Improvements in Alternating Electric Current Meters.
Year: 1899

page_text: Date of Application, 30th Oct., 1899-Accepted, 23rd Dec., 1899
COMPLETE SPECIFICATION.
Improvements in Alternating Electric Current 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 us from abroad by William H. Pratt,
residing at Lynn, County of Essex, State of Massachusetts, 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:-
This invention relates to meters for alternating current curcuits, the object being
to provide an integrating wattmeter of the induction motor type which will cor-
rectly register the energy consumed in a single-phase alternating current circuit
or in a polyphase circuit in which the load is symmetrically distributed with
respect to the phases.
In meters of the induction type as commonly organized, a metallic disk con-
nected to a registering train is given a torque by two coil systems, one of which
is in a potential circuit in shunt to the mains or otherwise furnished, with a
current proportional to the potential difference across the mains, and the other
in series with the work, or otherwise furnished with a current varying in
magnitude and phase with the current to be measured, the potential circuit being
retarded in phase approximately 90 degrees behind the impressed electro-motive
force by interposing suitable reactance in the shunt circuit.
With this arrange
ment, and with non-inductive load, the torque varies directly as the product of
the current through the series coil by the electro-motive force at the shunt
terminal. If there be inductive load on the work circuit, as induction motors,
the lagging component of the current is not measured by the meter, since the
torque is reduced by the reduction in the phase displacement between the current
and potential flues.
A source of error in such meters results from the friction of the parts and
from a tendency sometimes to run fast on light load or even to run on no load
due to a dis-symmetry of the shunt coil. Our invention is designed to obviate
these difficulties. We carry it out by providing in the shunt circuit an auxiliary
coil inductively related to the torque-producing disk and usually out of inductive
range of the motive coils, and providing it with an adjustable magnetic shading
device by which a creeping or shifting polar field may be effected, thereby exert-
ing a slight forward torque on the disk. Sufficient only in value to balance.
the friction of the parts, thus affording an initial tendency of the meter to move
in the proper direction, but a tendency which does not disturb the accuracy
of its record, but improves it. The reactance of this auxiliary coil is small as
compared with the reactance of the balance of the high-potential circuit, so that
the adjustment of its shading piece will have but an insignificant effect upon
the total reactance of that circuit and will have no appreciable effect on the
constant of the meter at full load. Heretofore shading pieces have been used in
connection with the main-high-potential coil, but their use in that relation is
objectional since their adjustment disturbs the phase relation of the torque-pro-
lucing circuits, and thus materially affects the constant of the motor, since a
change of adjustment changes the reactance of the shunt coil, which of necessity

