Improvements in Electric Meters for Alternating Current Circuits.
Year: 1898

page_text: Date of Application, 6th Oct., 1898-Accepted, 26th Nov., 1898
COMPLETE SPECIFICATION.
Improvements in Electric Meters for Alternating Current Circuits.
Comp
ᏙᎥᎢ
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Streetsan
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Albert G. Davis,
residing at Schenectady, in the County of Schenectady, State of New York, 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
statement:—
It is well known that a watt meter should measure the product of the current by
the voltage by the cosine of the angle of lag between the current and the voltage.
This condition is only attained in induction meters when the magnetisms one to the
current coil and the potential coil are ninety degrees from each other in time, or a
pure energy current. This requires is the flux due to the current coil is to be in
phase with the current in the line, that the flux due to the potential coil shall lag
ninety degrees, a condition which is obviously difficult to produce. Various devices
have been suggested for adding to the lag of the current in the potential coil or of
the magnetism generated thereby.
In the watt meters which are not of the induction type, it is also true that it
is in general necessary to adjust artificially the relation between the currents
in the various coils, or of the fluxes generated thereby.
The present invention consists in adjusting the phase of the current in a
coil of an electric meter, and particularly in the current coil of an induction
meter, by shunting the coil by a self induction, properly adjusted to produce
the desired result."
In the drawings attached to this specification, representing an embodiment
of the invention, Fig. 1 is a general view of a system of distribution involving
the improved meter, while Fig. 2 is a view of the meter in elevation.
Referring more particularly to Fig. 1, T is a transformer whose secondary
is connected by mains A, B to the lamps or other translating devices. L.
C is
the current coil of the meter, and D is the potential coil, both coils acting on
an armature E. These coils are shown double in Fig. 2, as is usual in such
devices.
The potential coil D is connected in shunt to the mains A, B, in series with an
artificial self-induction F, so adjusted as to cause the current in the potential
coil to lag as far as possible behind the electromotive force on the mains A, B. It
is difficult in practice to cause this lag to exceed eighty degrees. Instead of
attempting to correct, this error, by artificially lagging the current in the potential
coil D enough to bring about the ninety degree relation between the fluxes, the
current in the current coil C is artificially caused to lead by a corresponding amount.
This is performed by placing in shunt with the coil and in series with the
translating devices, the artificial self-induction G, preferably a reactance coil with
open magnetic circuit. The current flowing from the transformer T to the
translating device will divide, a portion passing through the current coil C, and a
portion through the self induction G. It is obvious that the self induction will take
current, lagging behind the electro-motive force behind its terminals, which will
ID 077

page_text: leave a leading current for the current coil. By properly adjusting the value of the
lagging current taken by the self-induction, with relation to the total current passing
through the instrument, it is possible to cause the fluxes induced by the coils C, Ď
to bear to each other a true, or approximately true, ninety-degree relation, when
the current in the translating devices L is in phase with its electro-motive force,
and to automatically adjust their phase relations to measure their true energy when
the current in the translating devices lags.
The structure of the instrument is shown in Fig. 2. It will be seen that the
coils C, D embrace the armature E, which is of the short circuited type, shown
here as a cylinder, and mounted on the shaft H supported in suitable bearings.
K is a disc of copper or suitable metal, rotating in the field of the permanent.
magnets M, M, to act as a retarding device; while N is the counter or register
usual in such instruments.
Having now particularly described and ascertained the nature of our 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. The method of securing a proper phase relation between the currents
in the coils of an electric meter, which consists in artificially taking current
through a circuit in multiple with the coil the phase of whose magnetism is to be
advanced.
2. The combination of an electric meter, of a current coil, a potential coil, and a
self-induction in shunt to the current coil.
3. The combination of an electric meter, of a current coil, a potential coil, a short
circuited armature in inductive relation to both coils and a self-induction in shunt
to the current coil.
4. The combination of an electric meter, of a short circuited armature, a current
coil in series with the mains, and a potential coil in shunt to the mains, with
artificial self-induction in series with the potential coil, and a second artificial self-
induction in shunt to the current coil.
Dated this 4th day of October 1898