Improvements in Apparatus for Measuring the Phase Difference of Alternating Currents and Idle Currents.
Year: 1898

page_text: Date of Application, 11th Nov., 1898 --Accepted, 18th Mar., 1899
Improvements in Apparatus for Measuring the Phase Difference of
Alternating Currents and Idle Currents.
We, DR. JOSEF TUMA, University Professor, of IX Lazarethgasse 10, and MAX
RAPHAEL KALDEGG, Merchant, of I Schottenring 23, both of Vienna, Austria, 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:-
The present invention relates to an apparatus by means of which the phase-
difference of two alternating currents of the same frequency is measured as an angle
and this difference can be ascertained or the idle current can be measured by a
direct single reading.
This apparatus consists essentially of a fixed exterior coil-cross (i.e. of two coils
arranged at right angles to each other), and of a movable interior coil; both the
movable coil and the stationary coil-cross are in electrical connection with the leads
of the alternating currents the phase-difference of which is intended to be measured.
This connection is effected in such a manner that in the fixed coil-cross a circular
rotary field, as homogeneous as possible, is produced and the movable coil is thus
caused to turn until it assumes a position which encompasses with the zero or
initial position of the same, an angle representing the phase-shift, which angle can
be read off directly. If now the deviation is brought back to the zero position by
means of a torsion spring, this affords means for the direct ascertaining of the idle
current.
For this purpose the electrical connection is effected in such a
manner that
one coil of the fixed spherical coil-cross consisting of thick wire having a small
resistance, is connected with the lead of one of the alternating currents (the
main current) by means of the primary coil turns (consisting of thick wire) of
a transformer free from iron, through a low resistance whilst the second coil of
the coil-cross, made of thin wire of high resistance is connected with the secondary
coil turns (made of thin wire) of the said transformer. The moveable coil is
connected with the lead of the second alternating current, and for the purpose
which will be described presently, can be temporarily included in a branch of the
main current by means of a switch.
For the purpose of the correct adjustment of the instrument the thin wire coil of
the coil-cross is encompassed by a second winding of thick wire which is connected
with a branch of the main current, a small resistance (1/100 ohm) being interposed
in this connection, whilst in the lead going to the secondary coil a resistance is
included which can be adjusted at will. In this manner, by a suitable adjustment
resistance means is afforded of shifting the phases of the fields which are
originated by the currents circulating in the two coils through exactly an angle
of 90° as required.
The accompanying drawings shew in Figs. 1 and 2 two vertical longitudinal sections
taken at right angles to each other of one construction of the said apparatus.
Fig. 3 shews a horizontal section through the instrument, taken on the line x-x
11

