Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to an AC-DC or DC-AC electric power con-
verting station (hereinbelow called DC converting station) in a DC transmis-
sion system, and more particularly to a sealed DC converting station in which
each constructional unit or element i5 arranged so as to be conveniently
maintained and inspected or exchanged in case of a fault.
Recently, a DC power transmitting system having many characteristic
features superior to an AC power transmitting system has been put to practical
use. In the DC power transmitting system, indoor-type, air-insulated and air-
cooled controlled semiconductor switching elements, for example, thyristors,
are utilized as one of the most important units of a power convcrting station,
with the thyristors and the controlling units thereof being installed indoors
in many cases. In the meantime, oil-cooled and oil-insulated-type thyristors
have been developed and used commercially in accordance with the requirements
for units having large capacities and operating at high voltages. However,
units and elements in a converting station, such as thyristors, DC transformers,
DC potential transformers, a reactors, arresters, and disconnecting switches,
are connected to each other through bus bars supported by insulators in the
air or through bushings.
On the other hand, a compact power converting station air tightly
sealed and insulated with sulfur hexa-fluoride ~SF6) gas has been built for
use as a converting station in an AC power transmitting system to overcome
problems such as air pollution, public ha~ards, earthquakes and the lack of a
sufficiently large site to accommodate the station. For many of the same
reasons, SF6 gas insulation is also strongly desired in DC converting
stations for insulating the air-insulated parts of bushings and supporting
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insulators. Particularly, as to air pollutions, since the DC flashover
voltage (~ under contaminated conditions is lower than the AC ~lashover
voltage (~ under similar contaminated condition, as shown in Figure 1, the
problem of air pollution determines that whether DC power transmission is
practicable or not.
In the AC converting sta~ion, the constructional units or elements
are arranged about circuit interrupters which are the most important elements
for the station and need periodical inspection and maintsnance. For this
reason, the circuit interruptors are constructed to be compact. Likewise, in
the DC converting station too, it is important to arrange units or elements
by taking into consideration the location of the thyristors which are the
most important units in this station, requiring periodic inspection and
maintenance. In the DC converting station, since DC bus bars and AC three
phase bus bars are used and since a plurality of thyristors are connected in
series to obtain a high voltage, the arrangement or location of these bus
bars and units are naturally different from that of the AC converting station.
SUMMARY OF THE INVENTION
Accordingly, a principle object of this invention is to provide a
sealed DC electric power converting station in which constructional units or
elements are connected through SF6 gas insulated condui~-type bus bars, with
each unit or element being arranged so that the thyristors can be maintained
and inspected periodically or exchanged easily.
According to this invention, there is provided a sealed DC power
converting station which comprises a bus bar group including at least one gas
insulated conduit three phase AC bus bar, a gas insulated conduit first DC
bus bar, and a second DC bus bar, the bus bar group being disposed at a
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- central portion of said station; a first group of sealed controlled semi-
conductor switching units disposed on one side of the bus bar group and a
second group of sealed controlled semiconductor switching units disposed on
the other side of said bus bar group opposite the first group of switching
units, the first and second group of switching units being connected to the
bus bar group through disconnectable gas insulated connection ducts; a sealed
smoothing reactor adapted to be connected in series with a DC transmission
line, the reactor being connected to the first DC bus bar through a dis-
connectable gas insulated connection duct; and, an arrestor provided for
each of said gas insulated connection ducts.
BRIEF DESCRIPTION OF THE DRAWINGS
This and other objects of the invention will ~ecome apparent by
reference to the following detailed description taken in conjunction with the
accompanying drawings, in which:
Figure 1 shows a graph representing AC flashover voltage
characteristics b under contaminated conditions and DC flashover voltage
characteristics a under contaminated conditions;
Figure 2 shows a main circuit connection on the positive side of a
DC converting station;
Figure 3 is a circuit connection according to this invention which
corresponds to Figure 2;
Figure 4 shows a plan view of an arrangement of the units of the DC
converting station according to this invention;
Figure 5 is a view taken along the line V-V in Figure 4; and
Figure 6 is a view taken along the line VI-VI in Figure 4.
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~C171706
- DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the accompanying drawings, par~icularly to Figure 2
showing the main circuit on the positive side of a typical DC power convert-
ing station, two thyristor converters TVGl and TVG2 respectively energized
by transformers TRl and TR2, not shown, are connected in series. When the
output of the power converting station is ~250 kV, +125 kV is assigned for
thyristor group TVGl and +125 kV for thyristor group TVG2. The thyristor
groups TVGl and TVG2 include respectively thyristors Vl through V6 and V7
through V12. There are also provided arresters LAl through LA12 for pro-
tecting the thyristors Vl through V12, respectively, against overvoltage,
and a smoothing reactor DCR, and arresters LA13 and LA14 respectively at the
input and output ends of the reactor DCR. DCL designates a line for trans-
mitting the output of ~250 kV, and DSl designates a disconnecting switch.
Regarding the negative side, the main circuit of the DC converting
station is connected in the same manner as described above regarding the pos-
itive side except that the polarity of the thyristors is reversed.
