The invention relates to a method of installing a valve module of a voltage source converter (VSC). In particular, although not exclusively, the invention relates to installing a valve module, comprising a number of sub-modules, of a high-voltage direct current (HVDC) VSC.

HVDC (high-voltage direct current) electrical power transmission uses direct current for the transmission of electrical power. This is an alternative to alternating current electrical power transmission which is more common. There are a number of benefits to using HVDC electrical power transmission.

In order to use HVDC electrical power transmission, it is necessary to convert alternating current (AC) to direct current (DC) and back again. Historically this has been done by using mercury arc valves which are sometimes known as line- commutated converters (LCC).

However, recent developments in the power electronics field has led to an increased use of voltages-source converters (VSC) for AC-DC and DC-AC conversion. Voltage source converters typically comprise six valves, each comprising a number of valve modules. Each valve module comprises a number of sub-modules mounted in a rack. In one example, each valve may comprise 48 valve modules, each containing eight sub-modules. In one valve, all of the sub-modules are connected in series. Each sub- module typically comprises a switching device, such as one or more insulated gate bipolar transistors, a capacitor and control and monitoring circuitry.

In a voltage-converter installation it is necessary to structurally support and electrically insulate the valve modules. According to an aspect there is provided a method of installing a valve module of a voltage source converter, comprising: constructing an insulation assembly by installing a plurality of insulator posts, each having a support plate at its upper end, and loosely connecting a plurality of insulator braces between the plurality of insulator posts;

lowering the valve module onto the insulation assembly; securing the valve module to the respective support plates; and tensioning the plurality of insulator braces. The valve module may have a plurality of feet. The valve module may be lowered such that each foot of the valve module rests on a respective support plate. Securing the valve module may comprise securing the feet to the respective support plates. Loosely connecting the insulator braces means that they are connected so that they stay in place, but to not exert an excessive force on the remainder of the structure. It should be appreciated that the order that the method steps are presented in need not be limiting unless it is expressly stated or implicit. Tensioning the insulator braces may be completed after securing the feet of the module. The insulator assembly may structurally support and electrically insulate the valve module. Each insulator post and insulator brace may comprise an electrical insulator.

The valve module may comprise a metal rack or the like. The valve module may house one or more sub-modules, and may house them side-by-side. The valve module may be a HVDC voltage-source converter (VSC) module and the sub-modules, if present, may be HVDC VSC sub-modules. The feet may simply be the corners of the module or may be specifically designed feet elements. The feet may comprise fixing elements such as holes, through which bolts can be passed to bolt the feet to the support plates. Securing the feet may comprise bolting the feet to the support plates.

The number of insulator posts may be the same as the number of insulator braces, which may be the same as the number of feet of the valve module. There may be four insulator posts, four insulator braces and the valve module may have four feet. In other embodiments, there may be more insulator posts and braces.

Each of the plurality of insulator posts may be installed substantially vertically. The plurality of insulator posts may be installed on a horizontal base, such as a floor.

The method may comprise installing a plurality of floor plates. The number of floor plates may be the same as the number of insulator posts. The base of each insulator posts may be attached to a respective floor plate.

Each insulator brace may be connected (directly or indirectly) between an upper part of one insulator post and a lower part of another, such as a diagonally opposite, insulator post. In one embodiment the insulator posts are connected to a bracket at a lower end of one insulator post and to a bracket or lug at the top of another insulator post. Each insulator brace may be connected to a floor plate, which is at the bottom of the insulator posts. At least four insulator posts may be installed in positions such that the centreline of the base of each insulator post is aligned with the centrelines of the bases of two other insulator posts along orthogonal axes. In other words, in plan, the insulator posts may form a perfect rectangle. The floor plates may be installed with their centrelines at the same positions.

The plurality of insulator posts may define a space that is substantially a rectangular parallelepiped. Each insulator brace may extend substantially along the space diagonal of the rectangular parallelepiped.

Prior to lowering the valve module, one or more set-up bars may be fitted between insulator posts to maintain a desired spacing between at least some of the support plates. A set-up bar may be fitted between each adjacent pair of insulator posts.

There may be four set-up bars fitted between four insulator posts. The set-up bars may be detachably fitted, such as by using pins/dowels and holes. Each set-up bar may be fitted between the support plates of the respective insulator posts. The method may further comprise removing the or each set-up bar after securing the feet of the valve module to the support plates and/or after tensioning the insulator braces.

