DE102017206915A1 - Apparatus and method for high power DC transmission - Google Patents

Abstract

It is a device (1) for DC transmission with a superconducting transmission line (3,3a), wherein the transmission line (3) - a vacuum-insulated sheath (13) for thermal separation of a radially inner portion (9) of the transmission line (3) of a outer environment (15) and - a plurality n superconducting conductor wires (5) which are arranged together within the vacuum-insulated sheath (13), - wherein the device (1) at least a number n of power converters (6a, 6b), wherein each of the superconducting conductor cores (5) or each group of combined conductor cores (5) is assigned at least one power converter (6a, 6b), and wherein the device (1) is configured to carry a plurality of conductor cores (5) guided together within the sheath (13) ) are supplied with a direct current from one another with the same polarity. Furthermore, a method for transmitting direct current is specified with such a device characterized by the step of feeding current of the same polarity into a plurality of conductor wires (5) of the superconducting transmission line (3) guided within the common sheath (13).

Description

The present invention relates to a DC transmission apparatus having a superconducting transmission line, the transmission line having a vacuum-insulated shell for thermally isolating a radially inner portion of the transmission line from an external environment. Furthermore, the invention relates to a method for transmitting direct current with such a device.

There is a need for transmission lines for low-loss power transmission over long distances. In the transmission of high electrical power over longer distances AC lines are increasingly unsuitable because the self-inductance of the transmission lines leads to high AC losses. For distances in excess of a few tens of kilometers, therefore, DC transmission lines are more suitable for transmitting higher electrical power with less loss. For such a DC transmission usually an available alternating current is rectified, transmitted as DC and then fed by inverter stations again into the AC grid. In particular, as a result of the increasing connected load of regeneratively generated energy far away from the consumers, the demand for such devices for the transmission of high electrical power over longer distances is increasing. In order to be able to transmit these high powers with normally conducting lines, increasingly higher voltages are used for the DC transmission according to the prior art, for example nominal voltages of 320 kV or 525 kV. A disadvantage of conventional, normally-conductive lines is their limited current-carrying capacity, which leads to the fact that in many cases several lines must be laid in parallel in order to transmit the required power. This leads to high costs and sometimes also to a high space requirement. In an embodiment as an overhead line, large distances between the individual lines must be maintained in order to avoid flashovers in between. When transmitting via wired conductors, the conductors within the cables must be isolated from the environment using sufficient voltage-resistant dielectrics. Such insulated cables are typically used as submersible submarine cables and / or subterranean cables. A disadvantage of normally-conductive transmission lines for high-voltage direct-current transmission is that the required thick dielectric insulation layers simultaneously act thermally insulating. By means of this insulating effect, combined with the heat generation by electrical losses, such transmission lines heat up strongly at higher powers, which can lead to damage of the materials, in particular of the insulating layer. The power transmitted through a transmission line is therefore often limited by the heating of the conductor.

To solve the problem of the low current carrying capacities of such DC lines, DC lines with superconducting conductor elements have been proposed, which can transport the current almost lossless and with very high current densities. However, the superconducting conductor elements in such lines must be cooled by an additional cooling device to an operating temperature below the critical temperature of the superconductor. This operating temperature may, for example, be between 4 K and 100 K, depending on the choice of superconducting material. In known superconducting transmission lines, this cooling is achieved by the transport or circulation of a fluid coolant, for example in a closed circuit, through the interior of the line. For this purpose, feed devices for feeding coolant into the interior of the conductor are provided in the end regions of the line and optionally also in the region of intermediate cooling stations. In order to be able to feed direct current into such a superconducting transmission line, this line is often connected at one end region or both end regions with suitable power converters. For example, the lead may be connected in one end region to one or more rectifiers to convert alternating current into direct current. In addition, the line may optionally be connected to one or more inverters at the opposite end region to convert the DC current transported through the line back to AC for a consumer network. In principle, such superconducting transmission lines can be designed either as single-pole lines (for the transmission of direct current of only one polarity) or as two-pole lines (for the transmission of direct current of both polarities within a line).

A fundamental advantage of superconducting transmission lines is that DC current can be transported almost lossless at high currents. Thus, high powers can advantageously be transmitted at comparatively low voltages. The problem with this variant, however, is that standard available converters are often not designed for the desired high power range. In particular, inexpensive and reliable standard components are often not designed for the high currents that could transport the superconducting transmission lines. For example, the nominal currents of standard available converters are often limited to a few kiloamps. To this problem Even when superconducting transmission lines are used, higher transmission voltages are often used than would be necessary purely on the basis of the specifications of the transmission line. In other words, due to the specifications of the power converters, DC power of a given power is partly transmitted at higher voltage and lower power than would be optimal in view of the characteristics of the superconducting transmission line. This in turn results in greater demands on the dielectrics used to avoid voltage flashovers at the higher transmission voltages. In turn, this results in a higher cost of materials in the isolation of the individual conductor elements.

The object of the invention is therefore to provide a device for DC transmission with a superconducting transmission line, which overcomes the disadvantages mentioned. In particular, a transmission device is to be specified, which is suitable for the transmission of high power, at the same time relatively low cost of materials for the conductor insulation. Another object is to provide a method of transmitting direct current with such a device. The transmission should be made possible in particular at a comparatively low voltage level.

These objects are achieved by the apparatus described in claim 1 and the method described in claim 15.

