Improvements in Electricity Meters.
Year: 1893

page_text: Date of Application, 28th Oct., 1893
Complete Specification Left. 28th Aug., 1894-Accepted, 6th Oct., 1894
PROVISIONAL SPECIFICATION.
Improvements in Electricity Meters.
I, GEORGE HOOKнAM, of Nus. 7 and 8 New Bartholomew Street Birmingham,
Manufacturer do hereby declare the nature of this invention to be as follows:-
My present invention relates to improvements in the details of the meter for
alternating currents described by me in the Complete Specification Letters Patent
granted to me and numbered 13,123-1890. In the arrangement there described and
illustrated the driving force of the motor is obtained from the interaction of two
currents in different phases, one of these being a derived or shunt current. In
practice there are objections to this device in that it consumes an appreciable
amount of energy, and also that there is a great difference of potential between
parts of the meter. To obviate this I substitute for this shunt coil a closed
secondary circuit. This will also have a phase differing from that of the current to
be metered, and will supply motive force. In order to assist the starting of the
meter with small currents I may place a "choking" coil between the positive and
negative leads through which a very small current is always passing; or I may use
a condenser in the same way. The choking coil or the condenser need not be
included under the meter cover.
The armature may be floated by means of mercury and the fluid friction of the
mercury may form the regulating break.
By suitably varying the resistance of the secondary circuit I may compensate for
temperature erior.
Dated this 27th day of October 1893.
COMPLETE SPECIFICATION.
Improvements in Electricity Meters.
1, GEORGE HOOкнAM, of 7 New Bartholomew Street in the City of
Birmingham, Manufacturer, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer
tained in and by the following statement :-
My present invention relates to improvements in the details of the meter for
alternating currents described by me in the Complete Specification of Letters
Patent granted to me and numbered 13123 of 1890. In the arrangement thero
described and illustrated the driving force of the motor is obtained from the inter-
action of two currents in different phases, one of these being a derived or shunt
current. In practice there are objections to this device in that it consumes an
appreciable amount of energy, and also that there is a great difference of potential
between parts of the meter. To obviate this I substitute for this shunt coil a closed
secondary circuit. This will also have a phase differing from that of the current to
be metered, and will supply motive force.
In order to assist the starting of the meter with small currents I place a
"choking" coil between the positive and negative leads through which a very
small current is always passing; or 1 may use a condenser in the same way.
The choking coil or the condenser need not be included under the meter cover.

