Improvements in Three-phase Alternating Current Induction Meters.
Year: 1897

page_text: Date of Application, 8th June, 1897-Accepted, 25th Sept.,
1897
COMPLETE SPECIFICATION.
Improvements in Three-phase Alternating Current Induction
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 Charles P.
Steinmetz, of Schenectady, County of Schenectady, State of New York, United
States of America) and in waat manner the same is to be performed, to be particu-
larly described and ascertained in and by the following statement:
Our invention relates to alternating-current watt meters of the induction type
for measuring the energy of three-phase circuits. It is already known that two
"Thomson" watt meters,
dynamometer watt meters, for example, the well known
can be used to measure the total energy of a three-phase system by connecting
their series coils in two of the main lines and their potential coils between the
third line and the lines carrying the current coils. Our invention aims to pro-
vide a watt meter of the induction type which will likewise give a correct reading
of the energy in three-phase, three-wire, interlinked systems, whether the load be
balanced or unbalanced, or whether or not the load be inductive in character.
Our new meter consists of a closed secondary member of conducting metal,
such as copper or aluminium, and for this part of the meter there may be used
discs or cylinders, such as are now common in other induction meters. If such a
secondary member is acted upon inductively by current coils in two of the mains
of a three-phase system and by potential coils included in the circuit of electro-
electro-
motive forces which are respectively in quadrature with the
motive forces between the mains carrying the current coils and the third main,
there will be secured a correct registration of the energy in the system, and this
registration is secured by a single instrument rather than by meters having a
number of motor mechanisms arranged in the different branches of the system.
It is, however, not necessary that the potential coils be actually in circuit with
electromotive forces in quadrature with the main line electromotive forces as
pointed out, for the same result will be secured, if the potential coils are so arranged
and connected in circuit that the magnetisms set up thereby are the same or equiva-
lent to magnetisms induced by potential coils connected in the particular manner
already mentioned. For example, as will be explained more fully hereinafter, we
circuit with
may use two potential coils in
we
in
electromotive forces
quadrature, or
may use coils of greater number in the circuit of
électromotive forces of different phase relation, but so proportioned and
arranged as to establish a resultant magnetism which is the equivalent of the
magnetism of a single coil carrying a current of the theoretically proper phase
relation. We therefore wish to include both arrangements within our invention
no matter whether the magnetisms due to the potential coils are produced by
currents having the requisite phase relation, or are produced by the combination
of currents of other phase relation proportioned so as to give the proper resultant.
The accompanying drawings are diagrams showing the connections of the three-

page_text: phase meters made according to our invention, Fig. 1 showing one form, and
Fig. 2 a modified form; Fig. 3 is a diagram illustrating the connections and
electromotive forces of the meter shown in Fig. 1, and Fig. 4 is a similar diagram
explaining the operation of the meter of Fig. 2.
In Fig. 1 A, B, C are the three mains of the system. They may be interlinked
at the generator in either of the usual ways, that is, by what is known as the Y
or delta method of connection. D is the drum or cylinder forming the rotating
secondary element of the meter. E, E are current coils included respectively in
the mains B and C; F and F are the potential coils, G1, G2, G3 are resistances
having one set of terminals connected at a common joint g. The free terminal
of resistance G¹ is connected to line A. The corresponding terminal of resis-
tance G2 is connected through the potential coil to main B, and resistance G³
is similarly connected through the potential coil F to main C. The valve of these
resistances is so chosen as to afford substantially equal resistance between the lines
and common junction g, so that this point forms what is commonly called a
neutral point," which does not shift materially under different conditions of
load. The resistances, furthermore, preserve the proper phase relation of the
currents in the potential coils F, F¹.
66
Fig. 3 shows the connections of the coils and resistances in a convenient manner,
and also represents the electromotive forces which are present. Lines 1, 2; 3 are
respectively the electromotive forces between the different mains A, B, C, these
lines being drawn to form the equilateral triangle commonly used to show graphi-
cally the electromotive forces in a three-phase system. The potential coil Fand
resistance G³ is as shown in circuit betweeen main C and the neutral point g. and
the electromotive force between these points would be represented by a straight
line from the angle at C to the neutral point g. This line is omitted in the
diagram to avoid confusion. It is evident that this electromotive force will be in
quadrature to the electromotive force between the mains A and B represented by
line 1. Similarly the electromotive force in the circuit between the main B and
the neutral point g which includes potential coil F¹ would be represented by a line
drawn from the angle at B to the point g, and this electromotive force
will be in quadrature to the electromotive force between linés A
and C, represented by the line 3. Hence, with this arrangement, we have
two series coils E and E' included respectively in the mains B and C and by the
resistances G1, G2, G3, and the illustrated connections of the potential coils F
and F these potential coins are respectively included in circuits having electro-
motive forces in quadrature to the electromotive forces between the third main A
and the mains B and C carrying the current coils. As already explained, these
are the conditions under which, in accordance with our invention, an accurate
registration of the energy in the system is secured by a single induction meter.
The potential coils F and F¹, are, of course, displaced around the secondary D
a suitable angle from the current coils.
In Fig. 2 another arrangement is illustrated for accomplishing the same result
in a somewhat different way, but in a way giving equivalent effects, so far as the
operation of the meter is concerned, so that all such arrangements as this are to be
included within the broader definitions of our invention hereafter contained in the
claims. The mains are represented at A, B, C as before. A current coil E is
included in main B and a current coil E in main C, also as before. The potential
coils are connected as follows: Main A is connected through resistance G¹, and
potential coil F³, to main B. Main A is also connected inrough resistance G³
and potential coil F3 to the main C, and there is a circuit from B to C, which mav
be traced from the point a through potential coil F*, resistance G³ and potential
coil F¹. With this arrangement, the action of the current coils is the same a
before, the difference between the two modifications being in the arrangement of
the potential coils and resistances.
In Figs. 1 and 2 the armature of the meter shown is, for example, an aluminium
cylinder of about the same size as the armature of the well known Thomson

