HK1214891B - Converter station with diode rectifier - Google Patents

Description

Converter station with diode rectifier

Technical Field

The invention relates to a converter station for transmitting electric power, comprising: a current transformer having a DC voltage connection end and an AC voltage connection end; and at least one transformer connected to the ac voltage connection, wherein the transformer and the converter are arranged in an insulating material.

Background

Such converter stations are known, for example, from "Windpower plant control for the connection to multinational HVDC links" by s.bernal-Perez et al, IEEE,2012, page 2873. There, a device is disclosed in which a diode rectifier is connected on the dc voltage side to a dc voltage intermediate circuit. The direct voltage intermediate circuit extends between two voltage source converters, also referred to in english as "Voltage Source Converters (VSCs)". The diode rectifier is connected with the wind power plant through a transformer and an alternating current power grid. Furthermore, a filter unit arranged on the alternating voltage side of the converter is disclosed. On the dc voltage side, smoothing chokes are used to smooth the dc current generated by the diode rectifier.

From DE 2316327 a, a converter station is known which has a thyristor rectifier arranged in an oil-filled encapsulation housing.

The connection of a wind farm located in the sea to a land-side power supply system can be carried out economically only by means of direct current at great transmission distances. For this reason, in practice, converters are nowadays mounted on offshore platforms which are set up in the vicinity of wind farms in the ocean. The marine converter is connected to the wind farm via an ac power grid, wherein a dc voltage connection extends from a dc voltage connection of the converter to the land-side converter. These converters enable bidirectional power transfer. For starting the wind farm, a dc network is generated by a converter on the sea side, wherein the power supply required for this purpose can be drawn from a supply network on the land side. The wind turbines of the wind farm can thus be easily synchronized with the existing ac power grid. When the wind is strong, the desired reversal of the power flow, i.e. the transfer of power from the wind farm to the land-side supply grid, takes place. Nowadays, voltage source and self-commutated converters (VSCs) and, in particular, multilevel converters are used as converters. However, the installation of such converters in the sea is costly due to the always still large weight of the converters.

It has therefore been proposed to use diode rectifiers on the sea side instead of self-commutated converters, which have only passive power semiconductors in the form of diodes. Such diode rectifiers, though, can only achieve power transfer in one direction. It has the advantage that losses and weight are significantly reduced compared to self-commutated converters. Furthermore, compact power semiconductors can be used.

Diode rectifiers provide a fixed switching relationship between the dc and ac voltages at their terminals. Furthermore, diode rectifiers generate harmonics not only on their ac voltage side but also on their dc voltage side. For this reason, a transformer of the type mentioned at the outset is necessarily required. This component makes the converter station mentioned at the outset heavier and more space-consuming, which results in high manufacturing costs, in particular when used on the sea.

Disclosure of Invention

It is therefore an object of the invention to provide a converter station of the type mentioned at the outset which is as compact as possible.

This object is achieved within the scope of the invention by providing at least one encapsulation housing in which at least one part of the current transformer and at least one part of the transformer are jointly arranged, wherein the joint encapsulation housing is filled with an insulating material.

According to the invention, not only the transformer but also the current transformer is arranged in the insulating material. The term insulation material shall in the scope of the present invention include all gases, fluids and solids having improved insulation properties with respect to ambient air. Due to the improved insulation properties, the individual components of the current transformer which are at unequal potentials can be arranged at a smaller distance from one another without causing a voltage breakdown. The current transformer is also arranged in the insulating material within the scope of the invention. The insulating material needs to be removed only for maintenance. For this purpose, for example, the encapsulation housing, in which the current transformer is arranged, is provided with an inlet and outlet device, via which the insulating material can be tapped or filled. A converter station according to the invention can have, for example, a converter which forms a 6-pulse bridge with its current or voltage valves. One of the dc voltage terminals of the 6-pulse bridge is connected, for example, to ground potential. The other dc voltage terminal is then connected to the land-side converter, for example, via a unipolar dc voltage connection. It is also possible to build a 12-pulse bridge known from high voltage direct current transmission. The 12-pulse bridge has two 6-pulse bridges which are connected in series on the dc voltage side. Its connection point is usually at ground potential. Each 12-pulse bridge is connected to the ac power grid via a separate transformer. The windings of the two transformers are connected differently from each other, so that different phase shifts are achieved on the transformers. Of course, the converter station can also have two 6-pulse bridges, one terminal of which is at ground potential.

