IMPROVEMENTS IN DYNAMO-ELECTRIC MACHINES
Year: 1880

page_text: LETTERS PATENT to John Hopkinson, of 4, Westminster Chambers, in the
City of Westminster, Civil Engineer, and Alexander Muirhead, of 27, Regency
Street, in the City of Westminster, for an Invention of "IMPROVEMENTS
IN DYNAMO-ELECTRIC MACHINES."
PROVISIONAL SPECIFICATION left by the said John Hopkinson and
Alexander Muirhead at the Office of the Commissioners of Patents on the
24th November 1880.
JOHN HOPKINSON, of 4, Westminster Chambers, in the City of Westminster,
Civil Engineer, and ALEXANDER MUIRHEAD, of 27, Regency Street, in the City
of Westminster. "IMPROVEMENTS IN DYNAMO ELECTRIC MACHINES,"
This Invention has for its object improvements in dynamo-electric machines
and lamps for electric lighting.
Our improvements relate to the machines for producing the electric current and
to the lamp for exhibiting the lights.
The collector or commutator which is used when a continuous current is desired,
we make with the metal pieces to which the wires of the armature are connected
air insulated. The metal pieces are carried on insulating discs at their ends, only
having air insulation in that part on which the collecting brushes or their
equivalents rub. To reduce the sparks which occur between the commutator and
the collecting brushes we divide the collecting brush into parts, and that part
which is latest in contact with any section of the commutator passes the current
through a resistance, thus gradually checking the current as the contact is broken.
The same effect may be obtained by interposing equivalent resistances in the
commutator itself.
Where the arrangement of the machine is such that the armature coils lie in
planes parallel or nearly parallel with the plane of revolution of the armature, we
construct the armature thus:-
•
The circumference of a pulley is surrounded with a series of layers of sheet iron
insulated more or less completely from each other. On one or both sides of the
ring thus formed radial slots are cut to admit the coils of insulated wire, which
thus lie in planes parallel with the plane of revolution of the pulley.. When a

page_text: continuous current is required we place coils on both faces of the armature and
arrange them alternately, so that when one coil is at its dead point, those near to
it on the opposite face are producing their maximum effect. The field magnets
are made in a manner similar to the armature, though not necessarily with
precisely the same number of coils, but it is cheaper to make their cores of solid
wrought iron; in some cases we construct them of cast iron. It is advantageous
to cut grooves in the face of the iron and to fill up the grooves with insulated
sheet iron, so stopping the local currents in the cores which would otherwise occur.
Both in the armature and in the magnets we pack each coil close against its
neighbour; each coil is thus of approximately quadrilateral form.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Hopkinson and Alexander Muirhead in the Great Seal
Patent Office on the 24th May 1881.
JOHN HOPKINSON, of 4, Westminster Chambers, in the City of Westminster,
Civil Engineer, and ALEXANDER MUIRHEAD, of 27, Regency Street, in the City
of Westminster. "IMPROVEMENTS IN DYNAMO ELECTRIC MACHINES."
This Invention has for its object improvements in dynamo electric machines.
To reduce the sparks which occur between the commutator and the collecting
brushes, we divide the collecting brush into parts, and that part which is latest
in contact with any section of the commutator passes the current through a
resistance, thus gradually checking the current as the contact is broken. The same
effect may be obtained by interposing equivalent resistances in the commutator
itself.
T
Where the arrangement of the machine is such that the armature coils lie in
planes parallel or nearly parallel with the plane of revolution of the armature,
we construct the armature thus:-
The circumference of a pulley is surrounded with a series of layers of sheet iron
insulated more or less completely from each other. On one or both sides of the
ring thus formed radial slots are cut to admit the coils of insulated wire, which
thus lie in planes parallel with the plane of revolution of the pulley. When a
continuous current is required we place coils on both faces of the armature and
arrange them alternately, so that when one coil is at its dead point, those near to
it on the opposite face are producing their maximum effect. The field magnets are
made in a manner similar to the armature, though not necessarily with precisely
the same number of coils, but it is cheaper to make their cores of solid wrought
iron; in some cases we construct them of cast iron. It is advantageous to cut
grooves in the face of the iron and to fill up the grooves with insulated sheet iron,
so stopping the local currents in the cores which would otherwise occur.
Both in the armature and in the magnets we pack each coil close against its
neighbour; each coil is thus of approximately quadrilateral form.

