Note: Descriptions are shown in the official language in which they were submitted.
~,A2 1 1 76 '~7iLE. PI~N THIS A~lcNr~
T~TRANSLATION
~lectrical energy transmission system
The invention relates to a process and a device for the
er~n~ ;rAl transmission of low-power electrical energy
over large distances.
The transmission of electrical energy over large dis-
tances takes place either on a three-phase basis or on a
single-phase basis using the customary grid frequency of
50 Hz to 60 Hz. At thesé transmission frequencies, the
inductive voltage drop on the transmission line is con-
siderable, since the inductive voltage drop is frequency-
~p~n~nt To transmit electrical energy the voltage is
selected to be appropriately high, so that as a conse-
quence of a smaller current the line losses decrease. The
transmission of high power takes place by means of a
high-voltage direct current transmission (HVDCT), whereby
the line losses are still dependent only upon the ohmic
resistance and the current flowing through.
A high-voltage direct current transmission system exhi-
bits on the input side and on the output side in each
instance a current rectifier-transformer, which trans-
forms the voltages of the connected three-phase current
grids to a magnitude corresponding to the transmission
direct voltage. By means of current rectifier systems
disposed in three-phase current bridge circuits, the
three-phase voltage is converted into a direct voltage.
A plurality of such bridges are connected in series on
the direct current side to increase the transmission
voltage and transmission power; in this case, the center
of the series circuit is in most cases grounded. At the
same time, by means of an appropriate secondary star
delta connection of the transformers, the h~ -n;r
component on the three-phase current and direct current
side is reduced as a consequence of the twelve-pulse
reaction. In certain circumstances, additional filter
circuits are also required on the direct current side.
i~21 1 7~'tq
-- 2 --
Both three-phase current grids are encumbered with an
inductive reactive power - approximately 50 to 60 % of
the active power - as a result of the commutation pro-
cesses in the current rectifier.
A direct current open air~line is more economical than a
three-phase current line of the same transmission capac-
ity, since it can be better utilized in terms of voltage
and current and moreover requires only two conductors.
This gives correspondingly fewer insulators, lighter
pylons and a smaller line width; this is of very substan-
tial importance when crossing a built-up area. ~owever,
the current rectifier stations cost considerably more
than normal transformer installations. Where ~VDCT is to
be employed, these additional costs of the station must
be balanced by the line savings; this presupposes a
minimum distance. The PC~n( ; r~l limiting distances for
a two-point connection for 800 to 2500 MW are between 500
and 1500 km. Taps on the direct current line for extract-
ing or feeding in power may be provided by parallel-
connected or series-connected int~ ~;Ate stations;
however, these have an unfavorable effect on the economy.
In energy transmission grids, not only the active power
balance but also the observance of the reactive power
balance must be taken into account by the grid operators.
While a non-compensated active power balance results in
frequency deviations, a non-compensated reactive power
balance results in voltage fluctuations. Reactive power
is generated or respectively consumed by power stations,
consumers and by the longitudinal and transverse imped-
ances of the transmission lines and transmission cables.On the one hand, the magnitude of the inductive or capa-
citive reactive power is dependent upon the voltage,
while on the other hand the active power flux also has an
effect on the reactive power balance in the transmission
grid. Capacitors which are switched in in the case of
high transmission power levels can produce the reactive
C~2i l 7~
- 2a -
power requirement of the transmission lines.
~ ~ i l 7~97
-- 3 --
Capacitors switched into the line set reduce the effec-
tive line i -~Anre and thus, at a high load current over
long lines, contribute to increasing the stability by
reducing the eranSmission angle.
As is known, isolated localities are supplied with energy
from the three-phase supply grid by means of a single-
phase transmission line; in this case, the transmission
frequency is equal to the grid frequency. A further
possibility for the supp~y of electrical energy to such
localities consists in that diesel sets are provided on
site. In the case of this possibility, however, the fuel
supply must be guaranteed. ~oth supply systems are,
however, nn~con~
The object of the invention is to specify a process and
a device for the ec~n~ l transmission of low-power
electrical energy over large distances.
According to the invention, this object is achieved in
that the energy is transmitted on a single-phase basis
and a load-dependent voltage drop of the transmission
line is appropriately compensated.
