Improvements in Dynamo-electric Machines.
Year: 1886

page_text: Date of Application, 7th Apr., 1886.
Complete Left, 7th Jan., 1887.
Complete Accepted, 1st Mar, 1887.
RESERV
Improvements in Dynamo-electric Machines.
We JOHN PLATE of Salford Iron Works Manchester in the County of Lancaster
Engineer and JOHN HOPKINSON F.R.S. of 4 Westminster Chambers in the City of
Westminster Civil Engineer and EDWARD HOPKINSON of the aforesaid Salford Iron
Works Engineer do hereby declare the nature of our said Invention to be as follows:-
Our Invention relates to the construction of the armatures of dynamo machines
enabling them to carry greatly increased currents without undue heating, mechanical
straining or disturbance of the magnetic field. The existence of large currents in the
armature in dynamo machines as ordinarily constructed involves a displacement of the
brushes and a consequent reduction in the magnetic field unless the device commonly
known as compound winding be adopted.
By our invention we are enabled to obtain the advantages of compound winding by
a displacement of the brushes in the opposite direction and we avoid the sparking
which would otherwise ensue by introducing suitable resistances in circuit with a
portion of the brushes.
Dynamo machines for carrying large currents have been frequently constructed
with bars of copper instead of wires. In order to secure the hars against the great
circumferential strain we provide the whole or a portion of them with snugs which
engage into metal dises which form a portion of the core of the armature. We make
the end connections by means of copper strips which we attach to the ends of the bars
either by bending the strip beneath the bar or over the bar or introducing it into a
saw cut at the end of the bar securing good contact either by soldering or drawing the
bar and the strip together by means of a screw or screws screwing into a thread in the bar
itself or a thickened end of the strip or a plate preferably of steel, beneath the end of
the strip. When the bars are few in number we use two series of copper strips, as
has already been done, but when muinerous we find it advantageous to use four series

page_text: of strips. With powerful magnetic fields bar armatures are liable to heating from
local currents in the individual bars. We obviate this by duly graduating the dis-
tribution of the field round the armatures so that its intensity shall not too rapidly
increase or diminish at the edges of the pole pieces. This we accomplish either by
suitable extensions at the edges of the pole pieces or by causing the pole pieces more
closely to approximate to the armature at the centres than at the edges.
J. HENRY JOHNSON,
47, Lincoln's Inn Fields, London, W.C.,
Agent for the said John Platt, John Hopkinson,
and Edward Hopkinson.
COMPLETE SPECIFICATION.
Improvements in Dynamo Electric Machines.
We JOHN PLATT of Salford Iron Works Manchester in the County of Lancaster and
JOHN HOPKINSON F.R.S. of 4 Westminster Chambers in the City of Westminster and
EDWARD HOPKINSON of the aforesaid Salford Iron Works 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 :-
Our Invention relates to the construction of the armatures of dynamo electric machines
enabling them to carry greatly increased currents without undue heating mechanical
straining or disturbance of the magnetic field. Our improvements are applicable to
armatures of the form known as the Hefner-Alteneck and also to those of the Gramme
and Disc type which may be used either for generators of electric currents or for
tranformers of Electrical energy into mechanical energy.
Dynamos of these types have been constructed with bars in place of wires whereby a
greater section of copper for carrying the currents is obtained.
The bars being exposed to a tangential stress we secure them on the armature by
means of snugs or lugs which engage into metal discs or plates forming part of the
armature core but it is not necessary that each bar should have a snug or lug thereon
as a portion of them only may be so provided.
In order to complete the circuit between opposite bars at the one end of the
armature and to make the connections to the commutator at the other end we use
strips of copper which form two series of spirals in two planes at right angles to the
shaft. The connections between the bars and the strips of copper can be made in any
suitable way-For example we may bend the strip beneath the bar or over the bar or

