Improvements in and connected with Electric Meters for Alternating Currents.
Year: 1893

page_text: Date of Application, 30th Aug., 1893
Complete Specification Left, 30th May, 1894-Accepted, 30th Aug., 1894
PROVISIONAL SPECIFICATION.
Improvements in and connected with Electric Meters for Alternating
Currents.
I, JAMES SWINBURNE, of Broom Hall Works, Teddington, Middlesex,
Electrical Engineer do hereby declare the nature of this invention to be as
follows:-
My invention has reference to electrical measuring instruments in the forms of
Voltmeters, Amperemeters, Wattmeters, Ohmmeters, step indicators & meters for
alternating currents.
The alternating current Wattmeter may be described first. This instrument
consists of a disc of platinoid or other conductor with a low temperature coefficient
mounted on an arbor so that it can turn between two crowns of magnets, the system
having the appearance of a small multipolar dynamo with a disc in the place of an
armature. Half of the magnets are excited by the main current, & the other half
by means of a shunt circuit across the mains, the pressure & current magnets being
arranged alternately. The magnetic circuit is arranged so that the time constant
of the pressure circuit is as high as possible. The pressure & current poles thus
induce currents in the revolving disc. The currents induced by the pressure coils
are in circuits which pass between the current poles, so as to be under the influence
of their field; & the currents induced by the current magnets are under the
influence of the pressure fields. As the induction due to the current coils is in
step with the main current, the currents induced by them in the disc are a quarter
of a period out of step with the main current. If the apparatus is measuring the
power on a circuit of no time constant the shunt current lags practically a quarter
of a period, & so does its induction. Its induction is therefore in step with the
currents induced in the disc by the main circuits. Torque is therefore produced,
proportional to the product of the main current, multiplied by its frequency & the
pressure divided by the frequency; that is to the power. Again the pressure coils
induce disc currents proportional to the pressure, and in step with it, & these pass
under the field produced by the current coils, this field being in step with the
current there is thus further torque proportional to the product of the pressure &
the current. If the main pressure & the current are out of step the torque will be
proportional to the real, not the apparent power. To make such an instrument
accurate the time constant of the pressure coils must be very large. To secure_this
I use as small an air space as possible, & leave plenty of room for the wire. It is
sometimes necessary to use an additional choking coil in series, in order to get a
higher time constant. A small transformer may also be used to transform a high
pressure down, an arrangement not permissible in an ordinary wattmeter.
movement of the disc is opposed by a spring, & an index reads the watts. This
instrument may be "set up so as not to start from zero, & in any case can read
right round a circular scale. The magnet system is conveniently made by rolling
up a thin strip of sheet iron into a disc with a central hole. Radial grooves are
then milled out of one side. Two of these rolls with the disc between them form a
system. The coils are best placed on alternate sides, so that if an eight pole
system is used, four pressure coils are placed on one half occupying the eight grooves,
& four current or main coils on the other half. The disc of platinoid may have a
thick rim of copper to give greater conductivity, & rings of copper may be put on
inside, where they clear the iron, for the same purpose.
The
Sometimes I make the working part of the instrument like a small double
current motor with a laminated iron motor, the embedded wires being of some

page_text: metal with a low temperature coefficient, and the magnetic circuit having very
small air spaces.
The voltmeter for alternating currents differs from the wattmeter in its
winding only. It is wound with two sets of coils, one having a large & the other
a small time constant. These circuits are arranged in parallel. When the
frequency is constant this instrument reads correctly, even if the difference of time
constant is not very great; but if the frequency varies the time constant of the
circuits should be as different as possible.
An ampere meter again differs from a wattmeter in the windings only.
The two circuits are in parallel, & both are wound with large wire, one being of
platinoid or other wire of high resistance & small temperature coefficient, & the
other being copper.
The ohmmeter is wound not with two sets of coils but with four. Two sets are
arranged as a wattmeter & two as an ampere-meter, & these sets act differ-
entially. The disc is not controlled by a spring, but is cut away so that it takes
up a position such that its reading is R where CR is the power. Instead of a
compound of watt & ampere meter, the instrument may be a combination of
watt & voltmeter which reads r so that Er is the power. This instrument is well
adapted for testing the insulation of systems of distribution.
