Improvements in Dynamo-electric Generators and Motors.
Year: 1887

page_text: Date of Application, 27th June, 1887
Complete Left, 8th Sept., 1887.
Complete Accepted, 11th Oct., 1887.
PROVISIONAL SPECIFICATION.
Improvements in Dynamo-electric Generators and Motors.
We, ALEXANDER PELHAM TROTTER, and HENRY WILLOCK RAVENSHAW, both of
Bull Green Works, Halifax, Yorkshire, and WALTER THOMAS GOOLDEN, of 2 Victoria
Mansions, Westminster, in the county of Middlesex, Electrical Engineers, do hereby
declare the nature of this invention to be as follows:-
This invention relates to improvements in dynamo-electric generators and motors
and has for its object the providing of means whereby the electromotive force of the
armature of a dynamo-electric generator may be modified, such modification being
obtained by altering the useful, or inductive, effect of the field magnets without
reducing their magnetic saturation to such an extent as would render their magnetism
liable to become unstable.
It is well known that the electromotive force of a shunt wound generator may be
modified by introducing a variable resistance into the shunt circuit, while in the case
of a series wound generator a similar resistance may be placed as a shunt to the field
coils, or the coils of the field magnets may be wound in sections, provision being made
for cutting the sections out of, or placing them in, circuit, or otherwise altering the
disposition of their connections, as may be required.
In all these methods, however, the modification of the electromotive force is
obtained by weakening the whole magnetic field, and as this weakening of the
magnetic field cannot be carried far without producing an unstable condition of the
same it follows that the range within which the modification of electromotive force can
be effected is thereby limited.
Now in dynamo-electric generators, or motors, constructed in accordance with this
invention provision is made whereby the useful magnetism may be modified through
a considerable range, while at the same time the main, or field, magnets, are always
maintained at practically their normal state of saturation, and thus the electromotive
force of a generator may be varied by modifying the useful magnetism without the
usual consequent risk of magnetic instability arising therefrom.
In its general method the invention consists in applying to a single horse shoe, or
other suitable form, of field magnet, a second, or additional, magnetic circuit, such as

page_text: a similar horse shoe field magnet, which, when working under the conditions of a
minimum electromotive force, would offer comparatively so much smaller a magnetic
resistance than the armature and its air space that nearly all the lines of force would
be diverted through it. Though described as applied to a single horse shoe field
magnet it will be understood that, similarly, to a multiple system of field magnets,
one, or more, of the additional magnetic circuits may be applied.
This second, or additional, magnetic circuit is provided with coils in the same
way as the main magnet, and by passing a current through these coils the diversion
of the magnetism of the main magnets may be obstructed until, with a certain
strength of current, no lines of force would pass through the second, or additional,
magnetic circuit and the electromotive force of the armature would then be
produced solely by the whole useful magnetism of the main magnet, this condition
corresponding to the normal electromotive force, or output.
Further, as the second, or additional, magnetic circuit is similar to the main
magnet it follows that it may be used in the same way and by increasing the current
through its coils it may be caused to assist the main magnet until the effect of the
two is combined, thus doubling the output of the generator as at first described and
attaining the conditions of maximum electromotive force.
In the case of a shunt wound generator the current through the coils of the second
magnet may be controlled by the addition of a resistance in series with it, while in
the case of a series wound generator the current through the coils of the second
magnet may be controlled by a resistance arranged as a shunt on the coils, or by
dividing the coils into sections, or they may be shunt coils. The resistances in either
case, whether arranged in series with shunt coils, or as shunts on series coils, may be
controlled by hand, or by any suitable automatic regulator, or they may automatically
regulate the current through themselves, by the relation between the electromotive
force and their own resistance.
In carrying this invention into practice in its simplest form an ordinary series
wound "Gramme" machine, from which it is desired to produce a constant current,
is employed, the two half bars, or cores, on one side of the pole pieces forming, when
properly wound, the main, or field magnet, while the other two half bars, or cores,
form, when wound, the second, or additional magnet.
Though the invention has so far been described as applied to a dynamo-electric
generator only it will be understood that the magnetic field of an electro-motor may
be similarly modified by the diversion of lines of magnetic force through a second
magnet.
In order that the changes in the electromotive force of the armature may be
effected with rapidity and certainty a break should be made in the continuity of the
magnetic circuit. This may be effected either by an air space, or by the intro-
duction, and intervention of a suitable non-magnetic metal shield, which may
conveniently take the shape of a collar, or tube, on the outer end of the bar, or
core, which passes through the yoke or side of the machine, washers, of non-magnetic
material, being also used if necessary.
371
.
1037

