The present disclosure relates generally to the field of high voltage power converters and is concerned with a valve arrangement in which insulation is obtained by means of at least an insulating gas. The valve arrangement of the present disclosure may be applicable in for instance offshore platforms.

BACKGROUND

A high voltage direct current (HVDC) converter station is a type of station adapted to convert high voltage direct current (DC) to alternating current (AC) or the reverse. An HVDC converter station may comprise a plurality of elements such as the converter itself (or a plurality of converters connected in series or in parallel), an alternating current switch gear, transformers, capacitors, filters, a direct current switch gear and other auxiliary elements. Electronic converters may be categorized as line- commutated converters using e.g. thyristors as switches or voltage source converters using transistors, such as insulated gate bipolar transistors (IGBTs), as switches (or switching devices). A plurality of solid-state semiconductor devices, such as thyristors or IGBTs, may be surrounded by capacitors and connected together, for instance in series, to form a building block or a valve unit of an HVDC converter. A challenge in the construction and design of an HVDC converter station is the electrical insulation of the different parts of the HVDC converter station since an increased in distance between the various parts of an HVDC converter station improves insulation but at the same time results in an HVDC converter station with larger dimensions. This may raise a number of difficulties relative to e.g. installation, transport and cost, in particular for offshore applications. For at least such

applications, there is a general need of more compact solutions. SUMMARY

An object of at least some embodiments of the present disclosure is to wholly or partly overcome the above disadvantage of prior art systems and to provide a more compact alternative to the prior art.

This and other objects are achieved by means of a valve arrangement as defined in the appended independent claim. Other embodiments are defined by the dependent claims. According to a first general aspect, there is provided a valve arrangement comprising a plurality of valve units (for example at least two valve units) electrically connected in series. A first valve unit includes a container in which at least one stack of converter cells is arranged. The container is at least partially filled with an electrically insulating gas. The valve arrangement further comprises at least one first connector including a first busbar element electrically connecting a cell of the first valve unit at one end of the container to a cell of a second valve unit. The first connector is insulated by an electrically insulating gas. Further, the valve arrangement comprises at least one second connector including a busbar element for connection of another cell of the first valve unit at another end of the container.

In the above defined valve arrangement, electrical insulation of the converter cells within a valve unit is obtained by means of an insulating gas enclosed in the container. Further, the container is equipped for connection of a busbar at both ends (e.g. opposite ends) of the container which allows for a more compact arrangement of the valve units. The valve units are electrically connected in series.

In the above defined valve arrangement, a valve unit includes a first connector at one end of its container for connection of a converter cell of its stack to a cell of the stack of a second valve unit (e.g. an adjacent one or a successive one in the valve arrangement). Further, a second connector is provided at another end of the container for connection of another cell of the stack of the first valve unit. Accordingly, the valve unit itself provides for a more compact solution in that a conductor or busbar for connecting the plurality of converter cells forming the stack extend from one end of the container to another end, which reduces the space constraints for air clearance and the need of any extra shielding elements as it would be the case if both connections to an input cell of the valve stack and an output cell of the valve stack were located at the same end of the container, i.e. close to each other.

According to some embodiments, the second connector is configured to connect a cell of the first valve unit to a cell of the stack of a third valve unit (e.g. an adjacent one or a successive one in the valve arrangement). The second connector may be electrically insulated.

According to some embodiments, the first connector and the second connector may be located at opposite ends of the container. In particular, the first connector may be configured to electrically connect an upper cell of the valve stack (e.g. the one located on top of the stack) to an upper cell of a stack of the second valve unit. Analogously, the second connector may be configured to electrically connect a lower cell of the valve stack to a lower cell of the valve stack (e.g. the lowest one in the valve stack) of a third valve unit. For example, in the case of a cylinder-like container (or enclosure), the first connector may be arranged at a first base of the cylinder-like container and the second connector may be arranged at a second base of the cylinder-like container opposite to the first base.