Such an energy transmission exhibits the following
advantages:
- line width lower as compared with three-phase trans-
mission,~5 - resistance on the part of the population lower on
account of inconspicuousness,
- adequate for low power levels (0.5 to 20 MM) and
large distances (50 to 300 km).
CA2i 1 76Y7
-- 4 --
In this case, the series capacitor serves to keep the
transmission voltage low. In contrast to high-power
transmission systems, in this case higher degrees of
compensation can be achieved, whereby the same voltage
and loss conditions as in the case of a high-voltage
direct current transmission system are approximately
achieved. In the case of the use of a transmission
frequency of 50 to 60 ~z, single-phase loads can be
supplied with energy without the participation of a
frequency changer. Since the power of the energy to be
transmitted is low, also only low short-circuit currents
arise in the event of a short circuit, so that the
problems encountered in the case of high-power series-
c~ ~ncated lines do not occur.
In an advantageous process, the energy is transmitted by
means of a high transmission voltage with a transmission
frequency different from zero.
Such an advantageous energy transmission exhibits the
following advantages:
20 - The inductive voltage drop becomes substantially
smaller, whereby in the case of equal energy to be
transmitted the transmission voltage can be selected
to be lower,
- in consequence of the lower transmission voltage,
the pylon height for the transmission line is
reduced, whereby low-cost pylons are used,
- a plurality of neighboring localities, which are
situated in isolated locations, can be supplied with
energy via a tie line with a plurality of taps.
A particular advantage of this energy transmission system
consists in that alternative energy sources, such as
water, wind energy and solar energy, which are converted
into electrical energy remote from consumers, can be
ec~,n( ;CA11Y transmitted.
t~A2i 1 76~7
- 5 -
In one : ~i L, the device for the tran~miCci rn of low-
power electrical energy over large distances _ c~s a
single-phase transmission line, a grid input, a capacitor
bank, which is disposed in the path of the tr~ncmicsion
line, and a control and regulating device for the control
of an appropriate ,. ~ncation. By means of this embodi-
ment, a low-power energy can be economically transmitted,
since, as a consequence of this appropriate ~ ncation
the transmission voltage can be kept low.
In a further em.bodiment of the device, a three-phase load
is connected by means of a frequency changer to the
transmission line. As a result of this, it is possible to
supply even three-phase loads econ~ 'r~l ly with low-power
energy over large distances, by means of a single-phase
transmission line; in this case, the frequency changer is
advantageously linked to the transmission line by means
of a transformer. By means of the potential-separated
attachment of the frequency changer to the transmission
line, the frequency changer does not need to be designed
for the high transmission voltage, whereby the costs of
this frequency changer can be kept low. To generate the
consumer frequency, known current converter circuits, for
example a pulsed frequency changer, are provided.
For the further explanation of the invention, reference
is made to the drawing, in which two ' ';-~rts of the
device according to the invention for the transmission of
low-power electrical energy over large distances are
diagram.matically illustrated.
Figure 1 shows a first : 'o~;r t of the device accord-
ing to the invention and in
CA~ 7
-- 6 --
Figure 2 there is shown a second '_';~-nt of the
device in greater detail.
Figure 1 shows an energy transmisSion system according to
the invention, which system comprises a grid input 2, a
capacitor bank 4 with an associated control and regu-
lating device 6 and a single-phase transmission line 8.
Moreover, there is further provided a grid protection
device 10, comprising a power switch 12, a current pickup
device 14 and a protective device 16. The capacitor bank
4 is disposed in the path of the single-phase trans-
mission line 8. This capacitor bank 4 can also be accom-
modated in a transmitting switching station. This
capacitor bank 4 can be switched in or out as a whole or
in a plurality of partial capacitors (segments) in
series. Such a capacitor bank 4 comprises a plurality of
series capacitors, in parallel with which in each
instance a surge voltage arrester is electrically con-
nected. A parallel circuit comprising a bypass power
switch and usually a spark gap is electrically connected
in parallel with the surge voltage arrester. Moreover,
each segment is provided with an attenuation element
(choke). Such an equivalent circuit can be inferred from
the article "Geregelte Parallel- und R.~; h_nkl , C~A~tion
[Regulated Parallel and Series Compensation]" by G.~.
