Improvements in Dynamo Electric Generators and Motors.
Year: 1893

page_text: Date of Application, 1st Aug., 1893-Accepted, 7th Oct., 1893
COMPLETE SPECIFICATION.
Improvements in Dynamo Electric Generators and Motors.
A communication from HARRIS JOSEPH RYAN, of Cornell University, Ithica, in
the State of New York, United States of America, Professor.
I ALFRED GEORGE BROOKES of 55 & 56 Chancery Lane in the County of
London 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:-
This invention has for its object to improve the construction of dynamo electric
generators and motors in a manner to neutralize the reactionary armature currents
and thereby prevent the consequent shifting of the neutral point with its attending
evils. In dynamo electric generators the magnetizing forces of the field tend to
produce magnetic lines running from the south to the north poles of the field and
straight through the armature, the direction of the magnetic field then extending
direct from one to the other pole of the field. When, however, the armature is
set in motion and is permitted to generate current, the currents in the armature
windings which pass around the armature core tend to magnetize the said core in
such a manner that the magnetic lines stand at right angles to or crossing the
magnetic lines extending between the field poles.
The effect of these cross magnetic lines set up in the armature is to twist or
distort the magnetic field normally extending straight across from one field pole to
the other, and to twist said field into an angular position, being the mean position
between the two opposing magnetic fields.
The result of this distortion of the magnetic field is to shift the diameter of
commutation which is always at right angles to the field, from its normal position
between the poles forward into an angular position at right angles to the distorted
or angular field, the neutral point which always lies in the diameter of commutation
being, therefore, also shifted.
This shifting of the diameter of commutation and neutral point causes sparking
at the brushes, falling off of potential and kindred irregularities in the action of
the machine. To overcome these deleterious effects it has heretofore been the
custom to so increase the magnetizing force of the field as to overpower the
reactionary armature currents and maintain the field magnetism substantially in its
normal position or as nearly in such position as possible.
This method, however, involves an abnormal consumption of energy which
would not otherwise be needed, and after all the desired end is but very imperfectly
accomplished.
To overcome this distortion of the field without employing the abnormal
field current it has been attempted to neutralize the armature reactions by
balancing or opposing the same by means of strong stationary coils to produce an
opposite magnetizing effect, these opposing coils in some instances being secured to
the surfaces of the pole pieces and in other cases let into the recesses or grooves
in the pole pieces. Both of these methods are objectionable, the first because it
is difficult to properly secure the opposing coils to the pole pieces, and also
because it necessarily increases the gap between the armature core and the pole
pieces; and the second because any considerable cutting away of the surfaces of
the poles breaks the continuity of the magnetic field and causes fluctuations in the
electromotive force developed by the armature coils as they cross this in regular
field. In the efforts to neutralize the reactionary armature currents of the
armature without creating other equally injurious effects, as above mentioned, my

page_text: correspondent has discovered that by placing the opposing or counteracting con-
ductors of the balancing coils in holes or openings entirely beneath the surfaces
of the pole faces and cutting a very thin slot from these holes out to the pole
faces that no injurious effects whatever result from the use of the balancing
coils.
In the drawings
Fig. 1. represents an end view of the pole pieces and armature of a four pole
dynamo electric machine to which my invention is applied.
Fig. 2. a sectional view on the dotted line X, X, said figure showing the method
of winding the coils.
Figs. 3 and 4 sectional and plan views respectively showing a modified form,
being especially adapted to a two pole generator, and
Figs. 4 and 5 yet other modifications to be described.
Referring to the drawings S, N, S', N', of Fig. 1 are the pole pieces of the
generator and A the armature.
a, b, c, d, etc., are the holes through the pole pieces.
These holes may be circular, or rectangular, or oval, or whatever shape will best
accommodate the conductors.
The points to be observed, in determining the shape and position of the holes
are these, they must be of sufficient size to accommodate the required number
of conductors in each hole and this in turn will be determined by the ampere
turns on the armature, the aggregate cross section of metal between the holes
must be as great as the mean cross section of the poles, the holes must be
placed back from the pole faces a distance dependent on their width, this distance
being such as will peimit the magnetic lines to flow around the holes so as to
give a uniform distribution of magnetism on the pole faces, the slots from the
hole to the pole faces may and should preferably be as thin as possible, in any
case being thinner than the space between the pole face and armature core.
The object of these slots is to prevent local magnetic circulation immediately
around the conductors of any one hole.
The thinnest possible air gap will serve, by its comparatively high reluctance,
to practically prevent all such local circulation.
The coils may be wound with any suitable conductor, but copper ribbon is
preferable.
The winding is best applied in as many separate coils as there are pole pieces,
each coil embracing one half of two poles.
Thus the conductor starting at in Figs. 1 and 2 passes first up through
hole, then across to hole c, down and back to hole b, up and across to hole c,
down and across to hole a, up and across to hole d, down and across to hole a, up
and across to hole d, and finally down to the other end of the coil.
If copper
ribbon is used for the winding, the various turns of the coil need not cross each
other but may be wound over and over as indicated in Fig. 2, thus making a
neat and compact winding and one which does not cross the ends of the armature
in any way and avoids thereby interfering with the easy removal of the
armature.
The winding of each coil should embrace one half the holes in each pole
piece and the current must circulate through each coil in such a way that it
will pass in the same direction through all of the holes of all pole pieces of like
polarity and in the opposite direction through the holes of the other pole.
The various coils may all be connected in series, and in series with the armature,
or the coils may all be in parallel and in series with the armature, or a com-
bination of series and parallel may be used.
In choosing any method of connection, however, the point must be observed
that the total number of ampere turns through the pole pieces shall be the same,
approximately at least, as the total number of ampere turns on the armature.
The chief advantages resulting from the use of my invention are these:-It is
well understood by dynamo designers that the narrower the air space between the

