Title of Invention

"A PASSIVE COOLING DEVICE FOR ELECTRICAL SWITCHGEAR"

Abstract

This invention relates to a passive cooling device for electrical switchgear, in particular for an electricity generator circuit-breaker (2), and switchgear including such a device. The passive cooling device has a casing (14) which defines an internal volume containing a dielectric gas. Said passive cooling device protrudes from the protective cladding (4) through an opening (28) so that one surface of the device is exposed to the exterior of an upper part of the protective cladding (4). Said device comprises at least a circulation tube (30) having an inlet end (32) and an outlet end (34) for natural convection of the dielectric gas in the internal volume of the circuit-breaker. The inlet end (32) and the outlet end (34) of said circulation tube (30) are connected to said surface of the electrical switchgear exposed to the exterior of an upper part of the protective cladding (4).

Full Text

TECHNICAL FIELD The invention relates to . electrical switchgear, in particular to generator circuit-breakers, to contactors, and to switches. More precisely, it relates to a passive cooling device for electrical switchgear, in particular a generator circuit-breaker disposed vertically inside protective cladding and having a casing which defines an internal volume containing a dielectric gas, said passive cooling device protruding from the protective cladding through an. opening so that one surface of the device is exposed to the exterior of an upper part of the protective cladding, said device comprising at least a circulation tube having an inlet end and an outlet end for natural convection of the dielectric gas in the internal volume of the circuit-breaker. Conventionally, a generator circuit-breaker, also referred to as a "power station circuit-breaker", is situated in a set of busbars between an alternator and a transformer. It is disposed in protective metal cladding to protect it from the outside air. A space sufficient for electrical insulation is provided between the live boxes constituted by the poles of the circuit-breaker and the protective cladding which is at ground potential. The cladding is filled with a gas, generally dry air, at atmospheric pressure or at a slightly higher pressure. The circuit-breaker has an interrupting chamber filled with an insulating gas at a pressure of a few bars, it being possible for the insulating gas to flow between the interrupting chamber and the boxes of the circuit-breaker. The circuit-breaker is fully airtight relative to the air of the cladding. It is connected to the power station and to the grid respectively by an incoming conductor and by an outgoing conductor, the conductors passing through the cladding in dielectrically leaktight manner. A generator circuit-breaker is already known. (FR 2 800 905) that is provided with a passive cooling device which comprises a hollow insulator situated in the cladding and having a first end connected to the top box of the circuit-breaker. That insulator is disposed substantially vertically in order to enable the insulating gas to flow by convection between the interrupting chamber' of the circuit-breaker and the hollow portion of the insulator. A second end of the insulator is connected in leaktight manner to an opening provided in the top portion of the metal cladding. The cooling device further comprises a cooling circuit outside the cladding, which circuit makes it possible for the insulating gas of the circuit-breaker to flow by natural convection to form a loop from the top box to the bottom box of the circuit-breaker. The circuit-breaker is in a vertical position in the cladding and is supported by another hollow insulator which stands on a grounded metal support box. The support box is provided with a passageway so as to enable the cooling circuit to communicate with the circuit-breaker so that the insulating gas can flow around a looped circuit. That cooling device is very satisfactory as regards the effectiveness of the cooling of the interrupting chamber. That makes it possible to increase substantially the nominal current that the circuit-breaker can withstand in operation. Unfortunately, that device is relatively costly and voluminous. A precise object of the invention is a passive cooling device that remedies those drawbacks. The device must be less expensive to manufacture, and more compact, while also providing cooling that is sufficiently effective, in order to procure a significant gain in nominal current. These aims are achieved by the fact that said inlet end and said outlet end of said circulation tube are connected to said surface of the electrical switchgear exposed to the exterior of an upper part of the protective cladding. By means of theses characteristics, the area of heat exchange between the dielectric gas and the outside air is increased without significantly increasing the overall dimensions of the switchgear, in particular in the height direction. The dimensions on the ground are diminished. All of the device is on one side of the cladding so that the dismantling of the device is eased. In a preferred embodiment, the inlet end of the circulation tube is situated at a height greater than the height of the outlet end of the tube. By means of this characteristic, preference is given to one direction of circulation for the dielectric gas, and the effectiveness of the natural convection is thus increased. In a particular embodiment, the inlet end and the outlet end of the circulation tube are separated from each other by a separator plate. The circulation tube may be mounted on a plate that closes of.f the opening formed in the top wall of the protective cladding. The circulation tube may also be connected to a cooling box mounted outside the protective