Electrical Potential in Systems of Electrical Distribution.
Year: 1886

page_text: Date of Application, 25th Oct., 1886.
Complete Left, 14th July, 1887.
Complete Accepted, 9th Sept., 1887.
[Communicated from abroad by JOHN W. HOWELL, of the City of New Brunswick,
in the County of Middlesex, and State of New Jersey, in the United States
of America, Electrical Engineer.]
Electrical Potential in Systems of Electrical Distribution.
I, BENJAMIN JOSEPH BARNARD MILLS of the firm of Harris and Mills of
23 Southampton Buildings in the county of Middlesex, Patent Agent do hereby
declare the nature of said invention, to be as follows:-
This invention relates to a novel method and apparatus for indicating or regulating
the pressure of electrical circuits and especially those in a system of electrical
distribution by which instruments of very much simpler construction than those now
in use are enabled to be used which instruments also will not be liable to get out of
adjustment. In the installation of distributing systems it is considered essential to
keep the pressure the same at several points in the system, these points being the ends
of the feeding circuits where they join the distributing mains. In order to keep the
pressure at these points the same, wires called pressure wires are run back from them
to the station and indicators are connected with these wires which show the pressure
and enable the feeders to be properly adjusted to correct the pressure at their
outer ends.
The indicators hitherto employed bave been absolute instruments, that is each is
connected directly to the two wires whose difference of potential is to be kept constant
and the electro motive force of the lines is applied directly to the indicator which
indicates directly the pressure at that point, so that an absolute measure of the
pressure at each of those points is had and each of the indicators which measures this
pressure must be kept in accurate adjustment independently of all the others; these
indicators are liable to get out of adjustment at any time and cause a wrong pressure
to be kept at one or more feeders. In the system which constitutes the present
invention absolute indicators are used at one point in the system only and the pressure
at all the other points is measured by comparing it electrically with the pressure at
this point, that is to say, electrical forces derived from two points are made to have a
cumulative or differential action upon an instrument whose movement is the resultant
of such forces.

page_text: The same principle can also be applied for automatic regulation as well as indication
as will be presently explained.
In explanation of the principle of the invention, suppose two electrical circuits 1, 2
and 3, 4, in which it is desired to maintain the pressure or difference of potential at
the same constant. 1, 2 is provided with an absolute indicator of any known form
which shows the difference of potential between its two conductors. To show whether
or not the pressure at 3, 4 is the same as that at 1, 2 an electrical comparison of the
pressures of the two circuits is produced by connecting the positive conductors of the
two circuits together by a bridge wire and the negative conductors together by
another similar bridge wire. In these two bridge wires is placed a comparativ
instrument. This is a differentially wound instrument such as a high resistanc
differential galvanometer so that equal currents flowing in the same direction across
the bridge wires will neutralize each other and currents flowing in opposite directions
across the bridge wires will act together in producing movement of the instrument.
Suppose the potentials at 1, 2 to be represented by 200 on the positive conductor (1)
and by 100 on the negative conductor (2) and that this difference in potential-100-
is the pressure it is desired to maintain constant in both circuits. If the potentials
are the same at 3, 4 no current flows through the galvanometer, and the needle
remains at zero. If at 3, 4 there are potentials represented by 202 and 102, then on
each bridge wire and on each galvanometer coil there is a current caused by a
difference of potential of 2. As in each bridge wire this current flows from 3, 4
to 1, 2 the currents neutralize each other and there is no deflection. This is a correct
indication since the difference between 3 and 4 is 100 as desired. But if at 3, 4
there should be potentials represented by 202 and 104 the currents in the galvano-
meter coils will be in the same direction as before, but one being caused by 2 units
and the other by 4 units a deflection will be produced by the larger current which
will show that the difference of potential is 98 instead of 100.
If at 3, 4 we have 202 and 98 one coil of galvanometer will carry a current from
circuit 3,4 to circuit 1, 2 and one from 1, 2 to 3, 4 and these currents will act
together on the needle and produce a deflection showing the difference of potential as
being 104.
The standard circuit 1, 2, will be regulated by reference to its absolute indicator
while the circuit 3, 4 and as many other circuits as may be connected with 1, 2 will
be regulated by reference to their respective instruments.
In practice the absolute indicator for the standard feeding circuit may be connected
across the pressure wires of that circuit which extend from its point of connection
with the main or lighting conductors and the bridge wires extend from these standard
pressure wires to the pressure wires of each of the other feeders of the system, a
comparative indicator being thus connected between the standard feeder and each of
the other feeders. This is for a two wire multiple arc system.
For a three wire or compensating system the pressures between positive and neutral
and between neutral and negative conductors of the standard circuit may be shown
respectively upon each of two absolute indicators while comparative indicators are
placed in bridge wires from the wires of the standard circuit to the corresponding
wires of the circuits to be compared therewith. Of course double the number of
comparative indicators as for a two wire system, will be required.
The comparative indicators have a particular advantage in connection with a
three-wire system of distribution, since they enable it to be determined whether
current is flowing over the neutral wire of any feeder by a direct comparison o
the potentials in the neutral wires of the two or more feeders. This is done by
simply breaking the bridge wires connecting positive conductors as well as those
connecting negative conductors, leaving the bridge wires between neutral conductors
alone in connection with the instruments.
The comparative indicators then act as simple galvanometers and show the
differences in potential between the neutral conductors. Since the flow of curren
on neutral conductors indicates an unbalanced system, the comparative indicator
enable the fault to be located and remedied.