The DC transmission device according to the invention has a superconducting transmission line. This transmission line comprises a vacuum-insulated sheath for thermal separation of a radially inner portion of the transmission line from an external environment and a plurality of n superconducting conductor cores which are guided together within the vacuum-insulated sheath. The device furthermore has at least a number n of power converters, wherein each of the superconducting conductor cores - or each group of combined conductor cores - is assigned at least one power converter. Furthermore, the device is designed to act on a plurality of common conductors guided within the shell conductor with a direct current of mutually same polarity.

In other words, this is a multi-wire line, in which the individual conductor wires are arranged together in a line cryostat, wherein either each conductor core or each group of combined conductor wires is connected to at least one own power converter. In each case a plurality of such jointly thermally insulated conductor wires are assigned together to an electrical pole. In other words, a plurality of such jointly insulated conductor wires are provided for a given current flow direction. It is possible, but not essential, that all conductor wires arranged together in the cryostat are assigned the same current flow direction. If this is true, then it is a single-pole transmission line. However, it is also possible, and in connection with the present invention may be advantageous if only a subset of the present within the common shell conductor wires are assigned together a current flow direction and if a different subset of the present within the shell conductor wires are assigned to the other current flow direction , In such a case, it is therefore a two-pole transmission line.

A significant advantage of the embodiment according to the invention - regardless of whether it is a single-pole or two-pole transmission line - is that by the presence of multiple wires per pole energy transfer at high power rating is possible, while still power converters, each with a relatively low rated power or rated current can be used. On the one hand, this is made possible by the fact that overall transmission takes place at comparatively low voltage and comparatively high total current. As a result, the requirements on the dielectrics to avoid voltage flashovers are comparatively lower than would be the case with a higher transmission voltage. On the other hand, power converters with low rated currents and rated voltages can be used, since the total current to be transmitted is divided into several partial currents (in the respective conductor wires) and the conductor wires are connected individually (or in combined groups) with power converters which are each assigned separately , As a result, the rated current relevant to each individual power converter is reduced to the partial current of a conductor core (or a group of conductor wires). Overall, therefore, the device according to the invention allows a DC transmission with high total power, the requirements for the dielectric isolation of the superconducting transmission line used are comparatively low (which leads to material savings in the transmission line) and further wherein the requirements for the rated power of the respective power converters are also relatively low (which allows the use of inexpensive and reliable standard components).

The method according to the invention serves to transmit direct current with a device according to the invention. It comprises the process step of feeding current of the same polarity into a plurality of conductor cores of the superconducting transmission line disposed within the common sheath. In this case, the conductor wires can in particular be insulated from one another. The advantages of the method according to the invention arise analogously to the advantages of the device according to the invention described above.

Advantageous embodiments and further developments of the invention will become apparent from the dependent claims of claim 1 and the following description. The described embodiments of the device according to the invention and of the method according to the invention can advantageously be combined with one another.

The device preferably has a cooling device for cooling the radially inner region of the transmission line to a temperature below a transition temperature of the superconducting conductor wires by means of a fluid coolant. In this embodiment, the transmission line suitably enables a DC transmission in the superconducting state of the conductor wires. Thus, an approximately lossless current transport in the superconducting material used can be achieved. Suitably, the cooling device comprises at least one feed device for feeding coolant at an end region of the transmission line. Generally, the transmission line preferably has at least one coolant channel, which is designed to transport fluid coolant along a longitudinal direction of the transmission line and which is arranged within the common vacuum-insulated sleeve, so that the conductor wires guided therein can be effectively cooled by the coolant.

The transmission line of the device preferably has at least one such coolant channel, which jointly surrounds the superconducting conductor cores disposed within the common sheath. In this case, for example, a plurality of such conductor wires can be arranged together within such a coolant channel and thereby guided side by side. On the other hand, it is also possible that a plurality of conductor cores are arranged concentrically around each other and that at least one radially outer coolant channel surrounds these concentric conductor cores together in a ring. Optionally, further such coolant channels can also be arranged between such concentric conductor wires. It is essential in all these different variants that the conductor cores, which are thermally insulated by the common vacuum-insulated sheath, can also be cooled together by the coolant in the coolant channel surrounding them together, and thus that the expenditure on equipment for cooling the plurality of conductor cores is advantageously low. In this case, the vacuum-insulated sheath may particularly preferably limit the coolant channel surrounding the conductor cores radially outwards. In principle, however, it is also possible in the context of the present invention that each of the conductor wires is cooled individually, or that, for example, combined groups of conductor wires are each cooled separately from one another. This can in turn be done for example by coolant channels, which are each associated with such individual conductor wires or groups of conductor wires.

Preferably, the individual conductor leads routed within the common vacuum-insulated sheath are insulated from one another by means of a dielectric insulation layer such that a potential difference between the individual conductor cores of at least 3 kV can be maintained during operation of the device. Even more preferably, even a potential difference of at least 9 kV or even at least 15 kV between the individual conductor wires lie, without the risk of voltage flashovers exists. In particular, such an insulation layer should also be present between those conductor wires of a transmission line which are designed to transmit DC current of the same polarity. Even if the individual conductor wires of such an electrical pole have approximately the same voltage in a normal operation of the transmission lines, this embodiment is nevertheless useful, for example in the event of a failure of a power converter (which is assigned to a specific conductor wire or group of conductor wires) the current transport over to be able to maintain the other leader lines. In such an operating state, there is a considerable potential difference between the affected adjacent conductor wires and the electrical insulation between an active and an inactive conductor wire becomes relevant. In this embodiment, it is also possible to intentionally deactivate individual conductor cores in the case of a partial load operation of the transmission device, for example in which the (or) power converter assigned to this conductor core is / are switched off in a targeted manner. To minimize the potential difference, a deactivated conductor can, for example, high impedance to the potential of an adjacent conductor wire and / or to another, suitable for reducing the potential difference potential.

