Improvements in Systems of Electrical Distribution.
Year: 1898

page_text: Date of Application, 2nd Aug., 1898-Accepted, 29th July, 1899
COMPLETE SPECIFICATION.
Improvements in Systems of Electrical Distribution.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street, in
the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Charles P. Steinmetz,
residing at Schenectady, in the County of Schenectady, State of New York, United
States of America, Electrical Engineer), and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:-
The present invention comprises a method of and apparatus for reacting by means
of motors upon a single phase generator in such a way as to produce multiphase
current. It also comprises a method of and apparatus for producing multiphase current
from an ordinary single phase distribution system by means of motors or generators
connected in series across the mains, or across the secondary of a transformer fed
from the mains, and various other features which will be hereinafter more particularly
pointed out and claimed.
In the drawing attached to this Specification,
Fig. 1 is a diagrammatical illustration of an embodiment of the invention;
Figs. 2 and 3 are diagrams of electromotive forces: and
Fig. 4 is a diagram of the improved system in a slightly different form.
Referring more particularly to Fig. 1, A is a single phase alternating current
generator, of which A¹ is the armature, and A³ the field. The field winding is excited
by a direct current exciter E, whose output is controlled as usual by the rheostat R.
From the rings A3, A4, of the generator A, wires 1, 2, lend to the system of
distribution. Lamps L, or other single phase translating devices, may be connected
to the mains at any desired point.
It will be seen that the system thus far described is the equivalent of any ordinary
single phase distribution system. As is well known, such a system is not well adapted
for driving motors. We therefore connect across the mains in series two synchronous
machines, M1, M2, which may be independently driven generators, but which in the
preferred form are ordinary synchronous motors. These machines each consist of an
armature and a field magnet the fields being excited from a direct current generator M,
and controlled by rheostats R1, R2. These machines, whether generators or motors,
are free to arrange themselves in a multiphase relation with respect to the main
generator.
As the main generator A, and the machines M1, M2, are in series, they will tend to
arrange themselves so that the vector sum of their electromotive forces is zero, or in
other words, so that the vectors which represent their electromotive forces form a
closed figure. As in the form shown there are only three electromotive forces acting
namely the potential difference across the mains due to the generator A, and the
electromotive forces of the two machines M1, M2, the figure a triangle. As a
triangle is fixed when the lengths of the three sides are given, it is evident that the
phase relations of the systems are stable.
The phase differences between the various electromotive forces may be varied by
properly adjusting the magnitudes of the electromotive forces of the various machines.
For example, if the three electromotive forces are equal an equilateral triangle will

page_text: result, as shown in Fig. 2. If, however, one of the electromotive forces, as for
example that of the generator A, is equal to the square root of two times either of the
others, a two phase system results as indicated in Fig. 2.
As the three electromotive forces acting on the system are thus maintained in a stable
multiphase relation, it is evident that multiphase current may be taken off. In
Fig. 1 is shown a third wire 3, leading from the junction b, between the two
machines M1 and M2. If the electromotive forces of the three machines are equal, the
wires 1, 2, 3, will form a symmetrical three phase system, of which all the energy is
supplied from the single phase generator A. Multiphase motors K, may be run
such a system as usual, through the transformer T if preferred, and will start under
load and run with all the advantages of multiphase machines.
on
A
The system shown in Fig. 4 is similar in principle to that already described.
generator A feeds, through a step up transformer T¹, mains 1, 2, which lead to a
distributing system. Single phase translating devices, as lamps, L, L,, may be
supplied through ordinary transformers T2, T2, wherever desired. But where multi-
phase currents are needed, as for the operation of motors, it is preferred to connect
in series with the secondary of the transformers T³ two synchronous motors or other
synchronous dynamo electric machines, M', M². The secondary of the transformer T³ in
this arrangement corresponds with the generator A in Fig. 1, and constitutes a source
of electromotive force which is automatically maintained, by the mutual reactions, in
a multiphase relation with the electromotive forces of the two machines. Connections
are made from the junctions a, b, c, to a distribution system 11, 21, 31, on which
multiphase motors K and lamps L' may be run.
We have also shown single phase translating devices as lamps, at L², connected to
the secondary mains between the secondary of the transformer and the machines M¹, M².
Lamps so placed will not unbalance the system, as they do not effect the current
flowing in the mains 11, 21, 31.
It is obvious that these improvements may be applied to existing single phase
plants, and will enable such plants to supply motors and lights over the same wires
without expensive changes in their installations, by simply placing a pair of
motors M1, M2, at one or more sub-stations, and loading wires therefrom to points
where power is desired. The improvements also secure the advantage of the
simplicity and economy of transmission inherent in a single phase system, in
combination with the advantages of a multiphase system, and enables us to run single
phase and multiphase translating devices from the same generators without unbalancing
the system.
It will be obvious that where machines M1, M2, are generators, they may be driven
by any suitable power which will leave them sufficiently free to arrange themselves in
the required phase relation, so that where they are motors they may act not only as
phase changers, but also to furnish mechanical power or they may, if preferred, act
also as rotary transformers, as is well understood in the art.
It will be seen that various changes may be made without departing from the
'spirit of the invention. Therefore we do not limit ourselves to the specific forms
shown and described.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same is to
be performed, we declare that what we claim is :-
1-The method of producing multiphase electromotive forces which consist in
generating single phase current, transmitting it to a distant point, and generating
by the action of said current two separate electromotive forces in machines free to
adjust themselves to any desired phase relation with the original current, and
maintaining by the mutual reactions of the said machines upon each other and upon
the original current a polyphase relation between the electromotive forces of the
.system.
2nd-The combination with a single phase alternating current system of
distribution, of two synchronous motors connected in series across said system, and

page_text: connections from said system and from intermediate points between the two motors
to a multiphase translating device.
Dated this 30th dox of Tule 1900
THE BRITISH THOMSON-HOUSTON COMPANY LIMITED.
A. R. MONKS,
Director.
ALFRED CLEMENTS,
Assistant Secretary.