Improvements in and relating to Dynamo Electric Machines.
Year: 1893

page_text: Date of Application, 27th Dec., 1893-Accepted, 24th Mar., 1894
COMPLETE SPECIFICATION.
Improvements in and relating to Dynamo Electric Machines.
I, ELIHU THOMSON, a citizen of the United States, residing at Swampscott,
in the County of Essex, and State of Massachusetts, United States of America
Electrician, 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 methods and means for compounding a dynamo
electric machine or generator of electricity so as to maintain a potential which is
fairly constant under load, or to obtain an increased potential in passing from light
to full load, or in general to increase the effect of the field magnetism of such
machine as the load comes on.
My invention dispenses with the ordinary series winding, such as is present in
compound wound dynamos, although the principles of my invention might be used in
conjunction with such compound winding. I am able, by my invention, to
construct a machine, the excitation of the field of which may be maintained either
by a shunt to the mains, or by a separate excitation fairly constant in character,
while the voltage of the machine is maintained, as the load comes on, automatically,
without having recourse to the passage of current through a series winding affecting
the field, and therefore without incurring the inconveniences which may arise in the
use of such compound machines when used to charge storage batteries, or accumu-
lators, from possible reversals of current and reversals of the effect of the series
field. I am also enabled to run such dynamo-electric machines in multiple without
the use of equalizers, or equalizing connections, such as are commonly employed
with compound-wound machines.
By so constructing dynamo-electric machines I have been able to maintain the
full potential of the machine during a variation of work from no load to full load,
the field magnets having no series winding whatever.
In my invention I may use any form of armature suitable for rotation in the field,
and the generation of currents in the winding, and therefore in describing my
invention I will assume that a good type of armature has been employed, and will
not, therefore, describe the winding. It may be remarked, however, that the
armature may be wound with the Gramme winding or have a drum winding, with
any of the various modificatious thereof. It may be made with or without
projections, though I prefer an armature having projections and the winding set
in between the projections. The body of the armature should have plenty of
laminated iron.
The principle of my invention is to make the current which flows in the armature
winding, under load, so act as to produce a field of force in which the armature winding
moves, and which field will be in proportion to the load on the armature, and
therefore increases the electromotive force, or counteracts any decrease of electro-
motive force which might be suffered under load. This, briefly stated, is
accomplished in my method, by placing opposite those parts of the armature
which become polarized by the currents flowing therein, iron masses or what
might be called dead poles, which only become active when the armature is under
load.
.
In the accompanying drawings,
D
the eccential features of my invention.

page_text: is a diagram illustrative of the actions involved.
Fig. 5 is a figure showing the application of my invention to a multipolar
dynamo.
Fig. 6 is a further diagram showing the application of my invention to other
forms of apparatus.
Figs. 7, 8 and 9 are drawings showing a modified embodiment, and Fig. 10 is a
further diagram illustrative of the actions.
In Fig. I let A represent any good form of armature suitable for revolution
opposite field poles, and provided with a commutator K in the ordinary way. Let
it be revolved in the direction shown by the arrow, and the brushes B, B applied
just in front of the field poles wound with coils S, S¹. The connections from the
brushes are carried out and the load, as of lights, batteries, or motors, L, L, fed
therefrom. The coils S, S', are made of comparatively fine wire and are put in
shunt to the brushes of the machine, by connections, as shown, which constitute a
shunt winding. As an alternative construction, the coils may be put in circuit with
a separate source of current from the exciter E as indicated by a dotted circuit in
the figure.
The excitation provided by the coils S2, S' acting on their appropriate poles
presented to the armature A should be such that the machine gives its normal
potential, and the poles acted on by the coils S2, S', may be carried up to a high
state of magnetization if desired, or the coils, S2, S₁, may be given a very high
magnetic force, as there is no need of limiting the magnetization for the sake of
obtaining a further strengthening of the poles during working. In addition to the
wound poles S, S', I provide a pair of poles D, D', which I may term dead poles
under light load, as they are not magnetized by any winding applied to them, and
when the armature is not developing current these masses D and D', which are
connected magnetically exterior to the armature, remain unmagnetized, but when
the armature is under load they become active magnetic poles, because they are
presented to the armature in the area included between the dotted lines a a and bb.
The dotted line a a represents the diameter of commutation where the brushes are
applied, and the dotted line bb represents the diameter of neutrality, or the
diameter at which brushes placed one on each side would give no difference of
potential. The dotted line represents, in fact, a line showing the neutral
magnetic points of the armature core considered as a magnet, and it will be seen
that the poles D, D', are applied in the quadrant between the lines a a and b b.
If the machine be properly proportioned an effect of more or less perfect
compounding is obtained; that is to say, properties are conferred upon the machine
similar to those which are obtained by winding the field magnets with coils or a
series winding, in addition to the shunt winding, or separately excited winding, and
as this result is accomplished without resorting to series winding there is no danger
of reversal in charging accumulators, and there is no need of equalizing connections
when such machines are run in multiple. The machines to be run in multiple
should preferably not be proportioned as to obtain an effect of over-compounding
by the practice of my invention.
Instead of connecting the magnetic masses D, D' as shown in Fig. I they may
he separated altogether from the magnetic structure bearing the coils S³, S', and
they may be connected around the armature, as shown in Fig. 2, and may, in fact,
forin the means for supporting the bearings of the armature, as there indicated in
section, or, as in Fig. 3, the magnetic masses or poles D, D', may be connected at
one end only to a single bearing to be used as at J. All that is required is that
these magnetic masses D, D', shall be sufficient in section, and be so intimately
connected with the magnetic resistance of the circuit through them from the
armature, as will give the described effect, and for this reason I prefer an armature
with teeth or projections, or what is now sometimes called an "iron-clad " armature,
running close to the parts D, D'.
To exemplify the actions in my invention, reference is had to Fig. 4. Assuming
the armature to be stationary and that current is applied through the armature

