Improved Alternating Current Meter and Method of Measuring Alternating Currents.
Year: 1894

page_text: COMPLETE SPECIFICATION.
Improved Alternating Current Meter and Method of Measuring
Alternating Currents.
We, JOHN FORREST KELLY, of 40 Bartlett Avenue, Pittsfield, County of
Berkshire, State of Massachusetts, Electrician, and WILLIAM STANLEY, of
Dawes Avenue, Pittsfield, County of Berkshire, State of Massachusetts,
Electrician, all in the United States of America, 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 :-
The inventions relate respectively to the art of and to the class of apparatus
employed for, measuring and indicating the amount of current passing over a given
circuit, and have for their objects to provide a reliable method of and a simple
means for measuring currents of the alternating class.
In describing the inventions, the alternating current metre will be described, and
in connection with such description the method will be disclosed, reference being
had to the accompanying drawings, in which :-
Fig. 1 is a perspective view of the meter,
Fig. 2 is a front view of the field magnet on a slightly reduced scale with parts
cut away so as to show its poles,
Fig. 3 shows on a slightly reduced scale a projection of the field magnet pole
piece upon the disk, and
Figs. 3, 4 and 5 show modifications of details of the meter.
In the drawing, M represents an inducing system consisting of a laminated field
magnet, the pole pieces P, P, of which are brought face to face and cut so as to
leave a wedge-shaped space between them; C the exciting coil of the field-magnet
in series with various translating devices L, L, supplied from a source of alternating
current G; D an induced conducting system consisting of a disk of homogeneous
copper, or other good electrical conductor, supported at its centre by a suitably
mounted axis A, so as to lie between the pole pieces and be free to rotate from
either end of the wedge-shaped air-space towards the other. Upon the passage of
an alternating electric current through the coil C, the armature will revolve in the
direction from the wide and towards the narrow part of the wedge-shaped air-
space. The energizing coil C is made of very low resistance and the quantity of
energy consumed in passing through it and operating the meter is very little.
BB are fans or vanes connected with the armature shaft and act to retard its
speed.
Connected with the armature shaft is an indicating train I, of any well known
construction, upon the dial of which the revolutions of the armature disk are
indicated.
In the construction shown in Figs. 1, 2 and 3, the armature is a plain copper disk
extending beyond the pole pieces on each side.
In the construction above described, the reluctance in the magnetic circuit, by
reason of the wedge-shaped air-gap, is not symmetrical with the figure of the field
of the magnet, when energized, froin which it results that the magnetic flux is not
symmetrical with the figure of its field; or, as may be said, the field of force is
asymmetrical, by which is meant that the distribution of the flux is not the same on
both sides of the centre of its figure. Such a field magnet, when energized, by an
alternating current, has an alternating asymmetrical field of single or uniform
phase and will induce currents in the conductor D, lying within its field which tend
to produce relative motion between the inducing and induced systems. If the
induced conducting system is mounted symmetrically about an axis around which
one of the members is free to rotate, there will be continuous rotation of that
D
077