page_text: Instead of connecting the absolute indicator with a standard feeding circuit,
there may be provided a local station circuit directly from the dynamos in the
station or from the omnibus wires into which the dynamos feed and from which
the feeders extend; in this local circuit the absolute indicator is placed and the
pressure at the end of each feeder is compared with said local circuits pressure
by a comparative indicator placed in bridge wires between the local conductors
and the pressure wires of the feeder. It will be readily understood that this
arrangement is equally well adapted to three wire and two wire systems.
In carrying out this arrangement an incandescent electric lamp which forms a
fixed resistance is connected across the omnibus wires in the station and has an
adjustable resistance in series with it. An absolute indicator is also connected
across the omnibus wires and also in series with the adjustable resistance and by
adjusting this resistance the lamp may be kept at the standard candle power
desired for the system and the same difference of potential is made to exist
across the lamp terminals as is desired at the outer ends of the feeders. Additional
wires run from the terminals of the lamp and the bridge wires containing the
comparative indicators run from these additional wires to the pressure wires of each
of the feeders.
This invention it will thus be seen reduces the number of absolute indicators to one
in a multiple arc system and to two in a three wire system, the pressure at all other
points being shown on differential galvanometers which, arranged for this purpose,
I call comparative indicators.
Central stations as at present erected upon the Edison system use from eight to
twelve indicators. Each of these an absolute indicator and has to be kept in
adjustment independently of the others. This requires a great deal of attention and
time and if the instruments are not kept in adjustment they will give wrong
indications.
The comparative indicators however require no adjustment after being once set up
and as it is only necessary to keep one or two absolute indicators in adjustment it or
they will receive more attention and the regulation will be improved.
The comparative indicators also can be made for much less money than absolute
indicators and where ten to twelve are used this makes a large saving.
Instead of a differential galvanometer there can be used a differentially wound
polarized relay which will close one of two circuits and light one of two lamps
connected with such circuits when the pressure is different from that at the absolute
indicator; thus by observing which lamp is lighted it is known whether the pressure
of any feeder is above or below the standard.
In these galvanometers or relays the resistance of each coil must be, as will be
well understood, large enough when compared with the resistance of the pressure
wires to bring the difference of potentials to the instrument and not have any
noticeable loss on the pressure wires.
The differential galvanometer or polarized relay may be arranged to close one of
two circuits when moved from the normal position, and thus control and cause to
operate in one direction or the other any suitable intermediate mechanism which
will throw into and out of circuit an adjustable resistance and in this manner the
resistance of a feeder and the pressure at its outer end may be regulated
automatically.
The absolute indicator may be of any desired form. The inventor prefers to employ
one on the Wheatstone Bridge principle as described in his prior patents.
B. J. B. MILLS.
By Harris & Mills,
23, Southampton Buildings,
Agents,

page_text: Electrical Potential in Systems of Electrical Distribution.
e
I, BENJAMIN JOSEPH BARNARD MILLS of the firm of Harris and Mills of
23 Southampton Buildings in the County of Middlesex, Patent Agent, do hereby
declare the nature of this invention, communicated to me from abroad by John
W. Howell of the City of New Brunswick in the County of Middlesex and State of
New Jersey in the 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 stateinent :-
This invention relates to a novel method and apparatus for indicating or regulating
the pressure of electrical circuits and especially those in a system of electric distri-
bution, by which instruments of very much simpler construction than those now in
use are enabled to be used which instruments also will not be liable to get out of
adjustment. In the installation of distributing systems it is considered essential to
keep the pressure the same at several points in the system, these points being the ends
of the feeding circuits where they join the distributing mains. În order to keep the
pressure at these points the same, wires called pressure wires are run back from them
to the station and indicators are connected with these wires which show the pressure
and enable the feeders to be properly adjusted to correct the pressure at their outer
ends.
The indicators heretofore employed have been absolute instruments, that is each is
connected directly to the two wires whose difference of potential is to be kept constant
and the electro motive force of the lines is applied directly to the indicator which
indicates directly the pressure at that point so that an absolute measure of the
pressure at each of those points is had, and each of the indicators which measures
this pressure must be kept in accurate adjustment independently of all the others;
these indicators are liable to get out of adjustment at any time and cause a wrong
pressure to be kept at one or more feeders. In the system which constitutes the
present invention absolute indicators are used at one point in the system only and the
pressure at all the other points is measured by comparing it electrically with
the pressure at this point, that is to say, electrical forces derived from two points are
made to have a cumulative or differential action upon an instrument whose movement
is the resultant of such forces.
The same principle can also be applied for automatic regulation as well as indication
as will be presently explained.
In the accompanying drawing forming a part hereof,-
Figure 1 is a view in diagram illustrating the principle of the invention.
Figure 2 a similar view showing the application of the invention, for indication, to
a two-wire multiple are system of electrical distribution,

