Improvements in Apparatus for the Measurement of Alternating Currents.
Year: 1898

page_text: Improvements in Apparatus for the Measurement of Alternating
Currents.
We, GEORGE KEITH BULLER ELPHINSTONE, of 101, St. Martin's Lane, in the County
of London, Electrical Engineer, and ARTHUR CECIL HEAP, of The Firs, Tyler's Green,
in the County of Buckingham, Electrical Engineers, do hereby declare the nature
of this invention to be as follows:-
In the case of alternating current amperemeters, we use a small transformer
consisting of a suitable winding through which the current to be measured passes,
and a secondary winding, both being disposed symmetrically on a laminated iron core,
so arranged as to ensure as far as possible the saine number of lines of magnetic force
passing through the two windings; the iron core being formed into a closed magnetic
circuit to avoid all possible magnetic leakage-the section and length of the laminated
magnetic circuit are also chosen with the same object in view.
The terminals of the secondary winding mentioned above can be joined up to the
primary winding of an instrument similar in general construction to that forming the
subject of our Specification No. 26399, 1897; so that the indications given by such an
instrument may be independent to a very large extent, to changes in the periodicity
at which the current to be measured is supplied; and, the indications of the
instrument, being proportional to the difference of potential between the terminals
of the secondary winding of the small transformer above mentioned, indicate the
changes of value of the current flowing through the primary winding of the trans-
former...
One object of the arrangement described above, is to enable one measuring
instrument to be employed with several different ranges, by means of the use of
several differently wound transformers suitable for such ranges, or to enable one
instrument to be joined up to any one of several different circuits as required, and so
give indications of the current flowing in each by means of a separate transformer
being kept in each circuit.
In the case of a Wattmeter, the current measurement is effected in the manner above
described, the secondary winding being connected to a winding placed on an iron circuit,
similar to that in use in an instrument described in our Spécification No. 26399, 1897,
this winding having a high impedance, the electromotive force measurement being
obtained by joining a primary winding of an entirely separate transformer across the
wires, between which it is desired to measure the pressure, and by connecting the
secondary winding of this transformer to a moving coil, similar to that described in
the instrument described in our Specification No. 26399, 1897-a small resistance
being interposed between the secondary winding of the transformer and the moving
coil when required.
Inasmuch as instruments worked on this plan can be used equally well, either, as
indicating or recording instruments the arrangement described above has the
advantage of keeping the instrument itself on a circuit, entirely independent of the

page_text: main circuit itself-so that, in the ease of high tension circuits the instrument can
be handled with safety.
Dalad 3th of A
1000
COMPLETE SPECIFICATION.
Improvements in Apparatus for the Measurement of Alternating
Currents.
We, GEORGE KEITH BULLER ELPHINSTONE, of 101, St. Martin's Lane, in the
County of London, Electrical Engineer, and ARTHUR CECIL HEAP, of The Firs, Tyler's
Green, in the County of Buckingham, Electrical Engineer, 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:-
In the case of alternating current amperemeters we use a small transformer con-
sisting of a suitable winding through which the current to be measured passes, and a
secondary winding, both being disposed symmetrically on a laminated iron core so
arranged as to ensure as far as possible the same number of lines of magnetic force
passing through the two windings, the iron core being formed into a closed magnetic
circuit to avoid all possible magnetic leakage-the section and length of the
laminated magnetic circuit are also chosen with the same object in view.
The terminals of the secondary winding mentioned above can be joined up to the
primary winding of an instrument similar in general construction to that forming
the subject of our Patent No. 26399, 1897; so that the indications given by such an
instrument may be independent to a very large extent, to changes in the periodicity
at which the current to be measured is supplied; and, the indications of the instru-
ment being proportional to the difference of potential between the terminals of the
secondary winding of the small transformer above mentioned, indicate the changes of
value of the current flowing through the primary winding of the transformer.
One object of the arrangement described above, is to enable one measuring instru-
ment to be employed with several different ranges, by means of the use of several
differently wound transformers suitable for such ranges, or to enable one instrument
to be joined up to any one of several different circuits as required, and so give indi-
cations of the current flowing in each by means of a separate transformer being kept
in each circuit.
In the case of a Wattmeter, the current measurement is effected in the manner
above described, the secondary winding being connected to a winding placed on an
iron circuit, similar to that in use in an instrument described in our Patent No. 26399,
1897, this winding having a high impedence-the electromotive force measurement
being obtained by joining a primary winding of an entirely separate transformer across
the wires, between which it is desired to measure the pressure, and by connecting the
secondary winding of this transformer to a moving coil, similar to that described in
the instrument described in our Patent, No. 26399, 1897-a small resistance being
interposed between the secondary winding of the transformer and the moving coil
when required.
Inasmuch as instruments worked on this plan can be used equally well, either, as
indicating or recording instruments the arrangement described above has the
advantage of keeping the instrument itself on a circuit, entirely independent of the
main circuit itself-so that, in the case of high tension circuits the instrument cau
be handled with safety.