With container is meant an enclosure or tank in which a plurality of converter cells may be arranged to form a stack of converter cells. The container may extend along an axial direction between a first end (or base or extremity) and a second end (or base or extremity) located at two distant positions along the axial direction. The distance between the two ends of the container along the axial direction corresponds to the height of the container. With a stack of convert cells is meant a column of converter cells, i.e. a plurality of converter cells stapled on top of each other. The valve arrangement may then be considered as an arrangement of columns next to each other wherein a column corresponds to a stack of converter cells, a column being arranged within a container at least partially filled by an insulating gas. It will be appreciated that there may be a gap with insulating gas between two successive converter cells of the stack. The cell stack of a valve unit may be arranged along an axial direction along which the container extends such that a number of positions are defined along the axial direction and cells are arranged at such positions. The cell stack may include a number of converters with HV capacitor shields (or HV corona shields). According to some embodiments, the plurality of valve units may be arranged side by side which provides a more compact solution.

The valve arrangement may correspond to an arm of a power converter station. The number of valve units in the valve arrangement and the number of cell positions in each valve unit determine the total number of cell positions in the arm.

According to some embodiments, the container of a valve unit may extend along a vertical direction such that the valve units are standing next to each other. According to an embodiment, the first connector may be arranged to electrically connect an upper cell of the stack of the first valve unit to an upper cell of a stack of the second valve unit (e.g. connecting the cells positioned at the highest levels in two successive valve stacks). Analogously, the second connector may be arranged to electrically connect a lower cell of the stack of the first valve unit to a lower cell of a stack of the third valve unit (e.g. connecting the cells positioned at the highest levels in two successive valve stacks).

According to some embodiments, the busbar element of at least one of the first connector and the second connector may be U-shaped. Such a shape facilitates the connection of e.g. an upper cell of a first valve unit to an upper cell of a second valve unit, still providing the necessary air clearance. Adjacent valve units may have the same number of converter cells or be designed such that they substantially have the same height to facilitate the connection of cells between two successive valve units. In some embodiments, the second and third valve units are equivalent to the first valve unit. However, in other embodiments, any number of cells may be used in the valve units or valve units of different heights may be used. According to some embodiments, the plurality of valve units may be aligned to form at least one row or a matrix of columns.

According to some embodiments, at least one of the valve units of the valve arrangement may include a plug-in cable termination or a gas-insulated busbar for connection to an alternating current (AC) transmission line and another one of the valve units may include another plug-in cable termination or a gas-insulated busbar for connection to a direct current (DC) transmission line. In a configuration with only two valve units, the first valve unit may include a plug-in cable termination or a gas- insulated busbar for connection to an AC transmission line at one end of its container while at its opposite end the first valve unit is connected to the second valve unit via the first connector electrically insulated by gas. A cell at an opposite end of the second valve unit may then be connected to a DC transmission line via a plug-in cable termination or a gas-insulated busbar. According to some embodiments, the busbar element of the second connector may be embedded in a solid insulating material (such as e.g. epoxy) or located in a pipe at least partially filled by an insulating gas.

According to some embodiments, the second connector may comprise an insulated compartment in which the busbar element for connection of the other cell of the first valve unit (e.g. for connection with the third valve unit) is arranged. The insulated compartment may form a base of the valve arrangement. In these embodiments, the valve units may be standing on top of a compartment or cabinet in which the connectors (or connecting elements) for connecting a valve unit to another, or for connecting the valve units to an AC or DC transmission line, are arranged. The compartment may for example be arranged at the bottom of the containers of the valve units. The compartment may therefore be used as a base frame for installation of the containers of the valve units. According to some embodiments, the compartment may include a solid insulating material (such as e.g. epoxy) or an insulating gas for electrical isolation of the busbar element(s) used for connection of cells between successive valve units.

According to some embodiments, a spacing element (or spacer) including insulating material may be arranged at one end of the container of the first valve unit for separating the container of the first valve unit from containers of adjacent valve units. A spacing element may for instance be arranged at a junction between one end of the container of the first valve unit and one of the first connector and/or the second connector. However, the spacing element may also be arranged within the container along a busbar used for connecting the converter cells of the stack, i.e. before the structural (or physical) junction between the container and the first connector. For example, the first valve unit may be equipped with two spacing elements for separation from the second valve unit and the third valve unit (or any other elements to which the cell of the first valve unit is connected). The spacing elements may also be used for supporting the valve stack which extends from one end of the container to another end. However, in some embodiments in which the second connector includes an insulating material and one end (e.g. the bottom end) of the container is sealed by such an insulating material, the valve unit may include only one single spacing element (in particular for sealing the top end of the container).