According to the invention, at least one encapsulation housing is provided, in which at least one part of the converter and at least one part of the transformer are jointly arranged. Both members are arranged in the same insulating material. In this housing, a connection network of the converter, if present, is of course also provided. The package housing is suitably at ground potential.

When using a converter station for a wind farm connection, it can be advantageous if the transformer and the converter are arranged on different bases.

Advantageously, at least one smoothing choke is provided at the dc voltage connection of the converter. The smoothing choke suppresses harmonics on the direct voltage side and thus serves to smooth the direct current.

Advantageously, at least a part of the smoothing choke is arranged in the encapsulation housing. Thus, the current transformer, the transformer and the smoothing choke are arranged in the same insulating material.

According to one advantageous embodiment of the invention, the converter and the transformer and, if necessary, the smoothing choke are each arranged in a housing, wherein the housing are connected to one another. In this way, these components can be electrically connected to one another without the use of complex feedthroughs that switch conductors at high voltage potential from one insulation environment to another or to the ambient air. The encapsulation of the components of the converter station, which is usually located on earth potential, also protects these components from external environmental influences, which can cause damage, in particular when the converter station is set up in the sea or in a lake.

The insulating material can in principle be a gas, a fluid or a solid. Suitably, a protective gas known in energy transmission and distribution, such as sulphur fluoride or the like, is used. However, it is particularly advantageous to use a fluid, for example a suitable insulating oil, as the insulating material. The oil provides cooling in addition to insulation. Furthermore, it is suitable within the scope of the invention to provide a coolant for cooling the insulating material. The coolant is arranged in or beside the encapsulation housing.

Suitably, the converter is a thyristor rectifier or a diode rectifier. In particular, it is advantageous in the context of the invention if the converter is a diode rectifier. Diode rectifiers have only passive, i.e. uncontrollable, power semiconductors, which are lightweight and cause little losses.

Suitably, the converter has a plurality of sub-converters with dc voltage sides connected in series or in parallel. By means of these sub-converters, the converters can be simply scaled and can then be easily adapted to the respectively present current or voltage requirements. In this case, it is also particularly advantageous within the scope of the invention if the subconverters are subcoded diodes, each of which is formed exclusively by an uncontrollable power semiconductor in the form of a diode.

According to a suitable embodiment, each sub-converter is connected to a sub-transformer on the ac voltage side, the sub-converter and the sub-transformer being arranged in a common sub-encapsulation housing. According to this advantageous embodiment, components corresponding to branches (Strang) of a wind farm to which a plurality of wind turbines are connected can be produced, for example. The sub-enclosure can stand in the ocean in a simple type and manner, for example in a manner on the basis of a wind turbine. The converter stations can thus be arranged distributed in the sea or lake, whereby the set-up and thus the costs can be further simplified.

Advantageously, a sub-smoothing choke is arranged in the sub-encapsulation housing. The sub smoothing choke is connected to the sub converter on the dc voltage side. In this case, the subconverter is expediently a subcodeboctor rectifier.

Each subconverter expediently has two dc voltage terminals, which can be bridged by means of a jumper switch. According to this advantageous embodiment, for example in the event of a fault, a sub-converter station, for example comprising a sub-diode rectifier, a sub-transformer and a sub-smoothing choke, is connected across. If the sub-converter station is connected to a section of the wind farm, for example to a branch of the wind farm, this section can also be bridged in this way. This is advantageous because faults can occur not only in the respective component, but also in a branch or branch of the ac power network connected to the component.

Expediently, a filter unit is provided on the ac voltage side of the converter. The filter unit serves for reactive power compensation and for filtering out harmonics of the fundamental wave formed in the normal operation of the diode rectifier. The filter unit may also comprise or consist solely of a wind turbine.

