Note: Descriptions are shown in the official language in which they were submitted.
96/80
Fk/lu
A method and a device for continuously controlling the phase
angle in electrlc en rgy transmission ~g~
BACKGROUND OF THE INVENTION
The present invention relates to a method for
continuously controlling the phase angle in electric energy
transmission equipment and to a device for carrying out this
method.
When for example several energy transmission lines
are connected together, an effort must be made to match the
phase angles of the alternating voltages connected together.
This improves the transmission characteristics of the line and
reduces any e~fects reflected back to the generators. This
effort is made more difficult because the phase angle of a
voltage fed into a transmission line is rotated along this line
and by the load at the end of this line if this load is not a
pure resistance.
For this reason, so-called shunt transformers are
used in interconnected grids for matching the phase angles of
the voltage in the various parts of the grid to each other.
The shunt transformer induces in each conductor of the line a
quadrature-axis voltage component which is superimposed on the
input voltage and the phase angle of which is displaced by 90
with respect to that of the input voltage so than an output
voltage is generated the phase angle of which is displaced with
respect to that of the input voltage.
In addition, a controllable phase-shifting device
having at least two series-connected reactive impedances has
been disclosed (German Offenlegungsschrift 2,853,358, published
June 4, 1980 and the cognate U.S. Patent No. 4,302,716,
granted November 24, 1981). Between the impedances a tap has
been provided and in series with this tap at least one
electrically controlled current switch which is preferably a
bidirectional thyristor. This phase-shifting device makes it
~3~r'
, . ~
- 2 ~
possible to ro-tate, in small steps and in both possible
directlons, the phase angle of the voltage tapped off. The
rotation of the phase angle is generated by the reactive power
in the reactive impedances which is why the amount of this
rotation determines the required rated power of the impedances.
In this arrangement the rated power reaches about one quarter
of the power-handling capacity ror a rotation by 6~. For
economic reasons, the phase-shifting device described can,
therefore, be used only to a limited extent for energy
transmission lines in spite of its technical advantages.
SUMMARY OF THE INVENTION
:
It is the object of the invention to create a
method and a device for carrying out the method by means of
which the phase angle o~ the secondary voltages can be
displaced selectively in one and/or in all directions
(longitudinally, diagonally and transversely) over a large
range of angles. This displacement is intended to make
possible an industrial implementation and is not to be caxried
out by means of reactive power.
According to the invention, this object is achieved
by the feature that at least one continuously adjustable
voltage source providing a correcting voltage having a selected
phase angle is inductively added to the input voltage.
This results in a vectorial addition of two
voltages, which addition can be separately controlled or
regulated for each phase.
The device according to the invention is provided
with a continuously adjustable voltage source which is
connected via a recti~ier circuit to a correcting-voltage
source.
The method according to the invention, or the
corresponding device, makes it possible continuously to
compensate energy systems even with great variations in
reactive power loading.
A self-controlled inverter makes it possible to
set, in a simple manner, phase angles which have been selected
at will.
A particularly economical arrangement is realized when
the rectifier circuit comprises a bridge circuit equipped with anti-
parallel-connected thyristors.
In order to attain a reduction in the control design
effort it is advantageous to provide the voltage source with an
exciter transformer which is connected to the input voltage, and the
secondary winding oE which is finely stepped.
A further advantageous construction contemplates
stepping the secondary winding of the exciter transformer in accordance
with a power series. This permits a further reduction in the control
design effort since the range, which is to be continuously controlled
or regulated, can be selected to be almost randomly small.
~RIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects
other than those set forth above, will become apparent when
consideration is given to the following detailed description thereof.
Such description makes reference to the annexed drawings wherein:
Figure 1 shows the principle of vectorial addition of
a correcting voltage to the input voltage in an arbitrary direction.
Figure 2 shows a basic diagram of a circuit arrange-
ment for the vectorial addition of a compensation voltage in one phase
of a line network.
