Improvements in Alternating-current Energy Meters :
Year: 1897

page_text: Date of Application, 28th Sept., 1897-Accepted, 5th Feb., 1898
COMPLETE SPECIFICATION.
Improvements in Alternating-current Energy 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
invention (which has been communicated to them from abroad by Robert Shand,
of 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 relates to an electric meter of the induction type which
will register accurately the true energy on inductive circuits irrespective of the
As is now
phase relation between current and electromotive force in the circuit.
well understood by electricians, the current tends to lag behind the electro-
motive force in circuits supplying induction motors or other inductive loads;
and this lag is apt to vary from time to time under different conditions of load.
Certain meters have heretofore been proposed which have been specially designed
for avoiding inaccuracies of reading due to such lagging of currents, and the
present invention is an improvement upon meters especially adapted for this kind
of work, though the meters will operate also satisfactorily on non-inductive
circuits.
In the accompanying drawing, Figs. 1, 2, and 3 are diagrams illustrating the
invention and explaining its mode of operation.
In Fig. 1, A, B are the mains of an alternating-current circuit. The meter
comprises a current coil C carrying current which may be equal in value to the
total main line current, or a definite proportional part thereof and in the same
phase. Coil C is shown included in one of the mains B, though a number of
equivalent arrangements are well understood by electricians. A potential coil C¹
is coupled across the mains A, B, and is made of high self-induction, so as to lag
the current in this circuit behind the electromotive force through an angle some-
what less than 90°. A self-induction coil C is shown included in series in this
circuit, to assist in producing the lag.
A transformer T is also employed whose primary is connected across the
mains A, B, and whose secondary is closed through an auxiliary coil C³ wound in
conjunction with the potential coil C', so that both coils have a common magnetic
axis.
As
It is a matter well known in the art that the revolving couple acting on the
armature will be proportional to the watts to be measured and independent of
the lag of the load-current when the alternating currents have a certain fixed
periodicity and the phase relations hereinafter mentioned are established.
a consequence if the armature is damped by the usual disc and permanent magnet
arrangement or any other device giving a retarding force proportional to the
speed, then the speed, or in other words the reading of the watt meter, will be
proportional to the energy to be measured.
The secondary or rotating member of the meter may be of any desired con-
struction, and this will be connected to the recording mechanism through gearing
as usual. The rotating member or armature is shown in the diagram at D.

page_text: In Fig. 2 the arrangement of the coils relatively to the armature of the meter
is shown. Here the armature is shown as a cylinder 1). The current coil C
of coarse wire surrounds the cylinder in one plane, while the potential coil C
and supplementary potential coil C³ are superimposed and surround the cylinder
in a plane at right angles to coil C. Of course the design of the meter, when
constructed, may vary greatly.
It is preferred to connect the transformer T across the consumption circuit, as
shown in full lines, but it may be coupled so as to form a partial shunt. For
example, one terminal of the transformer T is shown in dotted lines, connected
to an intermediate point in the induction coil. C³ instead of leading directly to
main A as in full lines.
The actions are shown diagrammatically in Fig. 3, assuming the electro-
motive forces and currents to be sine functions.
In that figure the line o e represents the voltage and the line o c¹ the current
in the coil Clagging actually. probably about 80° or 85° behind o e.
The current of the coil C³, from the secondary of the transformer, will obviously
have a constant phase relation with the line voltage o e and may be represented
by o c³.
It is evident that by properly adjusting either o c' or o ca or both, a resultant o
may be obtained at 90° from oe which will also have a constant numerical
relation to o e.
By this means a resultant field may be obtained equivalent in effect to that of
a current lagging 90° behind the line voltage.
Whether or not these phase relations exist, is determined by trial or experi-
ment after methods well understood by electrical workers.
Having now particularly described and ascertained the nature of the 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. In an induction meter the combination of a current coil, a potential coil, a
transformer whose primary is coupled across the circuit mains, and a third coil
in the secondary circuit of the transformer, all said coils being in inductive
relation to the rotating armature, substantially as described.
2. The combination in an induction meter of a current coil, a potential coil in
a shunt circuit of high self-induction, and an auxiliary coil connected across the
secondary of a transformer whose primary is connected across the current mains,
said potential coils co-operating to establish a magnetic field substantially 90°
from the electromotive force applied to the potential coil as described.
3. The combination in an alternating-current induction meter of a current
coil, a potential coil in a shunt circuit of high self-induction lagging the current
therein somewhat less than 90° from the electromotive force applied to the
potential coil, an auxiliary potential coil superimposed upon the said first-named
potential coil, and a transformer whose primary is connected across the consump-
tion circuit and whose secondary to said auxiliary coil, the phases of the currents
in said potential circuits being so chosen that their action upon the armature is
equivalent to that of a simple potential coil carrying current 90° dephased from
the electromotive force applied to the potential coil.
Dated this 28th dox of Sontember 1807