Improvements in Direct-current Transformers.
Year: 1894

page_text: Date of Application, 12th Sept. 1894
Complete Specification Left, 12th June, 1895-4ccepted, 27th July, 1895
Improvements in Direct-current Transformers.
We, ALEXANDER BEWICKE BLACKBURN and THOMAS LARGE BOYDEN both
of Bushbury Works, Wolverhampton, Electrical Engineers, do hereby declare the
nature of this invention to be as follows:-
This invention relates to transformers having an armature or armatures provided
with two or more windings one or more of which is or are supplied with electric
current which operates the machine as a motor thus enabling induced current to be
taken from the other winding or windings usually at a different voltage depending
on the ratio of active conductors to each other. The said invention is especially
applicable to machines where the ratio of transformation is large or where the
current is collected at a very low voltage, such as is frequently the case in machines
for electro-chemical work and the like. In such instances it is usually necessary to
employ a much larger number of conductors on the low-tension winding or windings
than are necessary for the production of the requisite electro-motive force with of
course a correspondingly increased number of conductors on the high-tension winding
or windings the general result being decrease of efficiency and increase of weight,
size and cost.
In order to obviate this difficulty the transformer is constructed according to this
invention with four or more poles the conductors of the low-tension portion of the
armature are arranged in multipolar parallel winding in which the whole number of
conductors round the periphery is divided into sections depending on, and divisible
by, the number of pairs of poles, each section being available to produce the full
low-tension electro-motive force the current being collected by separate brushes
from each section, those of similar sign being connected in parallel and to their
proper terminal.
The conductors on the high-tension portion of the armature are arranged in
multipolar series winding in which the total number of conductors round the
periphery are arranged as many in series as are required for the production of the
maximum electro-motive force required any single conductor carrying half the
total current when brushes are applied at only two points on the commutator.
Another feature of this invention consists in a method for cross-exciting the
poles of such double-wound multipolar machines so as to compensate for any
variation in the electro-motive force generated in the opposite halves of the
armature such as may arise from want of symmetry in the magnetic field. For
this purpose there is added to each magnet limb a coil which is connected at one
extremity to the brush situated on the opposite side of the same diameter and
collecting current from the parallel winding. The other extremities of the coils
are connected in two groups to the terminals leading to the external circuit, one
group from the positive and the other group from the negative brushes. By this
means any variation in the voltage at one brush causes corresponding strengthening
or weakening of the magnet field on the opposite side and thereby tends to correct
any difference of potential between the two brushes.
Dated this 12th day of September 1894
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, Agents.

page_text: improvements in Direct-current Transformers.
We, ALEXANDER BEWICKE BLACKBURN and THOMAS LARGE BOYDEN
both of Bushbury Works, Wolverhampton, in the County of Stafford, Electrical
Engineers, 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 direct current transformers having armatures provided
with two or more windings one of which windings is supplied with electric current
which operates the machine as a motor, thus enabling an induced current to be
taken from the other winding or windings usually at different voltage depending on
the ratio of active conductors to each other.
This invention is specially applicable to machines where the transforming ratio
is large or where the current is collected at a very low voltage such as is frequently
the case in machines for electro-chemical work and the like. In such instances it
has hitherto been usual to employ a much larger number of conductors on the low
tension armature than is desirable with of course a correspondingly increased
number of conductors on the high tension winding or windings, the general result
being loss of efficiency and increase in weight, size and cost.
In carrying out our invention and to obviate these objections we construct the
transformer with four or more poles and we arrange the conductore for the low
tension portion of the armature or windings (which are preferably made of
compressed strand and inserted into slots a² on the periphery of the core as
illustrated at a in Figure 1) in what is known as multipolar parallel winding as
illustrated by Figure 3 in which the whole number of low tension conductors round
the core is divided into sectious depending on and divisible by the number of pairs
of poles, each section being available to produce the full low tension electro-motive
force the current being collected by separate brushes from each section as illustrated
by Figures 2 and 3 those of similar sign being connected in parallel and to their
proper terminal as seen in Figure 2.
The conductors on the high tension portion of the armature or windings we
arrange in what is known as multipolar series winding (as illustrated by Figure 5)
in which the total number of conductors round the core is arranged as many in
series as are required for the production of the maximum required electro-motive
force any single high tension conductor carrying half the total current when
brushes are applied at only two points on the commutator as illustrated by
Figures 4 and 5. The winding in this case covers the entire surface of the core
(as illustrated at b in Figure 1). In order to obviate the disadvantage sometimes
experienced with parallel wound armatures due to an unsymmetrical position of the
armature, we arrange that the low tension current is made available for cross-
excitation (as illustrated by Figure 2) by which a compensating effect is introduced,
any excess current flowing to or from one or more of the collecting points being
carried round the magnets at the opposite part of the armature.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is,―
1. In direct current transformers the use of multipolar parallel winding in

page_text: 2. In direct current transformers the method of compensating by cross excitation
of the field magnets substantially as hereinbefore described.
Dated this 12th day of June 1895.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.