Figure 3 shows a variant of the circuit arrangement
of Figure 2 which is provided with a rectifier bridge circuit;
Figure 4 shows a circuit arrangement for a three-
phase system with vectorial addition transversely to the input voltage;
Figure 5 shows another circuit arrangement provided
with a secondary winding, stepped in accordance with a power series, of
- 3a -
an exciter transformer;
Figure 6 shows a circuit arrangement for the switchable
selective vectorial addition in the longitudinal, transverse and
diagonal directions; and
Figure 7 shows an illustrative vector cliagram
resulting from the circuit arrangement in Figure 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to Figure 1, the input voltage of a high-
tension line is designated by U. The phase relationship of this
input voltage U shows a phase angle (~ which is leading (capacitive
load) or lagging (inductive load) within a certain time interval,
depending on varying loads applied to the high-tension line. By
inductively adding a corrective voltage U~ with a phase angle ~',
a phase rotation by ~ is produced. The resultant output voltage
is designated by U'; the current and the voltage have the
deslred relationship with respect to one another.
In a circuit arrangement, Figure 2, the
high-tension line HL is shown symbolized by means of its input
voltage U and its output voltage U'. The voltages U and U',
respectively, are measured at the secondar~v side of a
correcting transformer ZT. The secondary winding of the
correcting transformer ZT carries a correcting voltage UZ which
has been ~roduced, on the one hand, by an exciter transformer
ET and, on the other hand, by a voltage source 1. The voltage
source 1 is formed by a correcting-voltage source 3, a
suhsequent rectifier circuit 2 and an electronic power circuit
LE. The electronic power circuit is supplied with a
measuring/control signal S.
The operation of this circuit arrangement is based
on the fact that a correcting voltage UZ is added inductively
via the correcting transformer ~T to the input voltage U
resulting in the output voltage U'. In this arrangement, a
constant alternating voltage UK, displaced by a fixed phase
angle with respect to the voltage U, and a variable alternating
voltage UV which is connected in series with the alternating
voltage UX is connected into the circuit via the exciter
transformer ET. The phase relationship and the amplitude of
the alternating voltage UV are varied by the measuring/control
signal S. For this purpose a self-controlled inverter is used
which consists, in a manner known in itself, of the
correcting-voltage source 3, the rectifier circuit 2 and the
electronlc power circuit LE.
The advantage o~ such a circuit arrangement
consists in the fact that only the instantaneous change ~ in
phase angle needs to be controlled or regulated. Reactive
powers present over greater time intervals can be compensated
at least approximately by the exciter transformer ET with its
constant alternating voltage UK.
The circuit arrangement according to Figure 3 is
again provided with an exciter transformer ET to the primary
side of which an input voltage UXO is applied The output or
- 5 ~ r~
excitation voltage Uk at the transormer ET is fed to a bridge
circuit equipped with antiparallel-connected thyristors 4-7'.
In this bridge circuit, a correcting current IZ, which has been
formed therein and which flows through the primary winding of a
correcting transformer ZT, is commutated. The current I of a
high-tension line HT having an input voltage U flows through
the secondary winding of the correctiny transformer ZT. Due to
the inductive addition of the correcting voltage UZ the
high-tension line HL adjusts to a vo1tage U' which is
compensated in phase and amplitude. The transformer ZT is
wound in opposite directions which is also symbolized in the
varlous Figures of the drawings by means of dots at the primary
and secondary winding.
Each of the thyristors 4-7' is provided with its
own extinction circuit, known in itself, and permits continuous
adjustment of the correcting voltage UZ for any arbitrary phase
angle between the output voltage UK of the transformer ET and
the correcting current IZ.
As a variant to this arrangement, also only a single
pair of antiparallel-connected thyristors 4,4' can be provided
with their own extinction circuit, the remaining thyristors
5-7' being extinguished at the zero transition of the current.
As a further variant, the e~tinction -facilities can
be omitted at all the thyristors; current transfer then takes
place by mens of natural commutation.