According to some embodiments, a spacing element may comprise a first portion extending in a direction transverse to an axial direction along which the container extends. The spacing element is used for sealing the container. In some embodiments, the spacing element may further comprise a second portion extending along at least one of an outer wall of the container of the first valve unit and an outer wall of the first (or the second) connector.

According to some embodiments, the insulating gas in the container may be at least one of sulfur hexafluoride (SF6), Nitrogen (N2), air and dry air. According to some embodiments, the insulated gas for insulation of the second connector (for example in a pipe or a compartment as described in some of the preceding embodiments) may also be at least one of sulfur hexafluoride (SF6), Nitrogen (N2), air and dry air. It will be appreciated that the gas may be a mixture of different gases such as a mixture of SF ₆ and N ₂ . It will be appreciated that the present disclosure is not limited to such gases and that other insulating gases may be envisaged. Further, the gas may be a compressed gas, i.e. a gas under a certain pressure higher than the atmospheric pressure.

According to some embodiments, a converter cell may comprise a capacitor shield, a capacitor element and at least one switching device. The switching device may for example be a semiconductor-based component including e.g. thyristors or IGBTs. In a more specific embodiment, the cell may be a disk-type cell with a disk-shaped capacitor element within which the switching device (or semiconductor components used to build at least part of a converter) is arranged.

According to some embodiments, the stack of converter cells may be arranged coaxially to an axial direction along which the container extends, thereby providing an even more compact valve unit. According to some embodiments, the container may have a cylindrical shape. In some embodiments, the valve stack is formed with disc-shaped converter cells, thereby forming a column of converter cells having a cylindrical shape, which provides an even more homogeneous electric field. As a result, the gas clearance may be further reduced, and an even more compact valve arrangement is provided.

Generally, it will be appreciated that the container may include an electrically conductive material such as a metal. Alternatively, the container may be made of another material coated with an electrically conducting layer on its outer surface. The electrically conductive material or coating of the container may then be used for grounding.

According to some embodiments, the valve arrangement may further comprise an electrical shield for insertion of the stack of converter cells at one end of the container and/or an electrical shield for insertion of the stack of converter cells at an opposite end of the container.

According to some embodiments, a power converter station may be provided. The power converter station may include at least two valve arrangements as defined in any one of the preceding embodiments. The power converter station may be a high voltage direct current (HVDC) converter station.

The present disclosure is applicable for high voltage power equipments with various voltage levels in which it is desired to provide an insulated environment. The present disclosure is generally advantageous for applications in which a more compact power equipment is desired, such as in applications where space for installation of the electric power equipment is limited and/or for offshore wind farm applications. It will be appreciated that other embodiments using all possible combinations of features recited in the above described embodiments may be envisaged.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments will now be described in more detail, with reference to the following appended drawings:

Figure 1 shows a schematic view of a valve unit in accordance with an embodiment;

Figure 2 shows a schematic view of a cell in accordance with some embodiments;

Figure 3 shows a schematic view of a valve stack in accordance with some embodiments;

Figure 4 shows a schematic view of an arrangement of valve units of an HVDC converter in accordance with some embodiments;

Figure 5 shows a schematic view of an arrangement of valve units of an HVDC converter in accordance with some embodiments; and

Figure 6 shows a schematic view of an arrangement of valve units of an HVDC converter in accordance with some embodiments. As illustrated in the figures, the sizes of the elements, layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of the embodiments. Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION

Exemplifying embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

With reference to Figure 1, a valve unit 100 according to an embodiment is described.

Figure 1 shows a cross-sectional view of a valve unit 100 comprising a container (or enclosure) 130 and a plurality of cells 120 arranged as a stack within the enclosure 130. The cells 120 are arranged on top of each other and connected in series to form an electrical equipment or system (e.g. a converter) within the container 130.

The container 130 may extend mainly along an axial direction 112 and may for instance have a cylinder- like shape extending from one base surface or region 118 to another base surface or region 119 (i.e. between two distant positions along he axial direction 112). In a specific embodiment, the enclosure 130 may be a cylinder extending along the axial direction 112 and the cells 120 are arranged on top of each other along the axial direction 112, thereby defining a number of cell positions along the axial direction 112.