page_text: Figure 5, a sumar view showing the invention appired for indication to a three-
wire or compensating system of distribution.
Figure 4, a similar view showing arrangement of the indicators in a system station
which may be employed.
Figure 5, a view partly in diagram of a modified form of comparative indicator.
Figure 6, a view partly in diagram illustrating the invention applied for automatic
regulation.
In explanation of the principle involved in the invention reference may be had to
the simple illustration, figure 1. Consider that it is desired to maintain at the same
constant the pressure in the circuits 1, 2 and 3, 4 and that 1, 2 is provided with an
absolute indicator of any known form which shows the difference of potential between
1 and 2. To show whether or not the pressure at 3, 4 is the same as at 1, 2 the
inventor produces an electrical comparison of the pressures of the two circuits by
connecting the positive conductors 1 and 3 of the two circuits together by a bridge
wire 5 and the negative conductors 2 and 4 by a similar bridge wire 6. In these
two bridge wires is located a comparative instrument A. This is a differentially
wound instrument so that equal currents flowing in the same direction across the
bridge wires will neutralize each other and currents flowing in opposite directions
across the bridge wires will act together in producing movement of the instrument.
This instrument A may be a high resistance differential galvanometer with one coil
in bridge wire 5 and the other coil in bridge wire 6. It is shown as a differential
galvanometer by conventional illustration in all the figures except figure 5.
Suppose the potentials at 1, 2 to be represented by 200 on the positive conductor 1
and by 100 on the negative conductor 2 and that the difference in potential, 100, is
the pressure it is desired to maintain constant in both circuits: If the potentials are
the same at 3, 4, no current flows through the galvanometer and the needle remains
at zero. If at 3, 4 there are potentials represented by 202 and 102 then in each
bridge wire and on each coil of galvanometer there is a current caused by a difference
of potential of 2. As in each bridge wire this flows from circuit 3, 4 to 1, 2 the
currents neutralize each other and there is no deflection. This is a correct indication
since the difference of potential at 3, 4 is still 100. If at 3, 4 there are potentials
represented by 202 and 104 the currents in the galvanometer coils will be in the same
direction as before, but, one being caused by 2 units and the other by 4 units, a
deflection will be produed by the larger current, as it should be since the difference of
potentials is 98 and not 100.
If at 3, 4 we have 202 and 98, one coil of galvanometer will carry a current from
circuit 3, 4 to circuit 1, 2 and one from 1, 2 to 3, 4 and these currents will act together
on the needle and produce a deflection, as they should, showing the difference of
potential as being 104.
The circuit 1, 2 will be regulated by reference to its absolute indicator, while
circuit 3, 4, and as many other circuits as may be connected with 1, 2 in the same
manner, will be regulated by reference to their respective instruments A, or these
instruments can be utilized to effect the regulation automatically as will be presently
explained.
In figure 2 the application of the invention for indication upon a two-wire system of
distribution is shown.
The street mains are illustrated by 7, 8. From the street mains at points B, C
and D are taken feeders 9, 10 supplying current to the mains from the central station,
and corresponding with the feeders are pressure wires 11, 12 running from points
B, C and D on mains back to the station. The feeders will have adjustable
resistances R for regulation. Hand adjusted resistances for this purpose are shown in
figure 4 and an automatically adjusted resistance is shown in Figure 6.
To the pressure wires from B is connected the absolute indicator E. This may be
the lamp indicator on the Wheatstone Bridge principle shown in the prior Patents
of this inventor, or any other suitable indicator. Bridge wires 5, 6 connect an
extra set of pressure wires, 17, 18 from B with those from C and D and in these
bridge wires are located the differential galvanometers A. Thus indications will be