page_text: constitutes a very considerable proportion of the entire reactance or the potential
circuit.
In the drawings, Fig. 1 is a side elevation of a meter embodying our improve-
ments, with its cover removed; Fig. 2 is a central vertical section; Fig. 3 is
a median horizontal section looking toward the torque-producing mechanism,
and Fig. 4 is a diagram showing the circuit connections for one type of alternating
current circuit.
Referring first to the diagram, 1, 2 represent two series coils, preferably having
air or non-inductive cores, connected in series relation to the consumption circuit.
3 is a reactance, 4 is a coil of high impedance having a laminated core confronting
the face of a disk of aluminium, copper, or other good conducting metal, and
symmetrical in relation to the series coils 1 and 2 on the opposite side of the
disk. 5 is an auxiliary coil of small reactance, located preferably at a point
out of inductive range of the current coils 1, 2 of the meter. This relation is not
absolutely essential, as the stray. field from the auxiliary coil acts merely to
assist or oppose the field from the high potential coil 4. The auxiliary coil is
provided with a thin iron core bent as indicated so. as to embrace a part of the
disk 6. The reactance of the circuit including the coils 3, 4 and 5 is adjusted
so as to produce as nearly as may be a ninety degree phase separation with
relation to the work circuits. By far the greater portion of the inductance is
in the coils 3 and 4, the small reactance of the coil 5 being insufficient to appreci-
ably disturb the phase separation of the series and shunt wound circuits by
changes of its adjustment. In co-operative relation to the field or poles of this
coil we mount an adjustable piece of copper capable of swinging through its
field of force so as to provide a variable torque not only to compensate different
degrees of starting friction but also to correct any tendency of the meter to
run backward. The relations and construction of the parts will be better under-
stood from an examination of Figs. 1, 2 and 3, in which, as will be seen, the
shunt coil 4 is supported in the frame so that its pole face confronts the upper
side of the metallic disk in symmetrical relation to the series coils 1 and 2
supported beneath the disk. The disk is affixed to a vertical shaft 7 which
gears into a registering train suitably mounted in a frame 8. A permanent mag-
net 9 is mounted on the frame so that its pole-pieces may embrace the disk near
its periphery, the position of the magnet being adjustable as indicated in Fig. 3,
by a set screw 10 engaging the walls of a slot in the adjustable piece which sup-
ports the magnet, the set screw passing through a part of the frame.
On the core of the shunt coil 4 us a closed-circuit coil 11 which acts to retard
the phase of the magnetism due to the shunt coil and thus contribute in effecting
a 90 degrees separation of the phases on non-inductive load, necessary to an
accurate intergrating function of the meter. The auxiliary coil 5, which con-
stitutes the essential feature of this invention has a core 12 composed of a few
laminae of soft iron bent so as to embrace the edge of the disk 6. Between the
disk and one of the faces of these polar extensions, is an adjustable piece of
metal 13, preferably formed in the shape of a ring, as indicated in Fig. 3, one
end of the strip of which the ring is formed being bent to pass between the
pole-piece 12 and the edge of the disk 6, and the other bent so as to rest on the
base of the instrument, the horizontal arm, shown at 14 in Figs. 1 and 3, being
pivoted on the base and provided with a slot co-operating with a set-screw 15
by which the position of the ring 13 may be adjusted with relation to the pole-
piece. This ring acts as a shading coil, the influence of the induced currents set up
by the alternating magneto-motive force of the poles being to create a creeping
tendency in the magnetic field, and thus exert a torque on the disk 6; this
torque may be varied by shifting the position of the shading piece 13 away
from a central relation to the pole-face. The wide range of adjustment given
this shading piece permits not only a forward adjustment to balance the friction
of the parts but in some cases a backward rotary effect on the disk to compensate
a forward initial tendency sometimes existing in the meter by reason of an un-

page_text: symmetrical relation of the potential coil, which gives the meter a tendency to
run too fast or even to run on no load.
The details of construction of the meter will be sufficiently understood from
the drawings without further description, suitable provision being made for
enclosing the parts and sealing them, as indicated.
The meter is shown as provided with six terminals, which adapt it for con-
nection with a three-wire single phase circuit, as exemplified in Fig. 4. The
meter however is adapted for operation on any symmetrically loaded circuit, and
may be used with a single phase two wire system or a multiphase system.
Having now particularly described and ascertained the nature of our 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. An alternating current motor having a registering device operated by an
induction motor, and an auxiliary torque-producing device for overcoming the
friction of the parts acting upon the motor-shaft and inductively independent
of the primary motor circuits.
2. An alternating-current meter having a register operated by an induction
motor, the primary circuits of which are in shunt and series relation to the
work circuit respectively, and an independent starting coil in the shunt circuit
for overcoming the friction of the parts.
3. In an alternating-current meter, recording mechanism, an induction motor
fed with current proportional to the load operatively related to the recording
mechanism, a starting coil for overcoming the friction of the parts fed with
constant current or in shunt to the mains, and a shading device adjustable with
relation to the pole of the starting coil for varying its torque.
4. An electric meter for alternating currents, provided with a register, an
induction motor for operating the same, the primary circuits of which are es-
sentially in series and shunt relation to the work measured by the meter, and
an auxiliary motive device for counter-balancing the friction of the mechanism
in the shunt circuit and of low reactance relatively to the aggregate reactance
of said circuit.
5. An electric meter for alternating currents, having an induction armature
connected with the recording device, two quarter phase circuits inductively re-
lated thereto, one in series and the other in shunt with the work, and a starting
coil of small reactance acting upon the recording device and provided with an
adjustable magnetic shading device to produce a shifting polar field.
6. An electric meter for alternating currents, having an induction armature
connected with the recording device, two quarterphase circuits inductively
related thereto, one of low reactance in series with the work and the other of
large reactance in shunt to the work, and a starting magnet in the shunt circuit
of low reactance, having an adjustable shading piece co-operating with its pole
and inductively related to the armature.
1000