page_text: winding by the brushes placed on the line a a, polarities would be induced in the
armature structure, as indicated by the letters near its periphery, or, in other words,
the armature would become a magnet and tend to complete a magnetic circuit
external to itself, and the neutral line of the magnet would be through bb. In the
operation of such a generator structure the pole S' would be magnetized by a coil
placed thereon, as a north pole N, N, and the pole S2 would be magnetized as a
south pole S, S. But with the current passing in the armature, as assumed at first,
or with the current which is now generated in the arinature by its revolution, there
will be induced by the armature magnetism after the armature is placed under load,
poles in D of south name or of south polarity, and polarity in D' of north character.
It will therefore be seen that on one side the line a a, or diameter of commutation,
the field will be all north due to S¹ and D', and on the other side the field will be
all south, due to S2 and D. The wire of the armature therefore will be cutting
magnetic lines in one direction on each side of the line a a, and in the other direction
on the other side of the line aa which is the condition for best work as a
generator. Assume, now, that the amature current is cut off, or ceases, as from
failure to have a load, or owing to translating devices, or other energy using
or storing devices, being cut off from the circuit, then the polarities of the armature
fail to manifest themselves except in so far as they are induced under the
poles S1, S2, which still remain active, and the poles D, D' become dead poles, and
the lines of magnetism which the armature had imparted to the circuit through
these poles will be withdrawn. The armature will then be working in a weaker
field, and thus the potential instead of increasing may be made to remain constant,
or be the same as when the armature was under full load, even though the armature
is without load. The compounding effect then in my invention is obtained by the
armature as a magnet to produce by induction a supplementary field instead of by
an external series winding. The armature is. thus revolved in a compound field
composed of a normal field and a supplementary field produced by induction from
the armature.
In applying my invention to a multipolar form of machine it is only necessary to
repeat the sequence of excited poles and dead poles, to use the term, around the
arinature in the proper manner. Thus in Fig. 5 a four-pole structure is shown.
As an illustration, the opposite brushes are connected and there are four brushes.
There are four poles excited either in shunt or by a separate excitation, S¹, S²,
$3, $*, and four of the armature magnetized poles D', D², D³, Dª, alternating with
the others, and placed in proper relative position, as represented in Fig. 1 or
Fig. 4. The number of poles of course will depend upon the construction of the
apparatus, and the arrangement may be extended to cover a multipolar machine
with many poles.
Fig. 6 is intended to show that the armature structure may be without a com-
mutator provided that the currents passing in it are such as will produce a definite
polarity in a definite direction, as a , which is the case when a commutator is used.
The invention might therefore become applicable to dynamos developing alternating
currents in suitable windings.
A further modification of the invention is shown in Figs. 7, 8, and 9. In this
case there are substantially two armatures or revolving bodies of magnetizable
laminated iron, as A, A', one of which, A, revolves between iron masses connected,
as D, D', and the other revolves between poles wound with coils S², S', forming
practically a separate field magnet system. The windings over the two armature
bodies A, A' are made substantially one, that is the conductors are carried over
both armature bodies, as plainly exhibited in Fig. 9, and form substantially the
same winding, the commutator connections being arranged in the ordinary way
with brushes B, B' to take off the current, as shown in Figs. 8 and 9.
In this case
the polar portions D, D' and the poles affected by the exciting winding S, S¹ will
be angularly displaced about in the relation shown in Figs. 7 and 8 if superposed
or if the gaps between the poles were to be placed in corresponding relation, there
would be a twist in the windings occurring between the armature bodies at the