Suitably, a power supply device is provided for supplying power to an ac power grid connected to the converter station. The power supply device satisfies the condition that the converter constructed as a diode rectifier only allows power flow in one direction. In the case of a wind farm connection, to which the converter station according to the invention is particularly suitable, it is generally necessary to supply the ac power grid connected to the converter station with electrical power. By means of this electrical energy, for example, the wind turbines of a wind farm can be adjusted and the rotor blades can be adjusted to the respective desired angle. The power supply device comprises, for example, a diesel engine, which drives a generator, wherein the generator generates the required electrical power, which is fed into an ac power grid connected to the wind farm.

Advantageously, however, the power supply is designed such that the diesel engine can be dispensed with, since it is a heavy maintenance task and always needs to be supplied with diesel fuel. In particular, when the converter station according to the invention is set up on the sea side, it is difficult to supply fuel in wind and humid conditions. For this reason, it is expedient in the scope of the invention to provide a power supply device which can be used to feed from a land-side power supply grid or a nearby sea-side alternating current grid. Such a power supply device comprises a power supply line extending at least partly in water, which is for example an alternating voltage line having a voltage in the range of 50 to 70 kV.

According to a different embodiment of the invention, the power supply device comprises a sub-converter which is connected on the direct voltage side in series with a sub-diode rectifier of the diode rectifier. With the aid of the sub-converters, it is possible for the dc voltage connection for connecting the converter station to the land-side supply network also to be used for providing a power flow in the opposite direction, i.e. from land to the wind farm. It is naturally expedient here for the sub-diode rectifier, as mentioned above, to be equipped with a jumper switch, by means of which a jumper across the sub-diode rectifier in the series circuit can be realized, so that power can be supplied from the converter on the land side via the direct-voltage connection and converted into an alternating voltage with the sub-converter. The ac voltage thus generated is then used to supply the connected wind farm.

Suitably, the transformer is connected to the distribution equipment. The electrical distribution system is, for example, a gas-insulated electrical distribution system, wherein a feedthrough is provided between the electrical distribution system and, for example, a transformer arranged in oil. As already mentioned above, a plurality of transformers can also be used within the scope of the invention. This also applies to electrical distribution equipment.

The power distribution device can be connected via an ac voltage line to a coupling-in element, which is connected to a land-side power supply system or a sea-side power supply system.

Drawings

Further expedient developments and advantages of the invention are the subject matter of the following description of the embodiments with reference to the drawing, wherein the same reference numerals refer to members acting in the same way, and wherein

Figure 1 shows an embodiment of a converter station according to the invention,

figure 1a shows a detailed view of a diode rectifier according to figure 1,

fig. 2 shows another embodiment of a converter station according to the invention, which connects a wind farm arranged on the sea side with land-side converters,

fig. 3 shows an embodiment of a sub-converter station, with a sub-diode rectifier, a sub-smoothing choke and a sub-transformer in a common encapsulating housing,

fig. 4 shows an embodiment of a sub-converter with a sub-transformer, an

Fig. 5 schematically shows a sub-converter station according to fig. 3 in a side view.

Detailed Description

Fig. 1 shows an embodiment of a converter station 1 according to the invention with a diode rectifier 2 arranged in an encapsulating housing 3 filled with insulating material. The insulating material is in the embodiment shown in fig. 1 insulating oil. Furthermore, the converter station 1 comprises a transformer 4 having a primary winding 5 and a secondary winding 6 inductively coupled to each other. The transformer 4 is arranged in an encapsulating housing 7 filled with the same insulating oil. For the purpose of passing the phase conductors connected on the ac voltage side between the transformer 4 and the converter 2, a hollow-cylindrical conveying line 8 is used, which is likewise filled with insulating oil. The encapsulation housing 3,7 is at ground potential.