Prior to lowering the valve module, a guide may be fitted to at least one of the support plates. The valve module may be lowered onto the insulation assembly such that the respective foot of the valve module is aligned with the guide. A guide may be fitted to each support plate. The guides may be L-shaped guides having perpendicular walls. There may be four guides. The method may comprise removing the or each guide after securing the feet of the valve module to the support plates and/or after tensioning the insulator braces.

Each insulator brace may have a first end and a second threaded end. Connecting a plurality of insulator braces may comprise, for each insulator brace: connecting the first end to one insulator post; passing the second threaded end through a hole or slot in another insulator post; and loosely threading a nut onto the threaded end. Tensioning the insulator braces may comprise tightening each nut. The first end may be provided with a connector, such as an eyelet, which can be connected to the respective part, such as a bracket, of an insulator post. The valve module may be lowered onto the insulation assembly using lifting equipment such as a crane or winch. The valve module may be supported by the lifting equipment until the insulator braces have been tensioned. The method may further comprise installing a second or further valve module adjacent to the first or previous valve module. The method may be substantially the same. The insulation assembly of the second or further installation may share one or more (such as two) insulator posts with the first or previous installation. The invention also concerns a voltage source converter installation, comprising: an insulation assembly comprising a plurality of insulator posts, each having a support plate at its upper end, and a plurality of insulator braces between the plurality of insulator posts; and a valve module located on and secured to the insulation assembly. The valve module may comprise a plurality of feet. The valve module may be located with each foot located on and secured to a respective support plate.

According to another aspect there is provided an insulator post comprising: an upper support plate and a lower support base with an elongate electrical insulator

therebetween; and a clamp which clamps a plurality of stacked shims between the upper support plate and the lower support base; wherein the clamp can be released to remove one or more shims and subsequently reclamped to change the overall length of the insulator post.

The post may comprise an upper flange to which the upper support plate is attached. The shims may be clamped between the upper support plate and the upper flange.

The clamp may be formed by the upper support plate and the upper flange. The upper support plate may be bolted to the upper flange with one or more bolts. The bolts may be loosened and/or removed to release the clamp. The shims may be provided with one or more holes or slots through which the bolts pass. The slots may be shaped such that one or more shims can be removed by loosening but not removing at least some of the bolts. The shims may be disc like and/or planar. At least some of the plurality of shims may be of a different thicknesses. The upper support plate may be at least partially rotatable with respect to the lower support base. The invention also relates to a method of adjusting the length of an insulator post in accordance with any statement herein, comprising releasing the clamp; removing one or more shims; and reclamping the clamp. The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 schematically shows part of a HVDC voltage-source converter (VSC) installation including two insulation assemblies and two valve modules;

Figure 2 schematically shows an insulator post used to construct the insulation assembly shown in Figure 1 ;

Figure 3 schematically shows the insulator post of Figure 2 with the support plate removed; Figure 4 schematically shows an insulator brace used to construct the insulation assembly shown in Figure 1 ;

Figure 5 schematically shows a partially assembled insulation assembly; Figure 6 schematically shows an enlarged view of the base of an insulator post connected to an insulator brace;

Figure 7 schematically shows an enlarged view of the support plate of an insulator post connected to an insulator brace;

Figure 8 schematically shows a close-up of the top of a partially assembled insulation assembly with set-up bars and guides being located in place;

Figure 9 schematically shows a partially assembled insulation assembly with set-up bars and guides located in place; Figure 10 schematically shows a valve module lowered onto the insulation assembly of Figure 9; and

Figure 1 1 schematically shows a completed insulation assembly with a valve module secured thereto.

In an AC-DC or DC-AC voltage source converter (VSC) sub-station which converts AC to DC or vice versa, there are typically six valves, each constructed from a number of valve modules, with each valve module containing a number of sub-modules electrically connected in series. Although not shown in detail in the figures, each valve module is typically in the form of a rack containing a number of, such as eight, sub- modules located side-by-side. Each sub-module typically comprises a switching device, such as one or more insulated gate bipolar transistors, a capacitor and control and monitoring circuitry. In one example, each valve comprises 48 valve modules, resulting in a 384 sub-modules which are connected in series.

