Improvements in Systems of Electric Distribution.
Year: 1895

page_text: Date of Application, 9th Feb., 1895-Accepted, 20th Apr., 1895
COMPLETE SPECIFICATION.
Improvements in Systems of Electric Distribution.
I, JAMES DEVONSHIRE, Secretary of The British Thomson-Houston Limited
of 38 Parliament Street, Westminster, in the County of Middlesex, (a communi-
cation to me from abroad by Charles P. Steinmetz of Schenectady, County of
Schenectady, State of New York, United States of America) 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 :-
This invention relates to a system of electrical distribution for multiphase
currents, by which currents 60° apart in phase may be converted into currents 120°
apart in phase, or the reverse. This renders possible the generation and distribution
of currents 60° apart in phase, and their conversion into currents differing by 120°
in phase which are suitable for operating three-phase motors of the ordinary type,
or other three-phase translating devices. It is also equally possible, as will be
explained hereinafter, to convert monocyclic currents into three-phase currents.
Hence by the present invention, monocyclic currents differing by 60° and true three-
phase currents become readily convertible the one into the other. Such a system
and the means for effecting this conversion, I intend to claim broadly.
The conversion of one system into the other is effected by two transformers in
which the primary and secondary windings occupy relatively a reversed relation,
so that in a 60° system the phase of one of the currents will be changed through an
angle of 180°, thus occupying a phasal relation with reference to the other two
currents such that all three are 120° apart.
In the accompanying drawing, Figure 1 represents in diagram a system of
distribution in which monocyclic currents are converted into three-phase currents,
and Figure 2 represents in a similar manner a system of distribution in which
three-phase currents are converted into monocyclic currents.
In Figure 1, G represents what I term a monocyclic generator_provided with a
field-exciting coil F, in circuit with a continuous current exciter E, which may be
either shunt or series wound. In the diagram it is shown as shunt wound, and is
regulated by a resistance B in the shunt circuit. The armature of the generator G
has a main winding W similar to that employed in ordinary single-phase alternating
generators and a supplementary or phase-modifying coil W₁ having one terminal
connected to a central point d in the main winding. The free terminals of the main
and supplementary coils are connected through collector rings and brushes R, R', R³,
with three mains a, b, c. The main and supplementary windings are so proportioned
that an electro-motive force is inaintained between the mains b c and a b 60° apart
in phase. For converting their currents into three-phase currents, two trans-
formers T T are employed, whose primary coils are joined in series at the point e;
their free terminals are connected to two of the mains a, c, and their connected
terminals at the point e are joined to the third main b. The secondary windings of
the transformers are coupled in a similar manner to mains a' b c but one of the
secondary coils as, for example, that of transformer T, is reversed, as shown in the
diagram. This will result in shifting the electro-motive force maintained between
the middle main and one of the outside mains through an angle of 180°, so that
the phasal relation of the electro-motive forces on the secondary side of the
transformers will be 120° apart instead of 60° apart, as they are on the
primary side.
The transformers may be given any desired ratio of transformation, so that the
potential of the secondary currents will be changed as well as their phase relation.

page_text: Instead of reversing one of the secondary coils, the same changes of phase may be
secured by reversing one of the primary coils. The secondary three-phase currents
inay be used for operating translating devices of any desired kind and coupled in
any desired manner, as, for example, lamps, or three-phase motors.
In the diagram a motor M is shown whose three coils are connected at corre-
sponding terminals to a common joint g and whose free terminals are coupled,
respectively, to the mains a' b¹ c'. Any other form of three-phase motor may be
substituted for that shown in the diagram. Other translating devices also may be
grouped on the mains a¹ b¹ c¹ in any ordinary manner.
In Figure 2 the generator G¹ is of the three-phase type, and the electro-motive
forces maintained between the mains a b c are 120° apart in phase. These currents
may be converted into a monocyclic system by two transformers T2 T3 connected in
series to the mains a b c in a manner similar to the transformers T T shown in
Figure 1, and already described. The secondaries of the transformers are connected
to mains a¹ b'c' but the secondary of transformer T' is reversed, so that the two
electro-motive forces between the main c¹ and the mains a¹ b' are 60° apart in phase,
instead of 120° as is the case on the primary side. The secondary currents may be
utilized for operating translating devices in any desired manner.
Motors may be run from all three mains by using a system of transformers T' To
in all respects similar to T T¹ as described in connection with Figure 1, or, by
modifying somewhat the construction of the ordinary three-phase motor, they may
be connected directly with the mains a' c'. This modification consists in reversing
one of the coils of the motor, as shown at m¹. Here the motor has three windings;
having one set of terminals connected to a common joint g, and their free terminals
to the mains, but instead of the arrangement shown at M, one of the coils, namely,f,
is reversed. I do not, however, claim this construction in the present Application,
but merely illustrate it to explain how motors of this type can be operated from the
mains a b c without reconverting the 60° currents which are supposed to flow
therein into true three-phase currents.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. The method of electrical distribution herein described, which consists in
generating three polyphase currents substantially 60° apart in phase, converting
such currents into three currents differing in phase by substantially 120°, and
utilizing such last named currents for operating translating devices of the ordinary
three-phase type, as described.
2. The method herein set forth, which consist in generating electro-motive forces
substantially 60° apart in phase, shifting the phase relation of one of the electro-
motive forces through an angle of 180° and thereby changing it from a 60° relation
to the other electro-motive forces to a 120° relation or the reverse, as described.
3. The combination of a three-main interconnected polyphase circuit, with means
for maintaining between such mains electro-motive forces substantially 60° apart in
phase with a transformer connected on one side to said means, and on the other side
to a corresponding set of mains, and means for changing the phase relation of the
transformed currents from 60° to 120°, or vice versa, as described.
4. The combination of a source of polyphase currents 60° apart in phase, with a
combined transformer and phase converter reducing the potential of the currents,
and converting them into currents 120° apart in phase, as described, and motors or
other translating devices of the ordinary three phase type operated by such
transformed currents.
5. The combination in a system of distribution, of a generator of the alternating
current type provided with a phase-modifying coil, and maintaining in a three-main
interconnected circuit electro-motive forces 60° apart in phase, with an interconnected
system of transformers, as described, transforining and converting the phase relation
of the currents from 60° into 120° as described.

page_text: 6. The combination in a polyphase distribution system, of two transformers
having their respective primary and secondary windings coupled in series and
arranged in inverse relation to one another, as described, with circuit connections
joining the free and connected terminals of the transformers, respectively, with the
mains of a polyphase distribution system.
7. The combination of an interconnected system of transformers coupled in series
and having the primary or secondary winding of one of the transformers reversed,
as described, with circuit connections to the mains of a polyphase distribution
system, whereby the phase relation of the transformed currents are altered as
set forth.
Dated this 8th day of February 1895.
JAMES DEVONSHIRE.