IMPROVEMENTS IN DYNAMO ELECTRIC MACHINES
Year: 1884

page_text: We, WILLIAM MATHER of the Salford Iron Works, Manchester in the County
of Lancaster Engineer, JOHN HOPKINSON F.R.S. of 4 Westminster Chambers in
the City of Westminster and EDWARD HOPKINSON of the Salford Iron Works
aforesaid Engineer do hereby declare the nature of our said Invention for
"IMPROVEMENTS IN DYNAMO ELECTRIC MACHINES to be as follows :-
Our Invention relates to improvements in dynamo machines and more par-
ticularly to that class of dynamo wherein the armature is of the type commonly
known as a Gramme ring. In order to augment the intensity of the magnetic
field and thereby increase the output of the machine we greatly increase the
section of iron in the magnets and pole pieces beyond what has been usual
hitherto in machines of this class and we construct the armature of plates of iron
forming a ring, the plates being insulated from each other by paper discs or other
suitable means. The section of the iron in the armature is not much less than the
section of the iron in the magnets, thereby ensuring that the magnetic induction is
not restricted by reason of the iron becoming too rapidly saturated. The interior
of the ring is entirely open allowing free admission of air on to the surface of the
conducting wires. We by this means secure many of the advantages of the old
type of Gramme ring, while on the other hand we have a field of not much
inferior intensity to that obtained in the improved form of Edison Machine for
which Letters Patent No 973 dated 22nd February 1883 were granted to one of
us (namely John Hopkinson).
An armature constructed in this manner is specially adapted to use in connection
with the improvements in the methods of ventilating dynamos and other improve-
ments described in the application for Letters Patent N° 768 dated 5th January
1884 made by two of us (William Mather and John Hopkinson).
Although our Invention is more directly applicable to the Gramme ring armature
we also apply it to the original form of ring armature known as the Pacinotti ring.
In order to control the field due to the current circulating round the armature
we extend the pole pieces so as to embrace a larger portion of the surface of the
armature, yet we cause the section of metal in this polar extension to be so small
that it has only a controlling effect. For convenience of construction we sometimes
arrange two magnets vertically with like poles above, the upper ends of the magnets
being connected by the upper pole piece, the lower ends by the lower pole piece;

page_text: in this arrangement in order to restrict the leakage of magnetic field we may make
lateral extensions of the under yoke or pole piece and carry the bearings of the
armature shaft on pedestals separated from these lateral extensions by suitable
plates of non magnetic matter. The foregoing more especially applies to that form
of machine wherein the magnetic circle is double but our Invention may with
equal advantage be applied to a single magnetic circuit machine. We further
construct the pole pieces in a special manner so that the exterior or bounding lines
are coincident or approximately so with the direction of the lines of magnetic
force; we thereby diminish the weight without diminishing the efficiency of the
machine When we use cast iron pole pieces we find it advantageous to let the
wrought iron into the cast iron so as to increase the surface of contact between
the two metals. In order to avoid the cost of making the turned shaft of the
magnet and the bore of the hole in the yoke a precise fit, we may sometimes make
use of a tightening bolt by means of which we bring the opposed surfaces of shaft
and yoke, through which the lines of magnetic force pass, into contact, leaving the
shaft a loose fit in other parts.
Our improvements are equally applicable whether the dynamo electric machine
is used for the generation of electricity or for the conversion of electrical into
mechanical power.