page_text: position marked T in Fig. 9, the amount of the twist being such as to throw the
induction in the two sections of the winding A, A' into proper relation to give
the effect of the angular displacement of one set of poles with respect to the other,
as exhibited in Figs. 7 and 8, which represent their relative positions when the
windings are straight. In this construction there is no polarity developed in the
magnetic circuit of D, D', until the armature is under load, when, as before,
the armature itself, by acquiring polarities, as indicated in Fig. 7, induces opposite
polarities in the field poles D, D', which have the effect of compounding or causing
the armature section A to become a generator in addition to the section A', when
under load. It will be well understood that if the current through the armature be
reversed from that which passes when the machine is a generator, the opposite
polarities will be induced in the poles D, D', as in Fig. 10, to what would exist
when the armature is used as a generator. The machine would become a motor
in the latter case, and the effect would be to weaken the generator field strength
under load and tend to maintain the speed of the motor under work. My
invention relates more particularly, however, to generators, as the difficulties of
commutation of a motor are increased when run in the way last described.
my
Having now particularly described and ascertained the nature of said
invention, and in what manner the same is to be performed, I declare that what I
claim is :
1. The method of sustaining or increasing the electromotive force of a dynamo-
electric machine, which consists in magnetizing pole pieces adjacent to the polarized
part of an armature by induction from the armature itself.
2. The method of sustaining or increasing the electromotive force of a dynamo-
electric machine, which consists in inducing polarity in pole pieces adjacent to the
polarized part of an armature by means of the current flowing in the conductors
upon the armature itself.
3. The method of sustaining or increasing the electromotive force of a dynamo-
electric machine, which consists in causing currents in the conductors upon an
armature to induce in an unwound field magnet a field of force in which the
armature moves.
4. The method of automatically sustaining or increasing the electromotive force
of a dynamo-electric machine, which consists in rotating the armature in a
compound field composed of a normal field and a supplementary field produced
by induction from the armature so as to vary in correspondence with the current
therein.
5. The method of sustaining or increasing the potential of the generated current
of a dynamo-electric machine during an increase of load, which consists in dividing
the magnet poles, magnetizing one pole of each division to approximately full
strength and inductively magnetizing the other pole by the armature magnetism in
correspondence to the increase of load.
6. The method of sustaining or increasing the potential of a dynamo-electric
machine in correspondence to an increase of load, which consists in placing masses
of iron having no conductor thereon adjacent to those parts of the armature lying
between the diameter of commutation and the diameter of neutrality.
7. A dynamo-electric machine having masses of iron with no conductor thereon
adjacent to those parts of the armature lying between the diameter of commutation
and the diameter of neutrality.
8. A dynamo-electric machine having two or more sets of poles co-acting to
develop electro-motive force in the armature winding, one pole of each set being
energized by the current in a circuit extended from the armature winding, and the
other pole of each set being inductively magnetized by the armature.
9. A dynamo-electric machine having its field magnet poles of each polarity
divided, one division of such pole being energized to full magnetization, and the
other division arranged adjacent to the polarized portion of the armature; whereby
on an increase of load the second division is strengthened by magnetic induction

page_text: from the armature in correspondence with the increase of load, thus acting, to
sustain or increase the electromotive force of the generated current.
10. A dynamo-electric machine having near each of its field magnet poles a
"dead pole," substantially as described.
11. A dynamo-electric machine having near each of its field magnet poles and
adjacent to the armature, a "dead pole," arranged on the same side of the diameter
of neutrality of the armature as the field magnet pole to which it is adjacent, as
set forth.
12. A dynamo-electric machine having a shunt wound field magnet, and two
"dead poles" magnetically connected and arranged between the diameter of
commutation and the diameter of neutrality of the armature, substantially as
set forth.
13. A dynamo-electric machine baving "dead poles" alternating with its field
magnet poles, all of said poles being magnetically connected, substantially as
described.
ינו בז
211
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.