cladding. In a particular embodiment, the circuit-breaker includes a hollow insulator disposed substantially vertically inside the cladding and having a bottom end connected to a box of the circuit-breaker and a top end connected in leaktight manner to the opening formed in the protective cladding. The invention also provides metal-clad electrical switchgear such as a metal-clad generator circuit-breaker including at least one passive cooling device of the invention. Other characteristics and advantages of the invention further appear on reading the • following description of embodiments given by way of illustration and with reference to the accompanying figures. In the figures: Figure 1 is a view of a n embodiment of a circuit-breaker of the invention; Figure 2 is a perspective view of a circulation tube mounted on a plate; Figures 3 and 4 are detail profile views of the circulation tube of the circuit-breaker of Figure 1; Figure 5 is a perspective view showing two circulation tubes mounted on a plate; Figure 6 is a variant embodiment of a circuit-breaker having an external cooling box; Figure 7 is' a detail view of a variant of the embodiment of Figure 6, including a circulation tube having a bend at one end; Figure 8 is a variant shape of the cooling tube. In Figure 1, a generator single-phase circuit-breaker 2 is disposed vertically inside protective metal cladding 4 for protecting it from the outside air. In known manner, the cladding 4 includes a top portion 6 constituting' a roof, the roof preferably being removable. The circuit-breaker 2 is shown in section on a vertical plane containing the axes of the incoming conductor 8 and of the outgoing conductor 10 of the circuit-breaker, which conductors are disposed horizontally. The circuit-breaker has an interrupting chamber 12 disposed inside an electrically insulating casing 14 and that separates a top box 16 from a bottom box 18 of the circuit-breaker while communicating with said boxes. An insulating gas, e.g. sulfur hexafluoride SF6, contained inside the circuit-breaker can thus flow freely between the interrupting chamber 12 and the boxes 16 and 18. Inside each box 16 and 18, contact equipment of the circuit-breaker 2 is electrically connected to the incoming conductor 8 or to the outgoing conductor 10. Each box is live, e.g. when the circuit-breaker 2 is closed, which makes it necessary for the protective cladding 4, which is at ground potential, to be at a distance away that is sufficient to guarantee electrical insulation. To this end, a support insulator 20 disposed under the bottom box 18 makes it possible to hold the circuit-breaker at the center of the cladding. As is known from the state of the art, such a support insulator is, for example, made of a ceramic, such as a porcelain, and is cylindrical in shape. It has an outside surface forming fins or "sheds" in order to lengthen the creepage distance of the insulator. The insulator is further provided with a longitudinal recess for passing an insulating control rod 22 suitable for driving the contacts of the circuit-beaker 2 by means of the rod being moved in translation or in rotation. In known manner, the recess of the support insulator 2 0 communicates with the inside of the bottom box 18. The recess is thus filled with a dielectric gas under pressure. The base of the support insulator is generally connected to a control box outside the cladding (not shown) in airtight manner. In conventional manner, such a control box encloses at least a portion of the control mechanism immersed in the dielectric gas under pressure. At the top end of the circuit-breaker, an insulator 26 is also provided to a longitudinal recess. The top insulator 26 can . be more lightweight in structure than the support insulator 20. It is disposed vertically above the top box 16. Like the suppprt insulator 20 and the insulating casing 14, the top insulator preferably has an outside surface forming fins in order to extend the creepage distance of the insulator, however it has almost no support function, and its structure is organized to withstand the higher pressure of insulating gas contained its longitudinal recess relative to the air in the protective cladding 4. The bottom end of the insulator 26 is fixed to the top box 16 and communicates therewith so that the insulating gas can flow through the recess in the insulator. The top end of the insulator is connected in leaktight manner to the plate 36. In the invention, cooling means communicating with the internal volume of the circuit-breaker 2 via at least one opening formed in the protective cladding are disposed outside the cladding 4. In the example described with reference to Figures 1 • to 4, said cooling means are constituted by a circulation tube 30. The tube 30 has an inlet end 32 and an outlet end 34, which ends open out in the longitudinal recess 27 of the top insulator 26. The ends 32 and 34 pass through the closure plate 36. It can be observed that the inlet end 32 of the circulation tube 30 is situated at a height greater than the height of the outlet end 34. Figure 2 is a perspective view showing the circulation tube 30 and the closure plate 36. As can be seen in Figures 3 and 4, the circulation tube 30 can be disposed in a vertical plane (Figure 3) , or else it can be disposed in a sloping plane (Figure 4) so as to make the circuit-breaker more compact in the height direction. Operation is as follows. The insulating gas contained in the internal volume of the circuit-breaker is heated up in the top box 16, and it rises towards the highest portion of the longitudinal recess 27 of the top insulator 26 in which the inlet end 32 of the circulation tube 30 is situated. The insulating gas penetrates into the tube 30, through which it flows in the direction indicated by arrow 38. While it is flowing