The described dielectric insulation layer should therefore be designed to electrically insulate each other from each other adjacent arranged conductor wires. The dielectric insulating layer should not necessarily be understood as a solid layer, but it may particularly preferably partially or even mainly formed by the fluid coolant become. It is only important that between the adjacent conductor wires a sufficiently dielectric for the respective voltage range dielectric is arranged in sufficient thickness.

Thus, the dielectric insulating layer may thus preferably comprise a fluid coolant. In particular, it may be formed at least in axial and / or radial portions of the transmission line majority of fluid coolant. This may be, in particular, the coolant flowing in an annular coolant channel in the longitudinal direction of the line, which is fed from one end of the line. An advantage of this embodiment is that, in the case of a voltage breakdown, the part of the insulating layer formed by the fluid coolant, unlike a solid-state dielectric, is not permanently destroyed, since this part can be replaced by an inflowing coolant. Such a design with coolant as part of the insulating layer is particularly suitable for the DC transmission in the lower voltage range and medium voltage range, so for example with voltages between 1 kV and 24 kV, since in this voltage range, for example, liquid nitrogen and liquid hydrogen are sufficiently puncture resistant. Particularly preferred is the use for the DC transmission in the voltage range between 1 kV and 9 kV.

The dielectric insulation layer may in particular be formed in majority by fluid coolant. In other words, a majority of the volume of the insulating layer may be due to fluid coolant. For example, the dielectric insulating layer may be formed substantially by the coolant-filled annular coolant channel, wherein the hollow cylindrical channel in addition to the coolant may have additional electrically insulating support elements for supporting the more inner elements of the conduit. Essential for this embodiment is that the transmission line has radially continuous axial segments and / or azimuthal segments in which the dielectric insulation layer is completely formed by fluid coolant. The optionally existing between these segments support elements may be web-like. They may be formed, for example, from stainless steel, glass fiber reinforced plastic and / or cast resin, with non-conductive materials being particularly preferred.

A significant advantage of the embodiments in which a significant proportion of the dielectric insulating layer is formed by coolant, is that compared to a pure solid insulation, a high weight saving and material savings can be achieved.

The dielectric insulating layer may also include at least one layer of paper embedded in coolant. In particular, the paper can be flowed around or flowed through by fluid coolant. The paper may advantageously be present as polypropylene-laminated paper (abbreviated PPLP), which is particularly resistant to breakdown. Such a PPLP layer consists of a laminate of a polypropylene film which is adjacent to both sides of cellulose paper. Advantageously, the dielectric insulation layer may also comprise a stack of a plurality of such papers, wherein the individual paper layers are respectively flowed around by a fluid coolant. If the dielectric insulation layer is formed by a combination of PPLP and fluid coolant, then advantageously particularly high dielectric strengths can be achieved.

The fluid coolant may be routed inside the transmission line at least on a majority part of the longitudinal extent of the conduit inside a smooth-walled tube. Under a smooth-walled tube is to be understood such a tube, which in addition to the natural production-related roughness of its surface has no regular, higher-level structure. In particular, the tube should not be formed as a corrugated pipe, at least in said majority part. By means of this embodiment, it is achieved that the flow resistance for the coolant to be transported is kept low and turbulences of the coolant are minimized. In this way, on the one hand, a sufficiently high mass flow rate of the coolant can be achieved in order to ensure the cooling capacity required over the line length, even in a low pressure range. On the other hand, heating can be kept low by associated with a turbulence mechanical friction losses. Furthermore, the thermally-effective surface is reduced in smooth-tube vacuum insulated conduits as compared to corrugated outer conduits, which in turn reduces cooling performance requirements. These features can advantageously contribute to enabling cooling of the conductor over particularly long line lengths, without the need for additional axially internal intermediate cooling stations. Particularly advantageously, the coolant channel is delimited over the entire length of the transmission line by a smooth-walled tube.

Smooth-walled coolant pipes basically have the disadvantage of lower mechanical flexibility when laying the transmission line. This disadvantage can be compensated for by arranging comparatively shorter segments with corrugated boundary tubes between individual segments with smooth-walled boundary tubes. So can still a higher Mobility of the line are made possible by bending at predetermined locations. Also, for example, caused by thermal expansion or shrinkage length compensation of the line, the arrangement of such segments with corrugated coolant tubes may be advantageous. The turbulence in these corrugated segments can still be kept low, that a corrugated ausgestaltetes outer coolant tube is lined with an inserted smooth pipe section, so that in the interior of this smooth pipe section flowing coolant in turn undergoes only a slight turbulence.

As an alternative to the previously described embodiments with substantially smooth tubes, however, it is basically also possible to design the coolant tube as a corrugated tube. An advantage of this alternative embodiment is that such a corrugated pipe can be easily positioned around the conductor wires by its greater flexibility.

In principle, the previously described (smooth and / or corrugated) coolant tubes can each be the common vacuum-insulated casing of the superconducting transmission line.