As will be described in more detail with reference to Figure 3, a cell may include at least one capacitor element and a switching device. The stack of converter cells 120 may include high voltage capacitor shields denoted 122 in which the capacitor element is arranged. The HV capacitor shield 122 of a cell 120 surrounds the switching device. In other words, a capacitor shield 122 of a cell 120 acts as a casing for the capacitor element. The capacitor shield may be formed as a toroid with a square section. In the stack, two successive converter cells, each comprising a capacitor shield with a capacitor element and a switching device, are separated by the insulating gas located within the container. In this configuration, an HV capacitor shield is considered to be part of a cell such that a cell includes a switching device, a capacitor element and its capacitor shield, in which case the stack includes a succession of cells disposed on top of each other with some gas gap between two successive cells. As depicted in Figure 1, the switching device of a converter cell 120 is surrounded by a HV capacitor shield 122.

The outer surface of the enclosure 130 may be made of an electrically conducting material, such as a metal, or may be covered by an electrically conducting material such that the outside surface of the enclosure 130 may be grounded. Figure 1 also shows a first connector 160 for connection of one end of the stack of the valve unit to another valve unit and a second connector 170 for connection of another end of the stack of the valve unit to yet another valve unit.

The container including the stack of converter cells may be closed or sealed. For example, a spacing element may be arranged at one of the ends or base surfaces of the enclosure. As depicted in Figure 1, a first spacing element 116 is arranged at one end 118 of the container 130 while a second spacing element 114 is arranged at an opposite end 119 of the container 130. More specifically, the first spacing element 116 may be arranged at the junction between the first connector 160 and the top end 118 of the container 130 while the second spacing element 114 may be arranged at the junction between the second connector 170 and the bottom end 119 of the container 130.

The first spacing element 116 and the second spacing element 114 may for example be made of an insulating material.

Alternatively, as will be described in more details with reference to e.g. Figure 4, a bottom end 119 of the container 130 may be sealed by means of an insulating material in which the busbar element of the second connector may be embedded for electrical insulation.

The first connector 160 includes a busbar element 161 arranged to connect the stack of converter cells (and more particularly an upper cell of the stack) to the stack of an adjacent valve unit (not shown in Figure 1 but in e.g. Figures 4-6). The first connector 160 may include a busbar element made of a single piece bent so as to connect two cells located on top of the stacks of two adjacent valve units. Alternatively, as depicted in Figure 1, the busbar element of the first connector 160 may include a plurality of segments. For example, the first connector may have a nodal element 162 for connecting a first segment of the busbar element to another segment of the busbar element extending along the axial direction 112 for electrically connecting the converter cells 120 in series. In the particular embodiment shown in Figure 1, the nodal element 162 is configured to direct a segment of the busbar element 161 in a direction intersecting (e.g. orthogonal to) the axial direction 112 along which the container 130 extends so as to reach an adjacent valve unit.

The second connector 170 includes a busbar element 171 arranged to connect the stack of converter cells (and more particularly a lower cell of the stack) to the stack of an adjacent valve unit (not shown in Figure 1 but in e.g. Figures 4-6). The second connector 170 may include a busbar element made of a single piece bent so as to connect two cells located at the bottom of the stacks of two adjacent valve units. Alternatively, as depicted in Figure 1, the busbar element of the second connector 170 may include a plurality of segments. For example, the second connector may have a nodal element 172 for connecting a first segment of the busbar element to another segment of the busbar element extending along the axial direction 112 for electrically connecting the converter cells 120 in series. In the particular embodiment shown in Figure 1, the nodal element 172 is configured to direct a segment of the busbar element 171 in a direction intersecting (e.g. orthogonal to) the axial direction 112 along which the container 130 extends so as to reach an adjacent valve unit.

The first connector 160 and the second connector 170 may be configured to direct a busbar element in opposite directions so as to reach the stack of two different valve units, thereby enabling a serial connection of the valve units to form a larger converter.

