Improvements in Induction Watt-hour Meters.
Year: 1897

page_text: Date of Application, 28th Dec., 1897-Accepted, 19th Feb.,
1898
Improvements in Induction Watt-hour Meters.
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 inven-
tion (which has been communicated to us from abroad by Elihu Thomson and
William H. Pratt, residing respectively at Swampscott and Lynn, in the County of
Essex, State of Massachusetts, United States of America) 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 has for its object to provide a Watt-hour meter capable of
accurately measuring the energy consumed in a single-phase alternating current
circuit, whether the load be inductive or non-inductive, and one which can be
adjusted for use on circuits of different frequencies.
In the accompanying drawings Fig. 1 is a section view of the improved meter taken
on line 1-1 of Fig. 2; Fig. 2 is a sectional view taken on the line 2-2 of Fig. 1;
Fig. 3 is a diagram of connections; Fig. 4 is a detail of the core upon which the
induction coil is wound, and Fig. 5 is a detail view of the motor mechanism.
Mounted upon a cast metal back B are brackets E and F, which support the parts
of the meter mechanism. Secured to the under side of the bracket E by clamps M¹
are permanent magnets M; revolving within the influence of these magnets is a
dise D of good conducting material mounted upon the armature shaft L and employed
to damp the rotation of the armature A in the usual manner.
In the operation of single phase meters wherein an inductance is employed to
cause the current in one set of coils to lag behind that of another set, it has been
found that when a short air gap is included in the magnetic circuit of the core of the
reactive coil, the readings obtained from the meter are practically correct throughout
its entire range, whereas, with a reactive coil having a closed core, the readings
obtained at one portion of the range are accurate, but away from this there is an
appreciable error. In the construction of the improved meter this fact is utilized,
and upon the upper side of the bracket is mounted an inductance I comprising a
The portion
two-part core having an air space between the parts, as shown in Fig. 4.
H of the core is rectangular and is cut away in the centre to receive the H-shaped
part P of the core; between the two is an air gap at points tt. By the arrangement
shown the total air gap between the parts of the core is always maintained the saine';
for example, assume for any reason that the core P is nearer to core H at one end
than the other, this will decrease the air gap at one end but increase it by a like
amount at the other end. The same would be true if the core were moved up or
down. On account of this arrangement it is unnecesssary to exercise more than the
usual care in assembling the meters, which is a decided advantage in reducing the
cost of construction.
It being necessary to separate the parts of the core from each other by an air gap
or a piece of non-magnetic material, the parts of the core are bolted to a piece of
German silver G, which in turn is secured to the two arms of the bracket E by
screws.
Connecting the outer ends of the bracket arms is a piece E' which supports the
jewel bearing J1 at the upper end of the armature shaft L; in addition to this the
registering mechanism R is also carried by E¹. On the upper end of the armature
shaft is a worm meshing with a worm wheel for actuating the recording

