Valve stack for high voltages

Abstract: Valve stack for high voltages, preferably for high voltage converter valves, comprising a number of electrically inter-connected valve modules (5), some of which are disposed above one another. To prevent a large fire in a valve module (5) from spreading upwards to valve modules (5) positioned above it, fire screens (8) are arranged between valve modules (5) located one above the other.

Description: The invention relates to a valve stack for high voltages according to the precharacterising part of claim 1. Such a valve stack may represent one or more high voltage converter valves or part of one high voltage converter valve. Air-insulated types of these converter valves are normally constructed in high valve stacks. These are composed of a number of electrically connected valve modules which may be arranged in floors one above the other with one or more valve modules on each floor. Each valve module comprises converter valves which may be of thyristor type as well as auxiliary equipment such as voltage divider circuits in which, inter alia, oil-impregnated capacitors may be included. The valve modules may also be arranged in other ways in the valve stack; however, at some location in the stack a valve module will always be positioned above another valve module. A large fire in a valve module may therefore spread upwards to a valve module positioned above it in a valve stack. The invention aims at developing a valve stack for high voltages in which the spread of fire from one valve module towards another valve module is largely prevented. To achieve this aim, the invention suggests a valve stack for high voltages according to the introductory part of claim 1, which is characterized by the features of the characterizing part of claim 1. Further developments of the invention are characterized by the features of the additional claims. The valve stack is divided into floors, and at least two floor planes are to be isolated from each other by the arrangement of fire screens below the valve modules lying on the upper floor. In this way, at least these two floors in a valve stack will be isolated from each other from the point of view of fire. Still better from the point of view of fire is, of course, that all valve modules positioned above each other are isolated from each other by means of fire screens positioned between them, although this may lead to certain problems as regards deteriorated accessibility of equipment existing in the stack and possibly, to a certain extent, deteriorated cooling. According to a suitable embodiment of the invention, each fire screen is formed from two plates arranged in L-shape, one of the plates being placed in a substantially horizontal position below one or more valve module. The other plate is placed substantially vertically between the last-mentioned valve modules and the centre shaft. The L-shaped screen is advantageously made in one piece from a sheet-formed glass-fibre material. The transition between the horizontal and the vertical plate of a screen is made rounded so as to ensure laminar flow of possible flue gases around the edge. The substantially horizontal plate is also provided with recesses or small trays for collecting any leaking oil from capacitors positioned above. The same plate is also inclined to a certain extent in a direction towards the outer edges of the valve stack to ensure that any water leakage is guided away from the valve module positioned below. To facilitate detection of a fire in a valve module without equipping each valve module with its own detection equipment, the flue gases are passed out into the centre shaft and up through this to the equipment for flue gas detection arranged in the roof of the valve hall above the valve stack. Any work platforms in the centre shaft are designed so as to let through these flue gases, for example in the form of a lattice-work of plate bands standing on edge, or of electrically insulating laminates. In a similar manner, the L-shaped fire screens are made with a rounded transition from a horizontal to a vertical plate so as to obtain laminar flow of flue gas around the edge. In those cases where the valve stack has a corona shield as a roof, this shield is provided with openings above the centre shaft for emission of flue gases, if any. By way of example, the invention will now be described in greater detail with reference to the accompanying drawings showing in Figure 1 a partially filled stand for a valve stack, Figure 2 a fire screen according to the invention, Figure 3 the same fire screen seen straight from above, Figure 4 a section A-A of Figure 3, Figure 5 an enlarged section B-B of Figure 3, Figure 6 an enlarged section C-C of Figure 3, Figure 7 an enlarged section D-D of Figure 3, Figure 8 a corona shield for the top of the valve stack, Figure 9 a work platform, arranged in the centre shaft, seen from the side, Figure 10 the work platform according to Figure 9, seen from above. Figure 1 shows a partially filled stand 1 for a valve stack 2 intended to be suspended by means of the insulators 3 from the roof of a valve hall. The valve stack comprises sixteen floors 4 arranged one above the other. On each floor there are four valve modules 5, two of which are located in the front part of the valve stack 5 and two in the rear part thereof, the two pairs of valve modules being separated by a vertical centre shaft 6 arranged between the modules. The contours of the centre shaft are clear from the work platforms 7. For the sake of clarity, only the upper floor 4 is equipped with valve modules 5 in the stand 1. In this case these valve modules include valves of thyristor type and auxiliary equipment which, inter alia, comprises oil-impregnated capacitors. In the third floor, counting from above, it is shown how the fire screens 8 are mounted with a substantially horizontal plate straight below a valve module 5 (not shown) and a vertical plate forming a demarcation towards the centre shaft. At the top the valve stack 2 is provided with a corona shield 9, in which openings 10 for any flue gases from the centre shaft 6 are provided. Straight above the valve stack in the roof of the valve hall, a flue gas detector 18 is arranged. The intention is for a possible fire in a valve module 5 to be rapidly detected by the flue gases from the valve module encountering the substantially horizontal part of the fire screen, arranged above the valve module 5, and there being deflected in a direction towards the centre shaft and up through this shaft and the openings 10 of the corona shield 9 to the flue gas detector 18. Figure 2 shows a fire screen 8 consisting of a substantially horizontal plate 11 and a vertical plate 12. The plate 11 is provided with recesses 13 for collection of inflammable liquids which may possibly leak from a valve module 5 mounted above the plate 11. The plane of the plate 11 itself is made such that, from the connecting line with the vertical plate 12, it slopes slightly outwards towards the outer contour of the valve stack 2 whereas the fixing ridges 14 which delimit the plate 11 in the lateral direction are horizontal. This means that any other leakage, dripping down onto the plate and not collected in the recesses 13, will run towards the outer contour of the valve stack 2. It is therefore suitable for apparatus containing burnable liquids to be arranged above the recesses 13 and for apparatus which are cooled by, for example, water to be placed above the smooth part of the plate 11. The vertical plate 12 is also provided with a number of vertical slots 15 intended to possibly receive vertically arranged, fire-resisting plates of laminate (not shown). These plates aim at limiting the horizontal spreading of fire within a valve module and will, of course, also contribute to reduce the risk of vertical spreading of fire. The slots 15 as well as the slight outward inclination of the plate 11 contribute to pass flue gases, if any, into the centre shaft 6 and upwards therein in a laminar flow. Figure 3 shows the fire screen 8 seen from above with the same reference characters inserted as in Figure 2. Figures 4-7 show different sections of Figure 3 with the same reference characters inserted. Figure 8 shows a corona shield 9 with openings 10, Figure 9 shows a work platform 7 seen from the side, and Figure 10 shows the same work platform seen from above. The work platform is designed to let through flue gases and may be formed from two longitudinal beams 16, between which bands 17 standing on end are provided. The valve stack may, of course, be composed in some other way than that described above with a different number of floors 4 and valve modules 5. The valve modules may also be arranged stepped. The main feature is the provision of a fire screen of the kind described below a suitable number of valve modules located above one another. As mentioned above, the fire screen may be formed form a sheet-formed glass-fibre material, but also other fire-resisting materials may, of course, be used.