page_text: COMPLETE SPECIFICATION.
Improvements in Dynamo Electric Generators and Motors.
We, ALEXANDER PELHAM TROTTER, and HENRY WILLOCK RAVENSHAW, both of
Bull Green Works, Halifax, Yorkshire, and WALTER THOMAS GOOLDEN, of 2 Victoria
Mansions, Westminster, in the county of Middlesex, Electrical Engineors, 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 relates to improvements in dynamo-electric generators and motors,
and has for its object the providing of means whereby the electro-motive force of the
armature of a dynamo-electric generator may be modified, such modification being
obtained by altering the useful, or inductive, effect of the field magnets without
reducing their magnetic saturation to such an extent as would render their magnetism
liable to become unstable.
it is well known that the electro-motive force of a shunt wound generator may be
modified by introducing a variable resistance into the shunt circuit, while in the case
of a series wound generator a similar resistance may be placed as a shunt to the field
coils, or the coils of the field magnets may be wound in sections, provision being
made for cutting the sections out of, or placing them in, circuit, or otherwise altering
the disposition of their connections, as may be required.
It has also been proposed to alter the output of a dynaino electric generator by so
constructing the field magnets that their pole pieces may be caused to approach nearer
to, or recede from, the armature as required; while in another form of generator it
was sought to attain the same object by constructing the yoke in two parts, one of
which was movable.
In all these methods, however, the modification of the electro-motive force is
obtained by weakening the whole magnetic field, and as this weakening of the magnetic
field cannot be carried far without producing an unstable condition of the same, it
follows that the range within which the modification of electro-motive force can be
effected is thereby limited.
Now in dynamo-electric generators, or motors, constructed in accordance with this
invention provision is made whereby the useful magnetism may be modified through
a considerable range, while at the same time the main, or field, magnets, are always
maintained at practically their normal state of saturation, and thus the electro-motive
force of a generator may be varied by modifying the useful magnetism without the
usual consequent risk of magnetic instability arising therefrom.
In its general method, and when it is desired to effect the modification of the
electro-motive force by means of the current itself, the invention consists in applying
to a single horse shoe, or other suitable form, of field magnet, a second, or
additional, magnetic circuit, such as a similar horse shoe field magnet, which,
when working under the conditions of a minimum electro-motive force, would offer
comparatively so much smaller a magnetic resistance than the armature and its air

page_text: .
space, that nearly all the lines of force would be diverted through it. When,
however, it is desired to effect the modification of the electro-motive force by
mechanical means, a keeper bridging the pole pieces of the field-magnet is employed.
This keeper diverts more or less lines of force from the armature according to its
proximity to the pole pieces without in any way reducing the state of saturation of
the field magnets; and its relative position thereto is controlled by means of a screw
or other suitable device.
Though described as applied to a single horse shoe field magnet, it will be under-
stood that, similarly, to a multiple system of field magnets, one, or more, of the
additional magnetic circuits may be applied, or that a larger, or additional keepers,
may be used as desired.
When the modification is to be effected electrically the second, or additional,
magnetic circuit is provided with coils in the same way as the main magnet, and by
passing a current through these coils the diversion of the magnetism of the main
magnets may be obstructed until, with a certain strength of current, no lines of force
would pass through the second, or additional, magnetic circuit, and the electro-motive
force of the armature would then be produced solely by the whole useful magnetism
of the main magnet, this condition corresponding to the normal electro-motive force,
or output.
Further, as the second, or additional, magnetic circuit is similar to the main magnet
it follows that it may be used in the same way, and by increasing the current through
its coils it may be caused to assist the main magnet until the effect of the two is
combined, thus doubling the output of the generator, as at first described, and attaining
the conditions of maximum electro-motive force.
In the case of a shunt wound generator the current through the coils of the second
magnet may be controlled by the addition of a resistance in series with it, while in the
case of a series wound generator the current through the coils of the second magnet
may be controlled by a resistance arranged as a shunt on the coils, or by dividing the
coils into sections, or they may be shunt coils.
The resistance in either case, whether arranged in series with shunt coils, or as
shunts on series coils, may be controlled by hand, or by any suitable automatic
regulator, or they may automatically regulate the current through themselves, by the
relation between the electro-motive force and their own resistance.
In carrying this invention into practice in its simplest electrical form an ordinary
series wound "Gramme" machine, from which it is desired to produce a constant
current, is employed, the two half bars, or cores, on one side of the pole pieces
forming, when properly wound, the main, or field magnet, while the other two half
bars, or cores, form, when wound, the second, or additional magnet.
In its simplest mechanical form a keeper, hinged to one pole piece of a generator,
is caused to approach nearer to, or recede from, the armature by means of a screw
engaging the free end of the keeper.
Though the invention has been so far described as applied to a dynamo-electric
generator only, it will be understood that the magnetic field of an electro motor may
De similarly modified by the diversion of lines of magnetic force through a second
magnet or keeper.
In order that the changes in the electro motive force of the armature may be
effected with rapidity and certainty when the electrical method is employed a break
should be made in the continuity of the magnetic circuit. This may be effected
either by an air space, or by the introduction, and intervention of, a suitable non-
magnetic metal shield, which may conveniently take the shape of a collar, or tube,
on the outer end of the bar, or core, which passes through the yoke or side of the
machine, washers, of non-magnetic material, being also used if necessary.
It is also desirable that in the keeper, a non-magnetic "break," either of air, or
non-magnetic material, should be used to avoid the sluggishness in the action of the
keeper that would otherwise arise from the presence of the complete magnetic
circuit.
Having thus set forth the nature of our invention and shown in what manner the

