Gas-insulated high-voltage electrical switchgear with overpressure relief

Abstract

Gas-insulated high-voltage electrical switchgear comprising a gas-insulated enclosure (1), wherein the enclosure (1) in turn comprises: - at least one switching means (2) with at least one switching / connecting - disconnecting - earthing function; - at least one protective element (3) incorporated inside a housing (4) housed in a removable fuse holder (5), said housing (4) being mounted between the switching means (2) and at least one busbar (7); and - a plug (9) forming part of the same removable fuse holder (5) and sealing the housing (4) by means of an elastic element (10) when the protective element (3) is incorporated; characterized in that it comprises an overpressure relief device (8) installed between the inner space (13) of the housing (4) and the outer space (14) of the enclosure (1), such that the overpressure relief device (8) maintains the inner space (13) of the housing (4) airtight under normal operating conditions while allowing the instantaneous evacuation of a flow of gas in case of excess pressure inside the inner space (13) of said housing (4), and wherein the elastic element (10) of the plug (9) is disposed where the overpressure relief device (8) is installed.

Description

Gas-insulated high-voltage electrical switchgear with overpressure relief OBJECT OF THE INVENTION The present invention has its field of application in electrical power distribution installations, in particular, it refers to a gas-insulated high-voltage electrical switchgear that has an overpressure relief device that is integrated into the housing where an overload and short-circuit protection element is incorporated. The objective of the invention is to keep the housing where the protective element is incorporated airtight while allowing the evacuation of excess gas when there is overpressure inside said housing without the protective element having acted, and thus avoid the activation of a mechanism to operate a means of maneuvering or personal injury when replacing the protective element. BACKGROUND OF THE INVENTION Currently, high-voltage electrical switchgear used in power distribution networks is installed in enclosures, usually metallic, called switchgear or cells. This switchgear includes operating devices, such as circuit breakers, that perform the functions of switching on / off, disconnecting, and grounding the installation. Thus, in cases such as a fault in the distribution line, an outage due to construction, maintenance, or load balancing, these operating devices can be activated to achieve the desired power distribution, prevent power outages for consumers, or ensure the protection of people and electrical equipment, such as transformers. In addition to switching devices, electrical switchgear also includes overload and short-circuit protection elements, such as fuses. The major advantage of fuses is their rapid response in the event of a short circuit. Consequently, they effectively protect electrical switchgear and electrical equipment, such as distribution transformers, against the dynamic and thermal effects of a short circuit. Therefore, an enclosure incorporating electrical switchgear may include at least one switching device, such as a load break switch that performs switching, disconnecting, and earthing functions, and at least one protective element, such as a fuse.The protective device is installed inside a housing, also known as a fuse holder tube. Specifically, the protective device is housed in a removable fuse holder within this housing. Generally, the switching mechanism is installed between at least one busbar of the main circuit and the housing that incorporates the protective device, while the housing of the protective device is installed between the switching mechanism and at least one branch busbar. In the case of electrical switchgear comprising a switching device and a protective element, such as a series fuse installed downstream of said switching device, there are two types of protective functions: linked fuses and combined fuses. In the first case, linked fuses, if one of the fuses blows, the switching device does not open, so the other two phases continue to function. Conversely, in the second case, combined fuses, when any of the fuses blows, the switching device completely cuts off the power supply. In the case of combined fuses, when a fuse blows, it releases a small piece called a striker, which causes the deformation of an elastic element by contact. This, in turn, triggers a mechanism that opens the switching device, cutting off power to all three phases. As mentioned above, some of the electrical switchgear, such as the switching equipment, the main circuit busbars, and the branch busbars, are incorporated into a metal enclosure and insulated in a gas, such as atmospheric air. The enclosure is airtight in cases where the gas used is not atmospheric air, such as sulfur hexafluoride (SF6), dry air, nitrogen, CO2, etc. Regarding the type of gas used, it's worth mentioning that the most widely used gas in recent years has been SF6 due to its excellent dielectric properties and, among many other advantages, the fact that it is non-toxic to humans. However, this gas has a significant environmental impact due to its high global warming potential (GWP = 22,800). For this reason, in recent years alternative gases have been sought, such as dry air, N2, O2, or CO2, or mixtures of fluoroketones with gases like CO2, N2, O2, air, or mixtures thereof, that can replace SF6 in this type of electrical switchgear. Likewise, the same insulating medium, such as a dielectric gas mentioned above, in some cases also allows the extinction of the electric arc generated between the switch contacts during opening and closing operations. One of the objectives of using a dielectric insulating gas is to reduce the distance between phases, that is, the distance between live parts, such as the distance between the main circuit bars or between branch bars, in order to achieve a more compact enclosure that is insensitive to external or environmental conditions such as pollution or humidity. Therefore, in order to maintain or reduce the dimensions of electrical switchgear as when using SF6, pressure is typically increased within the enclosures or sealed compartments of the switchgear, while maintaining the same distances between conductive parts or minimizing them. This necessitates measuring certain parameters inside the sealed compartments of the electrical switchgear, such as pressure and temperature. If measuring the pressure of SF6 gas in sealed enclosures is currently required to detect overpressures or gas leaks, for example, this is even more crucial when using alternative gases to SF6, which require a higher filling pressure for the sealed enclosures.This increase in the filling pressure of the hermetic enclosures can present a problem that did not exist previously with SF6 filling pressures. In the event of a leak of insulating gas from the hermetic enclosure into the fuse holder, the elastic element of the fuse holder deforms due to the increased internal pressure. This deformation causes the operating mechanism to activate even though no fuse has blown. Furthermore, after the operating mechanism activates and the three-phase circuit is opened, the pressure inside the fuse holder can continue to rise until it reaches equilibrium with the new gas volume (enclosure plus fuse holder). This pressure, which is on the order of the filling pressure, could injure an operator attempting to replace the fuse. In this regard, we can cite the solution defined in German patent application DE4116058A1, where the elastic element of the fuse holder tube comprises a pressure compensation orifice that prevents an increase in pressure inside the tube, and therefore avoids possible bulging or deformation of the elastic element itself caused by excess air pressure inside the tube. This excess pressure would cause an incorrect response from the operating mechanism. The pressure compensation orifice is closed when the elastic element is at rest, when it is not moving, while it opens when the elastic element moves or deforms, thus releasing the excess air that increases the internal pressure of the fuse holder tube. DESCRIPTION OF THE INVENTION The present invention has its field of application in electrical power distribution installations, in particular, it refers to a gas-insulated high-voltage electrical switchgear with overpressure relief, for example, electrical switchgear used in electrical transformation centers, distribution centers, substations, etc.Specifically, the electrical switchgear comprises an overpressure relief device applicable to electrical switchgear installed in gas-insulated