For use as a step indicator it is wound with two coils connected both in the same
way with the currents or pressures to be examined. For instance in the case of
alternators in parallel the whole station circuit is led through one set of coils,
& the current of one dynamo through the other. The instrument shows whether the
dynamo current is leading or lagging relatively to that of the whole station.
It is not necessary to run the whole of the electricity through the instrument, the
coils may be put in shunt to resistances in the dynamo & station circuits.
For measurements of very small quantities, the disc is suspended & controlled
by a torsion suspension such as a fine wire of phosphor-bronze. The ohmmeter
may have a fibre suspension, & a copper disc.
As the torque on the disc of the wattmeter is proportional to the power, the
instrument may be used as an energy meter. The movement of the disc is then
controlled by a damping arrangement such as a fan or foucault current disc. I
prefer the disc. The same disc will serve both purposes. The whole of the
magnets on each side of the disc are made permanently north & south by permanent
magnets, so that a permanent field is superposed on the alternating fields. As the
fields do not cover the whole disc, the direct induction sets up foucault currents
which retard the movement of the disc.
In alternating amperemeters & wattmeters & some other cases it is often
advisable not to lead the main through the instrument. An ordinary transformer
might be used, but this leads to inaccuracy, as the secondary current is not
proportional to the primary, & is not in step with it. I therefore arrange a divider,
which is wound like a little transformer with two circuits. These are branches of
the main circuit, & are so connected that one has the instrument in circuit. Thus,
if the instrument is to have one hundredth of the main current the divider has
two circuits, one of 1 turn, & the other of 99, these turns being wound in opposite
directions. The instrument circuit is also made 99 times the resistance of the
other, including the coils of the instrument. The core of the divider is thus
not magnetised unless the current is not divided accurately; & a very small
variation will be enough to cause induction, which tends to keep the
proportion true.
Dated this 29th day of August 1893

page_text: COMPLETE SPECIFICATION.
Improvements in and connected with Electric Meters for Alternating
Currents.
I JAMES SWINBURNE of Broom Hall Works Teddington Middlesex Electrical
Engineer 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 :-
My invention has reference to electrical measuring instruments in the forms of
Voltmeters, Amperemeters, Wattmeters, Ohmmeters, step indicators & meters for
alternating currents.
The alternating current Wattmeter may be described first. This instrument
consists of a disc of platinoid or other conductor with a low temperature coefficient
mounted on an arbor so that it can turn between two crowns of magnets, the system
having the appearance of a small multipolar dynamo with a disc in the place of an
armature. Half of the magnets are excited by the main current, and the other half
by means of a shunt circuit across the mains, the pressure and current magnets
being arranged alternately. The magnetic circuit is arranged so that the time
constant of the pressure circuit is as high as possible. The pressure and current
poles thus induce currents in the revolving disc. The currents induced by the
pressure coils are in the circuits which pass between the current poles, so as to be
under the influence of their field; and the currents induced by the current magnets
are under the influence of the pressure fields. As the induction due to the current
coils is in step with the main current, the currents induced by them in the disc are
a quarter of a period out of step with the main current. If the apparatus is
measuring the power on a circuit of no time constant the shunt current lags
practically a quarter of a period, and so does its induction. Its induction is
therefore in step with the currents induced in the disc by the main currents.
Torque is therefore produced, proportional to the product of the main current,
multiplied by its frequency & the pressure divided by the frequency; that is
to the power.
Again the pressure coils induce disc currents proportional to
the pressure, and in step with it, and these pass under the field produced by the
current coils, this field being in step with the current there is thus further torque
proportional to the product of the pressure and the current. If the main pressure
and the current are out of step the torque will be proportional to the real, not the
apparent power.
To make such an instrument accurate the time constant of the
pressure coils must be very large. To secure this I use as small an air space as
possible, and leave plenty of room for the wire. It is sometimes necessary to use
an additional choking coil in series, in order to get a greater time constant.
small transformer may also be used to transform a high pressure down, an
arrangement not permissible in an ordinary wattmeter on account of the consider-
able waste field in a small transformer. The movement of the disc is opposed by a
spring, & an index reads the watts. This instrument may be "set up so as not to
start from zero, and in any case can read right round a circular scale. The magnet
system is conveniently made by rolling up a thin strip of sheet iron into a disc with
a central hole. Radial grooves are then milled out of one side. Two of these rolls
with the disc between them form a system. The coils are best placed on alternate
sides, so that if an eight-pole system is used, four pressure coils are placed on one
half occupying the eight grooves, and four current or main coils on the other half.