page_text: same is to be carried into effect we will now proceed to more particularly describe the
same, reference being made to the accompanying drawings.
Figure 1 shows, diagrammatically, the arrangement for modifying the electro-
motive force, by electrical means, and as applied to an ordinary series wound
generator.
In this case the main magnet A, A, would be constantly magnetised, while the
second, or additional, magnet B, B, would vary in its magnetism, and consequently
in its capacity to divert more or less the lines of magnetic force from the armature,
with the amount of resistance offered by the rheostat placed in the shunt circuit as
shown. Assuming, by way of illustration, the resistance at C to be nil, then,
theoretically, the whole of the current would pass by the rheostat to the - (negative)
brush direct, the limbs B, B, of the second, or additional, magnet in this case
remaining unmagnetised and so diverting from the armature their maximum amount
of the lines of force, and the output of the machine would be correspondingly
decreased.
On the other hand when the resistance at C is increased to its maximum both the
magnets A, A, and B, B, would be equally magnetised and the output of the machine
would be correspondly increased. The necessary air space to ensure certainty and
rapidity in the changes of electro-motive force is conveniently left at D, E indicating
the external circuit.
Figure 2 shows a different arrangement, the magnets in this case being vertical
and placed side by side, instead of pole to pole, as obtains in the horizontal form,
A being the main magnet, and B the second, or additional, magnet.
It is obvious that to either of the above forms of magnets, one, or other, of the
arrangements of winding, as hereinbefore mentioned, may be applied.
Figure 3 shows one means for carrying this invention into effect mechanically.
In this case the main magnet A, A, wound in any desired manner, is provided with
extensions. B, B, of its pole pieces. These extensions are so bored out as to admit of
a rotary iron keeper K working freely therein. It is obvious that this keeper would
divert imore or less the lines of force from the armature according to its relative
position thereto, motion being imparted to the keeper by a worm and wheel, or other
suitable gearing, acting on the shaft upon which it is mounted.
Figure 4 shows a modification, in which the keeper K is binged at one end, its
relative position to the armature being controlled by a screw, worked by a spindle and
hand wheel a. Similarly a cam, or wedge, could be employed to effect the movement
of the keeper K.
Having now particularly described and ascertained the nature of our said Invention,
and in what manner the same is to be performed, we declare that what we claim is:
First The herein before described method of modifying the electro-motive force,
or output, of a dynamo-electric generator, by diverting more or less the lines of
magnetic force in the manner substantially as described and illustrated with reference
to Figs. 1 and 2 of the accompanying drawings.
Second The hereinbefore described method of modifying the electro-motive force,
or output, of a dynamo-electric generator, by diverting more or less the lines of
magnetic force in the manner substantially as described and illustrated with reference
to Figs. 3 and 4 of the accompanying drawings.
Third The application to an electro-motor of one or other of the hereinbefore
described methods, whereby its output or electro-motive force may be regulated or
modified.
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