page_text: The accompanying drawings show diagrammatically as much of our instrument as
is required to illustrate the invention.
Figs. 1, 2, 3, show one form of transformer suitable for use with alternating current
ammeters having ranges up to about 300 amperes. A is the iron circuit consisting
of a number of E-shaped iron plates Fig. 4 built up to the required section and
firmly bolted together, on the centre core B Figs. 2 & 4 the two windings P&S lie
as close over one another and as close to the iron core B as possible, the primary
winding P being capable of carrying the total current to be measured, the winding of
the secondary S being chosen according to the type of instrument to be connected to
its terminals. The winding is carefully insulated from the iron circuit and the two
windings P&S are insulated from one another.
Figs. 5, 6, 7 show another transformer suitable for currents of 1000 amperes and
greater currents. As before the two windings P & S are symmetrically disposed.
round the iron core B but in this case the primary winding is built up of a number
of pieces of copper strip p₁ p₂ in order to get rid of any magnetic leakage caused by
eddy currents in the copper of the primary winding.
Fig. 8 shows a transformer constructed as described above. The current to be
measured passes through the primary winding P of the transformer, the secondary
winding S has a current induced in it proportional to the primary current, the ends
of the secondary winding S being connected to the primary winding P₁ of an instru-
ment D similar in general construction to that forming the subject of our Patent
No. 26399, 1897. This instrument is adjusted to read amperes, by means of an
impedance C introduced in the connecting wires W W, and placed for convenience in
the case of the instrument, by comparison with a suitable standard ammeter placed
in series with the primary of the transformer; by such a combination of instrument
and transformer the indications of the instrument are made independent to a great
extent of the periodicity at which the current to be measured is supplied.
1
1
1 2
Fig. 9 shows a method of connecting three or more transformers T₁ T2 T3 whose
primary windings have different current carrying capacities so that only one indi-
cating instrument 1) may be used to read the currents in the primaries P, P, P3 of the
three transformers T, T, T. In order to do this we connect the ends of the secondary
winding of each transformer to two of the contact studs E, E, E, E, E, E, forming
part of a multiple switch, the two continuous strips F F of the switch being con-
nected to the primary windings P, P₁ of the indicating instrument D. By changing
the position of the contact strips GG¹ of the switch so that circuit is made between
any desired pair of contact studs E, E, E, E, E, E, and the strips, the current pass-
ing in the primary of either transformer can be read on the indicating instrument D.
Fig. 10 shows the method by which the current measurement is effected in the
case of a Wattineter. As before the primary winding P of the transformer T is
capable of carrying the total current which the Wattmeter is intended to measure,
the secondary winding S is then connected to a winding on an iron circuit H similar
to that in use in an instrument described in our Patent No. 26399, 1897, this winding
being chosen according to the quality of the iron used so that the induction in the
air gap J is proportional to the current in the winding K round it, this current being
also proportional to the current in the primary P of the transformer T, the electro-
motive force measurement being obtained by using an entirely separate trans-
former T, whose primary winding P, is connected across the source of electro-motive
force of supply which it is desired to measure and whose secondary winding S is
connected to a moving coil L similar to that used in the instrument described in our
Patent No. 26399, 1897, a small resistance R being interposed between the secondary
winding S, and the moving coil L for the purposes of adjustment.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that what we
cluin is:-
(1). On alternating current circuits for the measurement of current the use of a
transformer constructed in such a manner that magnetic leakage and eddy currents
.

page_text: are reduced to a minimum, the secondary winding being connected to an instrument
similar to that forming the subject of our Patent No. 26399, 1897, all substantially
as described.
(2). The combination of several transformers constructed as described, a multiple
switch and one indicating instrument for the purpose of reading the currents in
several circuits on one instrument, substantially as described.
(3). The use on alternating current circuits of a transformer constructed as
described whose secondary is connected to one winding of a Wattmeter for the purpose
of effecting the current measurement of such an instrument.
(4). The combination as described of a transformer and indicating instrument
connected together substantially as described, the primary and secondary windings of
the transformer being carefully insulated from one another to enable the instrument
to be handled safely on high tension circuits.