The disc of platinoid may have a thick rim of copper to give greater conductivity,
and rings of copper may be put on inside, where they clear the iron, for the same
purpose.
13
A
Sometimes I make the working part of the instrument like a small double current
motor with a laminated iron rotor, the embedded wires being of some metal with a
low temperature coefficient, and the magnetic circuit having very small air spaces.

page_text: In the accompanying drawings Figs. 1 & 2 are views of the acting system of the
instrument so far described. Two strips of thin sheet iron are rolled up like ribbon
into rolls with central holes. One 6 is shown in Fig. 1, it is rivetted together to
prevent unwinding, and one face has eight slots milled out of it, leaving eight
laminated pole pieces. In the eight slots four coils a a a a are arranged, and these
are coupled so as to embrace north & south poles alternately, the poles between the
neighbouring coils not being excited by them. The other roll of ribbon is similar,
but the coils cc Fig. 2 are arranged so as to excite the poles not excited by a a a a.
The faces of the field poles are arranged as in Fig. 2 with a disc of metal d
mounted on a spindle free to turn between them. If the currents in the sets of coils
are out of step there will then be torque tending to rotate the disc. For those
instruments in which the temperature variation of the resistance of the disc affects
the reading, the disc should be of an alloy with a low temperature coefficient. As
such an alloy is a bad conductor it may be advisable when a large torque is wanted
to put copper bands ef on the disc as shown in Figs. 3 & 4.
As it is difficult to secure a large enough time constant in the lagging coil in the
form shown in Figs. 1 & 2, I prefer the form in Fig. 5 with four slots and two coils.
The coils a a embrace north and south poles, and the poles not embraced by them
are excited by the coils on the other set of magnets.
Another form which is still better is shown in Figs. 6 & 7. The magnets are
here arranged as in a dynamo machine, and are stamped out of thin soft iron. The
central core is stationary, and there is a space left between the central core and the
poles. The coils are wound as shown, & c form one set, producing north and
south poles, that is to say acting on the same magnetic circuit, and a a form
the other set. The moving system here consists of a piece of metal tube mounted
on a suitable spindle so as to rotate on its centre in the gap between the magnets &
the central core. It is shown at in Fig. 7. Fig. 8 shows the tube with copper
or aluminium rings mattached to lessen the resistance, as in Figs. 3 & 4. It is
mechanically possible to make the form in Figs. 6 & 7 with less air space, so that
the time constant of the lagging coils may be high, and the loss by resistance and
back pressure by induction in the step coils small. By lagging coils I mean the
coils whose time constant is made large so that their current lags as much as
possible after the pressure upon them, and by step coils 1 mean those with small
time constant whose current is as nearly as possible in step with the pressure
on them, or which are arranged, for instance in the wattmeter, in series with an
external circuit.
The forms so far described can be made to read right round a circular scale, and
are therefore controlled by springs, when control is required, as in the case of watt,
volt, and amperemeters. Figs. 9 & 10 show one of many possible modifications
of my instrument. It is less expensive to make. The iron b is in the form of
E shaped stampings such as used in transformers. The lagging coils a a are
wound on
a closed magnetic circuit, and thus have a very large time constant
and need very little wire for a given alternating pressure. The step or series coil c
is single, and is wound on the central tongue. This tongue has an air space
between it and the cross piece or keeper of t. The moving system consists of a
loop of wire d on an arbor o, forming a closed circuit embracing the magnetic
circuit of the coils a a so as to form a secondary to them as primary. This
instrument is developed from that in Figs. 6 & 7 by joining h&h to the centre
piece and using a portion only of the tube l, & removing one of the poles and
coils ii. I mention this to show that the form shown in Figs. 9 & 10 is a variety
of the instrument whose principle is explained, and whose construction is indicated
in my Provisional Specification, though the form is not specially described therein.