The dielectric insulating layer may advantageously have a dielectric strength of at least 20 kV / mm. Thus, it can be designed so that it is resistant to breakdown, so that the device enables a direct current transmission at voltages above 1 kV and at the same time advantageously low thickness of the dielectric insulation layer between adjacent conductor wires. This thickness of the insulating layer may be, for example, between 1 mm and 10 mm.

The superconducting conductor wires can advantageously comprise conductor elements with a high-temperature superconducting material. High-temperature superconductors (HTS) are superconducting materials with a transition temperature above 25 K and in some classes of materials, such as cuprate superconductors, above 77 K, where the operating temperature can be reached by cooling with cryogenic materials other than liquid helium. HTS materials are also particularly attractive because these materials can have very high critical current densities, depending on the choice of operating temperature.

In particular, the high temperature superconducting material may comprise magnesium diboride. The conductor elements can particularly advantageously comprise magnesium diboride as the main constituent or even consist essentially of magnesium diboride. Magnesium diboride has a transition temperature of about 39 K and is thus considered a high-temperature superconductor, but the transition temperature is rather low compared to other HTS materials. The advantages of this material compared to oxide-ceramic high-temperature superconductors lie in its easy and thus inexpensive manufacturability. Magnesium diboride based conductors can be prepared particularly simply and favorably by aerosol deposition or by the so-called powder-in-tube process.

Alternatively or additionally, however, the conductor elements may also comprise other high-temperature superconducting materials, for example HTS materials of the second generation, ie compounds of the REBa ₂ Cu ₃ O _{x type} (REBCO for short), where RE stands for a rare-earth element or a mixture of such elements , Due to their high transition temperatures, REBCO superconductors can also be cooled with liquid nitrogen and, especially at temperatures lower than 77 K, have a particularly high current carrying capacity.

Other advantageous materials are HTS materials of the first generation, for example the different variants of bismuth strontium calcium copper oxide. Alternatively, superconducting pnictides can also be used. Due to their rather low transition temperature superconducting Pnictide come for an operating temperature of about 20 to 30 K in question.

In a preferred embodiment, the superconducting conductor wires may be arranged concentrically with each other. They may then, for example, together be surrounded radially by an annular coolant channel which extends between the concentric conductor wires on the one hand and the vacuum-insulated sleeve on the other hand. Alternatively or additionally, one or more coolant channels may be arranged radially between the individual conductor wires and / or within the innermost conductor wire. In the embodiment with annular coolant channels between the individual concentric conductor wires, these can in turn be designed such that the fluid coolant flowing in them forms a substantial part of the dielectric material which mutually insulates the conductor wires. Alternatively or in addition to such a coolant dielectric between the individual conductor wires, however, it is also possible in principle for a solid dielectric to be present between the concentric conductor cores.

The concentric superconducting conductor wires can preferably be arranged on a common rod-shaped carrier. Such a carrier may be formed for example as a solid core or as a tube for the transport of coolant. As a carrier material is particularly suitable metallic material, especially copper or a copper-containing alloy.

As an alternative to the embodiments with concentric conductor wires, the individual superconducting conductor wires can be arranged next to one another within the common sleeve. In this case, in particular, the individual conductor wires each have one or more conductor elements, which are each arranged on a core. In particular, each of these conductor elements may be band-shaped conductor elements. Again, the core may in particular be a metallic core, preferably a copper-containing core. Again, this core can be designed either as a solid rod or pipe (in particular for the transport of coolant).

In the variant embodiment with conductor leads routed side by side, they can generally be arranged either together on a common core or in each case on separate cores. There may also be a plurality of such cores, wherein in each case a plurality of superconducting conductor elements are arranged grouped on a common core. In principle, these individual superconducting conductor elements may belong either to a common conductor core or to separate conductor cores (whereby they should then be suitably sufficiently resistant to breakdown with respect to one another).

In the arrangement of several, in particular band-shaped, conductor elements on a common core, it is also possible in principle for a plurality of such conductor elements to be stacked one above the other. Alternatively or additionally, a plurality of such conductor elements may be helically wound around a common core next to each other. The juxtaposed spiral windings can optionally be insulated from one another by a corresponding dielectric insulation layer. Again, this dielectric insulating layer can again be formed mainly by the coolant or it may be a solid dielectric in the spaces between the individual spiral-shaped conductor elements.

sein, wobei i die Anzahl der konzentrischen Schalen um den zentralen Platz ist. Die entsprechende Zahlenfolge ist also
n = 7, 19, 37, 61, 91, ...The number n of the conductor wires of a transmission line may preferably be between 2 and 100, in particular between 7 and 37. Particularly preferably, the number n may be a so-called "magic number" which allows a regular arrangement of the conductor wires according to the pattern of a centered hexagon. n can therefore be an integer number according to the general formula $$\text{n}={\text{3i}}^2+\text{3i}+\text{1}.$$

where i is the number of concentric shells around the central place. The corresponding sequence of numbers is so
n = 7, 19, 37, 61, 91, ...

wobei i wiederum die Anzahl der konzentrischen Schalen um den nun vakanten zentralen Platz ist. Die entsprechende Zahlenfolge ist also
n = 6, 18, 36, 60, 90,...If the central location of such an arrangement is not occupied by a conductor core, but remains free, then the then preferred number n of the conductor leads results according to the general formula $$\text{n}={\text{3i}}^2+\text{3i}.$$

where i is again the number of concentric shells around the now vacant central space. The corresponding sequence of numbers is so
n = 6, 18, 36, 60, 90, ...

