An Improved System of Electrical Distribution by Alternating Currents.
Year: 1894

page_text: Date Claimed for Fatent under DCCL.
being date of first Foreign Application (in (26th Feb.,
United States of America),
Date of Application (in United Kingdom), 24th July, 1894
1894
Complete Specification Left. 24th July, 1894-Accepted, 9th Mar., 1895
Date of Application (in United Kingdom), 24th July, 1894
Complete Specification Left. 24th July, 1894-Accepted, 9th Mar., 1895
An Improved System of Electrical Distribution by Alternating
Currents.
I, CHARLES FELTON SCOTT, of Westinghouse Electric & Manufacturing
Company Pittsburg, Pennsylvania, United States of America Electrician do
hereby declare the nature of this invention and in what manner the same is to he
performed to be particularly described and ascertained in and by the following
statement:-
My invention relates generally to those systems of electrical distribution in which
polyphase alternating currents are employed.
In a system of electrical distribution according to this invention, currents of
different numbers of phases are employed, and the invention involves a novel
method of and apparatus for accomplishing the change from one number of phases
to another number of phases. The object being the transmission of electric
currents by the number of phases which best secures the highest economy and
convenience, this involves change to this number of phases from the number
generated at the source of current, or change from the number used.in transmission
to the number desired for translating devices, or both changes.
It has been demonstrated that a greater weight of copper conductor is require.l
for transmitting two-phase currents, that is to say, alternating currents the phases
of which differ from each other by 90°, than is required for the transmission of the
same amount of energy over the same distance with the same loss, by three phase
currents, that is to say alternating currents whose phases differ from each other
by 120°
On the other hand, for certain purposes, in alternating current work, it is desirable
to employ the two phase system, as it lends itself more readily to certain classes of
work. It is also frequently desired to generate two-phase currents instead of three
phase currents, and hence it is desirable to provide a method and means by which
two-phase alternating currents may be changed into three phase currents, either at
or near the generating point or at some other locality, and the energy may be
transmitted as three-phase currents. This is of special importance where the
distance to be traversed is great. At the receiving end it may be desired to employ
the energy in the form of three-phase currents, or to transform it again into two
phase currents utilizing it in that form. It is, however, desirable in some cases to
originally generate three phase currents, and, after transmitting the same..over
suitable conductors, to transform them into two phase currents. The potential of
the currents may be raised or lowered by the same operation or kept the same, to
suit the requirements of different cases. Again, it may be desired to generate two-
phase currents and operate translating devices by three phase currents.
In the accompanying drawings
:
Fig. 1 is a mathematical diagram designed to aid in a clear understanding of the

page_text: Fig. 2 is a diagram illustrating an organization of apparatus for generating two
phase alternating electric currents, transforming the same into three phase currents,
and transmitting the same to a distance and there utilizing them either as three
phase currents or transforming them into two phase currents.
Fig. 3 illustrates a system of apparatus for transforming three phase currents
into three phase currents of the same or a different potential.
Fig. 4 illustrates the employment of the invention in connection with single-coil
or auto-transformers instead of two coil transformers; and
Fig. 5 illustrates an organization for obtaining three phase currents upon four
conductors.
Fig. 6 illustrates a modified organization.
It is well known that if two conductors, in which are generated electro motive
forces differing by 90°, be connected in series, the electro motive force between the
free terminals is equal to the diagonal of a rectangle whose sides are proportional
to the two component electro motive forces. Assuming the diagonal to have
the value of 100, and the base 50, then the perpendicular will be equal to
about 86.6.
Referring to Fig. 1 assume that A. O. is an electro motive force of say about
86-6 volts, and O. B an electro motive force of 50 volts the maximum value of
which occurs when A. O. is zero, and that the coils in which these electro motive
forces are produced are joined together, then the electro motive force between the
free ends is proportional to the line A. B. and is therefore 100 volts. The phase
of the resultant, it will be seen, differs from O. A. by 30° and from O. B. by 60°.
In a similar manner the electro motive force O. A. may be combined with an electro
motive force O. C. 90° from the electro motive force O. A. and 180° from the
electro motive force O. B. The resultant is the electro motive force A. C. equal
to A. B. if O. C. is equal to O. B. in value. Therefore two electro motive forces
as O. A. and B. C. differing in phase 90°, can be suitably related to give two
resultants A. B. and A. C. equal in value but differing in direction. The values
selected for illustration give resultants each equal to 100 volts, which is also the
value of the line C. B. It follows therefore that from an electro motive force O. A.
and an electro motive force B. C. composed of two electro motive forces B. O
and O. C. each 90° from O. A. three electro motive forces can be produced equal
in value, the angular relations of which are those of an equilateral triangle.
The electro motive force O. A. may be obtained from a secondary of a trans-
former. The electro motive force O. B. may be obtained from the secondary of a
second transformer, the primary of which is supplied by current differing in
phase 90° from the current by which the first transformer is supplied. The
secondary of the first transformer may be connected to the middle point of the
secondary of the second transformer. This combination is then adapted to give
clectro motive forces corresponding to the diagram above described, if the number
of turns in the secondary of the first transformer be equal to the number of turns
in the second transformer multiplied by 0-866, and it will be found that the electro
motive force between any pair of free ends is equal to that between any other pair.
This condition proves the existence of the so called three phase relation. If, for
instance, three lamps be connected between the various pairs of terminals, it will be
found that the current in any lamp is 120° ahead of the current in one of the other
lamps, and 120° behind that in the remaining lamp.
Referring now to Fig. 2, G represents any suitable source of two phase currents,
that is to say, currents differing from each other 90° in phase. Two transformers
are indicated at H' and H2, the primary coils P1 and P thereof being respectively
connected with the source to receive currents differing 90° in phase. The secondary
coil Ao of one of these transformers has a length, the ratio of which to the length
of the secondary coil B. C. of the other transformer is as 0-866 is to 1. One
terminal of the coil Ao is connected with approximately the central point of the
coil B. C. The remaining terminals of these two coils are connected with main
line conductors L' L' and L³ respectively. If translating devices are connected as

