Improvements in Dynamo-electric Machines.
Year: 1891

page_text: Date of Application, 7th Aug., 1891
Complete Specification Left. 7th June, 1892-Accepted, 16th July, 1892
PROVISIONAL SPECIFICATION.
Improvements in Dynamo-electric Machines.
1, GEORGE FORBES, of 34 Great George Street, Westminster, Consulting
Engineer, do hereby declare the nature of this invention to be as follows:-
In' dynamo-electric machines generally, & especially in the type of continuous-
current machines without commutators, usually, but erroneously, called unipolar, it
is found that the armature current distorts the magnetic field of the field-magnets
and diminishes the electro-motive force. My invention consists in a means for
obviating this, and this is done by carrying the current along fixed conductors
between the magnet poles and the armature, or let into the polar faces, so that the
action of the current in these conductors in distorting the field is equal in magnitude
and opposite in direction to the distorting action of the current in the armature.
Dated this 7th day of August 1891.
GEORGE FORDES.
COMPLETE SPECIFICATION.
Improvements in Dynamo-electric Machines.
I,, GEORGE FORBES, of 34 Great George Street, Westminster, Consulting
Engineer, 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 :-
In dynamo-electric machines generally, and especially in the type of continuous-
current machines without commutators, usually but erroneously, called unipolar, it,
is found that the armature current distorts the magnetic field of the field-magnets
and diminishes the electro-motive force.
My invention consists in a means for obviating this, and this is done by carrying
the current along fixed conductors between the magnet poles and the armature, or
let into the polar faces, so that the action of the current in these conductors in
distorting the field is equal in magnitude and opposite in direction to the distorting
action of the current in the armature.
In order that my said invention may be fully understood and readily carried into
effect I will proceed to describe the drawings hereunto annexed.
Figure 1 is a front elevation, representing my invention as applied to one form
of my unipolar dynamo for which Patents have been granted to me (No. 311583
and 11,244).
I mean by "unipolar dynamo" a machine of this type continuous current without
commutator. .
A. B and C are three iron pole pieces connected by an iron bed. These pole
pieces surround the solid iron cylinder D D. A magnetizing coil is placed on the
central limb causing that to be a north pole say, and the other two south poles.
When the iron cylinder is rotated currents are generated in it passing from the
circumference to the centre at one end, and from the centre to the circumference
at the other end. All round the cylinder at the lines E F current collecting
brushes bear. The brushes at E and F usually form the terminals of the machine.

page_text: In order to get from, one brush to the other, through the machine, the current
traverses the solid iron cylinder and' distorts the magnetic field. In order to correct
this distortion the pole piece A is lined with a copper cylinder H which is electrically
insulated from it. One end of the cylinder is connected with the current collecting
brushes at F
•
One of the terminals of the machine is upon the other end of the cylinder H,
the other terminal being connected with the brushes at E.
Figure 2 shews another arrangement. In Figure 2 insulated conductors G are
let into the polar face all round. The ends of these are connected to two heavy
rings one at each end of the polar face, the rings being screwed to, but. insulated'
from, the pole piece. The positive. (say) brushes are put in electrical connection
with the adjacent. ring, the other ring then. forming, the positive-terminal' of the
machine:
It will be seen that the current flows through the pole piece first in one direction
via the solid iron cylinder and then back in the opposite direction through the pole
piece via the conductors let into its face..
An adjustment of the amount of current flowing, back through the copper con-
ductors,can be obtained by supplying, an external shunt to these conductors whose
resistance can be varied at will.
In Figure 3: a section of the winding of an ordinary drum armature; and
pole pieces is shown, together with insulated conductors let into the polar faces,
the current in which is to annul the distorting action of that in the armature
conductors, on the magnetic field.
One method of holding the conductors in position upon the pole pieces is to apply.
two rings at each end of the pole pieces, as shown in section. by Figure 4 where
J and K.represent the two rings with. the conductors clamped between. These rings
may be of a hard' insulating, material' as vulcanite. The conductors are all laid in
grooves in the inner ring, and then the outer ring is put on and the whole screwed
firmly to the pole pieces by means of the bolts LL.
In the drum armature as shown in Figure 3, M. N. being the line of commu-
tation, half the current generated by the armature, will flow downwards on the
right (say) of this line, and the other half flows upwards on the left of the line:.
In Figure 3 the number of wires on the polar faces is half the number on the
adjacent parts of the armature, and the connections of the wires on the polar faces
may be traced as follows:-the brush at M would be connected to the far end of
conductor No. 1., the near end of 1 to the near end of 16, the far end of 16 to the
far end of 2,, the near end of 2' to the near end of 17, and so on till the far end
of 30 is reached' which forms one terminal of the machine, the other brush being.
the other..
The total current flowing in the conductors on the polar faces will be equal in
magnitude and opposite in direction to the total current in the adjacent conductors.
Figure 5 is a section of a continuous current multi-polar machine.
.
O are the stationary pole pieces they are so wound that the polarity of any
pole piece differs from that of its neighbours on either side. P is the laminated iron
armature it is mounted' upon an axis and rotated. Q is the winding upon the
armature parallel to the axis. R are conductors interposed between the armature
and the pole pieces. The conductors R carry the current which corrects the
distortion of the magnetic field.
The same adjustment may be applied here as was described in connection with
the unipolar dynamo-viz. an adjustable shunt placed across the ends of the winding
on the polár faces.
For other kinds of winding for which it is not necessary to give separate drawings,
like arrangements are adopted, always bearing in mind that the distorting action
of the current in the armature on the field at any point should be counteracted by
a distorting action, equal in magnitude and opposite in direction to it, produced by
currents passed in the immediate neighbourhood.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what 1
claim is :-
1. Unipolar dynamo-electric machines having conductors between the magnet
5 poles and the arinatures conveying the current in a direction contrary to that in
which it flows in the armature, thereby correcting the tendency to distortion of the
magnetic field.
2. Dynamo-electric machines having conductors conveying current in a direction
such as to correct the tendency to distortion of the magnetic field resulting from the-
O current passing in the armature.
Dated this 7th day of June 1892.
CARPMAEL & Co.,
Agents.