page_text: The armature may be floated by means of mercury and the fluid friction of the
mercury may form the regulating break.
By suitably varying the resistance of the secondary circuit I may compensate for
temperature error.
Referring to the two accompanying sheets of drawings which illustrate a meter
constructed according to my invention―
Figure 1 is a front external elevation of a meter showing its various parts in
position.
Figure 2 is a vertical section through the disc armature and the mercury vessel
arranged by its fluid friction to supply the regulating break.
Figure 3 is a sectional plan of the armature and its mercury vessel, the section
being taken on the line y (Figure 2) and looking from above.
Figure 4 is a plan of the disc armature with its electro-magnet and the driving
spirals.
Figure 5 is a diagrammatic perspective view showing the armature disc and the
disposition of the primary and secondary circuits together with the positions of the
four driving spirals.
The same letters of reference indicate the same parts in the drawings.
The armature disc a by the rotation of which the current is measured is
preferably of aluminium and it is mounted by rods a' (Figures 1, 2 and 3) on a
spindle c which carries a pinion b and a paddle or paddle floats f. The spindle c is
mounted on conical or pointed ends as shown in section at Figure 2, and the
pinion 6 gears into indicating mechanism d of any ordinary construction. The
spindle c and its paddle blades are immersed in mercury contained in the case
or vessel and the said case is preferably provided with inwardly projecting
fixed blades as shown in Figure 3 to increase the resistance of the mercury to
rotation.
The vessel g has a side tube o¹ to enable the mercury to be filled in.
The leads carrying current to be measured are coupled up to the terminals h and i
and the said current passes by way of the wire / winding round the semi-circular
electro-magnet e preferably laminated or built up of sheets of iron.
The electro-magnete is thus excited by the alternating current to be metered and
part of the armature disc a rotates between the poles of the electro-magnet in a
magnetic field of which the average intensity varies with the quantity of current
passing through the meter.
Foucalt currents are thus generated in the armature disc which alternate with
the current, but in phase which lags behind the phase of the main current.
A closed secondary coil m is wound round the primary coil of the electro-magnet.
and this coil m continues to form four spirals kkkk' and in part of its course the
wire or coil m passes through the coil' m' inserted between connecting screws to
enable the resistance of the said coil to be adjusted. The primary coil on the
electro-magnet induces an alternate current in the said closed secondary coil m of
the same period as in the primary but also in phase which lags behind that of the
main current. This induced current passes through the spirals kk k¹ k¹ which are
arranged in series, but may be otherwise arranged. The currents passing through
the wire spirals are of the same phase as the Foucalt currents in the disc or
nearly so.
It is found by experience that the armature disc a rotates under the influence of
the currents in the spirals acting on the Foncalt currents generated in the disc.
As the electro-magnet e is excited by the current to be measured the magnetic
field varies as to its average intensity with the quantity of current passing through
the leads; the Foucalt currents generated in the armature disc a thus also vary with
the quantity ot current.
At the same time the quantity of current passing through the closed secondary
circuit and the spirals k k k' k¹´also varies with the quantity passing the primary.
The total power rotating the armature disc a thus increases as the square of the
quantity of current; this is resisted by the fluid friction of the mercury in the

page_text: vessel g resisting its rotation and as this resistance varies as the square of the speed
it follows that the armature disc a is caused to rotate at a rate proportional to the
quantity of current.
In Figure 5 the course of the wire round the electro-magnet e is indicated
diagrammatically and it is shown in double lines leaving the terminal h and
returning to the terminal i. The course of the closed secondary coil is clearly
shown by the thick black line m round the electro-magnet and forming the
spirals kkkk. Two of these spirals are disposed above the disc a and two
below, & being above and k¹ k¹ below. The disc a and the electro-magnet e are
shown in Figure 5 in dotted lines to make the windings clear.
As an alternative the current to be measured may be passed through the
spirals k k k k¹ and a secondary wire may be arranged in closed circuit acted on by
the primary wire and part of the secondary may be wound round the electro-
magnet e to excite it and induce currents in the armature disc a.
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. In meters for alternating or intermittent currents in which the rotation of a
disc or other solid of revolution is produced by the reaction of currents induced in
the said disc, the combination of a coil or coils forming part of a closed secondary
circuit with a primary coil carrying the current to be metered, the said primary
coil being caused to excite the clectro-magnet producing the said induced currents
as herein set forth.
2. In meters for alternating or intermittent currents in which the rotation of a
disc or other solid of revolution is produced by the reaction of currents induced in
the said disc, the combination of a coil or coils carrying the current to be
measured with a closed secondary coil induced by the primary current, part of the
secondary wire being wound round the electro-magnet to excite it as herein
set forth.
3. In meters for alternating or intermittent currents as hereinbefore described,
the combination of an armature disc so mounted that its rotation is resisted by fluid
friction, an electro-magnet excited by a coil carrying the current to be metered; a
closed secondary coil having driving spirals disposed about the armature disc all
substantially as and for the purposes herein before described.
4. The meter for alternating or intermittent currents hereinbefore described with
reference to the accompanying drawings.
5. In meters for alternating or intermittent currents as claimed in the preceding
claims, the use of a resistance coil as m in the secondary current for standardising
purposes.
6. In meters for alternating or intermittent currents the use of a "choking" coil
or a condenser to allow the flow of a small current to aid the meter in starting
substantially as hereinbefore described.
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MARKS & CLERK,
18, Southampton Buildings, London, W.C., and
13, Temple Street, Birmingham, Agents for the Applicant.