The converter station 1 also has two smoothing chokes 9 which are each connected to two dc voltage connections of the diode rectifier 2. Each smoothing choke 9 is arranged in a separate encapsulating housing 10 which is likewise filled with said insulating oil and which is on earth potential. The supply line 8 is in turn used to feed a dc voltage line between the smoothing choke 9 and the respective dc voltage connection of the diode rectifier 2. A mechanical switch 11 is also provided which can be used to connect the converter station 1 to a dc voltage connection 13 having two dc voltage poles 14 and 15. The transformer 4 is connected via an ac voltage conductor 16 to a switching device 17 having a plurality of three-pole switches, which is realized as a gas-insulated high-voltage switching device 17. One of the switches of the power distribution system 17 is connected to an ac voltage line 18, which is connected as part of a power supply to a coupling-in means for feeding power to the land side of the ac voltage line 18. The coupling-in means is for example a transformer. The power distribution system 17 is connected to different branches 22 of the ac voltage network, wherein a plurality of wind turbines is connected to each branch 22. Since only electrical energy can be transmitted from the wind farm to land by means of the diode rectifier 2, energy transmission in the other direction must take place via the ac voltage line 18. The ac voltage line 18 for this purpose suitably has an ac voltage of between 50 and 70 kV.

As can be seen from fig. 1, the transformer 4, the diode rectifier 2 and the smoothing choke 9 are arranged in the same insulating medium or insulating material, here in oil, so that the converter station 1 can be constructed compactly. The package housings 3,7,10 are all connected to each other. Instead of a cumbersome lead-through, it is possible within the scope of the invention to use a conveying pipe 8 which is likewise filled with insulating oil and through which the respective high-voltage conductor extends in the middle of the conveying pipe.

The structure of the diode rectifier 2 is shown in more detail in fig. 1 a. It can be seen that the diode rectifier 2 has three phase modules 19, the number of which corresponds to the number of phases of the ac power network connected to the transformer 4. Each phase module 19 has two dc voltage connections or terminals, which are polarized in opposite directions to one another and are marked with positive and negative signs. Furthermore, each phase module 19 has an ac voltage connection 20. Between the ac voltage connection 20 and each dc voltage connection, a diode valve 21 extends, so that each phase module 19 has two diode valves 21. The diode valve 21 comprises a series circuit of diodes, the number of which depends on the voltages present, respectively. A smoothing choke 9 is shown schematically and without an encapsulating housing on the direct voltage side of the diode rectifier.

The diode rectifier shown in fig. 1a is designed as a so-called 6-pulse bridge, which is known to the person skilled in the art of high-voltage direct current transmission. It is to be noted here, however, that the diode rectifier 2 may also have two such 6-pulse bridges which are connected to one another on the dc voltage side and to the same or different sections or branches 22 of the ac power supply system via different transformers. The transformer causes a phase shift of the alternating voltage transmitted by it, providing a 12-pulse bridge, also known per se. The connecting lines of the two 6-pulse bridges are expediently connected to ground. Of course, each of the two 6-pulse bridges can also be connected to ground at one of its dc voltage terminals independently of the other 6-pulse bridge. Even if the diode rectifier only forms a 6-pulse bridge, the 6-pulse bridge can be connected to ground potential at a dc voltage terminal, so that a so-called unipolar circuit is formed.

Fig. 2 shows a further embodiment of a converter station 1 according to the invention, which consists of sub-converter stations 29, wherein each sub-converter station 29 has a sub-transformer, not shown, and a sub-smoothing choke, also not shown. The sub-substations 29 are connected in series with one another on the direct voltage side. In addition, a subconverter 30 can be seen in the series circuit. Each sub-converter station 29 has a first direct voltage connection 31 and a second direct voltage connection 32, which can be connected to each other by means of a cross-over switch 33. Bridging of a defective sub-converter station 29 can thus be realized, for example, by means of the bridging switch 33.

The converter station 1 is arranged on an offshore platform, not shown, in the sea, approximately 100km from the shore 34, wherein a land-side converter 35 is connected to the converter station 1 via a dc voltage connection 36. It can be seen that each sub-converter station 29 is connected to one branch 22 of a wind farm 37, wherein the wind farm 37 is formed by a plurality of wind turbines 38.

The wind farm 37 requires energy even in the absence of wind. This energy is then supplied to it by means of the subconverter 30. For this purpose, all the sub-diode rectifiers 29 are closed, for example by closing the respective jumper switches 33, so that the sub-converters 30 are connected directly to the land-side converter 35, which land-side converter 35 is, for example, a modular multilevel converter. The multilevel converter is connected to a supply grid, not shown, and supplies the required power to a sub-converter 30, which sub-converter 30 supplies the power to the wind farm on the ac side.