Further, for electrical insulation between the converter cells 120, the container 130 may be at least partially filled with an insulating gas 115, which may for example be SF ₆ , N ₂ , air, dry air or a mixture of such gases. It will be appreciated however that the present disclosure is not limited to these examples and that other gases, in particular SF6-free gases, with similar insulation properties may be used. Further, a compressed gas with pressure of approximately a few bars may be used. For example, the enclosure 130 may be filled with SF ₆ at a pressure in the range of 2 to 6 bars.

In some embodiments, at least one of the cells, a group of cells or the stack may be detachably arranged such that it is removable from the container. In particular, the stack of cells may be detachable (or removable) from the enclosure, which is advantageous for example for repair or replacement of a cell of the stack, a group of cells or even the whole stack. Referring to Figure 1, the stack of cells 120 may be inserted or removed from the enclosure 130 by removing the first spacing element or spacer 116, the first connector 160 mounted at the top end of the cylinder- like container 130, thereby opening the container 130, and by optionally removing the second spacing element 114 and disassembling a top part of the container 130. Figure 1 shows that the container 130 may be made of at least two pieces wherein a main part is a cylinder in which cell stack is arranged and a top part is shaped as a bottleneck resting on the main part by means of a flange 117 so as to form a bottle-like container 130. The cylinder- like stack may then glide along the axial direction 112 within the cylinder- like enclosure 130.

In the valve unit 100 shown in Figure 1, the stack of converter cells may be arranged coaxially to the axial direction 112 along which the container 130 extends. In particular, the stack of cells may be maintained aligned along the axial direction 112 along which the container 130 extends by means of the spacing elements 114, 116 and the busbar (or conductor) 140 connecting the converter cells together in series wherein a first spacing element 116 maintains the busbar 140 at the top end 118 of the container 130 while the second spacing element 114 maintains the busbar 140 at the bottom end 119 of the container 130.

The valve unit 100 may also be equipped with a top capacitor shield 111 in which the stack of converter cells 120 is inserted at the top end 118 of the container 130 and with a bottom capacitor shield 113 in which the stack of converter cells 120 is inserted at the bottom end 119 of the container 130.

It will be appreciated that, although a cylinder-like shape provides some advantages for homogeneity of the electrical fields induced in such kind of electrical equipments, the present disclosure is not limited to such a shape of the enclosure and other geometries may be envisaged.

The components or elements of the valve unit 100, such as for example each one of the cells, a group of cells, the stack of cells, one or more of the top capacitor shield, bottom capacitor shield, first connector and second connector may be removable or modularized in order to facilitate their replacement without influencing the other elements. Referring more specifically to HVDC applications, a cylinder-type HVDC converter with a number of cell positions such as described with reference to Figure 1 is advantageous over traditional offshore converter station as it avoids, or at least reduces, the need of clearance for manual access to the elements of the valve unit.

Further, the voltages between the capacitors of the cells 120 (which might be of approximately a few kV) will be exposed to the compressed gas enclosed within the enclosure 130.

With reference to Figure 2, a cell 120 according to an embodiment is described in more detail. Figure 2 shows a cell 120 including a capacitor shield 122 and a switching device such as a semiconductor-based component 127. At least one capacitor element (not shown) is arranged or enclosed within the capacitor shield 122 (i.e. within the volume defined by the interior of the body of the capacitor shield). In the embodiment shown in Figure 2, the capacitor shield 122 surrounds the semiconductor component 127 and is disc-shaped. The capacitor shield 122 is annular and defines a center hole in which the semiconductor component 127 may be placed. The cell 120 shown in Figure 2 is therefore particularly suitable for forming a cylinder-like stack of converter cells to be arranged within a cylinder-like container.

Without loss of generality and for illustrating purposes only, the semiconductor component may be an arrangement of one or more thyristors or IGBTs, depending on the desired electrical equipment (e.g. type of converter).

A plurality of cells 120 may be arranged on top of each other along the axial direction of the container (in particular along a vertical direction but not necessarily) with a gas-gap between them to structurally form a stack (such as a cylinder in the case of a superposition of a plurality of disc-shaped cells). The plurality of cells 120 may be electrically connected via a busbar element 140 together to form the desired electrical equipment.