Thumm and P. Walther, printed in the journal "Elektrie",
13erlin 45, 1991, No. 3, pages 88 to 90. The switching in
and switching out of the capacitors of the capacitor bank
4 takes place by means of a control, regulating and
monitoring device 6 in that in each instance a parallel
power switch, or an electronic switch, for example a
thyristor, is opened and respectively closed. A further
improvement is possible by means of a stepless, regulated
_ ~n~ation. A known possibility consists in connecting
a suitably dimensioned choke in series with the thyristor
switch. Such a circuit is printed for example in Christl
et al. "Advanced Series Compensation with variable
T -~AnAe~/ '~PRI Nov. 90 in Eigure 3.
~2i 1 16~-l
,
The protection of each capacitor of the capacitor
bank 4 in the event of a grid short circuit is guaranteed
by the parallel arresters, by the triggerable spark gap
and/or by the parallel power switch. Moreover, the
capacitor bank 4 is protected by means of the grid
protection device 10, for example in the case of a grid
short circuit.
A medium-voltage grid can be provided as grid input 2.
Moreover, it is possible to use alternative energy
sources, such as water, wind energy and solar energy,
which are available remote from consumers, as grid
input 2. Thus, alternative energy can be used economic-
ally for supply to remote consumers; in this case, this
energy is transmitted economically by this transmission
system. The frequency of the grid input 2 is 50 to 60 Hz,
but can also be substantially lower, but different from
zero Hz. ~y reducing the transmission frequency, the
voltage drop of the transmission line 8 is reduced,
whereby the same energy can be transmitted with a low
transmission voltage.
The length of the transmission line 8 in the case of this
energy transmission system according to the invention is
between a few kilometers and a few hundred kilometers and
the energy which is to be transmitted is approximately
0.5 to 20 MW. Since the effective line impedance can be
to a large extent compensated, the same voltage and loss
conditions as in the case of a high-voltage direct
current transmission system are achieved. In this case,
the series capacitor 4, in contrast to the known use,
serves rather to keep the transmission voltage low, so
that the initially recited advantages are achieved.
l,~2~ 1 i6~1 8 -
Figure 2 shows a further '-~; nt of the device accord-
ing to the invention, in which identical elements bear
identical reference symbols. In this ~-~i nt~ a
single-phase load 18 and a three-phase load 20 are
connected to the end of the transmission line 8. Since
the voltage value of the single-phase load 18 is
different from the value of the transmission voltage, for
the potential-isolating coupling of the load 18 use is
made of a transformer 22. The three-phase load 20 is
likewise coupled via a transformer 24 to the transmission
line 8; in this case, a frequency changer 26 is provided
between transformer 24 and load 20. }3y means of this
frequency changer 26, for example a pulsed frequency
changer, a three-phase supply voltage at 50 to 60 hz is
obtained from a single-phase grid voltage at 50 to 60 ~z.
1ikewise, the frequency changer 26 can be used, in the
case of the use of a far lower transmission frequency
than 50 ~z, to generate from this transmission frequency
in turn a customary consumer frequency of 50 to 60 hz. As
a result of the use of the transformer 24, the frequency
changer 26 does not need to be designed for the high
transmission voltage, whereby the economy of the trans-
mission system is considerably increased.
As can be inferred from Figure 2, the three-phase load 20
is supplied with electrical power by means of a tap 28
from the transmission line 8. As compared with a high-
voltage direct current transmission device, in the case
of this transmission system taps 28 on the transmission
line 8 can be realized for the extraction or feeding in
of power, without in this case unfavorably influencing
the economy.
In this ~ -'i t, a three-phase high-voltage supply is
provided as grid input 2. The value of this three-phase
high voltage is step-down-transformed by means of an
input transformer 30 to the value of the single-phase
~A~l 176~7 9
transmission voltage. As a result of this, this trans-
mission system can be connected to any voltage level,
without the economy being unfavorably influenced.
3y means of this transmission system, remote localities
can be supplied with low-power electrical energy economi-
cally over a large distance by means of a single-phase
tie line.
