field
normally excited from constant potential mains.
My present invention consists in compounding or regulating the motor by action
of a coil which carries current varying with the load and instead of being applied
to the same core as the constant current shunt which produces a constant exciting
influence, is applied to a separate core but acts upon the armature conductors
connected on the same or separate armature cores in the proper manner to keep
the speed of the machine constant by proper variation in the magnetic state or
condition.
My invention consists further in giving to some portion of the magnetic circuit
through which the separate coil might act to reverse the main field, a restricted
magnetic section or magnetic carrying capacity so that the influence of the
compounding coil may not be so great as to overcome the effect of the magnetism
of the main field or field magnet of substantially constant power. Such restricted
magnetic section or carrying capacity might be in the core of the regulating coil
itself such core being in such case so small or so deficient in magnetic capacity
as to be insufficient to overbalance the effect of the main or principal field even if
it (the core of the regulating coil) be saturated, or in case a separate armature
core or portion of armature core be used for the portion of coil or armature
coil upon which said regulating magnet core acts, then the restricted section might
exist in the said core or portion of core in such way as to prevent the influence
of the regulating coil from being carried to an amount overcoming the main
field. The restricted magnetic section or carrying capacity might exist at any other
point in the magnetic circuit through which the influence of the regulating coil
might operate.
My invention also consists in other features and modifications of the invention, as
hereinafter more particularly described' and claimed.
I have herein shown my invention as carried out in a machine in which one set
of coils affecting the poles or maguets of fairly constant magnetism are in shunt to
the armature, or connected directly across the main while the other set of coils
carrying the varying current and operating as another set of poles or field magnet
cores are in direct circuit with the armature. The latter poles and field cores are
in direct circuit with the armature. The latter poles and field cores are also shown
of very much smaller capacity or rather much smaller section or magnetic carrying
capacity than the others so that should they become saturated in the reverse direction
they would not prevent the motor from still maintaining a torque such that it
normally possesses.
I have shown in the accompanying Figures 1 to 5, of the drawings, ways of
carrying the invention into practice.
In Fig. 1, we have a typical figure showing an electric motor fed by the
mains a, b, which may be of constant potential or nearly constant potential.
The field magnets or field magnet poles which are presented to the armature are

page_text: n this case four in number, two of which constituting one set, are energized by the
coils S, S', which as seen are in shunt across the mains a, b, while another set of
ield poles much smaller in size and magnetic capacity, acting on a different longi-
udinal portion of the armature, are energized by the regulating coils D, D', in the
main circuit of the motor armature the commutator of which is seen at C.
X, is the armature shaft, A, the armature and B, B', the commutator brushes.
The armature core may, as shown, be divided into two separate portions or, as seen
in Figure 4, may be upon one continuous core throughout the whole extent of the
armature. The winding or direction of current flow is opposite in the magnets D, D',
as compared with the magnet coils S, S', that is they produce opposite poles
presented to the same side of the armature or to the same portions of the armature
winding between the commutator brushes. Under a light load or a load which
turns the motor only there will be but little current flowing in the coils D, D, and
the motor is then simply a motor revolving in the shunt field provided by the
coils S, S, and it therefore maintains a certain speed depending upon the strength
of those poles. When a load is thrown upon the armature which tends to arrest
its rotation a current then flows in the main circuit coils D, D', which produces a
counter electro-motive force in the armature windings or produces poles of opposite
polarity to those produced by S, S¹, on the same armature wire. By the current
passing in the coils D, D', therefore, we have an opposing influence to the effect of
the field produced by the current passing in the coils S, S', which is equivalent to
a differentiation of their power though it is done through an entirely separate
source, the opposing field tending to set up a counter electro-motive force instead
of an effect produced by mere weakening of the main fields S, S', as in the ordinary
case.
