pergy meters for Alternating Currents.
Year: 1899

page_text: pergy meters for Alternating Currents.
We, SIEMENS BROTHERS & Co. LIMITED, of 12, Queen Anne's Gate, Westminster,
in the County of London, Electrical Engineers, do hereby declare the nature of this
invention (as communicated to us from abroad by Siemens & Halske Aktien
Gesellschaft, of Markgrafen Strasse 94, Berlin S.W., Electrical Engineers,) and in
what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement :-
In electricity meters acting on the Ferraris system, that serve to measure the
work of alternating currents, it is necessary that there shall be a phase-shift of 90°
between the magnetic field produced by the main current and that produced by the
shunt current.
If this condition is not fulfilled any work in which the current has a greater
phase-shift relatively to the pressure, will be defectively measured to the extent of a
percentage that will increase with the phase-shift.
Various methods have been proposed for producing a magnetic field shifted 90°
relatively to the pressure either directly or by means of a current shifted 90° rela-
tively to the pressure. All the arrangements hitherto proposed suffer however from
the want of a ready means of adjustment.
The adjustment of such meters has to be effected in two directions; firstly, the
indications of the apparatus must have a certain prescribed relation to the work
measured; and secondly, there must exist between the pressure and the magnetic
field a phase shift of 90°
The first named condition can be fulfilled by varying the amount of the current
or pressure field.
For fulfilling the second condition, the relations determined by the first condition
have to be altered again, so that it is only possible to fulfil the said conditions.by
means of approximative trials, involving a great deal of trouble.
The present invention relates to an arrangement that not only allows of the accurate
adjustment of the extent of the pressure field but also that of the desired phase-shift
of 90° almost independently of the adjustment of the pressure field.
Referring to the accompanying diagrammatic drawings, m n Fig. 1 represent the
coils of the measuring apparatus that serve for the production of the main current
field and ce and fd those for the production of the pressure field.
The pressure coils are combined with resistances free from induction e d, cf, and.
ef, in a similar manner to the Wheatstone's bridge, e f forming the diagonal
resistance.
The bridge thus constituted is connected in series with an inductance coil 8, between
connecting terminals a b on the circuit to be measured.
The adjustment of the strength of the pressure field is effected by the corresponding
alteration of the resistances c and d which are preferably made equal. These

page_text: resistances: carry that part of the pressure current which does not serve for the pro-
duction of the shunt circuit field. The greater they are, the greater will be the shunt
circuit field, whereby also the sensitiveness of the measuring instrument will be
increased.
For accurately adjusting the phase-shift the diagonal resistance e f is employed.
By increasing this resistance a phase-shift below 90° is obtained and by decreasing.
it, the phase-shift is increased above 90°.
Assuming the currents in the pressure coils ce and df to be respectively, and i
and the currents in the resistances cf, de, and ef respectively equal to i, i, and ig,
and lastly assuming to be the total current branched from the points ab and flowing
through the inductance coil 8, then :--
In the diagram at Fig. 2 the length ce = fd represents the pressure at one 2
pressure coil, e d=
= c f the pressure at one lateral resistance of the bridge, and.
lastly e f the pressure of the diagonal resistance. db is the pressure of the
inductance coil sand cb the pressure at the terininals.
The currents i =eg and i = e give together the current.ic
-
ek which has à
phase shift relatively to its pressure. The total current of the bridge i = el is 2
obtained from and 2 . As.now the current is to have a phase shift of 90°
relatively to the terminal pressure, the direction cab at right angles to ek is given.
In order to complete the diagrain the pressure of the inductance coil 8 must be.
included.
This is represented by the length d b. As will be seen from the diagram, the a
pressure d has a phase shift p relatively to the current which is less than 90°,
consequently the described arrangement can be actually carried out with the desired.
result.
A further treatment of the diagramn Fig. 2, whether graphically or mathematically
is equally difficult.
By approximation it was found that the phase-shift of the current i relatively..
to the terminal pressure cb can be varied between the limits of 80° and 100° by
means of the resistance ef, while the current i, varies about 5 per cent. assuming
constant.terminal pressure.
Experiments made in this direction, showed the correctness of the assumed pro- 4
portions of the diagram.
As in the adjustment, it is only a question of a few degrees, it results that in the
employment of the above described arrangement the variation of current flowing
through the pressure coils can be practically quite neglected.
Having now particularly described and ascertained the nature of this 4
invention and in what manner the same is to be performed, we declare that what we
claim is :-
In energy meters for alternating currents an arrangement for effecting a phase-
shift of 90° between the current. producing the pressure field, and the terminal.
pressure, wherein the pressure coils of the measuring apparatus are included in two b
opposite sides of a Wheatstone bridge, the other two sides and diagonal of

page_text: which are formed by resistances as free as possible from induction, while an
inductance coil is included in front of the said bridge device, substantially as
described.
ABEL & IMRAY,
Agents for the Applicants.