Improvements in Systems of Electrical Distribution.
Year: 1895

page_text: Date of Application, 9th Feb., 1895-Accepted, 20th Apr., 1895
COMPLETE SPECIFICATION.
Improvements in Systems of Electrical Distribution.
I, JAMES DEVONSHIRE, Secretary of the British Thomson-Houston Limited
of 38 Parliament Street, Westminster in the County of Middlesex, (a com-
munication 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 polyphase
currents, and its principal novel feature consists in an arrangement whereby motors
of the three-phase type may be operated from line circuits in which flow currents
60° apart in phase, with only a slight change in the construction of the motors
from that of ordinary well-known machines of this class. This change consists in
reversing one of the three coils of the motor so that the current flows through
this reversed coil in an opposite direction from that in the ordinary motor, and
thereby produces the same effects so far as the operation of the motor is concerned
as has been heretofore secured by currents differing in phase by 120°.
In the accompanying drawing, Figure 1 shows in diagram a system of distribution
embodying the invention, and Figure 2 shows in a similar manner, a somewhat
modified system of distribution also embodying the invention.
a,
b.
In Figure 1, G is a generator of the "monocyclic type" as I term it. It is
constructed in the same manner as the ordinary single-phase alternating dynamo,
except that there is added a phase-modifying coil on the armature for maintaining
an out-of-phase electromotive force upon a third main, constituting with the other
mains an interconnected polyphase circuit. The field coils of the generator are
represented at F, and are in circuit with a direct current exciting machine E, which
is shunt-wound, and is regulated by a resistance R in the shunt winding. The
main armature coil of the generator is shown at C, having its terminals connected
through collector rings and brushes B, B¹, with distributing mains
A phase-
modifying coil C₁ is connected at one end with a central point in the main
winding C, and its free terminal leads to a circuit main c, through a collector ring
and brush B². The phase-modifying coil occupies a displaced position in the field
of force relatively to the main coil of substantially 90°. With this arrangement
out-of-phase electromotive forces will be maintained between the mains a, c,
and b, c, which in this instance are assumed to differ by substantially 60°. This
phasal relation is secured by properly proportioning the windings of the main
and supplementary coils, so that the resultant electro-motive forces generated by
the coil C¹ and the respective halves of the main winding differ in phase by the
desired amount.
For transforming the currents flowing on the mains to a lower potential, two
transformers T, Tare used, whose primary windings are connected in series and
which are coupled at their free terminals and at the central point c with the three
mains a, b, c.
The secondary windings of the transformers are joined in series and
connected in an exactly similar manner to secondary mains a, b, c. A three-
phase motor M is provided with the three usual coils e, e', 2, two of which, e and e' have
corresponding terminals connected at a common joint t, while the third coil has its
opposite terminal connected to the same joint. The winding it will be observed
is of the usual Y-pattern and differs from the ordinary construction only in the

page_text: The free terminais or the coils are connected respectively
to the mains a¹, b¹ c¹.
With this arrangement currents flow between the mains a¹, c¹ and b, c, which
differ by 60° in phase, but by reversing the direction of the current in the coil e
the relation of the currents, so far as the operation of the motor is concerned,
is changed so that the motor operates in a similar manner to any ordinary three-
phase motor when its terminals are connected to mains carrying currents 120° apart
in phase.
İn Figure 2, g¹ represents an ordinary single-phase alternating dynamo supplying
single-phase currents to mains a, b which are transformed to a lower potential by
the transformer T2. A phase-converter P is wound with main and phase-modifying
coils C, C, arranged relatively to one another in the same manner as the
corresponding windings upon the generator G, illustrated in Figure 1. The
exciting current which flows through the field winding F is in this case also
supplied by a continuous current exciter E, shunt-wound and provided with a
resistance R in the shunt winding for permitting ready regulation. The machine P
will maintain upon the main e¹ which is connected with the free terminal of the
phase-modifying coil C¹, an out-of-phase electromotive force such that currents
differing by 60° in phase may be derived from the mains a¹, e', and ', c'. These
currents are transformed by transformers T T', which are connected in circuit in
the same manner as the corresponding transformers in Figure 1. The secondary
currents upon the mains a, b, c¹ may thus be given any desired potential, though
their phase relation will be the same as that existing on the primary side of the
transformers. A three-phase motor M' having coils e, el, e² may be operated with
currents derived from these mains in the same manner as motor M in Figure 1, the
winding of the motor being the same, and the coil e² being reversed. In fact, the
system of distribution illustrated in Figure 2 is very similar to that of Figure 1,
except that the monocyclic currents are not generated directly at the power station,
but are derived from single-phase currents at convenient points in the system
where three-phase motors are installed. The machines wound as are the
motors m, m', may also serve as generators when driven by a suitable source of
power. They will then generate currents of the same phase relation as they
receive when running as motors that are of the same phase as the monocyclic
generator G, in Figure 1, as already explained. Hence in the clains which are
hereinafter made for the machines distinguished from the system of distribution of
which the machines form a part, I intend to cover its use both as a generator and
a motor.
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 I
claim is :-
1. The method of distribution herein described, which consists in generating
and distributing to a desired point or points polyphase currents approximately
60° apart in phase, and operating motors of the three-phase type thereby by
reversing the direction of the current flowing in one of the windings of the motor,
as set forth.
2. The combination in a dynamo electric machine of the three-phase type, of
three magnetizing coils connected at one end to a common joint, and at their free
ends to collector rings or similar circuit terminals, and having one of the coils
reversed, as described.
3. The combination of a source of polyphase alternating currents approximately
60° apart in phase, and in interconnected three main circuit for distributing such
currents, with a motor of the three-phase type with the coils connected
respectively to the circuit mains and having one of its coils reversed, as set
fortb.
4. A dynamo electric machine of the three-phase type provided with a
Y-winding, in which corresponding terminals of two of the coils and the opposite

page_text: terminal of the third coil are connected to a common joint, and the free terminals
to collector rings, in connection with a source of polyphase currents substantially
60° apart in phase which are fed to the motor coils, as set forth.
Dated this 8th day of February 1895.
JAMES DEVONSHIRE.