enclosures or cells, wherein the electrical switchgear includes within the enclosure at least one switching means, such as a load break switch or short-circuit current circuit breaker with at least one switching / connecting, isolation, and earthing function, and at least one overload and short-circuit protection element, such as a fuse incorporated in a housing or fuse tube, housed in a removable fuse holder that forms part of the same fuse tube, the switching means and the protection element being installed in series between at least one main circuit busbar and at least one branch busbar. The housing incorporating the protection element is mounted between the switching means and at least one branch busbar. The overpressure relief device of the invention solves each and every one of the problems mentioned above. Therefore, the overpressure relief device keeps the fuse holder or tube sealed under normal operating conditions of the electrical switchgear, while simultaneously allowing the instantaneous evacuation of a flow of gas in the event of excess pressure inside said fuse holder or tube. The overpressure relief device is installed between the interior space of the fuse holder or tube and the exterior of the electrical switchgear enclosure, that is, between the interior volume of the fuse holder or tube and the atmosphere, so that the evacuated gas flows out to the exterior of the electrical switchgear enclosure.For example, it may be installed in the removable fuse holder base on a plug that is part of the same removable fuse holder base and that hermetically seals the fuse holder tube when the protective element is installed. The overpressure relief device may consist of a non-return valve, a vent plug, or a vent filter that allows the internal pressure of the housing or fuse holder tube of the protective element to be maintained within certain values. Consideration has been given to installing the overpressure relief device in an elastic element that acts as a sealing gasket between the interior of the fuse holder or tube and the exterior of the electrical switchgear enclosure, or in an insulating component comprising the removable fuse holder base plug that closes the enclosure. This way, if gas leaks from the gas-insulated enclosure into the protective element's housing, causing a pressure increase inside the housing, the elastic element will not deform, and therefore no operating mechanism will be activated. The overpressure relief device will allow a portion of the leaked gas to escape to the outside of the protective element's housing. In short, an increase in the filling pressure of the electrical switchgear enclosures will not contribute to incorrect operation of the switching device in the event of a gas leak in the protective element's housing. Therefore, the purpose of the overpressure relief device is to evacuate a flow of gas in the event of excess pressure inside the protective element's housing, preventing deformation of the elastic element and the consequent activation of the switching device's operating mechanism without the protective element having tripped or melted. In this way, the switching device will only be activated if any of the fuses blow, not due to overpressure in the protective element's housing. Furthermore, due to the evacuation of excess gas from inside the housing of the protective element, the pressure is prevented from continuing to increase, thus avoiding any risk of personal injury, for example, when an operator replaces a protective element. DESCRIPTION OF THE DRAWINGS To complement the description being made and in order to help a better understanding of the characteristics of the invention, according to a preferred embodiment thereof, a set of drawings is included as an integral part of said description, in which, for illustrative and non-limiting purposes, the following has been represented: Figure 1.- Shows a single-line diagram relating to an electrical protection switchgear of the combined fuse type comprising a three-position operating means (cut / connect, sectioning and grounding), as well as a protection element installed in series between said operating means and a branch bar, where the overpressure relief device of the invention is applicable. Figure 2.- Shows a perspective view of the electrical switchgear of Figure 1 comprising a gas-insulated enclosure and where one of the fuse holder bases has been removed from the housing of the protective element for better visualization. Figure 3.- Shows a detail of the sectioned front elevation view of the housing that incorporates the protection element, as well as the removable fuse holder base where the overpressure relief device is installed on the elastic element according to a first embodiment of the invention. Figure 4.- Shows a detail of the sectioned front elevation view of the housing that incorporates the protective element, as well as the removable fuse holder base where the overpressure relief device is installed on an insulating piece of the removable fuse holder base according to a second embodiment of the invention. PREFERRED EMBODIMENT OF THE INVENTION A couple of examples of preferred embodiments are described below, referring to the figures cited above, without limiting or reducing the scope of protection of the present invention. The gas-insulated high-voltage electrical switchgear with overpressure relief of the present invention can be, for example, applied in protective electrical switchgear, such as that of the type having combined fuses, comprising a gas-insulated enclosure (1), and wherein the electrical switchgear comprises within the enclosure (1) at least one switching means (2), such as a three-position load break or short-circuit current switch (break / connect, disconnect and earth) and at least one overload and short-circuit protection element (3), such as a fuse incorporated in a housing (4) and housed in a removable fuse holder (5), the switching means (2) and the protection element (3) being installed in series between at least one main circuit busbar (11) and at least one branch busbar (7), specifically,The housing (4) incorporating the protective element (3) is mounted between the operating means (2) and at least one branch bar (7), as shown in Figures 1 to 4. As shown in Figures 3 and 4, the electrical switchgear of the invention comprises an overpressure relief device (8) installed between the interior (13) of the housing (4) and the exterior (14) of the enclosure (1) of the electrical switchgear, for example, in the removable fuse holder (5) on a plug (9) that forms part of the same removable fuse holder (5) and that hermetically seals the housing (4) when the protective element (3) is installed. In this way, the overpressure relief device (8) keeps the housing (4) hermetically sealed under normal operating conditions of the electrical switchgear while allowing the instantaneous evacuation of a flow of gas in the event of excess pressure inside said housing (4). Specifically, as can be seen in Figure 3, according to a first embodiment of the invention, the plug (9) of the removable fuse holder base (5) that closes the housing (4) comprises an elastic element (10), which acts as a sealing gasket between the interior space (13) of the housing (4) and the exterior (14) of the enclosure (1) of the electrical switchgear, and where the overpressure relief device (8) is installed, passing from side to side through the elastic element (10). According to a second embodiment of the invention, as shown in Figure 4, the plug (9) of the removable fuse holder base (5) that closes the housing (4) comprises an insulating piece (12), which acts as a support between the protection element (3) and the plug (9), and where the overpressure relief device (8) is installed, passing in this case from side to side both the elastic element (10) and the insulating piece (12). The overpressure relief device (8) is capable of venting a flow of gas to the outside of the fuse holder tube or housing (4) in the event of excess pressure inside the housing (4), preventing deformation of the elastic element (10) and the subsequent activation of the operating mechanism (6) of the switching device (2) when the protective element (3) has not activated. Furthermore, by venting the excess gas from inside the housing (4) of the protective element (3), the pressure is prevented from increasing further, thus avoiding any risk of personal injury, for example, when an operator replaces a protective element (3).Consideration has been given to the possibility that the overpressure relief device (8) may consist of a non-return valve, a vent plug or a vent filter that allows the internal pressure of the housing (4) of the protective element (3) to be kept within certain values.