It is best to limit the size of the cores or magnetic carrying power of the
cores D, D', as compared with the cores upon which the coils S, S', are wound, in
such way that should the coils of the cores D, D', be even saturated by the
excessive flow of current or receive their maximum magnetization they would still
be only a small fraction of the magnetic field of the machine and therefore not
reverse in effect the entire magnetic field of the motor. Thus it would be well to
make the cores D, D', only say from 10 to 20 per cent. of the section of the
cores S, S', when fairly well magnetized or, to put it in another way, the carrying
capacity for magnetism even at the maximum of the cores D, D', should be but a
fraction of the effect which may be produced in the cores of the coils S, S', when
in setion. By this means and by properly proportioning the effect of the windings
a compensation for a falling off in speed may be obtained in the motor which will
maintain its speed at the normal even though the load may be varied from nothing
to full load, and the result will be that the speed would increase under load in such
a manner that should there be a decrease of speed in transmission from the motor
to shafting or through shafting to any driven machinery the speed of the driven
machinery would be maintained constant while the motor is actually increased in
speed under load. This might be called a compounding of the speed of the motor
for load as by its means an increase of say ten or fifteen per cent. of the motor
under load as compared with its speed under no load is or can be readily obtained,
and at the same time there is no danger of a very great overload reversing the
magnetic conditions and upsetting the torque of the motor. A. variable shunt may
be placed around the direct field circuit, and a variable resistance may be arranged
to vary the relative strengths of either of the shunt field coils, as usual with
dynamos and motors and as indicated.
A modification in the way of carrying my invention into effect is seen in Fig. 2.
In this case the small magnet or the poles affected by the smaller cored magnet are
excited by the coils D, S2, the coil D, being a coarse coil in circuit with the
armature, as shown, through the brushes B, B, and the coil S2, being in the shunt
circuit across the inains either in circuit with the main shunt coils S, or in a
separate shunt by themselves. The effect is that when both the coils S, S2, are
doing work and no current is flowing in D, which is the condition under no load,

page_text: there is so little current in the coil D, that its effect is almost inappreciable, and
both poles corresponding to these coils affect the armature in a like way or in the
same direction to produce a counter electro-motive force during the revolution of
the armature A, A, but when the load is put on so that the current is passed
through the coil D, it opposes or differentiates the effect of the coil S 2, and under
.considerable load may even overcome it so that a reversal of the magnetization of
the core is produced and an effect produced similar to that in Fig. 1, at this stage.
It is evident, however, that since the smaller core or smaller field pole is affected
not only by a magnetization in the reverse direction to the main field pole or core,
but also a differentiation from magnetization in the same direction that a much
smaller accessory or differentiating magnet may be used in this case than in the
case of Fig. 1, to produce equivalent results, as in this case the effective range is
from magnetization by the coil S 2, to a considerable degree to magnetization in the
opposite direction overcoming the effect of the coil S 2, and producing a lowering
of the counter electro-motive force in the armature which results in an increase in
the speed under the conditions. It is obvious that the construction of Fig. 2 is
the preferable one.
It will be readily seen that the main shunt winding S, Fig. 2, might of course
be carried around both sections of the field pole while the direct circuit winding D,
is carried only over one portion of the field pole, that is a single coil S, might be
made to enclose both portions of the field cores and affect them in shunt while the
direct current only affected the smaller section which will be alongside of it.
This is one of the best constructions in fact for motors of this character.
I do not limit myself to any particular arrangements of the field poles with
respect to each other and the armature, as it is obvious that many departures may
be made in this particular.
In Fig. 3, S, S', are the large poles affected by the shunt winding and D, D',
the differential poles. The armature is of the ring pattern divided as to its core
into two sections, one of which is affected by one set of poles and the other by the
other poles or winding, by coupling to a commutator as in the ordinary cases.
Here the shunt winding affects the cores or poles S, S', and the two windings D, S2,
would be allowed to affect as in Fig. 2, the smaller cores D, D'.
Fig. 4 only differs from this in having an armature A, extending all the way
through as one core and affected by the fields.
In Fig. 5, a further modification is shown in which the armature itself is divided
and the two parts or subdivisions are connected in series from a, through the
. commutator of the armature A, over to the commutator of the similar armature
whose brushes are marked B, B1. The effect is the same though the construction
is more difficult and complicated and it requires two commutators. The windings
of the armatures A, A', is of course to be made on a basis similar to that of the
former armatures, that is by winding it divided in such a way that an electro-
. motive force in the armature A', the smaller of the two can never rise to a point
. to entirely overcome the effect in the armature A. The arrangement of Fig. 5, is
evidently similar to the coupling of two armatures up to run together by placing
them on the same shaft or by a rigid connection or by a belt and providing one
with a shunt field and the other with a differential field.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed as communicated to me
from abroad, I declare that what I claim is:
.
1. The combination, in an electric motor, of a divided armature core, two field
magnets acting respectively upon the two parts of the divided armature, and means
for varying or changing the relative effects of said field magnets in proper manner
to restore the speed to normal.