page_text: Fig. 4 shews the apparatus as seen from below.
Fig. 5 is a diagram explaining the action of the apparatus.
The apparatus consists of two (stationary) coils A' and A2 forming a coil-cross.
In order to obtain a circular rotary field as homogeneous as possible the wire turns
of these two coils are made of spherical shape. In the practical execution of the
invention the coils are constructed in the shape of pairs of hemispherical cups, as
shewn in Figs. 1 and 2. The wire turns of the coil A¹ affixed to the standard B of
the apparatus consist of thick wire a¹ of small resistance and for this reason there
might be substituted for this coil a hollow copper body of spherical shape cut into a
spiral form.
The coil A2, the turns of which are in a direction perpendicular to those of the
coil A¹ is encompassed by the coil A¹ and is composed of a great number of turns
of thin wire a² of high resistance.
Besides this coil A2 is provided with a second external layer of auxiliary turns a³ of
thick wire, the purpose of which will be explained presently.
The ends of the wires a¹ and a² are connected respectively with the terminals I, I
and II, II by means of the leads enclosed within the standard and shewn in the
diagram, Fig. 5.
In the interior of the hemispherical coil-cross A¹ A² is arranged a coil S which
can revolve round the vertical spindle s the latter being connected with the axis of
the pointer Z enclosed within the box D and playing over a circular scale. The said
axis of pointer Z is pivotted on a centre point.
The bottom end of the spindle s passes through the spherical coils to the exterior
thereof and is provided with two conducting points 81. 82 which are put in electrical
connection with the ends of the wire forming the inovable coil. This electrical
connection is established in such a manner that from the coil S two wires are led to
the hollow spindle of the coil, are conducted within the same downwards and are
then connected with the two points s¹ 82. These points are either immersed in
mercury cups q¹ q' affixed to the terminals 2 or there are provided separate leads
consisting of thin wire spirals. The mercury cups or the said thin wire spirals are
connected with the terminals III III.
On the under side of the bottom-plate B¹ of the standard are arranged two double
switches T and T2 which can be operated by means of the handle levers H¹ (Fig. 3)
and H2 (Figs. 2 and 3). The switch T is constantly brought back into its closed
position by means of the spring t (Fig. 4) and is for the purpose of alternately inter-
rupting and closing the circuits of both windings a² a² of the interior fixed coil A2 of
the coil-cross.
The switch T is to enable the operator as hereinafter described, to switch the
movable coil S into a branch of the circuit of the current flowing through the exterior
fixed coil A¹ in order to test the correct adjustment of the apparatus. The following
is a detailed description of the action of the apparatus, reference being made to the
diagram Fig. 5 of the accompanying drawings. L1 L2 and are the two
leading wires for the alternating currents, the phase-difference of which is to be
determined.
The first alternating current (the main current) passes through the primary
turns p¹ (made of thick wire) of a transformer free from iron to the exterior primary
coil A of the fixed coil-cross. In the lead 11 of this main current a small resistance
W is interposed.
The secondary winding p³, of thin wire, of the transformer is connected by means
of the lead ps with the turns a², also of thin wire, of the secondary coil. If J
designates the intensity of the first alternating current (the main current) the
intensity of the current circulating in the primary coil, will be expressed by the
following formula

page_text: This current induces in the secondary turns 22 of the transformer and in the
secondary turns a² of the coil A² a current having the following measurements:
Electromotive force - € = K a J cos, a t (k being a constantà
-==
The angle a t will be diminished by a certain angle 4.
In order to cause the angle to disappear from the formula the fields originated by
the two currents in the windings a¹ a² of the coil-cross must have a phase-shift of
exactly 90°.
This is attained by means of the following arrangement:
Above the thin wire winding a² of the secondary coil A2 is coiled a thick wire
winding a³ which has in its current a small resistance W (1/100 ohm) and is
switched into a branch of the main current (L 12). Thus through this wire a³ a
current will flow which will possess an equal phase with the main current circulating
through the primary coil and the intensity of which will be in a constant relation to
that of the main current. Besides, in the lead p³ conducting to the secondary wind-
ing a2 of the coil A² a resistance Wr is interposed which can be regulated at will.
By means of this resistance Wr the secondary current can be modified in such a
manner that the phase of the magnetic field generated by the secondary current in
conjunction with the branch current circulating through the auxiliary windings a³,
will differ from that of the field generated by the main current by an angle of 90°.
S is the movable coil connected with the lead 2 of the second alternating current.
T2 is the double key or double switch, by means of which the movable coil S can
be switched into a branch n of the main current, a resistance W being interposed in
the lead. In this manner through the inovable coil a current will flow possessing the
same phase as the main current.
If now the circuits of the two windings 2 and 3 of the secondary coil A² of the
coil-cross are alternately interrupted and closed, the pointer Z of the instrument
should not make any jerking motions or oscillations, if the instrument is correctly
adjusted.
For interrupting (and closing) the two circuits serves the double key or double
switch T which, as can be seen from Figure 5, is common for both leads conducting
to a² a³.
If during the action of this switch T¹ the pointer should make a throw, it becomes
necessary to modify the resistance Wr in such a manner as to obtain the above
mentioned characteristic feature of the correct adjustment of the instrument.
When the instrument is correctly adjusted (and assuming that there will be no
distorted current-curves) in the fixed coil-cross a rotary field will be generated which
will cause the movable coil to turn and to assume the position which, with the zero-
or initial position, will encompass the angle of shift and this latter can be read off
directly on the circular scale K.
=
a
The mathematical deduction from the above cited explanations is as follows. It is
assumed that the intensity of the main-current i J sin. t and that the field
generated by the same is F₁ = €1 J sin. a t. The current induced in the transformer
free from iron is, as above mentioned:

