Improvements in Systems of Electrical Distribution.
Year: 1899

page_text: Date of Application, 11th Nov., 1899-Accepted, 18th Dec., 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
our said invention (which has been communicated to us from abroad by Charles
P. Steinmetz, of 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:-
In three wire systems in which the neutral or compensating conductor is
connected to a point having a potential intermediate between and fixed with
respect to the main conductors with which it co-operates, and in other systems
having compensating or neutral conductors likewise related to main conductors
with which they co-operate, there is an inherent lack of means for regulation
in cases where the system supplies an unbalanced load and under other conditions
where it is desired to alter the potential difference between the compensating
conductor and the main conductors. Our invention aims to do away with this
objection, and it accomplishes this result by means of an electro-motive force
device arranged in circuit with the compensating couductor, the desired regula-
tion being effected by varying the electro-motive force of said device, either at
will or automatically as desired.
While our invention is applicable to all systoms possessing the general
characteristics above described, we have considered it sufficient to illustrate its
mode of application to one system only of the general type, since its application
to other systems will be readily understood therefrom. The particular system
which we have taken for purposes of illustration is that in which two main
conductors lead from the direct current terminals of a rotary converter and
operate in conjunction with a compensating conductor which is led back and
connected to a neutral point on the alternating current supply system.
The scope of our invention will be clearly apprehended by reference to the
appended claims while its specific character and mode of application will be
made apparent by reference to the following description taken in connection
with the accompanying drawings, in which Fig. 1 represents a diagram of a
distributing system embodying our invention, and Fig. 2 shows a detail.
In Fig. 1, a, b, c, represent the main conductors of a three-phase or other
suitable alternating current supply system to each of which conductors is con-
nected one of the leads d, e, f, for supplying the primary of the multiphase
transformer T. In this instance me three primary coils g, h, i, are connected
in closed circuit, otherwise known as a delta connection, with the leads d, e, f,
connected respectively to the junctions of the coils. The secondaries of the
transformer consist of three coils j, 7, with one terminal of each coil
connected to one of the supply conductors, m, n, o, leading to the collector rings
of a rotary converter R. The other terminals of the secondary coils are con-
nected together, thus forming a point of neutral potential with respect to the
electro-motive forces impressed by the rotary converter R upon the direct current
mains, connected to the direct current end of the rotary.
A conductor N is shown as connected to the common connection of the
coils j, k, 1. This conductor includes in circuit therewith the electro-motive
force device E, and operates in conjunction with the mains p, q, to form a three

page_text: wire system. The conductors of this system are shown in juxtaposition at
r, s, t. The three wire system thus formed is applicable to any of the known uses
to which three wire systems are adapted and for this reason we consider it
unnecessary to illustrate the use of translating devices in connection therewith,
since the same is already known in the art.
The electro-motive force device E as shown in Fig. 1 consists of a series cou-
nected dynamo electric machine connected in circuit with the compensating con-
ductor. This machine is intended to be positively driven in any suitable
manner such for example, as by connecting its armature mechanically with the
shaft of the rotary converter or to a separate electric motor or to any other
suitable source of power. In order to adjust the electromotive force of the
machine a resistance X may be shunted about the field winding as a whole
or about any suitable portion thereof. This resistance serves as a by-path for
the current Howing through the machine and acts to alter the strength of the
field F in reverse ratio to its magnitude. While we have thus shown a suitable
field regulating means, it will of course be understood that any other suitable
device may be employed, such for example, as one which operates by changing
the number of field turns or by varying the reluctance of the magnetic circuit
of the machine. When the three wire system becomes unbalanced, more current
flows on one side than on the other, and the difference between the loads is
taken care of by means of current flowing over the neutral conductor. When
this current flows, it energizes the field of the electro motive force device E
and an electro motive force is produced by the device in opposition to the flow of
current in the compensating conductor. This electro-motive force increases with
increase of current and thus compensates automatically for variations in load,
and so preserves a balance between the two sides of the system.
As will be readily understood, the electro-motive force of the device E is
added to that existing between the compensating conductor and one of the
mains, and is subtracted from that between the compensating conductor and
the other main. The maximum electro-motive force of the device E is therefore
required to be only half of the maximum difference between the potentials
existing between the neutral and the outside mains of the system, while its
current capacity is represented by the difference between the currents flowing
in the two sides of the system. Where a ten per cent. variation of electro-
motive force and a twenty per cent, variation in current between the two sides
of the system is permitted as a maximum, the electro-motive force device is only
one half of one per cent. of the capacity of the rotary converter supplying the
system, and is thus of almost negligible size and cost.
In cases where it is desired to regulate the system by hand, different arrange-
ments may be employed, such for example as indicated in Fig. 2, in which
Grepresents the armature of the electro-motive force device connected in series
with the compensating conductor N, the field winding If being excited, not by
current from the compensating conductor, but from some separate source of
electro-motive force, as for example, from two of the mains of the three wire
system. A combined rheostat and reversing switch Y or other appropriate means
may be employed for controlling at will the field of the electro-motive force
device.
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 automatically regulating a three wire system which consists
in passing current from the compensating conductor through the field and
armature of an externally driven dynamo electric machine.
2-The method of regulating an electrical distribution system having a com-
pensating conductor, which consists in causing the current in the compensating
conductor to automatically set up a counter electro-motive force proportional
thereto.