2. The herein described method of regulating for constancy of speed and increase
of speed under load in electric motors, consisting in producing, effective rotation by
two field magnets or portions of field magnets and two corresponding portions

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f motor armature conductor connected, one portion of field magnet having a
estricted capacity, and decreasing the magnetism of the lesser or restricted portion
on a decrease of speed.
3. The herein described method of compounding an electric motor, consisting in
maintaining a rotation by a derived circuit coil or its equivalent as described acting
upon one part of the armature or armatures with a substantially constant effect, and
applying at another part a regulating opposing influence incapable of overbalancing
the effect of the main field magnetism.
4. The herein described method of compounding in electric motors, consisting in
establishing two motor poles or sets of poles polarized in a direction such that they
will conspire to produce rotation at light load, and reversing the polarity of one
upon increase of load beyond a predetermined amount.
5. In an electric motor, the combination, substantially as described, of two sets
of field magnet poles, both normally polarized, so as to conspire to produce rotation,
from cores of different capacity, the less core being constructed with reference to
the desired capacity of regulation and an opposing coil applied to the core of less
capacity, as and for the purpose described.
6. The combination in an electric motor, of an armature having a divided core,
field magnet poles of fairly constant strength located at one portion of said core,
and variable or speed regulating field magnet poles located at the other portion of
said core and incapable of overbalancing or overcoming the effect of the constant
field poles, as and for the purpose described.
7. In an electric motor, the combination with an armature having a divided core
and having its conductor or conductors extended across from one of said divisions
to the other, of two sets of field magnets of different capacity located respectively
at said divisions, as and for the purpose set forth.
8. The combination in an electric motor, of constant field magnet cores of large
magnetic capacity, and differential field magnet cores of smaller magnetic capacity,
and an armature with a divided core the separate divisions of which are affected
respectively by said magnet cores.
9. The combination in an electric motor, of two field maguet cores or sets of
cores one of less magnetic capacity than the other, a derived circuit coil exciting
both sets of cores, and an opposing main circuit coil applied to the core of less
capacity, as and for the purpose described.
10. The combination in an electric motor, of two or more sets of electro-magnetic
field poles, one set having a comparatively constant magnetization, and another set
of much smaller maximum magnetic capacity as compared with the first set and
having its magnetism dependent upon the load on the motor, and opposite to that
of the main fields under heavy load.
11. The combination with a revolving armature, having a divided core, of
constant and variable field electro-magnet poles of different size at the different
divisions of said core and applied to the same or connected armature conductors.
12. The combination with an armature having a divided core and armature
conductors passing over both divisions thereof, of a constant field electro-magnet,
5 and a smaller variable field magnet acting respectively at said divisions upon the
same portion of said conductor.
13. The combination, substantially as described, of two field magnet cores of
different size producing a compound field for connected armature conductors,
field coils S, S 2, wound on the larger and smaller cores respectively and carrying
50 current of substantially constant amount, and a differential or regulating coil D
carrying current of variable amount and wound upon the smaller core.
14. The combination with an armature having a divided core, of a field magnet
having two sets of cores provided with poles of different width but of substantially
the same circumferential extent and located respectively at the division of said
55 armature, and arranged on the same line parallel to the axis of the armature, and
means for differentiating the magnetic effects of said sets of cores.
15. A field magnet having a set of field magnet cores wound with fine wire, and

page_text: -a smaller variable or regulating set wound with coarser wire and arranged in the
same line with the first parallel to the shaft of the machine, in combination with an
armature having a divided core the divisions of which are located at the poles of
the field and regulating magnets respectively.
16. The combination with an electric motor run from constant potential wires
and having a field coil connected in a branch across said wires, of an armature
having a divided core of which one division is located at said field coil, and a
compound coil wound on a separate core or support from the first and acting upon
the other division of said armature, said second coil carrying current varying with
the counter electro-motive force of the motor armature and being properly related
or proportioned to the first to maintain the speed of the motor under changes
of load.
17. The herein described method of regulating an electric motor, run from a
constant potential circuit, for differences of speed, which consists in varying its
counter electro-motive force by causing all its poles to conspire to produce a high
counter electro-motive force for a low speed, and reversing the polarity of a
part of said poles to produce a lower counter electro-motive force for higher
-speed.
For the Applicant,
J. C. CHAPMAN,
70 Chancery Lane, London, W.C., Chartered Patent Agent.