page_text: We, WILLIAM MATHER of the Salford Iron Works, Manchester in the County
of Lancaster, Engineer JOHN HOPKINSON F.R.S. of 4 Westminster Chambers in
the City of Westminster and EDWARD HOPKINSON of the Salford Iron Works
aforesaid, Engineer do hereby declare the nature of our invention for "IMPROVE-
MENTS IN DYNAMO ELECTRIC MACHINES" 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 improvements in Dynamo electric machines and more
particularly to that class of such machines wherein the armature is of the type
commonly known as a "Gramme ring" or of the earlier form known as the
Pacinotti ring. We greatly augment the intensity of the magnetic field and
thereby the output of the machine by increasing the section of iron in the magnets
and pole pieces beyond the section that has hitherto been used in machines of this
class. To the same end we construct the armature so that the section of iron is
not much less than the section in the magnets thereby ensuring that the magnetic
induction is not restricted by reason of the iron becoming too rapidly saturated.
We are thus able to obtain at low cost a field of not much inferior intensity to that
obtained in the improved form of Edison machine for which Letters Patent N° 973
dated 22nd February 1883 were granted to one of us namely John Hopkinson.
In order to reduce the weight of the pole pieces we may construct them so that
their bounding lines are approximately coincident with the lines of magnetic
induction and by special polar extensions explained hereinafter in reference to the
drawings we produce a weak field near the neutral point capable of controlling any
tendency to sparking at the commutator.
In that form of our machine wherein the magnetic circuit is formed partly of
cast iron and partly of wrought iron we so apportion the section of the two metals.
and their surface of contact that the resistance to magnetization may be not
greater in one part of the circuit than in another.
The interior of the ring is entirely open allowing free admission of air on to the
surface of the conducting wire and in connection therewith we may with special
advantage make use of the improved means for the ventilation of dynamo electric
machines for which Letters Patent N° 768 dated 5th January 1884 were granted
to two of us namely William Mather and John Hopkinson.
Our improvements are equally applicable whether the dynamo electric machine
be used for the generation of the electric current or for the conversion of electrical
into mechanical power.
In order that our Invention may be better understood we refer to the accom-
panying drawings wherein Figure 1 shows the armature in longitudinal section
wbilst figure 2 shows a cross section together with one arrangement of magnets
having a single magnetic circuit Figures 3 and 3" show an elevation and a plan of
the same machine Figures 4. 5 and 6 show the several views of a dynamo
constructed with a double magnetic circuit Figure 4 being a cross section Figure 5
a side elevation and Figure 6 a plan Figure 7 shews the extension of the pole

page_text: pieces whereby the field at the neutral point is controlled-It will be understood
that all the figures are to a certain extent diagrammatic as details of construction
which are not necessary to the explanation of this Invention are omitted In all the
figures a a represents the shaft b the commutator c a boss with arms c² to carry
the core d which consists of soft iron plates or wire continuous in the direction of
the lines of force but divided into sections in the direction of the length of the
armature by paper or other insulator-The curved form of the pole pieces to avoid
useless weight is shown in Figure 2 the bounding line being approximately
coincident with the line of magnetic induction The pole pieces e e may be of cast
We let the latter into the pole
iron and the magnet limbs f f of wrought iron
pieces as shown in the sections to secure that at no part of the cast iron shall the
sectional area be less than at least half as much again as the sectional area of the
wrought iron cores.
In the double magnetic circuit form of machine shewn in figures 4. 5 and 6 we
for convenience extend the under yoke or pole pieces to form the base of the
machine to which the pedestals carrying the bearings of the armature shaft are
bolted To restrict the leakage of magnetic field we make the pedestals of non
magnetic material or separate them from the base by a plate of non magnetic
material.
The extension of the pole piece shown at e³ in Figure 7 is of small sectional area
compared with the other parts of the pole piece and the area may be further
reduced by making the polar extension extend only through a portion of the depth
of the pole piece.
In order to avoid the cost of making the turned core of the magnet and the bore
of the hole in the yoke a precise fit we may sometimes make use of a tightening
setscrew m m by means of which we bring the opposed surfaces of core and yoke
through which the lines of magnetic force pass into contact leaving the shaft a
loose fit in other parts.
Having now described and particularly ascertained the nature of our Invention
and the manner in which the same is or may be used or carried into effect we
declare that what we claim is
First. The dynamo electric machines constructed substantially as herein described
with reference to the accompanying drawings.
Second. The arrangements of magnets and pole pieces shown in figures 4. 5 and 6
whether used with the armature shown or with other armatures.
Third. The arrangement of letting the wrought iron cores of the magnets into
the cast iron pole pieces substantially as and for the purpose specified.
Fourth. The use of polar extensions of small area substantially as and for the
purpose herein described with reference to Figure 7 of the accompanying drawings.
Dated the 26th day of August 1885.