Figure 3 shows a circuit connection diagram of the units shown in
Figure 2 and connected according to this invention, in which three phase bus
bars 3~ BUSl and 30 BUS2 connected respectively to the transformers TRl and
TR2 are shown and aligned in the central portion of the drawing. On both
sides of the three phase bus bar 3d BUSl thyristors Vl, V3, V5, and V2, V4,
V6 of the thyristor group TVGl are disposed and on both sides of the three
phase bus bar 3d BUS2 thyristors V7, V9, Vll and V8, V10, V12 of the thyristor
group TVG2 are located. These three phase bus bars 3~ BUSl and 3d BUS2 are
connected to a phase rotation bus bar, not shown, at two points thereby
enabling easy connection of these three phase bus bars to the thyristors of
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both groups. A DC bus bar 1~ BUSl on the positive side of the thyristor
group TVGl, a DC bus ba~ 1~ BUS3 on the negative side of the thyristor ~roup
TVG2, and a DC bus bar 1~ BUS2 extending commonly on the negative side of
TVGl and on the positive side of TVG2 are all linearly arranged respectively
along the three phase bus bar 3~ BUSl, along the three phase bus bar 3~ BUS2
and along the three phase bus bars 3~ BUSl and 3~ BUS2. A DC power trans-
mission line DCl is derived from the end of the DC bus bar 10 BUS3 adjacent
the thyristor group TVG2 through the smoothing reactor DGR, and the DC bus
bar 1~ BUSl is connected to the negative side of group TVGl through the
disconnecting switch DSl. LAl through LA12, LA13 and LA14 are all arresters.
A concrete connection of the converting station described above is
shown in Figures 4, 5 and 6. Bus bars 3~ BUSl, 3~ BUS2, 1~ BUS2 and 1~ BUS3
are shown as SF6 gas insulated conduit-type bus bars, which are supported by
a supporting frame 11 substantially horizontally with respect to the ground.
The bus bars 3~ BUSl and 3~ BUS2 are disposed at the lower level and DC bus
bars 1~ BUS2 and 1~ BUS2 and 1~ BUS3 are at ~he upper level. The bus bars
3~ BUSl and 3~ BUS2 are not connected to each other electrically, but their
ducts are communicated with each other. From the portion near the center of
the ducts three phase cables 3~ CBl and 3~ CB2 are fed out in an air-tight
manner for connection with the transformers TRl and TR2 respectively. The
DG bus bar 1~ BUSl is insulated by air, as will be described in detail herein-
below.
The thyristors Vl through V12 disposed on the both sides of the bus
bars are formed as oil-insulated and oil-cooled sealed unit structures provided
with wheels so that each unit may be movable on rails 12 laid on the ground.
The smoothing reactor DCR is also formed as a sealed unit provided with wheels
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which can be moved on the rails 12.
The all conduit-type bus bars and the units of thyristors, as well
as the smoothing reactor un~t DCR are connected mutually by SF6 gas insulated
connection ducts 13, in a manner such that short branch ducts 14 and 15 are
attached to the connecting parts of respective bus bars and the connecting
surfaces of thyristor units Vl through V12 and the smoothing reactor DCR,
respectively, and the connection ducts 13 are connected to these short branch
ducts 14 and 15 through flexible pipes 16 and 17. As shown in Figure 6, on
the output side of the reactor DCR there is also provided a short branch duct
18 which is connected through flexible pipe 19 and connection duct 20 to a
bushing Bg at the end of the power transmission line DCL. The protective
arresters LAl through LAl2 are incorporated into the connection ducts 13 and
20 and sealed thereto. The units of the thyristors Vl through V12, the smooth-
ing reactor DCR, and the arresters LAl through LA14 are separated from the
co~duit-type bus bars by interposing the flexible pipes 16, 17 and 19 there-
between. The DC bus bar 1~ BUSl on the positive side of the thyristor group
TVGl is, as mentioned above, insulated by bushings 21 mounted on the connection
ducts 13 of the thyristors V2, V4 and V6, and is connected to the disconnect-
ing switch DSl having a grounded terminal.
The power converting station provided with negative thyristors may
also be built as a sealed type station as mentioned above.
Generally since the DC bus bar 1~ BUSl is grounded through the dis-
conne~ting switch DSl, it is shown as being insulated by the atmosphere, but
it may be formed as a sealed bus bar when the station is operated with the
reverse polality. In such case, the DC bus bar ld BUS2 should be grounded
through a switch. When either one of the thyristor groups TVGl or TVG2,
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1071706
becomes inoperative, the power transmission may be made with one half the
voltage of the rated voltage by short circuiting the faulty thyristor group.
To this end a sealed switch may be arranged between the bus bars 1~ BUSl
and 1~ BUS2 or between 1~ BUS2 and 1~ BUS3.
According to this invention, as is clear from the foregoing, three-
phase AC bus bars and DC bus bars are located as gas insulated linear conduit-
type bus bars, with sealed thyristor units disposed on both sides, i.e.,
positive and negative sides, of these bus bars, with the thyristor units being
further separably connected to the bus bars through gas insulated connection
ducts incorporating arresters, respectively. Therefore, the periodic
inspection and maintenance of the thyristor units which are the most important
units of a power converting station can easily be performed and in the case
of a fault these units can easily be exchanged with spare thyristors. Further-
more, the transformers and one group of thyristor units are connected by one
sealed-type three phase bus bar and two sealed-type DC bus bars, and one of
these two DC bus bars can be commonly used in the case where a plurality of
groups of the thyristor units are arranged, so that the space for installing
the station can be drastically reduced.
It is to be understood by those skilled in the art that the fore-
going description refers to a preferred embodiment of this invention and that
various modifications and changes may be made without departing from the
scope and spirit of the invention as defined in the appended claims.
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