Improvements in Transforming, Rectifying, and Generating Electric Ourrents, and Apparatus therefor..
Year: 1893

page_text: Date of Application, 7th Mar., 1893
Complete Specification Left, 7th Dec., 1893-Accepted, 7th Mar.,
1894
PROVISIONAL SPECIFICATION.
Improvements in Transforming, Rectifying, and Generating Electric
Ourrents, and Apparatus therefor..
I, HERBERT Fraser FosteR, of 64, Cornwall Road, Westbourne Park,
London, in the County of Middlesex, Electrical Engineer, do hereby declare the
nature of this invention to be as follows:-
My invention consists in the combined application of both continuous and
alternating currents to transformers, either for the purpose of transforming
continuous currents from a higher to a lower potential without the use of a motor-
transformer, or for the purpose of rectifying or changing alternating currents into
continuous and vice-versa.
The manner in which I carry out my invention is as follows. I wind on the core
of a suitably designed transformer, preferably three coils, two of which form the
primary circuits and the third the secondary. One of the primary coils carries the
continuous current, the other the alternating current. The relative strengths of
these currents can be varied, and it is in this combined application of the two kinds
of currents that I am able to perform what I have herein above described. It must be
clearly understood that I do not confine myself to the use of transformers of three
coils only, I may use either two or more coils for the purpose of my invention.
In all alternating currents the electro-motive-force rises and falls in periodic
phases, a wave of electricity being produced first in one direction and then in the
reverse direction, whereas in a continuous current the flow is always in the same
direction.
Now, the effect of the continuous current coil on the core of the transformor is to
maguetise it, and it will tend to sustain that magnetism in a certain direction, but
the effect of the other coil will be to disturb this continuity by virtue of its
alternation, the phase at one moment coinciding with the continuous current and
increasing its amplitude by the sum of its quantity, then opposing and neutralising
it during the next phase by reason of its changed direction and by the difference of
its magnitude. It will be thus seen that there will be a periodic fluctuation
or alternation in the magnetism of the core of the transformer, which results in a
pulsating continuous current being set up in the third coil of the transformer before
referred to.
I now, enumerate some of the chief features of my invention.
Firstly. The combination of two currents one continuous and the other
alternating to any transformer of a suitable design for the purpose herein before
described.
Secondly. The combination of three or more coils to transformers for the purpose
of increasing or diminishing the electro-motive-force of either continuous or
alternating currents.
Thirdly. By varying or equalising the relative strengths of the two primary
currents of the. transformer, I can convert or alter the frequency, continuity, or
alternations of the current in the secondary coil.
As all transformers may be regarded as a species of dynamo of which the primary
coils correspond to the field magnets and the secondary coils to the armature, but
in which the magnetism of the iron core only is made to vary through rapidly
recurring cycles, it is evident that the above principles can also be applied to
suitably designed dynamo machines as well as transformers or in other words I can
rectify the currents given out by a dynamo by means of the inductive action thereon
of a current supplied to the dynamo from an external source.

page_text: It follows from the use of my invention that alternating current machines can be
run in parallel so as to feed the same set of mains without being in phase since the
current after conversion is always in the same direction.
Dated this 7th day of March 1893.
HERBERT F. FOSTER.
Hasoltine, Lake & Co.,
45, Southampton Buildings, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Transforming, Rectifying, and Generating Electric
Currents, and Apparatus therefor.
I, HERBERT FRASER FOSTER, 64 Cornwall Road, Westbourne Park, in the
County of Middlesex, Electrical 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 :-
My invention relates to the transforming and conversion of electric currents and
consists in the combined application of direct and alternating currents to
transformers.
The object of my said invention is to provide means for rectifying or changing
alternating currents into pulsating or direct currents or for transforming direct
currents from a higher to a lower potential, and vice versa, without, the use of a
motor generator.
In carrying out my invention I proceed as follows, that is to say, I wind on the
core of a suitably designed transformer, a series of coils preferably three in number
two of which form the primary circuits and the third the secondary circuit. One
of the primary coils carries a direct current and the other of the said coils an
alternating current, and it is by the interaction and simultaneous application of
these two kinds of currents, the relative strengths of which can be varied, that I
attain the objects of my invention. I vary often use only two coils on the trans-
former in which case one coil carries both the alternating and direct currents at the
same time the alternating current being generated in the coil by motive power
supplied to the transformer.
In order that my invention may be clearly understood will now proceed to
describe the same with reference to the accompanying drawings, in which
Figure 1 is a diagram intended to illustrate how the combined action of a
continuous current and an alterunting current produces a pulsating current in one
direction.
Figures 2, 4 and 5 are diagrammatic views of transformers constructed in
accordance with my invention.
Figure 3 is a diagrammatic view hereinafter fully explained.
Figure 6 is a sectional view of another type of transformer wound with coils in
accordance with my invention.
Referring now to Figure 1. This is a diagram consisting of three parts C, A
and P. U shows in a well known manner a current curve for a continuous
current, A the curve for an alternating current, and P the curve for a current
which results from the combination of C and A. The ordinates of the carves
reckoned from the zero lines 0-0 give the positive or negativo values of the
current for every instant of time the values of the time being taken horizontally
along the zero lines.
The continuous current is shown by a dotted straight line a, c parallel to the
linc o, o at a fixed distance away, this fixed distance being equivalent to the strength
of the current which is constant, or it may be merely a rectified alternating current
having the same frequency as the alternating current shewn at A. The alternating
current curve at A is a sine curve a, a the current rising to a positive maximum and