Figure 3 shows an example of a valve stack 150 wherein a plurality of converter cells is arranged on top of each other along an axial direction with a gas-gap 188 between the converter cells. The valve stack 150 includes a plurality of cells 120 which may be equivalent to the converter cell 120 described with reference to Figure 2. Figure 3 shows a cross-sectional view of the stack 150 of converter cells with a switching device 127 surrounded by a capacitor shield 122. Still, it will be appreciated that two successive cells in the stack may be identical or different from one to another. Figure 3 shows also a busbar 140 connecting the plurality of converter cells 120 in series to form a larger converter.

Figure 4 shows a valve arrangement 400 according to an embodiment. The valve arrangement 400 comprises a plurality of valve units 410, 420, 430, 440 and 450 (five in the present example) electrically connected in series. However, the present disclosure is not limited to a valve arrangement including five valve units. The valve arrangement may include any number of valve units such as for instance at least two valve units.

In the embodiment shown in Figure 4, the valve units are arranged side by side. Each of the valve units 410, 420, 430, 440 and 450 includes a container in which at least one stack 150 of converter cells is arranged. Each of the valve units may form at least part of a larger converter (which is formed by the serial connection of the plurality of the cell stacks of the valve units). The container of a valve unit may be at least partially filled with an electrically insulating gas 115. Each of the valve units 410, 420, 430, 440 and 450 may be equivalent to the valve unit 100 described with reference to Figure 1.

In the valve arrangement 400 shown in Figure 4, the containers (or valve units) extend along vertical directions such that the valve units are standing next to each other. The axial directions along which each of the containers of the valve units 410, 420, 430, 440 and 450 extend may be substantially parallel.

Further, the plurality of valve units may be aligned to form a row of columns, as illustrated in Figure 4. In particular, the valve arrangement shown in Figure 4 may form one arm of a converter station.

The valve arrangement 400 may further comprise at least one first connector 460 including a first busbar element 461 electrically connecting a cell 421 located at one end (in particular the top end) of a first valve unit 410 to another cell 441 located at one end (in particular the top end) of a second valve unit 420. The first connector 460 is insulated by an electrically insulating gas 465. More generally, the first connector 460 is arranged to electrically connect an upper cell of the stack of the first valve unit 410 to an upper cell of the stack of the second valve unit 420. As illustrated in Figure 4, the first connector 460 and in particular the busbar element 461 may be U-shaped.

In particular, the first connector 460 may include at least one pipe or tubular element arranged to connect one end of the container of the first valve unit 410 to another end of the container of the second valve unit 420. A busbar element 461 is located within the pipe to electrically connect the stack of cells of the first valve unit 410 to the stack of cells of the second valve unit 420. The pipe may be at least partially filled by the insulating gas 415 in order to insulate the busbar element 461.

The valve arrangement may also comprise a connector of the first type, i.e. similar to the first connector 461, for connecting the fourth valve unit 440 to the fifth valve unit 450. The valve arrangement may also further comprise a second connector 470 including a busbar element 471 connecting another cell located at another end of the first valve unit, in particular the lowest cell 431 of the first valve unit 410, to another cell 451 of a third valve unit 430, in particular the lowest cell 431 of the third valve unit. The second connector and in particular its busbar element 471 is electrically insulated. More generally, the second connector 470 is arranged to electrically connect a lower cell of the stack of the first valve unit 410 to a lower cell of a stack of the third valve unit 430.

The arrangement shown in Figure 4 is symmetric such that the fourth valve unit 440 and the fifth valve unit 450 are connected and arranged in a similar manner as the second valve unit 420 and the first valve unit 410. In this arrangement, each of the third valve unit 430 and the fifth valve unit 450 is equipped with one plug-in cable termination 482, 484 for connection to an electrical system (or to an external bus bar). The plug-in cable terminations (or any other gas-insulated bus-bars) may be used for connection of the valve arrangement to a transformer or a DC gas insulation system.

As shown in Figure 4, the valve arrangement 400 includes a plug-in cable termination 482 for connection of the cell stack of the third valve unit denoted 430 to an alternating current transmission line. Further, the valve arrangement 400 includes a plug-in cable termination 484 for connection of the cell stack of the fifth valve unit denoted 450 to a direct current transmission line. The plug-in cable terminations 482, 484 may be designed to connect to another valve unit or an electrical system via some kind of cable.