Fig. 3 shows the sub-converter station 29 in more detail. It can be seen that the sub-converter station 29 has a sub-encapsulating housing 39 in which two sub-smoothing chokes 41, one sub-diode rectifier 42 and one sub-transformer 40 are arranged jointly. The sub-package housing 39 is filled with insulating oil. Outside the sub-encapsulation housing 39, a mechanical dc switch 43 is visible, by means of which the respective pole can be connected to the jumper switch 33.

Fig. 4 shows the sub-converter 30 in more detail, which is not arranged in a separate encapsulation housing. The subconverter 30 does not have a smoothing choke on the dc voltage side. Smoothing chokes are not necessary in controlled or self-commutated subconverters. The subconverter 30 can also be bridged on the dc side by means of a jumper switch 33.

Fig. 5 shows the sub-converter station 29 in a schematic side view. It can be seen that the sub-transformer 40, the sub-smoothing choke 41 and the sub-diode rectifier 42 are arranged in a common encapsulation housing 39 filled with oil. Furthermore, a feedthrough 44 can be seen, by means of which the high-voltage line is converted from oil insulation to protective gas insulation, wherein the feedthrough extends through one or more walls of the respective encapsulation housing that are at ground potential. It can also be seen that the jumper switch 33 is likewise arranged in a packaging housing 45, which packaging housing 45 is filled with a protective gas, in this case sulfur fluoride. The lead-through 46 enables a cable connection to the housing 45 filled with protective gas.

Claims (11)

1. A converter station (1) for transmitting electric power, having: a converter (2) having a direct voltage connection and an alternating voltage connection; and at least one transformer (4) connected to the alternating voltage connection, wherein the transformer and the converter (2) are arranged in an insulating material,

wherein at least one encapsulating housing is provided in which at least a part of the current transformer (2) and at least a part of the transformer (4) are jointly arranged, wherein the joint encapsulating housing is filled with the insulating material,

characterized in that a power supply device (18,30) is provided for supplying an AC network (22) connected to a converter station arranged on the sea side with electrical power from a land-side power supply network or a nearby sea-side AC network, wherein a plurality of wind turbines are connected to different branches of the AC network connected to the converter station arranged on the sea side,

-wherein the converter (2) has a plurality of sub-diode rectifiers (42) connected in series on the direct voltage side and the supply device has a controlled or self-commutated sub-converter (30) connected in series with a sub-diode rectifier (42) on the direct voltage side, or wherein the supply device comprises a supply line in the form of an alternating voltage line (18) extending at least partially in water.

2. The converter station (1) according to claim 1, characterized in that at least one smoothing choke (9) is provided, which is connected to the direct voltage connection.

3. The converter station (1) according to claim 2, characterized in that at least a part of the smooth choke (9) is arranged in the encapsulating housing (3,7, 10).

4. The converter station (1) according to any of the preceding claims, characterized in that the insulating material is a protective gas or an insulating fluid.

5. Converter station (1) according to any of the preceding claims 1-3, characterized in that the converter is a thyristor rectifier or a diode rectifier.

6. Converter station (1) according to any of the preceding claims 1-3, characterized in that one sub-transformer (40) is connected to each sub-diode rectifier (42) on the alternating voltage side, wherein the sub-diode rectifier (42) and the sub-transformer (40) are arranged in a common sub-package housing (39).

7. The converter station (1) according to claim 6, characterized in that a sub-smoothing choke (41) is arranged in the sub-enclosure.

8. Converter station (1) according to any of the preceding claims 1-3, characterized in that each sub-diode rectifier (42) has two direct voltage terminals (31,32) which can be bridged by means of a jumper switch (33).

9. Converter station (1) according to any of the preceding claims 1-3, characterized in that a filter unit is provided at the alternating voltage side of the converter (2).

10. Converter station (1) according to any of the preceding claims 1-3, characterized in that the transformer (4) is connected to a distribution equipment (17).

11. The converter station (1) according to claim 10, characterized in that the distribution equipment (17) is connectable via an alternating voltage line (18) with a coupling-in member connected to a land-side supply network or to an ocean-side alternating current grid.