page_text: member. The relative rotation of the disk will be towards the strong side of the
field. If, however, the pole pieces are broadened so as to extend beyond the
induced disk, as shown in full lines w in Fig. 3^, the relative rotation of the disk is
from the strong and towards the weak side of the pole. This action is even more
pronounced if the disk is slotted radially at frequent intervals, as shown in dotted
lines in Fig. 3. When the disk is slotted the pole pieces may be narrower so as
not to extend up to the edge of the disk, as shown in dotted lines in Fig. 34.
=
The asymmetrical magnetic field above described may be produced by various
It
means. can be produced by varying the reluctance of the magnetic circuit in
other ways than that above described, as will be readily understood by those skilled
in the art, and also by varying the magneto-motive force in the different parts of
the field magnet by applying more windings of the energizing coil to some parts
than others, as shown in Fig. 4, in which the energizing coil is made up of two
parts, of which one C embraces the whole magnet, while the other C, embraces
but a part thereof, or by varying both the magneto-motive force and the reluctance
by cutting away the pole piece in the construction shown in Fig. 4, the cut-away
face of the pole piece being shown therein by the dotted line p. The form of the
induced conductor may also be varied if only it is symmetrical about an axle of
rotation, and the field magnet corresponds.
In addition to the main energizing coil C, which when the meter is in use, is in
series with the translating devices L, we may also have an auxiliary coil C³ shown
in Fig. 5, which forms a shunt across the supply mains X X and, if the magnetic
circuit varies in reluctance, embraces the whole core of the field magnet. This
coil, or the circuit containing it, should be of high resistance, so that the current
passing through it shall be very small, enough to nearly but not quite maintain
motion in the meter. In such a case a current is constantly passing through the
shunt coil which is sufficient to practically overcome the static friction of the
moving parts of the meter so that it will begin to move and register with a very
feeble current passing through the main energizing coil, this current being that to
be measured.
As the result of a series of experiments, we have discovered that the speed of the
armature above described, so long as it is moderate, tends to so vary in proportion
to the current passing through the energizing coil that if a load which varies.
directly as the square of its angular velocity is put upon the armature shaft, the
speed of the armature will vary directly as the passing current. One convenient
means of applying such a load is by means of vanes or wings B B which we have
applied directly to the armature shaft. These vanes should be of such size and
number that when the meter is used the speed of the armature is kept at a
moderate rate.
The method carried out by the meter, shown in Figs. 1, 2 and 3, above described,
consists in setting up an asymmetrical alternating magnetic field of single or uniform
phase by the current to be measured or a known part thereof, and by that field
inducing currents in a conducting system lying within it and mounted so as to be
free to iotate under the action of such inducing field and induced currents, retarding
the speed of the rotating conducting system by a load which varies directly as the
square of its angular velocity, and indicating or recording the number of the
revolutions of the conducting system. The method can also be carried out with a
meter in which the construction shown in Figs. 1, 2 and 3 is varied in accordance
with the modifications above described, and shown in Figs. 3, 4 and 5. The
method carried out by the construction shown in Fig. 5 has in addition the
overcoming of the static friction of the moving parts of the meter by other means
than the current to be measured.
Having now particularly described and ascertained the nature of our said inven-
tion and in what mauner the same is to be performed we declare that what we
claim is :
1. In an alternating current meter, the combination of a field maguet having

page_text: when energized, an alternating asymmetrical field of uniform phase, a rotating
armature having a conducting system symmetrical about the axis of rotation, and a
device for indicating or recording the revolutions of the armature and operated
thereby, substantially as described.
2. In an alternating current meter, the combination of a field magnet from the
pole pieces of which the magnetic flux is asymmetrical, alternating and of uniform
phase, a rotary armature having a closed conducting system symmetrical about the
axis of rotation and a device for indicating, recording or registering the revolutions
of the armature and operated thereby, substantially as described.
3. In an alternating current meter, the combination of a field inagnet having
when energized by an alternating current an asymmetrical field of uniform phase,
a rotating armature having a closed conducting system symmetrical about the axis
of rotation, a suitable retarding load, and a device for indicating, recording or
registering the revolutions of the armature and operated thereby, substantially as
described.
4. The method of measuring alternating currents which consists in producing by
such currents or a part thereof an asymmetrical alternating magnetic field of
uniform phase, by such field inducing currents in a conducting system lying within
it and symmetrically mounted so as to be free to rotate under the action of such
inducing field and induced currents, and registering the number of revolutions of
said conducting system substantially as described.
5. The method of measuring alternating currents which consists in producing by
such currents or a part thereof an asymmetrical alternating magnetic field of
uniform phase, by such field inducing currents in a closed conducting system lying
within it and symmetrically mounted so as to be free to rotate under the action of
such inducng field and induced currents, retarding the speed of the conducting
system and registering the number of revolutions, substantially as described.
6. In an alternating current meter a field magnet, having, when energized by an
alternating current, an asymmetrical, alternating field of single or uniform phase,
in combination with a disk of suitable material mounted symmetrically upon an axis
so as to be free to rotate and lie partly within the asymmetrical field, a suitable
retarding load and means for recording or registering the revolutions of the disk,
substantially as described.
1004
D. YOUNG & Co.,
11 & 12, Southampton Buildings, London, W.C.,
Agents for the Applicants.