page_text: armature core and pole pieces of a dynamo the smaller the amount of energy
needed to maintain the magnetic field, and consequently the greater will be the
efficiency of the machine.
Unfortunately, however, the smaller the amount of energy consumed in the field
coils, or more properly, the less the magnetic reluctance of the field circuit, the
more marked and disastrous will be the effects of armature reactions.
One of the chief advantages therefore, resulting from the use of balancing coils
lies in the fact that it permits the use of a very small air gap, it being perfectly
feasible, in fact, to reduce the air gap between armature core and pole pieces to
what is barely sufficient clearance for the free rotation of the armature, the
armature winding of course being placed underneath the surface.
Now if a small air gap is to be used it is of course essential that the balancing
coils should not be placed on the surface of the poles.
It is also very objectionable to place them in grooves, because these grooves
leave the pole surface irregular and make the magnetic distribution along it
broken and discontinuous, resulting in producing an intermittent electromotive
force in the conductors of the armature and also fluctuations of magnetism in the
core which very greatly increases the heating due to hysteresis.
The shorter the air gap the more marked and distinct will be these bad effects
of course.
By the use of my invention all of these bad effects are avoided, and a continuous
and even distribution of magnetism along the pole faces is obtained.
Thus it is possible by the use of my invention to greatly improve the design of
dynamo machinery, by using balancing coils and small air gaps, without incurring
any of the evils which might otherwise result from the use of such coils. It is
also a very great advantage to have the coils so placed and so wound that they
shall be compact and occupy as little space as possible, and especially so that
they shall not cross the ends of the armature, since they would thereby interfere
more or less with the accessibility of the armature and prevent its removal from
the machine.
By the use of my invention as in Figs. 1 and 2, the coils he compact against
the pole pieces and occupy so little space as to offer no obstruction to the free
inspection of the armature and since they do not cross the ends of the armature
they do not interfere in any way with the ready removal of the armature from its
bearings whenever this becomes necessary.
In Figs. 3 and 4 I have shown a single coil passed through suitable openings in
the opposing poles of a two pole generator.
Fig. 5 shows yet another method of running the coils through the holes, and
Fig. 6 yet another method, all of which are clearly intelligible from the drawings
alone.
This invention relates particularly to the method of applying the balancing
coils and securing all the advantages attendant upon their use without any of the
evils which may result, and, therefore this invention is not restricted to the exact
construction or method herein shown, for the same may be varied more or less
without departing from the spirit and scope of the invention.
Having now particularly described and ascertained the nature of the said inven-.
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. In a dynamo electric generator or motor, the construction or arrangement
and use of balancing coils wound through openings or holes in the pole pieces and
applied for the purpose of overcoming armature reactions, substantially as and for
the purpose set forth.
2. In a dynamo electric generator or motor, the construction or arrangement
and use of balancing coils applied for balancing armature reactions wound through
holes in the pole pieces, each of the said coils being wound spirally round and
round in one continuous coil, through holes in the pole pieces and with the

page_text: space between adjacent poles at the centres of said coils, substantially as shown
and described.
3. In a dynamo electric generator or motor the construction or arrangement
and use of balancing coils for overcoming armature reactions, each of said coils,
consisting of a ribbon shaped conductor wound spirally round and round through
holes in the pole pieces, in such a way that the separate layers shall nowhere cross
each other, substantially as and for the purpose described.
4. In a dynairo electric generator or motor, the combination with the pole
pieces, of a series of holes placed transversely beneath the pole surfaces, and con-
ducting coils wound through said holes, substantially as and for the purpose
specified.
5. In a dynamo electric generator or motor, a series of holes placed trans-
versely beneath the pole surfaces, the pole pieces, slots separating the metal
between the holes and the pole faces, and conducting coils wound through said
holes, for the purpose specified.
6. In a dynamo electric generator, or motor, the arrangement, or combination
and use of balancing coils, and their application for the purpose of overcoming
armature reactions substantially as and for the purpose set forth.
Dated the 20th don of Lul 1000
WM. BROOKES SON,
55 & 56, Chancery Lane, London, Agents for the Applicant.