through the tube, the dielectric gas cools by exchanging heat with the outside air. The cooled gas exits from the tube 30 via the outlet end 34 and flows back down towards the top box 16. Circulation by natural convection is thus established through the top box 16, the insulator 26 and the tube 30. The interrupting chamber 12 of the circuit-breaker is thus cooled continuously and effectively, thereby making it possible to achieve a significant gain in nominal current. It is understood that the tube 3 0 can be provided with fins (not shown) so as to increase its heat exchange area via which heat can be exchanged with the outside. Other solutions for increasing performance are to increase the number of tubes and/or to paint them with a dark color so as to increase the radiation. In addition, a forced ventilation system applied to the outside air can be installed above the protective cladding in order to accelerate the heat exchange and. in order to improve the cooling of the insulating gas. Figure 5 is a perspective view of a variant embodiment. Two circulation tubes 30 are mounted on the closure plate 36 in order to increase the flow of the dielectric gas and therefore the effectiveness of the cooling by natural convection. In addition, in this embodiment, the inlet and the outlet' ends of each of the tubes 30 are situated at the same height. That is why the closure plate 36 . is equipped with a separator plate 40 whose function is to separate the hot gases from the cold gases. A preferred circulation direction is given by the fact that one of the sides of the circuit-breaker heats up to a greater extent than the other side so that the insulating gas builds up on said one of the sides. The separator plate makes it possible to maintain said separation and, therefore, makes it easier to establish the natural convection and to keep it stable. Figure 6 shows a variant embodiment of the circuit-breaker of Figures 1 to 5. A cooling metal box 42, disposed outside the top wall 6 of the protective cladding 4 is connected in leaktight manner to the insulator 26. The internal volume 43 of the box 42 communicates with the longitudinal recess 27 of the top insulator 26 so as to form a space filled with insulating gas and airtight relative to the air inside or outside the cladding. A circulation tube 30 has an inlet end 32 and an outlet end 34 connected to the box 42. As can be observed in Figure 6, the inlet end 32 is situated at a height greater than the height of the outlet end 34 so as to establish, as explained above, circulation by natural convection, in the direction indicated by arrow 38, of the insulating gas contained in the internal volume of the circuit-breaker. In this variant, the gas is cooled by heat exchange with the inside surface of the box 42, and then by flowing through the tube 30. This makes it possible to cool the interrupting chamber 12 effectively and therefore to achieve a significant gain in the nominal current of the circuit-breaker. Figure 7 shows a detail" of a variant of an embodiment. The outlet end 34 of the circulation tube 3 0 has a downwardly-curved bend so as to achieve a further increase in the height difference relative to the height of the inlet end 32. These two provisions improve the effectiveness of the natural convection. Figure 8 . shows another variant embodiment. The tube 30 has an asymmetrical shape which makes it possible to give preference to one direction for circulation of the dielectric gas (arrow 38). Said tube can be mounted on a plate 36 such as the plate shown in Figure 1, or on a box such as the box 42 shown in Figure 6. We Claim; 1. A passive cooling device for an electrical switchgear such as a generator circuit - breaker (2) disposed vertically inside a protective cladding (4) and having a casing (14) which defines an internal volume containing a dielectric gas, said passive cooling device protruding from the protective cladding (4) through an opening (28) so that one surface of the device is exposed to the exterior of an upper part of the protective cladding (4), said device comprising at least a circulation tube (30) having an inlet end (32) and an outlet end (34) for natural convection of the dielectric gas in the internal volume of the circuit breaker characterized in that said inlet end (32) and said outlet end (34) of said circulation tube (30) are connected to said surface of the electrical switchgear exposed to the exterior of an upper part of the protective cladding (4) and in that the inlet end (32) of the circulation tube (30) is situated at a height greater than the height of the outlet end of the tube (34). 2. The cooling device as claimed in claim 1, wherein the tube (30) has an asymmetrical shape in order to facilitate circulation of the gas. 3. The cooling device as claimed in any one of claims 1 to 2, wherein the inlet end (32) and the outlet end (34) of the circulation tube are separated from each other by a separator plate (40). 4. The cooling device as claimed in any one of claims 1 to 4, wherein the circulation tube (30) is mounted on a plate (36) that closes off the opening (28) formed in the top wall (6) of the protective cladding (4). 5. The cooling device as claimed in any one of claims 1 to 4, wherein the circulation tube (30) is connected to a cooling box (42) mounted outside the protective cladding (4). 6. The cooling device as claimed in any one of claims 1 to 5, wherein the circuit-breaker comprises a hollow insulator (26) disposed vertically inside the cladding (4) and having a bottom end connected to a box (16) of the circuit-breaker and a top end connected in leak tight manner to the opening (28) formed in the protective cladding (4). 7. A metal clad electrical switchgear (4) including at least one passive cooling device as claimed in any one of claims 1 to 6.