The valve arrangement 400 may for example be a converter of a converter station (or at least part of it) and may be used for converting an incoming AC power to an outgoing DC power.

As already described with reference to Figure 1 , the containers of the valve units may be sealed by means of spacing elements. For example, a spacing element 416 may be arranged at one of the ends or base surfaces of the container of the first valve unit 410. A first spacing element 416 is arranged at a top part of the container of the first valve unit 410 while a second spacing element 414 is arranged at an opposite end (i.e. the bottom part) of the container of the first valve unit 410. The spacing elements may be made of an insulating material such as e.g. epoxy. The spacer 416 may comprise a first portion extending in a direction transverse to the axial direction along which the container extends for separating the first valve unit 410 from the second valve unit 420. The spacer (or joint) 416 may also comprise a second portion extending along the outer wall of the enclosure of the first valve unit 410 and a wall of the first connector 460.

In the arrangement 400 shown in Figure 4, an output of the first valve unit 410 is connected to an input of the second valve unit 420 (or vice versa) by means of the first connector 460, without any cable or bus bar in open air.

In the valve arrangement 400 shown in Figure 4, the busbar element 471 of the second connector 470 is insulated by means of an insulating gas 475 which may for example be SF ₆ , N ₂ , air, dry air or a mixture of such gases. It will be appreciated however that the present disclosure is not limited to these examples and that other gases, in particular SF6-free gases, with similar insulation properties may be used. Further, a compressed gas with pressure of approximately a few bars may be used. More specifically, the second connector 470 may be an insulated compartment in which a busbar element 471 for connecting a lower cell 431 of the first valve unit 410 to a lower cell 451 of the third valve unit 430 is arranged. Other connectors and in particular busbar elements may be located in the insulated compartment such as the busbar element denoted 472 used for connecting a lower cell of the second valve unit 420 to a lower cell of the fourth valve unit 440. The insulated compartment 470 forms a base of the valve arrangement at which the containers of the valve units 410-450 are arranged. The arrangement 440 shown in Figure 4 may be part of a converter station (or valve station) and may in particular represent one arm of such converter station. A valve station may then include three such arrangements, i.e. three phases. For each phase, the number of the valve units (i.e. the number of containers or cylinder tanks) may be different, which depends on the rated system voltage and how many cells is included in one tank.

Figure 5 shows a valve arrangement 500 equivalent to the valve arrangement 400 described with reference to Figure 4 except that the second connector may be equivalent to the first connector instead of being a cabinet (or compartment filled with an insulating gas). In particular, a lower cell 514 of the stack of a first valve unit 510 may be connected to a lower cell 551 of the stack of another valve unit 530 by means of a busbar element 571 located in a pipe 573 at least partially filled with an insulating gas 575. The insulating gas 575 may for example be SF ₆ , N ₂ , air, dry air or a mixture of such gases. It will be appreciated however that the present disclosure is not limited to these examples and that other gases, in particular SF6-free gases, with similar insulation properties may be used. Further, a compressed gas with pressure of approximately a few bars may be used. Except for the above mentioned difference in the type of second connector, all other features described with reference to Figure 4 may be combined with the configuration shown in Figure 5 to form other embodiments. In particular, Figure 5 shows an arrangement of five valve units 510, 520, 530, 540 and 550 electrically connected in series. However, any other number of valve units may be used to construct the valve arrangement, depending on the desired

application. In the embodiment shown in Figure 5, the valve units are arranged side by side. Each of the valve units 510, 520, 530, 540 and 550 includes a container in which at least one stack 550 of converter cells is arranged (as shown for the valve unit denoted 510). Each of the valve units may form at least part of a larger converter (which is formed by the serial connection of the plurality of the cell stacks of the valve units). The container of a valve unit may be at least partially filled with an electrically insulating gas 515. Except for the above mentioned difference with respect to the second connector 570, each of the valve units 510, 520, 530, 540 and 550 may be equivalent to the valve unit 100 described with reference to Figure 1 or the valve units 410, 420, 430, 440 and 450 described with reference to Figure 4.