Figure 1 shows part of a valve of a HVDC voltage-source converter (VSC) installation 1 comprising two insulation assemblies 10 secured to a floor and located side-by-side. A valve module 12 is located on and secured to each insulation assembly 10 such that they are located side-by-side. Although only two insulation assemblies 10 and two valve modules 12 are shown, it should be appreciated that a full installation may include many more insulation assemblies 10 and modules 12. Further, in some embodiments, valve modules 12 may be stacked on top of one another with a separate insulation assembly, which may be substantially of the same construction, disposed between them.

Each insulation assembly 10 comprises four substantially vertical insulator posts 14 and four insulator braces 16. Each vertical insulator post 14 has a support base 18 at its lower end, that is bolted to a floor plate 20 that is installed in the floor, and a support plate 22 at its upper end. The floor plates 20 are installed such that they form a rectangle (in plan). Therefore, the centreline of each of the fours bases 18 is aligned with the centrelines of two other bases 18 along orthogonal axes. The four

substantially insulator posts 14 define a space that is substantially a rectangular parallelepiped. Each insulator brace 16 substantially extends along one of the space diagonals. Specifically, each insulator brace 16 extends from a lower part of one insulator post 14 to an upper part of a diagonally opposite insulator post 14. The insulator braces 16 are tensioned to keep the insulator posts 14 vertical and the support plates 22 horizontal and located in a common plane. With the insulator braces 16 tensioned, the insulator posts 14 are substantially vertical and therefore the centreline of each of the four support plates 22 is aligned with the centrelines of two other support plates 22 along orthogonal axes (i.e. they form a rectangle in plan). As will be described in detail below, each insulator brace 16 is directly connected to a lower part of a respective insulator post 14. However, it should be appreciated that the insulator braces 16 may be indirectly connected to a lower part of an insulator post 14, such as by being connected to the floor plate 20.

As can be seen from Figure 1 , two adjacent insulation assemblies 10 have two common insulator posts 14 (the middle two insulator posts). However, each insulation assembly 10 has separate insulator braces 16. Each valve module 12 is essentially a rack containing a plurality, in this case eight, VSC sub-modules located side-by-side and electrically connected in series. The valve module 12 has four feet 13, one at each corner. Each foot 13 is located on and is bolted to a respective support plate 22 to secure the valve module 12 in place. The insulation assembly 10 therefore structurally supports and electrically insulates the valve module 12. As shown in Figure 2, each insulator post 14 is generally linearly extending and has a base 18 at its lower end and a support plate 22 at its upper end. The base 18 is in the form of a flange and has a lower tubular sleeve 24 axially extending therefrom. The support plate 22 has a substantially horizontal support surface and, as will be described in detail below, is detachably attached to an upper flange 26 from which an upper tubular sleeve 28 axially extends therefrom. The support plate 22 is at least partially rotatable in this embodiment in order to aid alignment during installation. An electrical insulator member has a lower end located in and secured to the lower sleeve 24 and an upper end located in and secured to the upper sleeve 28. In this

embodiment, the insulator member is a pultruded polymeric member, such as glass- reinforced plastic (GRP). A protective rubber covering 30, sometimes referred to as a "shed", surrounds the insulator member and helps to prevent electrical creepage. In this embodiment, the base 18, support plate 22, lower sleeve 24, upper flange 26 and upper sleeve 28 are made from metal such as steel coated with zinc. It should be appreciated that other suitable materials could be used. The base 18 is provided with two brackets 32 (only one is visible in Figure 2) in the form of a projection having a hole 34 that extends therethrough in a horizontal plane. The support plate 22 is provided with two angled lugs 36 that are inclined upwards with respect to the horizontal support surface of the support plate 22. The angled lugs 36 are provided with holes 38 that extend therethrough. As will be explained in detail below, the insulator braces 16 are connected to the brackets 32 and the lugs 36.

The support plate 22 is provided with a plurality of holes. Four of these holes are used to bolt the support plate 22 to the upper flange 26 from the underside. Holes are also provided such that the feet 13 of the valve module 12 can be bolted to the support plate 22. The remaining holes are used to precisely locate set-up bars and guides that are used during construction of the insulation assembly 10. Grooves (not shown) are also machined into the surface of the support plates 22 along X and Y axes to aid alignment during construction.