Documents:

1638-del-2005-Abstract-(03-01-2012).pdf

1638-del-2005-abstract.pdf

1638-del-2005-Claims-(03-01-2012).pdf

1638-del-2005-claims.pdf

1638-del-2005-Correspodence Others-(03-01-2012).pdf

1638-DEL-2005-Correspondence Others-(24-11-2011).pdf

1638-DEL-2005-Correspondence-Others (12-11-2009).pdf

1638-DEL-2005-Correspondence-Others-(13-05-2009).pdf

1638-del-2005-correspondence-others.pdf

1638-del-2005-Description (Complete)-(03-01-2012).pdf

1638-del-2005-description (complete).pdf

1638-del-2005-Drawings-(03-01-2012).pdf

1638-del-2005-drawings.pdf

1638-del-2005-Form-1-(03-01-2012).pdf

1638-DEL-2005-Form-1-(13-05-2009).pdf

1638-del-2005-form-1.pdf

1638-del-2005-form-13-(13-05-2009).pdf

1638-del-2005-form-18.pdf

1638-del-2005-Form-2-(03-01-2012).pdf

1638-del-2005-form-2.pdf

1638-del-2005-form-3.pdf

1638-del-2005-form-5.pdf

1638-DEL-2005-GPA (12-11-2009).pdf

1638-del-2005-GPA-(03-01-2012).pdf

1638-del-2005-Petition-137-(03-01-2012).pdf