Alternatively, however, the number n of the conductor wires can also be an integer multiple of such a "magic number" or "magic number plus one".

In such an embodiment with a vacant central space, a central coolant channel may advantageously extend at this point.

A general advantage of the embodiments with a relatively high number of conductor wires (for example, at least 7 conductor wires) is that this relatively high degree of parallel connection of individual wires within a pole enables DC transmission with a high overall rating, without the need for a single converter high performance specification needed.

The fluid coolant may advantageously comprise nitrogen, hydrogen, helium and / or neon. In particular, the coolant may consist entirely of one of these substances. In general, the coolant may be present in the liquid, gaseous and / or supercritical state. In this case, the choice of the coolant can be suitably adapted to the desired operating temperature of the selected superconductor. For example, second generation HTS materials can be well cooled with liquid nitrogen, while magnesium diboride can be cooled particularly advantageously with liquid or supercritical hydrogen. The use of a supercritical coolant, in particular supercritical hydrogen, is particularly advantageous since, in this state, the formation of bubbles due to boiling of the coolant in the coolant channel is ruled out and thus the dielectric strength is increased when the coolant is used as the dielectric isolation agent. The operating temperature of the superconducting conductor element can, for example, when cooling with hydrogen between 20 and 35 K. or when cooling with nitrogen between 65 and 80 K.

The individual power converters can preferably be designed in each case for an operating current of at most 4 kiloamps. For example, they can be designed for an operating current of between 1 kilo-ampere and 2 kilo-ampere each. In this rated current range, in contrast to even higher currents, a large selection of inexpensive and reliable standard components is available.

Alternatively or additionally, the individual power converters can each be designed for an operating voltage of at most 9 kV, in particular at most 5 kV. For example, they can each be designed for an operating voltage between 1 kV and 9 kV, in particular between 3 kV and 4.5 kV. In contrast to even higher voltages, this range of voltages also offers a large selection of inexpensive and reliable standard components.

Generally preferred in the device, the n power converters can be configured as a rectifier. In other words, they may be configured to convert an alternating current into a direct current to be fed into the conductor wires of the transmission line. With this type of feed, the entire transmission device is then suitable for transporting a power, which was originally available in the form of alternating current, within the transmission line as direct current.

Alternatively or - particularly preferred - in addition to this embodiment, each having one rectifier per conductor core, the device may also comprise n inverters. In other words, the device may be equipped with n power converters, which can convert the DC transmitted rated current on the load side in an alternating current.

Regardless of the exact design of the power converters (eg as rectifiers, inverters and / or inverters), these can be implemented, for example, as IGBTs (Insulated Gate Bipolar Transistor), as thyristors and / or as MOSFETs (for metal oxide). Semiconductor field-effect transistor) be configured.

The DC transmission device may generally be preferably designed for a transmission power of at least 10 MW, in particular even at least 400 MW or even at least 1 GW. With the previously described line concept, such high powers can advantageously be transmitted without the individual power converters having to be designed for such a power range. This is achieved by transmission at low overall voltage and by splitting into parallel sub-current paths.

Preferably, the transmission device can be operated in the region of the superconducting transmission line in a DC voltage range, which lies within the voltage specification of a single power converter. In this embodiment, it is sufficient that each conductor core (or each group of conductor wires) is assigned in particular only one rectifier and / or only one inverter. This embodiment is particularly preferred because of its lower equipment cost. It can also be realized particularly well with the described multi-core concept, since a high power can be transmitted by the parallel current conduction in the individual conductor leads, without requiring a high voltage level.

However, if a higher voltage at the individual conductor wires is actually required to transmit the given power, then alternatively a series connection of several rectifiers and / or several inverters can be used at the respective end of the transmission line. With such a series connection, a larger voltage range can be made accessible than with a single power converter of the respective configuration (in particular a single rectifier or inverter per wire).

In a generally preferred embodiment, all the superconducting conductor wires of the described transmission line are designed for the transport of direct current with mutually identical polarity. It is then a single-pole transmission line. In this embodiment, it may be particularly preferable for the power transmission device to have a second such transmission line for transmitting direct current of the opposite polarity. In other words, it is then a total transmission device for two-pole DC transmission in two separate single-ended transmission lines. As an alternative to this embodiment, however, it is basically also possible to use only such a single-pole transmission line and to close the circuit via a ground line.

• 1 eine schematische Darstellung einer Vorrichtung zur Gleichstromübertragung nach einem ersten Beispiel der Erfindung zeigt,
• 2 eine supraleitende Übertragungsleitung einer solchen Vorrichtung nach einem zweiten Beispiel der Erfindung im schematischen Querschnitt zeigt,
• 3 eine supraleitende Übertragungsleitung nach einem dritten Beispiel im schematischen Querschnitt zeigt,
• 4 Teile einer supraleitenden Übertragungsleitung nach einem vierten Beispiel im schematischen Längsschnitt zeigt,
• 5 eine Übertragungsleitung nach einem fünften Beispiel im schematischen Querschnitt zeigt,
• 6 eine Übertragungsleitung nach einem sechsten Beispiel im schematischen Querschnitt zeigt und
• 7 eine Prinzipskizze einer Vorrichtung zur Stromübertragung nach einem siebten Beispiel zeigt.