page_text: indicated by dotted lines between L'and L, L' and L³, and L' and L³, as indicated
at d', d2 and d³, the maximum current will pass from L' to L³ through the
intervening device d' 120° before the maximum current passes from L' to L, which
in turn is 120° before the maximum current passing from L³ to L', and this is
120° before the next similar maximum value of the current from L₁ to L².
The three phase current thus produced may be transmitted to distances and there
utilised for operating three phase alternating current motors, such as indicated at K,
for instance, or any other suitable alternating current apparatus. The three phase
currents inay, however, be re-transformed into two phase currents by an organization
of transformers H3 H4, similar to those shown: t H H², but reversed, that is to-say,
having their connected coils connected with the lines L' L' L' and their
independent coils connected with two phase currents in lines h¹ h² h³ and hª.
This organization will transform the three phase currents into component two
phase currents ; that is to say, each of the forces A. B, B. C, C. A. Fig. 1 is
resolved into its components, as will be readily understood by reference to Fig. 1.
Certain advantages, as herein before indicated are secured by the transmission of
three phase rather than two phase currents, particularly the saving of energy in
transmitting over a given circuit, inasmuch as less copper is required for the three
phase currents than for transmitting two phase currents the same distance with the
same loss. The laws governing this effect are now so well established that they
need not be particularly set forth herein. Certain classes of work are best
performed by two phase currents, especially where the work is such as would tend
to unbalance the system that is to say to cause more load at times to be thrown
between one pair of conductors than between another pair of conductors.
It is found in practice that if a three phase machine be more heavily loaded on
one circuit than the others a considerably greater discrepancy exists between the
electro motive force on the loaded circuits and the electro motive forces of the
unloaded circuits than is caused by an equal difference between the loads on the two
circuits of a two phase machine. For this reason, it is usually necessary to provide
against unequal loads upon the different circuits of a three phase machine, whereas
a considerable difference is allowable between the circuits of a two phase machine.
When the load is most conveniently placed upon a single circuit instead of being
(qually distributed among several circuits, as for instance in incandescent lighting,
it is preferable to be able to load any circuit in a polyphase system without special
reference to others. The three phase system demands the distribution into three
fairly equal and balanced groups, whereas the two phase system requires division
into but two groups, the unbalancing of which does not cause great differences
between the pressure on the two branches. It is also readily seen that if the
load be placed upon circuits differing 90° the effect upon the generator due
to reaction of circuits one upon another and unbalancing of electro motive forces
is practically the same whether the load is placed directly upon circuits from
the generator or upon circuits after transformation or transmission by two-phase
circuits throughout, or upon two-phase circuits which are derived from three-
phase transmitting circuits from a two-phase generator, or upon two-phase circuits
derived by transformers from a three-phase circuit supplied either directly or by
transformers from a three phase generator.
For these reasons it is desirable to provide means in some instances for trans-
forming the three phase currents at the receiving end into two phase currents a
indicated. Any unbalancing of the load upon the conductors h h h³ and h* will
produce no detrimental result upon the lines L' L' L' although that load will be
distributed upon the conductors leading from the generator G in essentially the
⚫ame manner as upon the conductors ¹³ ³ h. The two wires h² and h³ may be
united as one wire as is well understood.
This will be more readily understood by considering the effects produced in
Fig. 2 by an unbalanced load upon the circuits
. If, for instance, the
circuit is open and all the load is upon the lead h³h then the energy required
for that circuit will be transmitted entirely through the conductors L³ L' by the