As best shown in Figure 3, initially, a plurality of stacked metal shims 40 are disposed and clamped between the upper flange 26 and the support plate 22 (which form a clamp). There are seven shims 40 in this embodiment, five shims having a thickness of 1 mm, one shim having a thickness of 0.5mm, and one shim having a thickness of 0.3mm. The shims 40 are generally disc-like and are provided with tabs 42 indicating their thickness. The shims 40 are provided with four slots 44 through which bolts 46, which are used to secure the support plate 22 to the upper flange 26, pass. The shims 40 allow the overall length (or height) of the insulator posts 14 to be adjusted. This may be useful since the insulator posts 14 can only be manufactured to a particular tolerance which may be to large to ensure a good assembly. On site, the rear bolts 46 can be removed and the front bolts 46 can be loosened to release the clamp between the support plate 22 and upper flange 26. The appropriate number of shims 40 can then be removed to ensure that the length of the insulator post 14 is within an acceptable tolerance. Once the appropriate shims have been removed, the bolts 46 are tightened once again to clamp the shims 40 between the upper flange 26 and support plate 22.

As shown in Figure 4, each insulator brace 16 is generally linearly extending and has two parallel eyelets 48 forming a saddle 49 at a first end, and a threaded connector 50 at the second opposing end. The holes of the eyelets 48 have an axis perpendicular to that of the insulator brace 16, whilst the threaded connector 50 is coaxial with the insulator brace 16. The insulator brace 16 has an electrical insulator member having a first end secured to the eyelets 48 and a second end secured to the threaded connector 50. In this embodiment, the insulator member is a pultruded polymeric member, such as glass-reinforced plastic (GRP). A protective rubber covering 52, sometimes referred to as a "shed", surrounds the insulator member and helps to prevent electrical creepage. As will be explained in detail below, the saddle 49 formed by the two eyelets 48 is designed to sit over one of the brackets 32 with the eyelet holes aligned with the hole 34, and the threaded connector 50 is designed to pass through a hole 38 in one of the lugs 36. The threaded connector 50 and eyelets 48 are metallic components made from steel coated with zinc. It should be appreciated that other suitable materials could be used.

A method of installing a valve module 12 of a HVDC voltage-source converter will now be described.

With reference to Figure 5, four floor plates 20 are installed in a horizontal floor (such as a concrete base or the like) such that the centreline of the floor plates 20 lie on the corners of a rectangle. This means the centreline of each floor plate 20 is aligned with the centrelines of two other floor plates 20 along orthogonal axes. In this embodiment, the horizontal spacing in the width direction (i.e. left to right) is 2050mm and the horizontal spacing in the depth direction (i.e. front to back) is 850mm. Of course, other suitable dimensions may be chosen. Four insulator posts 14 are then taken and, if necessary, shims 40 are removed to ensure that they are of the correct height. In this embodiment, the height of the insulator posts must be 3039mm +/- 0.2mm. Again, other suitable dimensions may be chosen. The base 18 of an insulator post 14 is then bolted down to each floor plate 20. The insulator posts 14 are substantially vertical, but because they are slightly flexible, they may not be exactly vertical. Therefore, the axes of the four insulator posts 14 may not be perfectly parallel to one another, meaning that the support surfaces of the support plates 22 may not be perfectly horizontal, and may not lie at the corners of a perfect rectangle. However, the four insulator posts 14 define an approximate rectangular parallelepiped.

Four insulator braces 16 are then connected between the four insulator posts 14, with each insulator brace 16 extending from a lower part of one insulator post 14 to an upper part of another diagonally opposite insulator post 14. Therefore, an insulator brace 16 extends substantially along each space diagonal (sometimes referred to as a triagonal) of the rectangular parallelepiped defined by the four insulator posts 14. With reference to Figure 6, for each insulator brace 16, the saddle 49 provided at the first end is located around the bracket 32 provided at the base 18 of an insulator post 14 such that an eyelet 48 is located either side of the bracket 32. A pin or bolt 54 is then passed through the holes in the eyelets 48 and the bracket 34 to secure the first end of the insulator brace 16 to the lower end of the particular insulator post 14. With reference to Figure 7, the threaded second end 50 of the insulator brace 16 is passed through the hole 38 in the lug 36 provided at the upper end of the diagonally opposite insulator post 14. A nut 56 is threaded onto the end of the threaded connector 50 and is loosely hand-tightened to avoid over-tensioning the insulator brace 16, which could cause the whole insulation assembly 10 to be skewed.