In a three-phase system, Figure 4, a high-tension
line HL is provided with phases R, S, T. An exciter
transformer ET is delta-connected between these phases so that
an addition of the voltage vectors is possible in the
transverse direction. The compensated phases are designated by
R' S' T'
,
For this purpose, the phase currents IR, IS, IT
are determined by ammeters 8-10 and the voltages UST and
URS by voltmeters connected between the phases. The
resulting signals Sl (IR, IS, IT) and S2 (UST, URS) control
a previously described electronic power circuit LE
equipped with thyristor bridge circuits. At the input
-- 6
the electronic power circuit for the voltage UER is shown
which is connected with a stepped winding of the secondary
side of the exciter transformer ET. At the output of
the el.ectronic power circuit LE a correcting voltage UZR
and a correcting current IZ appear which here also, as
previously described, result in a compensa-ted phase voltage
UR' by means of inductive addition in the correcting
transformer ZT.
The remaining phases are compensated in -the same
manner. The stepping of the winding on the secondary
side of -the exci-ter transformer ET allows -the control or
regulating range required in the electronic power circuit
LE to be reduced by suitably connecting the windings
together.
The circuit arrangement according to Figure 5 shows
an exciter -transformer ET,the secondary side of which is
provided with a vernier winding which is stepped in
accordance with a power series (3 ).
The bridge circuits 14-16 are again provided with
antiparallel-connected thyristors and are fed by the
voltages UKl-UK3. The required control range in the
thyristor bridge circuit 13, equipped with extinction cir-
cuits and fed by the alternating voltage UV, can be kept
very small by means of the appropriate connection - with
25 positive and negative phase relationship depending on the
winding direction. This makes i.t possible to have a
very cost-effective solution; the correcting voltage UZ
or the correcting current IZ, respectively, can be matched
to an optimum degree to the operating conditions of energy
30 transmission facilities.
A circuit arrangement for the selective arbitrary
addition of voltages in the longitudinal, diagonal, or
transverse direction is shown in Figure 6. In this
arrangement the exciter transformer ET is again provided
35 with vernier windings stepped in accordance with a power
series. However, these windings are duplicated for
each R, S, T phase and, accordingly, allow selective con-
necting together in arbitrary vector positions in the
-- 7
subsequent electronic power circuit LE.
The electronic power circuit LE, designated by the
sub-groups L = longitudinal, Q = transverse, is designed
by means of so-called series- and parallel-triacs, this
design being known in itself (German Offenlegungsschrift
2,634,742). The control variables of the phases
are designated by x, y, z; continuous regulation is
carried out in the aforementioned rnanner.
The vector diagram of Figure 7 illustrates the
operation of the circuit arrangement of Figure 6. The
vectors and their compensation variables are labeled in
accordance with their phase designations and control
variables.
The many possible combinations for controlling
and regulating the phase angle in electric energy trans
mission equipment by means of a circuit arrangement in
accordance with Figure 6 must be optimized in accordance
with the operating conditions. For this purpose a pro-
cess computer is advantageously used.
The method according to the invention and the
device for carrying out the method are particularly economical
since even in the case where the correcting voltage has
an arbitrary phase relationship, in each case only a
single correcting transformer is switched into the high-
tension line.
List of Desi.gnati.ons
.
U = input ~oltage
U' = output voltage
UKo, UK = constant alternating voltage
UV = variable alternating voltage (~, U = variable)
UZ = correc-ting voltage
HL = high-tensi.on line
R, S, T = phases of the HL
ET = exciter transformer
ZT = correcting transformer
LE = electronic power circuit with self-con-trolled
inverter (thyristors)
~, ~' = phase angle
IZ = correcting current
L = longitudinal component
Q = transverse component
x, y, z = control variables
1 = voltage source
2 = rectifier circuit
3 = correcting-voltage source
4,4' = thyristors with extincti.on circuit
4-7' = thyristors, antiparallel-connected
8-10 = ammeter
11-12 = voltlneter
13 = thyristor br~dge circuit with extinction
circuits
14-16 = thyristor bridge circuits
~ ~ _