In particular, the first connector 560 including a first busbar element 561 electrically connecting a cell 521 located at one end (in particular the top end) of a first valve unit 510 to another cell 541 located at one end (in particular the top end) of a second valve unit 520 may correspond to first connector 460 described with reference to Figure 4. The first connector 560 is insulated by an electrically insulating gas 565. The valve arrangement 500 may also comprise a connector of the first type, i.e. similar to the first connector 561, for connecting the fourth valve unit 540 to the fifth valve unit 550. As for the valve arrangement 400 shown in Figure 4, each of the third valve unit 530 and the fifth valve unit 550 may be equipped with one plug-in cable termination 582, 584 for connection to an electrical system (or to an external bus bar). The plug-in cable terminations (or any other gas-insulated bus-bars) may be used for connection of the valve arrangement to a transformer or a DC gas insulation system. As shown in Figure 5, the valve arrangement 500 includes a plug-in cable termination 582 for connection of the cell stack of the third valve unit denoted 530 to an alternating current transmission line. Further, the valve arrangement 500 includes a plug-in cable termination 584 for connection of the cell stack of the fifth valve unit denoted 550 to a direct current transmission line. The plug-in cable terminations 582, 584 may be designed to connect to another valve unit or an electrical system via some kind of cable.

Further, the containers of the valve units may be sealed by means of spacing elements 514, 516 which may be equivalent to the spacing elements 414, 416 described with reference to Figure 4. The valve arrangement 500 may for example be a converter of a converter station (or at least part of it) and may be used for converting an incoming AC power to an outgoing DC power.

Figure 6 shows a valve arrangement with five valve units 610, 620, 630, 640 and 650 standing next to each other on a compartment or cabinet 670. As compared to embodiments described with reference to Figure 4, in embodiments based on the configuration shown in Figure 6, the busbar elements for connection of lower cells of two adjacent valve units, such as e.g. valve units denoted 610 and 630 and valve units denoted 620 and 640, are embedded in an insulating material instead of being isolated by an insulating gas. The insulting material of the compartment 670 may be epoxy.

Figure 6 shows a valve arrangement 600 equivalent to the valve arrangement 400 described with reference to Figure 4 except that the second connector includes a compartment with a solid insulating material in which the busbar element 671 for connecting a lower cell of the stack of the first valve unit 610 to a lower cell of the stack of the third valve unit 630. Figure 6 shows a valve arrangement with five valve units 610, 620, 630, 640 and 650 standing next to each other on a compartment or cabinet 670. As compared to embodiments described with reference to Figure 4, in embodiments based on the configuration shown in Figure 6, the busbar elements for connection of lower cells of two adjacent valve units, such as e.g. valve units denoted 610 and 630 and valve units denoted 620 and 640, are embedded in an insulating material instead of being isolated by an insulating gas. The insulting material of the compartment 670 may be epoxy.

In the valve arrangement 600 shown in Figure 6, the first valve unit 610 includes a spacing element for separating its container from the containers of the adjacent valve units 420 and 430. The spacing element includes an insulating material and may for example be arranged at a junction between one end of the container of the first valve unit 610 and the first connector 660 connecting the cell stack of the first valve unit 610 to a cell stack of an adjacent valve unit 620. The first connector 660 may be equivalent to the first connectors 160 and 460 described above with reference to Figures 1 and 4. However, at the bottom end of the container, the cabinet 670 including insulating material acts as a spacing element between two adjacent valve units and no additional spacing element is necessary. Figure 6 illustrates also that the valve arrangement may be equipped with one plug-in cable termination for connection of one of the valve units, in the present example the third valve unit denoted 630, to an alternating current transmission line and with another plug-in cable termination for connection of one of the valve units, in the present example the fifth valve unit denoted 650, to a direct current transmission line. It will be appreciated that the plug-in cable terminations may be located at the end (or opening) of the containers of these valve units or connected to the cell stack (or a busbar element extending from the cell stack) of these valve units via a busbar element.

Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. In particular, although the examples shown in Figures 4 and 6 include five valve units, it will be appreciated that any other number of valve units may be used to form a power converter station (or at least part of it). Further, reference to a first, second, third, fourth and fifth valve units may be interchanged such as for instance the third valve unit is considered to be the first valve unit and vice versa.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word

"comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.