As shown in Figures 8 and 9, four linear set-up bars 58 and four L-shaped guide members 60 are then fitted to the assembly. There are two long set-up bars 58 that extend between the front left and right support plates 22 and the rear left and right support plates 22, and two short set-up bars 58 that extend between the left front and rear support plates 22 and the right front and rear support plates 22. The end of each set-up bar 58 is provided with a downwardly projecting pin, or dowel, that slots into one of the holes provided in the upper surface of the support plate 22. The dimensions of the set-up bars 58, and the positions of the dowels/pins and the holes in the support plate 22 are chosen such that when the set-up bars 58 are fitted, the centrelines of the support plates 22 have a horizontal spacing that corresponds to the horizontal spacing of the respective floor plates 20. Therefore, the set-up bars 58 act to keep the support plates 22 in the correct horizontal position relative to one another. The L-shaped guide members 60 have perpendicular side walls that aid in the alignment of the valve module 12. A guide member 60 is fitted to the upper surface of each support plate 22. Each L-shaped guide member 60 is provided with three downwardly projecting pins/dowels that locate in corresponding holes in the support plate 22. With reference to Figure 10, after the set-up bars 58 and guide members 60 have been fitted to the support plates 22, a valve module 12 is lowered onto the insulation assembly 10 using lifting equipment 62, such as a crane or winch or the like. The valve module 12 is gently lowered until each foot 13 is resting on a support plate 22. The feet 13 are aligned with the L-shaped guide members 60 to ensure they are in the correct position, and the X and Y alignment grooves machined in the surface of the support plates 22 are also used to visually indicate when correct alignment has been achieved. When the valve module 12 is in the correct position, the centrelines of the support plates 22 lie on the corners of a perfect rectangle and thus the centreline of each support plate 22 is aligned with the centrelines of two other support plates 22 along orthogonal axes. In this configuration, all the insulator posts 14 should be parallel to one another, ensuring that the support plates 22 are horizontal. The insulation assembly 10 thus defines a rectangular parallelepiped space.

The feet 13 of the valve module 12 are then bolted down onto the support plates 22 using the holes provided in the upper surface of the support plates 22. The insulator braces 16 are then tensioned by tightening the nuts 56 threaded onto the threaded connectors 50 of the braces 16. Tightening the nut 56 causes the threaded connector 50 to be drawn through the hole 38 in the lug 36 which tensions the insulator brace 16. The nuts 56 are progressively tightened one-by-one to ensure that the insulation assembly 10 remains square. Over tightening one nut 56 before tightening the others could skew the insulation assembly 10. Once all the insulator braces 16 have been tensioned to the required degree, a final check is performed to ensure correct alignment. Referring to Figure 11 , after this final check has been performed, the lifting equipment 62 is detached from the valve module 12 so that it is entirely structurally supported by the insulation assembly 10. The set-up bars 58 and guide members 60 are also removed from the support plates 22 and may be re-used for another build.

Referring back to Figure 1 , it will be appreciated that when a second insulation assembly 10 is constructed next to a first insulation assembly 10, only two insulator posts 14 need to be installed as the second assembly 10 will share two insulator posts 14 with the first assembly. Of course, in other embodiments adjacent insulation assemblies may not share any insulator posts 14.

It has been described that the insulation assembly 10 has four insulator posts 14 that each support a corner, or foot 13, of a valve module. In other embodiments, there may be more insulator posts 14, such as six or eight, for each insulation assembly 10. For example, there may be six insulator posts 14 defining a rectangular parallelepiped with six insulator braces 16. The insulator posts 16 may extend between the upper part of one post to the lower part of another post. It is not essential that the insulator posts 14 define a rectangular parallelepiped, and may form a space of a different shape. A number of valve modules 12 may be stacked on top of one another, as well, or instead, as being located side-by-side. If a number of valve modules 12 are stacked together, an insulation assembly may be provided between each valve module 12 to vertically separate and space them. The insulation assembly may be similar to that described above and may be constructed by substantially the same method.