In the following, the invention will be described by means of some preferred embodiments with reference to the appended drawings, in which:

• 1 1 shows a schematic representation of a device for direct current transmission according to a first example of the invention,
• 2 shows a superconducting transmission line of such a device according to a second example of the invention in a schematic cross section,
• 3 shows a superconducting transmission line according to a third example in schematic cross section,
• 4 Shows parts of a superconducting transmission line according to a fourth example in a schematic longitudinal section,
• 5 shows a transmission line according to a fifth example in schematic cross section,
• 6 shows a transmission line according to a sixth example in schematic cross section and
• 7 shows a schematic diagram of a device for power transmission according to a seventh example.

In general, the same or similar elements here are marked with the same reference numerals.

In 1 is a schematic representation of a device 1 for DC transmission according to a first embodiment of the invention. Only very schematically here is a superconducting transmission line 3 shown, which serves to transmit direct current over longer distances. This transmission line 3 has a plurality of individual superconducting conductor wires 5 of which four are shown here by way of example. In particular, however, it may also be a significantly larger number of such wires. As will become more apparent in connection with the following embodiments, these are conductor wires 5 be arranged in a common vacuum-insulated envelope, not shown here, which the interior of the transmission line 3 thermally insulated against a warmer outer environment.

The individual conductor wires 5 the transmission line 3 are each separately associated with them power converters 6a and 6b connected. In the example shown are the power converters 6a designed as a rectifier, with which therefore a DC parallel to the individual conductor wires 5 can be fed. As in 1 shown, these are individual rectifiers 6a electrically connected in parallel to each other, so that the total DC to be transported to several parallel current paths in the individual conductor wires 5 is split. On the opposite side of the transfer device 1 are the individual conductor wires 5 again with inverters 6b connected, which in turn convert the transmitted direct current in an alternating current. Also these inverters 6b are electrically connected in parallel to each other, so that in turn results in a summated alternating current on the output side.

In the example shown the 1 represents the superconducting transmission line 3 a single-pole line. The individual conductor wires 5 and the rectifiers respectively connected in series with them 6a So are switched so that by the individual conductor wires 5 each current of the same polarity is passed.

In an exemplary dimensioning of the electrical properties of the transfer device 1 are the power converters 6a and 6b and the individual conductor wires 5 designed for a voltage range below 3.3 kV. In this voltage range are the standard-compliant technical requirements for the power converters and the insulation of the conductor wires 5 advantageous relatively low, so that the design, manufacture, installation and operation accordingly relatively simple and thus inexpensive.

• - Für die Gleichrichter und/oder die Wechselrichter können IGBTs eingesetzt werden, welche für eine Nennspannung von etwa 3,3 kV und einen Nennstrom von etwa 1,5 kA ausgelegt sind.
• - Für die Gleichrichter und/oder die Wechselrichter können IGBTs eingesetzt werden, welche für eine Nennspannung von etwa 4,5 kV und einen Nennstrom von etwa 3 kA ausgelegt sind.
• - Für die Gleichrichter und/oder die Wechselrichter können Thyristoren eingesetzt werden, welche für eine Nennspannung von etwa 3,6 kV und einen Nennstrom von etwa 0,9 kA ausgelegt sind.
• - Für die Gleichrichter und/oder die Wechselrichter können Thyristoren eingesetzt werden welche für eine Nennspannung von etwa 7 kV und einen Nennstrom von etwa 1,3 kA ausgelegt sind.

In an alternative exemplary dimensioning of the electrical properties, however, the power converters and the conductor wires can also be designed for a slightly higher voltage range. By way of example, the following values for nominal voltages and rated currents are mentioned, which can be implemented relatively simply with standard components:

• - For the rectifier and / or the inverters IGBTs can be used, which are designed for a nominal voltage of about 3.3 kV and a rated current of about 1.5 kA.
• - For the rectifier and / or the inverters IGBTs can be used, which are designed for a nominal voltage of about 4.5 kV and a rated current of about 3 kA.
• - For the rectifier and / or the inverters, thyristors can be used, which are designed for a nominal voltage of about 3.6 kV and a rated current of about 0.9 kA.
• - For the rectifier and / or the inverters thyristors can be used, which are designed for a nominal voltage of about 7 kV and a rated current of about 1.3 kA.

2 shows a superconducting transmission line 3 a device for DC transmission according to a second example of the invention in schematic cross section. The device as a whole can be constructed as a whole as in 1 shown. In a radially inner area 9 the transmission line 3 For example, here are five individual superconducting conductor wires 5 , which in this example are concentric with each other in the form of nested cylindrical tubes. Again, the number of conductor wires shown as an example can 5 are exemplary of another and especially larger number of conductor wires. In the example shown, the individual conductor wires 5 each a support tube with a superconducting layer not shown here. This superconducting layer may be, for example, a superconductive coating on the carrier tube or it may also be a winding applied to the tube, for example a strip conductor.

The concentric nested conductor wires 5 are electrically isolated from each other. These are each between individual radially adjacent conductor wires 5 dielectric insulation layers 31 arranged. These dielectric insulation layers 31 For example, each can be made of fluid coolant 11 and / or a solid insulation. In the example shown, individual cylinder jacket-shaped coolant channels are in each case between the individual conductor wires 25b to 25e arranged so that a substantial part of the insulation effect can be taken over by the coolant itself. By way of example, there is also a paper insulation between the two innermost conductor wires 33 shown, wherein the paper in addition of fluid coolant 11 should be soaked. Alternatively or additionally, however, it is also possible in principle that between the individual concentric conductor wires 5 another solid insulation, such as plastic, is arranged. However, this is not shown here for the sake of clarity.