page_text: 3-The combination of an alternating current supply system, a rotary converter
fed therefrom, direct current mains leading from the rotary converter, a com-
pensating conductor operating in conjunction with said mains and connected
at one end to a neutral point on the alternating current supply system, and a
source of electro-motive force in circuit with said compensating conductor.
4--The combination of an alternating current supply system, a rotary converter
fed therefrom, direct current mains leading from the rotary converter, a com-
pensating conductor operating in conjunction with said mains and connected at
one end to a neutral point on the alternating current supply system, and a source
of variable electro-motive force in circuit with said compensating conductor.
5--The combination of an alternating current supply system, a rotary converter
fed therefrom, direct current mains lending from the rotary converter, a com-
pensating conductor operating in conjunction with said mains and connected at
one end to a neutral point on the alternating current supply system, and a
source of automatically variable electro-motive force in circuit with said
compensating conductor.
6 The combination of an alternating current supply system, a rotary converter
fed therefrom, direct current mains leading from the rotary converter, a com-
pensating conductor operating in conjunction with suid mains and connected at
one end to a neutral point on the alternating current supply system, and a
source of electro motive force in circuit with said compensating conductor and
responsive to change of current in said conductor.
The combination of a three wire system of distribution supplied with energy
derived from an alternating current system and a dynamo electric machine with
its field and armature in circuit with the compensating conductor of the three
wire system.
&-The combination of a three wire system of distribution supplied with energy
derived from an alternating current system and a dynamo electric machine with
its field and armature in circuit with the compensating conductor of the three
wire system and means for varying the ratio between the currents passing
respectively through the field and armature of the machine.
9. The combination of a three wire system and a dynamo electric machine with
its field and armature in circuit with the compensating conductor of the system.
10 The combination of a three wire system and a power driven dynamo electric
machine with its field and armature in circuit with the compensating conductor
of the system.
11 The combination of direct current mains, a compensating conductor co-
operating therewith, and a dynamo electric machine with its field and armature
in circuit with said compensating conductor.
12-The combination of direct current mains, a compensating conductor operat-
ing therewith, and a dynamo electric machine with its field and armature in
circuit with said compensating conductor, and a variable resistance in shuut to
sard field.
13--The combination of main conductors supplied with energy derived from an
alternating current system, a compensating conductor neting in conjunction there-
with, and a dynamo electric machine maintained of substantially constant speed,
and with its field and armature in circuit with said conductor.
Dated this 31st day of October 1899.
TUM DRITING ITIUMDUA TI
ALFRED CLEMEN PS,
Assistant Secretary,
W. MARTINDALE,
A. R. MONKS,
}
Directors.
DID.,