page_text: mechanism. Secured to the lower bracket F by screws is a field magnet structure K
(best shown in Fig. 5), made of laminated iron; this is provided with poles N and N¹
which are wound with coarse wire in a direction to produce unlike poles, and
unwound neutral poles O and O¹. Extending upwardly from the bracket are lugs e,
and secured thereto by screws is a laminated magnet Q, of the form best shown in
Fig. 5. Wound upon this magnet are fine wire coils S and S'; these are connected
in series with each other and the inductance I. The magnet Q and coils S S¹ have
their axes at right angles to that of coils C C¹, so that unlike poles will be created by
the coils SS at right angles to the poles induced by coils C C. The phase of
the current flowing in coils S S¹ owing to the large inductance I, and also to the
influence of the coils themselves, will lag behind the main EM F by an amount
somewhat less than 90°, and consequently the flux induced by S S¹ in inagnet Q will
tend to lag behind the flux induced by the coils C C¹ by an approximately equal
amount. In addition to the series coils CC the magnet frame K is provided with
coils ; these coils may either be closed upon themselves or connected in series in a
closed local circuit. The coils are preferably so connected that the electro-motive
force induced therein by the changes in magnetism is in the same direction. The
current in coils a induces, or tends to induce, a third flux which lags behind the flux
induced by coils S S¹, and these two fluxes combine to establish a potential flux passing
through the poles of the coils SS, which has a normal phase difference of 90° from the
main E M F. By adjusting the number of turns in coils a a or their conductivity,
it is possible to adjust the phase difference between the two energizing magnetic
fluxes as may be desired. The poles 001 are neutral with respect to the field
coils C C¹, but are inductively made poles by the flux in magnet Q which is at right
angles to that between poles N and N. The effect of this is to produce a shifting of
the magnetic fluxes in accordance with the phases of current in the two sets of
coils, and thereby cause rotation of the closed circuit arinature A between the
poles.
The armature consists of a cylinder of copper, aluminium or other good conducting
non-magnetic material, and is provided with a disc and hub A' for securing it to the
armature shaft J. The armature shaft is provided at the bottom with a jewel
bearing J and at the top with jewel bearing J'; both of which are adjustable so that
the position of the armature can be changed.
Situated in the lower part of the meter is a connection board U having
terminals mounted thereon, and at the front is provided a removable cover U₁.
Terminals c and c¹ are connected respectively to the field coils C and C¹ and are
included in the same side of the system. Terminals & and d¹ are connected together
by a strap d² and to the opposite side of the system. Extending from terminal c is a
wire which connects the fine wire coils S S₁ in series with the inductance I; the
opposite end of the inductance is connected by wire g to terminal d¹.
In Fig. 3 the meter is shown as connected to a single phase circuit having a
transformer T supplying current to the secondary system W, having a load consisting
of incandescent lamps, but which may comprise motors or other translating devices.
The field coils C and C¹ are included in series with one of the secondary mains, and
the winding S S¹ is connected in series with inductance I and both are connected
across the secondary main.
As the frequencies of working systems are often different, it is desirable to provide
a meter which will work equally well upon them all; to accomplish this the reactive
coil I is divided into sections, and a switch X arranged to vary the turns of the coil
in circuit, to adjust the meter for use on a system having a given frequency. For
example, assume that the meter has been employed on a system where the frequency
was sixty cycles per second, and it is desired to adjust the meter to work on a system
having one hundred and twenty-five cycles; the switch X would be moved to a point
where it would cut out the two end sections of the coil I; this would bring the same
condition of lag in the coils S and S that they had before, and the meter would
accurately register the consumption of energy. Preferably the various positions of
the switch would be marked with the frequency to which they correspond, and by

page_text: knowing the frequency of the system to which the meter was connected, it would be
a simple matter to adjust it for that system.
Having now particularly described and ascertained the nature of the said inven-
tion (as communicated to us from abroad) and in what manner the same is to be
performed, we declare that what we claim is :-
1. In an electric meter, the combination of a field magnet structure forming a
closed iron frame with poles for the current and potential fluxes at points 90° apart,
a cylindrical armature, and a magnet structure within the armature whose magnetic
circuit is completed through certain of the poles on the external frame.
2. The combination in an electric meter, of a closed magnetic field magnet frame
having inwardly projecting sets of poles for the current and potential fluxes arranged
concentrically around a centre, and an integral magnet structure constructed and
arranged to afford a much shorter air gap in the path of the potential flux than in
that of the current flux.
3. The combination in an electric meter of a closed magnetic frame having two
sets of inwardly projecting poles 90° apart, one set wound with a current coil, and
the second set unwound, a cylindrical armature, and an iron structure within the
cylinder on which is wound the potential coil, with its magnetic axis at right
angles to that of the current coil.
4. In an electric meter, the combination of a closed iron frame carrying a current
coil, a magnet structure within and separated from the frame by a space in which
the armature turns, and carrying a potential coil, and a closed circuit winding on the
frame arranged to increase the phase difference between the magnetic fluxes
energizing the meter.
5. In a motor mechanism for an alternating current meter, the combination of a
stationary laminated field magnet having two wound poles of opposite polarity and
two unwound neutral poles, field coils included in series with the load circuit, fine
wire coils mounted on the field magnet and connected in closed circuit relation, a
fixed laminated magnet mounted within the first and having poles adjacent to the
neutral poles of the field magnet, a fine wire winding thereon for creating a flux
lagging 900 behind the main E M F, and a cylindrical armature revolving between
the magnets.
6. In an alternating current electric meter, the combination of an inductance
comprising a closed circuit laminated iron core provided with a central opening, a
wound core mounted within the first and separated therefrom at all points by an air
gap, the arrangement, being such that as the air gap is decreased at one point, it is
increased at another, so that the total air gap reluctance is always maintained the
saine.
7. In an alternating current electric meter, the combination of an inductance
comprising a closed circuit iron core having a rectangular opening in the centre, an
H-shaped wound core mounted within the first and separated therefrom at all points
by an air gap, the arrangement being such that as the air gap is increased at one
side or end between the inner and outer core, it is decreased by a like amount
at the opposite point, so that the magnetic reluctance is always maintained the
same.
8. In an electric meter, the combination of a cast metal back, a laminated iron
core having an opening therein, a second core mounted in said opening and separated
from the core at all points by an air space, and a non-magnetic plate secured to the
back and forming a common support for both cores.
Dated the 28th day of December 1897