page_text: then falling through zero to a negative maximum. The current which is shewn
at P by the curve p, p, is the sum of these currents at every instant of time and is
found by integrating the values of the curves C and A to be a pulsating ourrent,
which in this case never crossos the zero line. This is due to the fact that the
relative strengths of the currents are such that during alternate half periods of the
alternating current the continuous current neutralizes the said alternating current,
and in the remaining half periods flows in the same direction as the alternating
enrrent and assists it. It is obvious that by varying the relative strengths of the
two currents C and A, currents of different kinds could be produced in a similar
fashion to that shewn at P.
Referring now to Figures 2 and 3. Figure 2 is a view more or less diagrammatic
of a transformer or converter constructed according to my invention wound with
two coils and Figure 3 is a diagram of a single coil to assist in the explanation of
the same.
B is a continuous current generator of any suitable design, that is to say, a
dynamo battery or the like which supplies a continuous current to the circuit. b.
Part of this circuit is shunted by a wire b'. C is a mass of iron forming a magnet
which is magnetized in one direction by the shunt current b'. D is another mass of
iron adapted to rotate between the poles of the magnet C. The mass D is shewn
for simplicity in this diagram in the shape of a shuttle armature and is wound with
two coils E, F, each coil being furnished with collecting rings e, e', f', ' on the
shaft of the machine. The current from B is led in by suitable brushes e, e to
the rings e, e', and circulates round the thick coil E. The current which is induced
in the thin coil F is taken off by brushes from the rings. If now the
armature D be rotated both the coils E and F have induced in thom an alter-
nating current which in the coil E is superimposed upon the continuous current
supplied to it by the brushes e, e³ and it is easily seen that the combined
magnetizing and mutual inductive effect of these coils is to cause waves of
magnetism in the same direction to be induced in the armature D. Now the coil F
has also an alternating current induced in it owing to the fact that it is joined up to
two rings and rotated in the magnetic field due to the magnet C but whenever the
current in coil is about to change its direction the continuous current in coil E
neutralizes the effect of the magnet C so that no current is induced in said coil F,
the result is that a pulsating current is induced in coil F which is collected by the
brushes","
This explanation may be further simplified by regarding the case as follows.
The coils E and F havo three currents working together two of the said coils being
arranged to have currents induced in them of equal or any other known power (and
if necessary with variable electro-motive force) the third current being continuous
and adjusted to be equal to or greater than the two induced currents taken together.
This third current is supplied to one of the two coils.. Hence, when tho said third
current is opposed in direction to the other two, all three currents become decom-
posed or noutralized. The ratio of the numbers of convolutions of wire in the two
coils depends mainly on the ratio of transformation, and as is well known, in electio
magnetic circuits the electric and maguetic phenomena always depend on the
numbers of ampere turns in the respective coils. As an instance in Figure 2
coils E and F have any 1200, ampere turns each of which E has 100 convolutions
and F1000 convolutions the current in E and F will then have to be 12
and 1-2 amperes respectively and the total ampere turns of the induced current will
be 2400. As we know the number of turns in E we have only now to ascertain
what amount of current has to be supplied by the generator B to the coil E to make
up 2400 which will be 24 amperes the resistance of the circuit E being understood
to be sufficiently small to allow that amount of current to pass. The nature of the
current in coil will, of course depend to a very large extcut on the current supplied
to coil E from the circuit band on the alternating current induced in said coil E and
in the coil F by the rotation of the armature D. As an example, the strength of
the continuous current supplied to coil E is equal to the sum of the strengths of