page_text: transformers H, and E, in the usual manner of a single coil in simple alternating
current systems. If however, the load is entirely upon the circuit h¹ h' then the
converters H and H³ will operate as in the simple alternating current system, the
circuit from the secondary of the transformer H¹ through the primary of
the transformer H' being by way of the conductor L' and through the two halves
of the primary coil of the transformer H in opposite directions, therefore
neutralizing the self induction, and by way of the conductors L' and L³, in opposite
directions through the two halves of the secondary of the transformer H2; thence
back to the other terminal of the secondary coil of the transformer H¹.
This condition, however, will not unbalance the electro motive forces upon the
three conductors L' L' and L³, so that three phase currents may be delivered from
these conductors, as, for instance, to a three phase alternating current motor K,
under practically the same conditions as if no load were upon either of the
transformers H³ and H*, or as if both converters were equally loaded.
It will also be understood that alternating current motors, or any other desired
apparatus, may be operated by currents delivered to the secondary circuits of the
transformers H³ and H, either jointly or independently. For illustration a two
phase alternating current motor is shewn at K'.
In some instances it may be desired to transmit the currents over the lines L' L³ L³
at a potential different from that produced by the generator G, in which case the
transformers H'H' may have their coils so proportioned as to increase or diminish
the electro motive forces. It is evident that this feature may be combined with
those already described. In like manner the transformers at H and H* may be
either raising or lowering transformers, or they may transform at the same
potential.
In some instances it may be desired to transform a three-phase current into a
three-phase current of a different potential, that is to say, without any change of
phase. This may be accomplished as indicated in Fig. 3 by transformers having
their primary and their secondary circuits both connected in the manner described
with reference to the secondaries of the transformers H' H².
In this figure G¹ represents a three-phase alternating current generator having
its three terminals connected with the other terminals A'o' C' of the primary coils
of the transformers H and H. The relations and connections of these coils with
each other are the same as described with reference to the secondary coils of the
transformers H' and H. The relations and connections of the secondary coils of
the transformers H³ and H are the same as described with reference to the
secondary coils of the transformers H' and H'.
In this figure I have also shewn two transformers H' and H in which the
divided coils are in the same transformers instead of being in different transformers,
as either arra gement may be used.
In some instances it may be desired to use single coil transformers, in place of
double coil transformers. Such an organization is illustrated in Fig. 4. The
generator G delivers two-phase currents and it is desired to transform the same to
three-phase currents to be transmitted over the lines L' L' L'. The cores of the
two transformers Hand H20 are each provided with equal coils, and these coils
are connected so that the relative number of turns in the two transformers between
the three-phase terminals are taken in the same manner as the secondary coils of
the transformers H' and H³.
This may be accomplished by leading the line L' from a point in the coil of the
transformer H' which is at a distance from the point of connection between this
transformer and the middle point of the other transformer H equal to 0.866
multiplied by the total number of turns of that coil.
The same result is obtained in the transformers H" and H" in which the dis-
position differs from that shown in H' and H in that the connection from the
middle of one coil is made in one case to the end of the second coil and in the other
case to an intermediate point of the second coil.
can be raised or lowered.
By this arrangement the E.M.F.

page_text: In some instances it is desirable to have the three phase currents transmitted
over four conductors instead of three conductors. This may be accomplished by
the organization shewn in Fig. 5, for instance, in which the construction is precisely
the saine as shewn in Fig. 2 with the exception that a fourth conductor L is led
from the point in the coil A o at a distance equal to two thirds of the length of the
coil from the end A. It will be found that the electro motive forces measured
from the line L' and each of the other lines L', L2 and L³ are equal, and that the
three electro motive forces differ from one another by 120°.
The production of these phases of electro-motive force by this method of making
connections is indicated in Fig. 1, wherein the upper two thirds of the vertical
line A O, and the two dotted lines, indicate the resulting electro motive forces, the
relative phases being represented by the relative positions of said lines.
In some cases it may be desired to couple two or more transformers together in
place of each of the transformers described with reference to Figs. 2, 3, 4 and 5,
and this may be done by connecting the primaries p' p p³ p¹ thereof in multiple,
as indicated in Fig. 6, and their secondaries either in multiple or in series, as
described; the connections, however, must be so arranged that a current entering
at the middle point o' will divide equally between the two branches and each
branch will pass an equal number of times in opposite directions around each
core of the transformers in this group and thus neutralize self induction. The
primaries may, however, be connected in series and the secondaries in either-
multiple or series.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is :-
1. The herein described method of transforming alternating currents of one
number of phases into currents of another number of phases, at equal or different
potential.
2. The herein described method of combining three phase alternating currents
for transmission of electrical energy with two phase currents for its distribution.
3. For the purpose of transforming two phase alternating currents into three-
phase currents, the combination of a pair of transformers having their primary coils
connected to the conductors of the one set of currents and having suitably
proportioned secondary coils connected to conductors for the other set of currents,
the ends of some of the primary or secondary coils being connected to points
between the ends of the other primary or secondary coils, and for converse trans--
formation of three phase currents into two phase currents, the converse connections
of the primary and the secondary transformer coils, substantially as described.
4. For the purpose of transforming three phase alternating currents into three.
phase currents of different E.M.F., the use of two transformers with extreme and.
intermediate connections of their coils as illustrated in Fig. 3.
Dated this 24th day of July 1894.
ABEL & IMRAY,
Agents for Applicant..