page_text: Recording watt meter. The coils acting on the armature are also about the same
size as those in the Thomson recording watt meter, or somewhat smaller where a
large number are used, and may be arranged in the same manner as in the
Thomson recording watt meter, or mounted on polar projections of an iron
magnetic circuit. The current coils consist of a few turns of coarse wire, the
potential or shunt coils of very many turns of fine wire of about the same size as
the shunt circuit, that is, the armature of the Thomson recording watt meter. The
resistances are about the same size also as in the Thomson recording watt meter.
Fig. 4 shows very clearly the order in which these are connected between the
different mains. Coils and F4 will be wound together in the meter so as to
have a common magnetic axis, and so also will coils F1 and F2. Coils F3 and F4,
however, are in circuits whose electromotive force and currents will be displaced in
phase as indicated in the diagram, so that these coils will tend to induce magnetism
of displaced phase, but the magnetism will combine, since the coils are wound
together, to form a resultant which may be indicated by the line af. This line
bears the same relation to the line connecting mains A and C as does, in Fig. 3, the
electromotive force in potential coil F to the electromotive force between mains A, B ;
so that the magnetizing effect of the coils 13 and F4 may be regarded as the
equivalent of the coil F in the arrangement of Fig. 3. Likewise the coils FI
and F2 which are in circuits of displaced phase, will combine to yield a resultant
magnetism in the direction of the line b-f, which is at right angles to the line
representing the electromotive force between mains A and B. Therefore, the
same magnetic conditions are produced by the arrangement in Fig. 4 which are
produced by the meter of Fig. 3; the coils F3 and F of Fig. 4 combining to do
the work of coil Fin Fig. 3, and coils F1 and F2 of Fig. 4 combining to do the
work of coil F1 in Fig. 3. The operation or this form of the invention will, there-
fore, be understood from the explanations already given.
It is of course designed that the usual co-operating parts of the meter shall be
employed, counting apparatus of any desired type, gearing for transmitting the
movement of the drum, and other usual mechanism; but none of these parts is
illustrated, as they do not constitute any part of our invention, and may be
indefinitely varied."
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. A three-phase induction watt méter, comprising a closed-circuit armature
and magnetizing coils comprising current coils in two of the main lines, and two
potential coils or sets of coils in circuit with electromotive forces which are in
quadrature with the electromotive forces between the third main and the two
mains carrying current coils, as described.
2. A three-phase induction meter, comprising a closed-circuit armature, and
primary magnetizing coils comprising current coils included in two of the main
lines, and potential coils connected across the lines and arranged to afford
magnetism in quadrature to the electromotive forces between the third main line
and the two other main lines carrying current coils, as described.
3. A three-phase induction meter comprising a secondary member, current coils
in two of the main lines and establishing a magnetization proportional to the
current in the system, potential coils connected across the lines and establishing
. magnetization in quadrature to the electromotive forces between the third main
and the mains carrying the current coils.
4. A three-phase induction meted, comprising a closed-circuit secondary
member current coils in two of the mains, resistances connected to the mains, and
potential coils connected across the mains through the resistances so as to preserve
the phase of the current in the potential coils and establish magnetization pro-
portional to the potential on the system and in quadrature with the electromotive
forces between the third main and the mains carrying current coils,

page_text: 5. A three-phase induction meter, comprising a secondary member, current
coils connected in two of the mains, resistance connected between the mains and a
neutral point, and potential coils connected between the mains carrying current
coils and the neutral point.
6. A three-phase meter comprising a closed-circuit secondary, current coils in 5
two of the mains, means for maintaining electromotive forces in quadrature
between the mains carrying current coils and the third main, and potential coils
included in th circuits of such last mentioned electromotive forces.