Claims

1. Gas-insulated high-voltage electrical switchgear comprising a gas-insulated enclosure (1), wherein the enclosure (1) in turn comprises: - at least one switching means (2) with at least one switching / connecting - disconnecting - earthing function; - at least one protective element (3) incorporated within a housing (4) housed in a removable fuse holder (5), said housing (4) being mounted between the switching means (2) and at least one busbar (7); and - a plug (9) forming part of the same removable fuse holder (5) and sealing the housing (4) by means of an elastic element (10) when the protective element (3) is incorporated; characterized in that it comprises an overpressure relief device (8) installed between the inner space (13) of the housing (4) and the outer space (14) of the enclosure (1),such that the overpressure relief device (8) maintains the internal space (13) of the housing (4) airtight under normal operating conditions while allowing the instantaneous evacuation of a gas flow in the event of excess pressure inside the internal space (13) of said housing (4), and wherein the elastic element (10) of the plug (9) is located where the overpressure relief device (8) is installed.

2. Gas-insulated high-voltage electrical switchgear according to claim 1, characterized in that the overpressure relief device (8) is installed on the plug (9).

3. Gas-insulated high-voltage electrical switchgear according to claim 2,characterized in that the plug (9) of the removable fuse holder base (5) that closes the housing (4) comprises an insulating piece (12) where the overpressure relief device (8) is installed.

4. Gas-insulated high-voltage electrical switchgear according to any of the preceding claims, characterized in that the overpressure relief device (8) is a non-return valve, a vent plug, or a vent filter that allows the internal pressure of the housing (4) to be maintained within certain values.

5. Gas-insulated high-voltage electrical switchgear according to any of the preceding claims, characterized in that the protective element (3) is a fuse.

6. Gas-insulated high-voltage electrical switchgear according to any of the preceding claims, characterized in that the switching means (2) is a load-break or short-circuit current circuit breaker.