Claims: Valve stack for high voltage converter valves, wherein the valve stack (2) is divided into a number of floors (4) located one above the other, each floor (4) comprising a number of electrically interconnected valve modules (5) including valves with associated auxiliary equipment, wherein the valve stack (2) is divided along a substantially vertical section into two stack portions separated by a vertically extending centre shaft (6), characterized in that at least between two adjacent floors (4) between the vertically adjacent valve modules (5) individual substantially horizontal fire screens (8) are arranged which do not contact each other. Valve stack according to claim 1,, characterized in that a fire screen (8) is formed from two plates (11, 12) arranged together in L-shape, one of the plates (11) being placed substantially horizontally below a valve module (5), the other plate being placed substantially vertically between the last-mentioned valve module (5) and the centre shaft (6). Valve stack according to claim 2, characterized in that the L-shaped fire screen (8) is manufactured in one piece with a rounded transition between the plates (11,12) forming the fire screen (8). Valve stack according to any of the preceding claims, characterized in that any work platforms (7) in the centre shaft are designed to let through flue gases passing through the centre shaft (6). Valve stack according to any of the preceding claims, which valve stack is provided at the top with a roof, possibly shaped as a corona shield (9), characterized in that said roof is provided with openings (10) above the centre shaft (6). Valve stack according to any of claims 2 to 5, characterized in that the plates (11) below the valve modules (5) are arranged slightly inclined towards the outer contour of the valve stack (2). Valve stack according to any of the preceding claims, characterized in that the substantially horizontally arranged plates (11) are provided with recesses (13) for collection of any inflammable liquid leaking from the valve module (5) positioned above them. Valve stack according to any of the preceding claims, wherein the valve stack (2) is arranged in a valve hall, characterized in that flue gas detectors (18) are arranged in the roof of the valve hail above the valve stack (2).

Inventors: ASTROEM URBAN, JOHANSSON MATS, RUETER FREDRIK, ASTROEM, URBAN, JOHANSSON, MATS, RUETER, FREDRIK, Aström, Urban, Rüter, Fredrik
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1992
Main classification: H02M7
IPC codes: H02M7