page_text: introduce it into a saw-cut at the end of the bar either by soldering or drawing the
bar and the strip together by means of a screw or by screws screwing into a thread in the
bar itself or into a projection of the bar or a plate (preferably of steel) beneath the end
of the strip.
When the bars are few in number we employ two series of spirals but when
numerous we find it advantageous to use four series of spirals.
To obviate the heating through local currents induced in the bars as they pass
through the edge of the magnetic field we form the pole pieces so that the intensity of
the field shall not increase or diminish too rapidly at the edges of the pole pieces-This
we effect by increasing the distance of iron to iron gradually from the middle of the pole
pieces to their edges and sometimes by the addition of suitable pole piece extensions-
The existence of large currents in the armature in dynamo machines as ordinarily
constructed involves a displacement of the brushes and a consequent reduction in the
magnetic field unless the device commonly known as "compound winding" be adopted-
By our Invention we are enabled to obtain the advantages of compound winding by a
displacement of the brushes in the opposite direction and we avoid the sparking which
would otherwise ensue by fixing some of the brushes in advance of the others and
introducing suitable resistance or resistances in circuit with them.
We will explain with reference to the accompanying drawings the manner in which
our Invention may be carried into effect.
Figure 1 shows a Section through a bar armature of the Hefner-Alteneck type, a a
are the bars and the spiral strips of copper at the commutator and pulley ends
respectively. The two bars a a are shewn each provided with three lugs or shugs y
which engage into the armature discs or plates de and
h
Figure 2 is an end view of the armature as seen from the commutator and showing
the spiral direction of the strips of copper which connect the longitudinal bars on
the armature-For the sake of clearness only six spiral connections have been shown.
Figure 3 shows a developement of a portion of the surface of the bar armature of
Figure 1: the bars a are shown in this case with a saw-cut at the ends to receive the
strips and b¹².
Figure 4 is a sectional elevation of a part of a bar armature showing a series of four
spirals on the commutator end, the bars of this armature being more numerous than
those of Figures 1 and 2. and consequently if the connecting spirals were arranged in
two series only they would be very thin and a great proportionate space would be
taken up by insulation-By arranging them in four series these inconveniences are
avoided.
Figure 5 gives a development of a portion of the surface of the bar armature
corresponding to the spiral connections shown in Figure 4-Various ways of making
connection between the bars and the spiral strips are shown by figure 6.
No. 1 shows the strip let into a saw-cut at the end of the bar and secured by a screw.
No. 2 shews the strip bent round over the top of the bar and screwed thereto.
Nos. 3 and 4 shew methods of fixing the strip underneath the bar. In No. 4 a steel
plate is put under the strip, the securing being effected by a screw as shewn. In all
cases other modes of fastening than by screws may be used for example brazing or
soldering.
Figure 7 illustrates the method of adjusting the brushes on the commutator and the
introduction of suitable resistances to reduce sparking. T and Tare the main terminals.
and are resistances inserted in the circuit of the brushes Im on one side and o p
on the other side. These resistances and the position of the brushes with respect to
each other may be varied to suit any type of machine.
Figure 8 explains the improvement we make in the shape of the pole pieces to avoid
the heating of the bars from local currents.
No. 1 shows the ordinary shape.
No. 2 that according to our improvement specially applicable to bar armatures,
whereby the distance of iron to iron is increased gradually from the middle of the pole

page_text: No. 3 shows the extensions of the pole pieces by an independent piece of metal
attached to them.
Having now particularly described and ascertained the nature of our invention
and in what manner the same is to be carried into effect we declare that what we claim, is.
First--In dynamo electric machines the combination of the snugs or lugs (y) with
ihe bars () and dises or plates (de) arranged substantially as and for the purpose
herein described with reference to figures 1, 2 and 4 of the accompanying drawings.
Second In dynamo electric machines the combination of the spiral strips and
bars a connected together substantially as described and shewn severally in Nos. 1, 2 3
and of figure 6 and by figures 1, 23 and 4 and 5 of the accompanying drawings for
the purpose herein described.
Third In dynamo electric machines the combination of the strips a and four rows
of spiral strips connected with the said bars substantially as and for the purpose herein
described with reference to Figure 4. and 5 of the accompanying drawings.
Fourth The combination with some of the brushes of dynamo electric machines
arranged as described of a resistance or resistances inserted substantially as shown in
figure 7 of the accompanying drawings for the purpose of obviating the sparking which
results from giving a negative lead to the brushes.
Fifth The formation of the pole pieces of dynamo electric machines for giving a
graduated magnetic field as explained with regard to Figure 8 of the accompanying
drawings thereby reducing the heating of the bars of a bar armature.
J. HENRY JOHNSON,
Agent.