To those who treat double or triple circuit machines as having what they call
"rotary fields" the identity of the forms is not self evident; but to those who have
studied the theory, and who have followed out the actions of the currents in
inducing secondary circuits in the moving system, and fields to act upon these

page_text: secondary currents, as explained in this Specification the identity of the various
forms of instrument illustrated is clear.
The form in Figs. 6 & 7 may be modified, the fixed centre part; and the tube
being replaced by a moving system made on the same lines as the rotor of a
multiple current motor. When necessary the wire on it is made of an alloy with a
low temperature coefficient.
The voltmeter for alternating currents differs from the wattmeter in its winding
only. It is wound with two sets of coils, one having a large and the other a small
time constant. These circuits are arranged in parallel. When the frequency is
constant this instrument reads correctly, even if the difference of time constant is
not very great; but if the frequency varies the time constants of the circuits
should be as different as possible.
An ampere meter again differs from a wattmeter in the windings only. The two
circuits are in parallel, and both are wound with large wire, one of platinoid
or other wire of high resistance and small temperature coefficient, and the other
being copper.
The ohmmeter is wound not with two sets of coils but with four. Two sets are
arranged as a wattmeter and two as an amperemeter, and these sets act differentially.
The disc is not controlled by a spring, but is cut away so that it takes up a position
such that its reading is R where C R is the power. The wattmeter part gives a
force proportional to E C & the ampere part to C2, so that the loose disc measures
their ratio E C/C or E/C which may be taken as the effective electromotive
force divided by the effective current, and called the effective resistance R which
gives the power when multiplied by C2. Instead of a compound of watt and
ampere meter, the instrument may be a combination of watt and voltmeter which
reads so that E2/r is the power. In this case the forces are proportional to E C
& E so that the instrument measures their ratio E2/E C or E/C which may be
written r so that Er is the power. This instrument is well adapted for testing
the insulation of systems of distribution.
The form I prefer is a development of Fig. 6. It is shewn in Fig. 11 a a are the
pressure coils. Their core h h is carried across in one piece, the stationary drum j
being part of the core. The moving system in Fig. 11 is a wire d; as in Fig. 9,
except that it is pivotted centrally. One of the other poles i carries the main
current coil c, and the other a noninductive pressure coil u.
The air spaces
between and jare arranged somewhat as shown so that the field is stronger
towards one side. The moving system which is free then takes up a position
so that the forces tending to move it in opposite directions are equal. The force on
the top part is proportional to the square of the pressure, and that on the bottom
part to the watts, so the ratio, indicated by the needle is a quantity r such
that Er is the power. Such an instrument will measure the insulation of a cable
or transformer system while in use, eliminating the effects of capacity or self
induction; but classing loss by dielectric hysteresis as loss by resistance. Put on
the main circuit it will act as a lamp counter. Instead of the circular form
in Fig. 11 a rectangular form made of stampings may be used as in Fig. 12.
The instrument may also be wound for multiple current circuits, for instance as
a wattmeter. The pressure coil is then connected across two of the three terminals,
and the current in the lines connected to each of the terminals is led round the
current coils, of which there are two sets, or two coils as the case may be. For
instance in Fig. 9 C is wound with two current coils which thus act on the
same core.
For use as a step indicator it is wound with two coils connected both in the same
way with the currents or pressures to be examined. For instauce in the case
of alternators in parallel the whole station circuit is led through one set of coils and
the current of one dynamo through the other. The instrument shows whether the
dynamo current is leading or lagging relatively to that of the whole station, so that
the driver can tell whether the field is under or over excited. It is not necessary
to run the whole of the electricity through the instrument, the coils may be put in

page_text: shunt to resistances in the dynamo and station circuit. A similar arrangement may
be adopted in the case of amperemeters. For measurements of small quantities the
disc is suspended & controlled by a torsion suspension such as a fine wire of
phosphor bronze. The ohmmeter may have a fibre suspension, and a copper disc.
The instruments Figs. 9 & 11 may also have their loops of wire suspended by fibres
with small magnetic controls, or by torsion or biflar arrangements.