page_text: had for regulating the three feeders to keep the desired pressure at the points
BC and D.
For a three-wire system (figure 3) the pressure at B between positive and neutral
and between neutral and negative is shown upon 2 absolute indicators E, while four
comparative indicators A show whether or not the pressure at C and D is the same
as at B. In this figure, for clearness of illustration, the bridge wires for comparative
indicators are shown as connected with the same pressure wires from point B as are
the absolute indicators.
The comparative indicators have a particular advantage in connection with a three-
wire system of distribution, since they enable it to be determined whether current is
flowing over the neutral wire of any feeder by a direct comparison of the potentials in
the neutral wires of the two or more feeders. This is done by simply breaking the
bridge wires connecting positive conductors as well as those connecting negative
conductors leaving the bridge wires between neutral conductors alone in connection
with the instruments. The comparative indicators then act as simple galvanometers
and show the difference in potential between the neutral conductors. Since the
flow of current on neutral conductors indicates an unbalanced system, the com-
parative indicators enable the fault to be located and remedied.
For a distributing system there may be provided a standard pressure by a local
station circuit directly from the dynamos in station or the omnibus wires 13, 14 into
which they feed and to compare the pressure at ends of feeders with this standard
pressure. This is shown applied to a two wire system in figure 4. The application
to a three wire system will take double the number of instruments (the same
number for each side or division of the circuit) as will be understood from figure 3.
With reference to figure 4, an incandescent electric lamp A', forming a fixed
resistance, is connected with omnibus wires 13, 14 in station and has an adjustable
resistance R¹ in series with it. An absolute indicator E is connected in multiple are
with the lamp A¹ and by adjusting R¹ with reference to E the lamp can be kept
at the standard candle power required for the system and the same difference in
potential is made to exist across the lamp terminals as is desired for outer ends of
feeders. The bridge wires with their comparative indicators are connected between
the feeder pressure wires and wires 15, 16 running from the terminals of this
lamp A'.
This invention it will thus be seen reduces the number of absolute indicators to one
in a multiple arc system and to two in a three-wire system, the pressure at all other
points being shown on differential galvanometers which, arranged for this purpose,
I
call comparative indicators. Central stations as at present erected upon the Edison
system use from eight to twelve indicators. Each of these is an absolute indicator
and has to be kept in adjustment independently of the others. This requires a great
deal of attention and time and if the instruments are not kept in adjustment they will
give wrong indications. The comparative indicators however require no adjustment
after being once set up and as it is only necessary to keep one or two absolute
indicators in adjustment it or they will receive more attention and the regulation will
be improved. The comparative indicators also can be made for much less money than
absolute indicators and where ten or twelve are used this makes a large saving.
Instead of a differential galvanometer there can be used a differentially wound
polarized relay which will close one of two circuits and light one of two lamps
connected with such circuit when the pressure is different from that at the absolute
indicator; thus by observing which lamp is lighted it is known whether the pressure
on any feeder is above or below the standard.
In these galvanometers or relays the resistance of each coil must be, as will be
well understood, large enough when compared with the resistance of the pressure wires
to bring the difference of potentials to the instrument and not have any noticeable
loss in the pressure wires.
The differential galvanometer or polarized relay may be arranged to close one of
two circuits when moved from the normal position, and thus control and cause to
operate in one direction or the other any suitable intermediate mechanism G. (figure 6)

page_text: which will throw into and out of circuit an adjustable resistance R, and in this
manner the resistance of a feeder and the pressure at its outer end may be regulated
automatically.
In figure 6 the arm of differential galvanometer is shown connected constantly with
one mercury trough c and standing normally between two others d, e and in this way,
by the connections shown, controlling two circuits to the intermediate resistance
adjusting mechanism G which is a well understood apparatus.
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. Indicating or regulating the pressure in two or more electrical circuits-in one
-the standard-circuit directly by the pressure therein, and in the others by a move-
ment produced upon instruments by the resultant of electrical forces acting cumulatively
or differentially on such instruments, such forces being derived from said standard
circuit and from said other circuits, substantially as hereinbefore described.
2. The combination in a system of electrical distribution, of two or more feeding
circuits, a standard circuit which may be one of the feeding circuits or a special local
circuit, an absolute indicator in said standard circuit, bridge wires connecting the
conductors of said standard circuit with like conductors of each of the feeding
circuits (or of each of the remaining feeding circuits if the standard circuit is one of
these) and differentially wound indicating or regulating instruments included one in
each pair of said bridge wires whereby indication or regulation of the pressure of the
circuits is produced by movement of said instruments due to an electrical comparison
between the pressure of the standard circuit and that of each of the other circuits.
1005
Dated this 14th day of July 1887.
BENJ. JOS. B. MILLS.
By Harris & Mills,
23, Southampton Buildings,
Agents.