The radially inner area 9 the transmission line 3 is against the warmer outer environment 15 through a vacuum-insulated casing 13 thermally insulated. In the example shown has this shell 13 an inner cryostat wall 13a and an outer cryostat wall 13b on, between which a vacuum V is formed. Within this vacuum space V may optionally be arranged as a radiation shield multilayer insulation. Between the vacuum-insulated casing 13 and the radially outermost conductor core 5 is an annular coolant channel 25a formed, which all internal conductor wires 5 surrounds together. So the conductor wires can by the coolant flowing here 11 (And also by the coolant in the more internal coolant channels) are effectively cooled. The outermost coolant channel 25a at the same time serves as a dielectric between the conductor wires 5 and the inner cryostat wall 13a , which can simultaneously act as a cable screen. In the example shown, a cavity is also in the interior of the innermost conductor core 25f formed, which can be used here as an internal coolant channel.

To the mutually concentric conductor wires in relation to the vacuum-insulated shell 13 To keep at a defined distance, here are several support elements 39 provided, three of which are shown here by way of example. Other support elements 39 may also be appropriate between the individual conductor wires 5 be provided as exemplified here for the two outermost conductor wires.

In 3 is a superconducting transmission line 3 according to another example of the invention shown in schematic cross-section. Again, the transmission line 3 several superconducting conductor wires 5 of which eight are shown here by way of example. Again, these are conductor wires 5 together within a vacuum insulated envelope 13 arranged. Furthermore, a coolant channel 25 provided, which the individual conductor wires 5 surrounds, so that these together with a fluid coolant 11 can be cooled. In contrast to the previous example, here are the individual conductor wires 5 on a common rod-shaped core 28 arranged. This core is formed here, for example, as an elongated copper core with an approximately circular cross-section. This copper core may for example be constructed of copper braid and thus have a relatively high mechanical flexibility.

In the example of 3 are the individual conductor wires 5 in cross-section over the circumference of the common core 28 arranged distributed. Along a longitudinal direction of the transmission line 3 For example, these individual conductor wires may be helically wrapped around the common core. You can use the entire length of the transmission line 3 be arranged electrically separated from each other. So they can in particular by an insulation layer, not shown here in each case from the inner core 28 be electrically isolated. The electrical separation of the individual conductor wires 5 with each other, for example, essentially by that in the coolant channel 25 flowing coolant 11 respectively. In addition, however, optionally also another insulation tape 32a be wound between the adjacent conductor wires, as exemplified herein for an adjacent pair of conductor wires.

A general advantage of the spiral arrangement of the conductor wires 5 on the core 28 is that the ladder assembly receives a relatively high overall mechanical flexibility. In the example shown are the individual conductor wires 5 each consisting of stacks of several superposed superconducting strip conductors 26 educated. However, it is also possible in principle to produce a similar spiral winding of individual (unstacked) strip conductors.

4 shows a partial region of a superconducting transmission line three according to a further embodiment of the invention in a schematic longitudinal section. For the sake of clarity, here is only an internal part of the transmission line 3 shown similar in the 2 or 3 within a vacuum insulated envelope 13 can be arranged and can be held there via support elements.

4 again shows a metallic core 28 which can also be configured here, for example, either as a solid core or as a stranded structure. Again, this is on this core 28 a plurality of superconducting conductor wires 5 arranged spirally wound. In contrast to the previous example, the individual conductor wires 5 here not from stacks of superconducting strip conductors, but in each case from side by side wound strip conductors 26 educated. Similar to the example of 3 can also be the electrical insulation between the individual conductor wires 5 for example, essentially by the coolant flowing in these structures 11 be formed. In addition, however, optionally also between the adjacent conductor wires an insulating tape here 32a be wound between, as exemplified here for the two middle conductor wires 5 shown.

5 shows a superconducting transmission line 3 according to a further embodiment of the invention in a schematic cross section. In this example, the transmission line points 3 twenty-eight individual conductor wires 5 which also together here within a vacuum-insulated shell 13 are arranged and together by an annular coolant channel 25 are surrounded. The twenty-eight individual conductor wires 5 are divided into seven groups, each group having a separate core 28 having. These cores can also be formed here from copper-containing material. Around each of these cores are four individual superconducting conductor elements 26 arranged in the form of individual strip conductors. The seven individual strands formed in this way are also here by supporting elements 39 in their position relative to the outer shell 13 held. The individual superconducting conductor elements 26 , which each have a conductor wire 5 are insulated from each other by dielectric layers. This dielectric is in the example shown by a combination of flowing coolant 11 and of a plastic insulation 32b formed, these plastic insulation each of the four conductor elements 26 of a nucleus together. The electrical breakdown strength between the individual conductor wires 5 So here is achieved by a combination of coolant dielectric and additional plastic dielectric.