In the instruments shown in Figs. 1 to 8 when wound as wattmeters, the torque
is proportional to the power spent in the circuit measured and if the spring control
is removed the disc d or drum l can revolve. If a break is applied whose torque is
proportional to the speed, the speed will be proportional to the power. The
instrument, if provided with a counting train then becomes an energy meter, or
integrating wattmeter. The break or damping arrangement I prefer, is the
foucault current or arago disc. The meter can thus be made by removing the
controlling spring of the wattmeter, and adding a connecting train and a copper disc
rotating between the poles of permanent magnets. I prefer, however, to use the
same disc or drum to serve both as driver and break.
In Fig. 13 the body of the instrument Fig. 5 is taken, b b being the laminated
iron bodies, & a a one system of coils, and c one coil of the other system, and d the
dise. The connecting train is not shown. The bodies are mounted on wrought
iron plates pq; and permanent magnets rr of which two are shown, are arranged
with all their north poles one way. Their magnetic circuits are then completed
across the air gap and through the disc d. There is thus a direct and permanent
field superposed on the alternating fields due to the coils. The alternating
fields rotate the disc, and its rotation is opposed by the direct or permanent
fields.
The
Fig. 14 shows the meter on the same principle with the drum or tube instead of
the disc. The upper part consists of the instrument shown in Figs. 6 & 7.
stampings g carry the two systems of coils a a c. The dum is not shown.
The permanent magnetic circuit is made by the permauent magnets of which
five are shown. These connect the stampings g with a cast iron pedestal g with a
central projections which carries the fixed core which is not shown in Fig. 14, but
which is seen at j in Figs. 6 & 7. The permanent magnetic circuit is thus through
the sides of the drum or tube, and its movement will be retarded. As the iron
does not cover the disc or the tube completely, foucault currents are caused by
rotation.
In alternating amperemeters and wattmeters & some other cases it is often
advisable not to lead the main through the instrument. An ordinary transformer
might be used, but this leads to inaccuracy as the secondary current is not
proportional to the primary, and is not in step with it.
I therefore arrange a
divider, which is wound like a little transformer with two circuits. These are
branches of the main circuit, and are so connected that one has the instrument in
circuit. Thus, if the instrument is to have one hundredth of the main current the
divider has two circuits, one of 1 turn, and the other of 99, these turns being wound
in opposite directions. The instrument circuit is also made 99 times the resistance
of the other including the coils of the instrument. The core of the divider is thus
not magnetised unless the current is not divided accurately and a very small
variation will be enough to cause induction which tends to keep the proportions
true.
I am aware of Patent 1383 of January 30 1888 granted to Messrs. Borel &
Paccaud, and am acquainted with the meters of Shallenberger & Ganz & do not
claim anything invented by them.
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. An alternating current instrument for measuring pressure, current, power,
annarent resistance an fan internating n

page_text: 2. An alternating instrument substantially as described and illustrated in
Figs. 1, 2, & 5, of accompanying drawings.
3. An alternating instrument substantially as described and illustrated in
Figs. 6, & 7.
4. An alternating instrument substantially as described and illustrated in
Figs. 9 & 10.
5. An alternating instrument substantially as described and illustrated in
Figs. 13 & 14.
6. An alternating instrument substantially as described and illustrated in
Figs. 11 & 12.
7. An alternating instrument with a moving system substantially as described
and illustrated in Figs. 3, 4, or 8.
8. An alternating instrument of the kind described with two or more magnetic
circuits in the same mass or masses of iron substantially as described.
9. An alternating meter with a permanent field superposed on the alternating
field, substantially as set forth.
10. An alternating voltmeter with two circuits of widely different time constants
substantially as & for the purposes set forth.
11. An alternating amperemeter with two circuits of widely different time
constants, substantially as & for the purposes set forth.
12. An alternating instrument for measuring the virtual resistance, substantially
as described.
13. An alternating step or excitation indicator substantially as described.
14. An alternating instrument in which a simple circuit acting as the secondary
to a circuit is movable in the field of another circuit, substantially as described.
15. A wattmeter for multiple currents substantially as described.
16. An energy meter for multiple current circuits substantially as described.
17. For use in connection with an alternating instrument a divider substantially
as described.
Dated this 30th day of May 1894.
v
JAMES SWINBURNE.