Improvements in Apparatus for Measuring Multiphase Electric Currents.
Year: 1899

page_text: Date of Application, 25th Oct., 1899-Accepted, 31st Mar., 1900
COMPLETE SPECIFICATION.
Improvements in Apparatus for Measuring Multiphase Electric
Currents.
We, HERMANN ARON, Ph.D., of 6, Lützowstrasse, Berlin, in the German
Empire, Professor, and ARON ELECTRICITY METER, LIMITED, of 46, Upper Thames
Street, in the City of London, 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:--
This invention relates to improvements in apparatus for measuring electric
currents of that class in which a three-phased current is conducted, not by three
conductors, as usual, but by four conductors, the fourth conductor being termed
the neutral conductor. The plant of an electrical central station of this kind,
in general, is connected by the so-called star-connection, the centre of the star
being connected to the fourth conductor, which, in most cases, is insulated,
although it could as well lead to earth.
Though in a plant of this kind, the star-connection is usually employed,
yet, the so-called triangular connection is equally practicable. The improved
apparatus according to this invention, as hereinafter described, will serve in all
cases and give true records, with either the star-connection, or with the triangular
connection, and also with currents the phases of which are unequally loaded.
In the accompanying drawings, Figures 1, 2, 3, 4 and 5 are diagrams, illus-
trating the theory upon which this invention is based as hereinafter more fully
described.
In the Specification of Letters Patent No. 21354 of 1891, granted to one of
us (Hermann Aron), there is for the first time, given a formula for connecting
three-phased electric current. A connection of this kind, however, cannot be
employed with three-phased currents having four conductors and phases unequally
loaded, because, in the latter case, an equation which, hitherto, has been utilised
by me, the said Hermann Aron, and by others who constructed the instruments
for measuring multiphase electric currents would no more be true, viz., the
equation, that the sum of the three feeding currents A + B + C = 0.
In the following will be explained how, even in this case, registering apparatus
may be constructed for triangular and star-connection combined as convenient.
Referring to the diagram, Figure 1, the currents flowing through the three
sides of the triangle are lettered .,, the respective tensions are lettered
E, E E, the currents flowing through the three radial lines are lettered b and c
and the respective tensions c₁₂ and lz.
The work performed in the combined triangular and star-connection will
read thus:-

page_text: Now, it is established that A + B + C + D = 0
it follows that W = AE, BE₁ – De̟
-
-
By summing up the three equations given above for the tensions ₁, е and ez,
right hand and left hand, it will be seen that:
e₁ + e + e = 0
as inuicated by rig. 4.
The first part of this formula is exactly the same as that stated in the specification
of the aforesaid Letters Patent No. 21354 of 1891, the last part of the formula, viz,
-
D)
J
(E,E,) accordingly, is the amount to be subtracted owing to the fact that the
current returns through the fourth conductor, and it is the supplementary
amount for the formula stated in the Specification of the aforesaid Letters
Patent.
This improvement also applies to meters of the motor type if there be supplied
in place of the pendulums armatures, and in place of ampere coils field magnet
coils. Although in such a case the diagram of connections would not be so
simple as in simple clock-work meter, still it is possible, and our Figure 5
shews our proposal in connection therewith.
As Figure No. 5 shews there must be for the purpose of utilising a common
axis two different armature coils regulated and connected to the specific tensions e,
and e, while the necessary field magnet coils of the armature connected to the
tension e, conducts the main current A and the necessary field magnet coils of
the armature connected to tension e conducts the main current B, it follows
that current C should act on both armature coils. To make this possible the
field magnets must have a second coil which on the sketch is shewn in dot and
dash lines, and this must be so adjusted that the main current C flows at first
through the first field magnet coil and acts on e, and hitherto through the
second field magnet coil and acts as well on tension, therefore it is necessary
to connect in series the second coil of both field magnets. As it is necessary that
the two armatures run in the same sense under the influence of the currents, the
two tensions must pass through the two pendulums in the same direction,
while the two currents A and B are passing in the same direction through the
magnet coils the current C must pass in the opposite direction.
Instead of fixing the two armature coils on a common axis they may just as
well be separated from each other and each of the said coils fixed on a separate
axis in such a manner that they represent two meters. In this case the readings
of the two meters must of course be added in order to get the same result.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, we declare that what we
claim is:-
1. Apparatus for measuring electric currents in a plant of three-phased
currents with four conductors, so constructed to utilize only three conductors A,
B and C in such a manner as to sum up the amounts of action of the currents
of two conductors A and B with the tensions e₁ and e, existing between them
and the fourth conductor, from which sum the amount of action of the current
in the third conductor C, combined with the sum of these two tensions, is being
deducted, substantially as, and for the purpose, herein before described.

page_text: 2. Apparatus for measuring electric currents in a plant of three-phased
currents with tour conductors, so constructed to utilize the amount of action of
the main current in only three conductors in such a manner, that the action
of the currents in two conductors; A and B, is combined with the tensions E₁
and E, and from the amount of the whole action thus obtained the third part
of the action of current D in the fourth conductor, combined with the difference
between the two tensions E, and F, is being deducted, substantially as and
for the purpose, hereinbefore described.
3. Clockwork meter for measuring electric currents in a plant of three-
phased currents with four conductors, so constructed that the third coil, arranged
between the two pendulums, simultaneously operates the influence of one current
on two different tensions existing in the two pendulums, substantially as and for
the purpose described.
4. Meter of the motor type for measuring electric currents in a plant of
three-phased currents with four conductors so constructed that two separate
field magnet coils act on two armatures in order to influence the one armature
from the one current and the other armature from the second current and both
armatures from the third current and substantially as and for the purpose
described.
Dated this 25th day of October 1899
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.