6 shows a superconducting transmission line 3 according to a further embodiment of the invention. Overall, this transmission line is very similar to that of the 5 , Here too are twenty-eight conductor wires 5 divided into seven groups, each with four band conductors 26 are arranged together on a core. In contrast to the example of 5 Here, however, the electrical insulation between the individual conductor wires essentially by the fluid coolant 11 achieved and not by an additional plastic insulation. For this purpose, the individual cores 28 by supporting elements 39 kept separate from those in 6 only one example is shown. The minimum distance between individual adjacent conductor wires 5 this may for example be at least 1 mm.

7 shows a schematic diagram of a device 1 for power transmission according to a further embodiment of the invention. In this example, the device 1 two superconducting transmission lines 3a and 3b on. These two transmission lines 3a and 3b For example, each may be similar to one of the 2 to 6 be designed. In particular, these two transmission lines are each again designed as single-pole lines with a plurality of conductor wires. By using both lines for power transmission a two-pole DC transmission is possible. The device for power transmission has a cooling device 7 on with in this example two separate cooling units 18 in which the fluid coolant 11 is cooled down again after heating in the cooling channels of the lines. Each of the transmission lines can be longitudinal 21 have an extension of, for example, several 10 km. Each of the two lines 3a and 3b has at one of its two ends a device 17 for feeding in by one of the cooling units 18 cooled down coolant in the radially inner region of the respective conduit. In the example shown, each of the two lines 3a and 3b just such a feeding device 17 up, for the lead 3a she is at the first end area 19a arranged, and for the line 3b she is at the opposite second end areas 19b arranged. The axially inside area 23 So is free for both lines of such feeders. The fluid coolant 11 circulates in this example in a closed circuit via the coolant channels 25 the two lines 3a and 3b , the two cooling units 18 and the coolant pipes arranged therebetween 47 and feeding devices 17 , The flow directions 27a and 27b of the coolant in the two lines are opposite thereto. Due to the thermal insulation of the radially inner areas 9 the lines 3a and 3b is achieved that their respective superconducting conductor elements over the entire longitudinal extent 21 the lines are kept at an operating temperature below the transition temperature of the superconductor.

Claims (15)

Device (1) for direct current transmission with a superconducting transmission line (3, 3a), wherein the transmission line (3) - A vacuum-insulated sheath (13) for the thermal separation of a radially inner region (9) of the transmission line (3) from an outer environment (15) and a plurality of n superconducting conductor cores (5), which are arranged together within the vacuum-insulated envelope (13), - wherein the device (1) has at least a number n of power converters (6a, 6b), wherein each of the superconducting conductor wires (5) or each group of combined superconducting conductor wires (5) is assigned at least one power converter (6a, 6b), - And wherein the device (1) is configured to apply a plurality of common within the sheath (13) guided conductor wires (5) with a direct current of mutually same polarity. Device (1) according to Claim 1 comprising a cooling device for cooling the radially inner region (9) of the transmission line (3) to a temperature below a transition temperature of the superconducting conductor wires (5) by means of a fluid coolant (11). Device (1) according to one of Claims 1 or 2 in that the transmission line (3) has at least one coolant channel (25, 25a) which jointly surrounds the conductor cores (5) for transporting fluid coolant (11) along a longitudinal direction (21) of the transmission line (3). Device (1) according to one of the preceding claims, in which the individual conductor cores (5) guided within the common sheath (13) are isolated from one another by means of a dielectric insulating layer (31) such that a potential difference occurs during operation of the device (1) between the individual wires (5) of at least 1 kV can be maintained. Device (1) according to Claim 4 in which the dielectric insulation layer (31) comprises a fluid coolant (11) and in particular consists at least in axial and / or radial subregions of the transmission line (3) of fluid coolant (11). Device (1) according to one of Claims 4 or 5 in which the dielectric insulating layer (31) has at least one layer of paper (33) embedded in a coolant (11). Device (1) according to one of Claims 4 to 6 in which the dielectric insulating layer (31) arranged between the individual conductor wires (5) has a dielectric strength of at least 20 kV / mm. Device (1) according to one of the preceding claims, in which the superconducting conductor wires (5) each comprise a high-temperature superconducting material, in particular magnesium diboride and / or a material of the REBCO type. Device (1) according to one of the preceding claims, wherein the superconducting conductor cores (5) are arranged concentrically to each other, wherein in particular radially between the individual conductor cores (5) concentric coolant channels (25b, 25c, 25d, 25e) are formed. Device (1) according to one of Claims 1 to 8th in which the individual superconducting conductor cores (5) are guided next to one another within the common envelope (13), wherein in particular the individual conductor cores (5) each have one or more band-shaped conductor elements (26), which in each case rest on a core (28) carrying them. are arranged. Device (1) according to one of the preceding claims, in which the number n of the conductor wires (5) of a transmission line is between 2 and 100, in particular between 7 and 30. Device (1) according to one of the preceding claims, wherein the power converters (6a, 6b) are each designed for an operating current of at most 5 kA and / or for an operating voltage of at most 9 kV. Device (1) according to one of the preceding claims, wherein the at least n converters (6a, 6b) are designed to convert from an alternating current into the conductor wires (5) of the transmission line (3) to be fed direct current. Device (1) according to one of the preceding claims, additionally comprising a second superconducting transmission line (3b) designed to transmit direct current with a polarity opposite to the first transmission line (3a). Method for transmitting direct current with a device (1) according to one of the preceding claims, characterized by the step of feeding current of the same polarity into a plurality of conductor wires (5) of the superconducting transmission line (3) guided within the common envelope (13).

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