page_text: carried into effect, we will proceed to describe the Drawings hereunto annexed.
DESCRIPTION OF THE DRAWINGS.
Figures 1 and 2 shew a convenient method by which, according to our Invention,
to reduce the sparks which occur between the commutator and the collecting
brushes in continuous current machines; a, a, a, are the segments of the com-
mutator insulated from each other; b', b, b, are the collecting brushes or their
equivalents carried on a spindle c; one of these brushes 6¹ is arranged in such wise
that there is an electrical resistance between the brush b¹ and the spindle c.
This resistance may be made in various ways, but we prefer that shewn in the
Drawing; d, e, are metal cylinders; to d the brush is attached, whilst e is in
contact with the spindle c. The space f between d and e is filled with a mixture of
plumbago and lamp black having a suitable resistance; the ends of the space fare
closed with discs of ivory. The brush b¹ is so adjusted by bending or otherwise
that it remains in contact with any segment of the commutator for a short space
after the other brushes have left contact with that segment. The effect is, that
instead of sudden rupture of continuity of the armature circuit connected to the
segment of the commutator a resistance is first introduced, and contact is not
broken till the current has been in some measure reduced. For the more
convenient adjustment of the machine we provide several sets of brushes having
different resistances, and we ascertain by trial and use that which gives the best
result. Instead of interposing a resistance between the brush 61 and the spindle c,
the commutator plate may be divided into two parts separated by an appropriate
resistance, and the brush b¹ may be in contact with that part which is outside of
the resistance. It is clear that the electrical effect will be the same as in the plan
more particularly described and which we prefer.
The collector or commutator which is used when a continuous current is desired
we make with the metal pieces to which the wires of the armature are connected
air insulated. The metal pieces are carried on insulating discs at their ends, only
baving air insulation in that part on which the collecting brushes or their
equivalents rub.
Figures 3 and 4 shew the armature we use in machines arranged so that the
coils lie in planes parallel or nearly parallel with the plane of revolution of the
armature. a is a pulley to be keyed on the shaft of the machine; it is surrounded
by a series of layers b of sheet iron more or less insulated from each other. In
one or both faces of this ring of layers of iron radial slots are cut for the reception
of the coils of insulated wire c. The best method of fixing the layers of iron we
believe to be the following:-On the pulley we coil a band of sheet iron and of
asbestos paper, so that the asbestos paper separates the successive layers of iron
from each other. When a sufficient thickness has been obtained radial holes are
drilled and bolts d are inserted and secured by the cottars e. If the bolts are put
in and cottared hot the layers of iron and paper are very firmly nipped onto the
pulley. The radial slots may now be cut. The Figures shew the armature as
arranged for a continuous current, that is, with the slots on one side halfway
between the slots on the other side of the armature. This is done in order that
the current may be more approximately continuous; but when an alternating
current is desired the slots in the opposite faces correspond. The connections of
the coils with each other may be varied according to the electro motive force
desired, as is usual and well understood.
Although we prefer to insulate the layers b the one from the other by asbestos
paper, the same result will be in part attained by painting the iron composing the
layers; and even were the layers superposed without any such precaution, a better
result would be obtained than when the armature is made solid and not stratified,
as described.

page_text: Figures 5, 6, and 7 shew a complete continuous current machine. a is the
armature already described; b, b, are the cores of the electro magnets with a
strong cast iron backing c, c. The cores are grooved as shewn, and the grooves
are fitted with sheet iron either painted or insulated with asbestos paper; d, d, are
the exciting coils, the connections of which are so arranged that the poles are
alternately north and south, and so that opposite to each north pole we have a
south pole; e is the commutator.
In place of forming the cores of the electro magnets of cast iron they may be
made from sheet iron coiled and more or less insulated and slotted to receive the
coils, as described, in respect to the armature.
The framing of the machine will be understood by inspection of the Drawing.
Figures 8, 9, and 10 shew a complete alternating current machine with permanent
magnets. a is the armature; b, b, are the steel magnets carried in two brass
frames c, c, c, c, attached to the cast iron frame d, d, d; e, e, are the terminals of
the armature coils on which press the collecting brushes f, f.
Having thus described the nature of our Invention, and in what manner it is
to be carried into effect, we claim,―
First. In a continuous current dynamo electric machine the introduction of a
resistance in the commutator before breaking contact, in the manner herein
described, or electrically equivalent thereto.
Second. The armature, whether for continuous or alternating currents, consisting
of superposed rings or layers of sheet iron with radial grooves for the coils, the
coils lying in planes perpendicular or nearly perpendicular to the axis of rotation,
substantially as herein described.
Third. The field magnets, whether for continuous or alternating currents, having
cores consisting either of superposed layers of sheet iron or of cast iron grooved
and inlaid with sheet iron provided with coils, and arranged substantially as herein
described.
Fourth. The dynamo electric machine herein described and shewn whether
arranged for continuous or alternate currents.
In witness whereof, we, the said John Hopkinson and Alexander Muirhead,
have hereunto set our hands and seals, this Twentieth day of May, in the
year of our Lord One thousand eight hundred and eighty one.