page_text: the currents induced in coils E and F owing to the rotation of the same. The
number of convolutions of the coils varies with the electromotive force required
from coil F.
•
The diagram, Figure 3 is in two parts the upper portion showing one position
of a single turn of coil E and the lower one shewing the position when said coil is
turned through 180° or half a revolution. In both these positions the current
induced in the coil is zero as the lines of force are passing directly through the coil,
that is the coil is in its neutral position. The darts shew the direction of the
direct current supplied to the coil, as the coil turns from position 1 to position 2
the current induced therein is in the same direction as shewn by arrows as the
continuous current, therefore the total current is increased but when the coil
reaches position 2 the alternating current changes in direction and now opposes the
continuous current so that no current Hows in the coil. The result is that n
pulsating current flows in the coil as hereinabove stated. Now if this current is
made sufficiently great so as not only to overcome its own induction but to act
inductively on a second coil such as F, Figure 2, it will cause the alternating current
which is circulating in such coil to become pulsating as aforesaid.
The coil F is shewn as being made of fine wiro with many moro convolutions
than the thick wire coil E. It therefore results that the pulsating current induced
in said coil has a higher electromotive force than the current supplied from the
circuit b. I can therefore change by this means a direct current of low electro-
motive force into one of a higher electromotive force. In a similar fashion by
varying the number of convolutions on coil F I can arrange that the current
induced in said coil will have a lower electromotive force than that supplied from
the circuit h. The machine therefore acts ns a "step-up or step-down
transformer for direct currents.
"
"
Figure 4 is a view similar to Figure 3 but illustrates a transformer with four
cuils instead of two. The said coils are joined two and two in parallel to the same
collecting rings. The action of the coils is similar to that above described with
reference to Figures 2 and 3. When the pulsating current in coil E reaches n
minimum then the current in corresponding coil E' is at its maximum value so that
the pulsating current produced is more steady and does not vary so much as that
in the coil E Figure 4. In the same way the current in coil Fassists the current
in coil F when the current in the latter is a minimum so that the current taken off
by the brushes f', is also less variable.
Figure 5 shows a transformer of another design. The rotating portion D is in
this case wound with three coils, E, F, and G. The current induced in coil G is
commutated by a suitable commutator g aud collected by fixed brushes g', 9' which
at the same time transmit the current to the collecting rings e and so that the
direct current which circulates round the coil E is supplied by the machine itself
instead of by a separate generator as shown in Figure 3. The current in the
magnét circuit is supplied from a suitable battery or generator B as is the case
with the device shewn in Figure 3. In this machine the current supplied by the
coil G to the coil E is a pulsating current and if coils E and G are similar the said
pulsating current will be similar to the alternating current set up in coil E excopt
that the former is rectified or commuted.
It will be noticed on referring back to Figure 1 that the resulting pulsating curve
shewn at p, p has only half the number of periods of either of the curves a, à or e, c.
It will therefore bo understood that the current resulting in the coil F in my
machines will have half the frequency of the alternate current which passes through.
the coil E.
In Figure 6 I shew a section of a transformer of well-known type in which there
are no moving parts. I wind three coils E, F, G on said transformer and then
pass an alternating current round coil E, and a direct or preferably a rectified
alternating current of same frequency as the current in coif E, round the coil G.
The current induced in coil F as explained with reference to Figures 2 and 3 will
be a pulsating current in ope.direction having half the frequency of the alternating

page_text: current in coil E and an electromotive force depending on the ratios of the number
of convolutions in the three coils. .
Although I have shewn in the drawings, machines of a particular type I wish
it to be clearly understood that any method of converting or rectifying currents
as herein described can be carried into practice with machines of any of the
ordinary types.
It is readily seen that if the currents from alternating current machines are
reotified or converted in the manner above described said machines can be connected
parallel so as to feed the same set of mains without being in phase since the
pulsating current is always in the same direction.
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. A method of rectifying or converting alternating currents which consists in
the employment of a transformer wound with two coils or two sets of coils, round
one of which coils or sets of coils the alternating current to be rectified and a direct
current are passed, a pulsating current being thereby induced in the second coil or
Bot of coils of the transformer.
2. The modification of my invention wherein I pass the alternating and the
direct currents through separate coils instead of through the same coil, aubstantially
as described.
3. A transformer constructed substantially as described with reference to any of
the Figures 2, 4, 5 or 6 of the accompanying drawings, and operating as, and for
the purpose, specified.
But non
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.