page_text: it follows that Wr must vary proportionally to a and that consequently
a constant.
W7"
must be
a
If for any the amplitude of F¹ be made equal to that of F₂ + F₂, the same will
if in the formula (3) will also be
2
Wr
a
a
be applicable also for any other quantities of ay
a constant.
The required modification of WF is effected in the manner described above and
the apparatus can also be arranged in such a manner that from the resistance it
is possible to read off the number of periods per second.
It follows from the above that the said two conditions are simultaneously fulfilled
by the same resistance and that consequently by the proper setting of W, a circular
rotary field will always be obtained.
r
If we now examine in this circular rotary field the movable coil, through which
flows a current i sin. (at +), we arrive at the following conclusions.
If the components of the rotary field be:
H₁
H. sin. a t and H, H. cos. a
=
t, and if the movable coil with the fixed coil
which generates the first component H, encompasses the angle p, the turning moment
produced will be:-
D kH, sin. p i sin. (at + )-kH₂ cos. p i sin. (a t + ) or
D
=
=
kH, i sin. (at + ) [sin. p a t-cos. p cus. a t] or
D k Hi sin. (at + ) cos, a t + p)
1 -
=
The mean turning moment will thus he D sin. (p) ki J, because H is
proportional to J.
In order that D may be equal to zero, the coil must be placed in such a manner
that 4p4 and thus it becomes possible to read off 4 p directly on the circular
scale.
If the instrument is electrically connected in such a manner that an alternating
current forms the main current, which flows through the primary turns of the
transformer and through the fixed spherical coils provided with thick wire winding,
whilst the movable coil together with a constant resistance interposed before it is
inserted in a shunt circuit of the same alternating current comprising a voltmeter,
in this case, when P == 0, D=ki J sin. .
If the instrument is constructed as a torsion instrument in such a manner
that by means of a spiral spring the movable coil is brought back to its zero position
proportional to J.
In order that D may be equal to zero, the coil must be placed in such a manner
that 4p4 and thus it becomes possible to read off 4 p directly on the circular
scale.
If the instrument is electrically connected in such a manner that an alternating
current forms the main current, which flows through the primary turns of the
transformer and through the fixed spherical coils provided with thick wire winding,
whilst the movable coil together with a constant resistance interposed before it is
inserted in a shunt circuit of the same alternating current comprising a voltmeter,
in this case, when = 0, DJ sin. ø.
P
If the instrument is constructed as a torsion instrument in such a manner
that by means of a spiral spring the movable coil is brought back to its zero position

page_text: and a pointer connected with this spring indicates the torsion thereof, the instrument
will measure the empty current J sin. o, if the tension and together with it i be
maintained constant, as is for instance the case in central stations.
Having now particularly described and ascertained the nature of this in-
vention and in what manner the same is to be performed, we declare that what we
claim is:-
1. Apparatus for measuring the phase of alternating currents consisting of a
stationary coil-cross, such as A1, A2 and a movable coil S which latter as well as
the windings a¹ a² of the coil-cross are connected with the leads L1 L2, for
the alternating currents in such a manner that a circular rotary field as nearly
homogeneous as possible is developed in the stationary coil-cross and the movable
coil is turned thereby until the angle which it makes with its zero position or
starting position represents the phase shift and can be read directly, substantially as
described.
2. In an apparatus such as is referred to in Claim 1 a stationary coil-cross
consisting of two pairs of hemispherical coils A1 A2 the exterior pair being wound
with thick wire a¹ and in circuit through a low resistance W and through the
primary winding p¹ of a transformer, with the lead L' carrying one of the alternating
currents (the main current) while the interior pair are wound with thin wire a² and
are in circuit with the secondary winding p² of the transformer, the said interior
pair being also provided with an external winding of thick wire ³, which external
winding is in circuit, through the resistance W, with a branch lead of the main
current lead L¹ and in conjunction with an adjustable resistance Wr in circuit with
the secondary winding a² of the coil A2, enables the instrument to be correctly
adjusted, substantially as described.
3. In an apparatus such as is referred to in Claims 1 and 2 suspending the
movable coil from a torsion spring so that the coil may be brought back to its zero
position and a pointer attached to the said torsion spring may indicate the idle
current, substantially as described.
Dated this 11th day of November 1800