Gas-insulated electrical equipment containing heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone.

Abstract

It proposes the use of specific gas mixtures, which make it possible to obtain medium or high voltage equipment with a low environmental impact also in terms of GWP and LCA. [Solution] The present invention relates to medium or high voltage equipment comprising a leak-tight enclosure in which electrical components are placed and a gas mixture for providing electrical insulation and / or for quenching electrical arcs that may occur within the enclosure, the gas mixture comprising heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone in a mixture with a diluent gas.

Description

[Technical Field]

[0001] The present invention relates to the field of electrical insulation and electric arc quenching in medium or high voltage equipment, in particular in high voltage equipment.

[0002] The present invention relates to medium or high voltage equipment in which electrical insulation and / or electric arc quenching is achieved by a gaseous medium comprising heptafluoroisobutyronitrile and heptafluoro(trifluoromethyl)ketone in a mixture with a diluent gas, in particular comprising either carbon dioxide and dioxygen or nitrogen and dioxygen.

[0003] The present invention relates to the use of a gaseous medium comprising heptafluoroisobutyronitrile and heptafluoro(trifluoromethyl)ketone in a mixture with a diluent gas, in particular comprising either carbon dioxide and dioxygen or nitrogen and dioxygen, as a gas for electrical insulation and / or electric arc quenching in medium or high voltage equipment.

[0004] More particularly, the present invention relates to the use of fluorinated ... heptafluoroisobutyronitrile, heptafluoroisopropyl(trifluoromethyl)ketone, carbon dioxide and dioxygen, or -Heptafluoroisobutyronitrile, heptafluoroisopropyl (trifluoromethyl) ketone, nitrogen and dioxygen The present invention relates to the use of insulation with low environmental impact based on a gaseous medium, including any of the following:

[0005] This insulator based on such a gaseous medium may optionally be combined with a solid insulator with a low dielectric constant. [Background technology]

[0006] In medium or high voltage substation equipment, electrical insulation, and where necessary electrical arc quenching, is typically performed by gases confined within the enclosure of said equipment.

[0007] Above and below, the expression "medium voltage" is used in the conventionally accepted manner, i.e., the term "medium voltage" refers to voltages above 1000 volts (V) for alternating current (AC) and above 1500 volts for direct current (DC), but not exceeding 52,000 V for AC or 75,000 V for DC.

[0008] Furthermore, the term "high voltage" is used in the conventionally accepted manner, i.e., the term "high voltage" strictly refers to voltages above 52,000V for AC and above 75,000V for DC.

[0009] Currently, the gas most commonly used in this type of equipment is sulfur hexafluoride (SF6). This gas exhibits relatively good thermal conductivity and dielectric strength with low dielectric loss. It is chemically inert and non-toxic to humans and animals, and recombines quickly and almost completely after being dissociated by an electric arc. Furthermore, it is non-flammable and remains reasonably priced.

[0010] However, SF6 has the major drawback of exhibiting a Global Warming Potential (GWP) of 25,200 (CO2 standard, 100 years) and remaining in the atmosphere for 3,200 years, making it one of the gases with the greatest global warming potential. Therefore, SF6 was included in the list of gases whose emissions must be limited in the Kyoto Protocol (1997).

[0011] The best way to limit SF6 emissions is to limit the use of this gas, which has led manufacturers to look for alternatives to SF6.

[0012] Although "natural" gases have no adverse environmental impact (carbon dioxide (CO2) has a GWP equal to 1, while nitrogen (N2) or air has a GWP of 0), they exhibit a dielectric strength much lower than that of SF6. Thus, for example, the alternating current (AC) (50 Hertz (Hz)) dielectric strength of air and nitrogen is approximately one-third of that of SF6. As a result, the use of these "natural" gases for electrical insulation and / or arc quenching in medium- or high-voltage equipment requires a significant increase in the volume and / or filling pressure of said equipment, which contradicts the efforts made over the past decades to develop equipment with a low life cycle assessment (LCA), i.e., to develop smaller, safer for personnel, and less bulky installations.

[0013] WO 2012 / 080246 describes the use of one or more fluoroketones in a mixture with air as a low-environmental-impact electrical insulation and / or arc-quenching means. Due to the high boiling points of the proposed fluids (i.e., 49°C for fluoroketone C6 and 26.9°C for heptafluoroisopropyl(trifluoromethyl)ketone (fluoroketone C5)), these fluids are found to be in a liquid state at the normal minimum pressure and operating temperature of medium- and high-voltage equipment. Therefore, the inventors must add a system to vaporize the liquid phase or heat the outside of the equipment to maintain the equipment temperature above the liquefaction temperature of the fluoroketone. The external vaporization system, especially the heating system, complicates the equipment design, reduces its reliability in the event of power interruption, and generates additional power consumption that can reach 100 megawatt-hours (MWh) over the equipment's lifetime. This also contradicts the goal of a low LCA, i.e., reducing the equipment's environmental impact, especially carbon emissions. From the viewpoint of low temperature reliability, if the power supply is interrupted at low temperatures, the gas phase of the fluoroketone will liquefy, thereby significantly reducing the concentration of the fluoroketone in the gas mixture and therefore reducing the insulating power of the equipment, which will not be able to withstand the voltage when the power supply is restored.

[0014] Furthermore, new gases have been developed that exhibit sufficient electrical insulating properties for use in high- or medium-voltage equipment. More precisely, these gases are mixtures of two molecules, one of which is present in the majority, and the other, heptafluoroisobutyronitrile, with formula (I): (CF3)2CF-CN(I) and CAS number 42532-60-5, present in a smaller amount. These gas mixtures have the advantage of being based on SF6 substitutes that exhibit a lower GWP than SF6 in solution in the host, or on diluent gases with very low GWPs, such as carbon dioxide (CO2), with a GWP of 1, or diluent gases with a GWP of 0, such as nitrogen (N2) or air. The heptafluoroisobutyronitrile gas used in these mixtures is sold by 3M™ under the trade name 3M™ Novec™ 4710.

[0015] WO 2014 / 037566 describes the use of such mixtures as insulating gases in high or medium voltage equipment associated with solid insulation.

[0016] WO 2015 / 040069 describes a specific insulating gas, namely, an insulating gas containing heptafluoroisobutyronitrile, CO2, and dioxygen (O2), with the dioxygen present in the gas medium in a range of 1 mol% to 25 mol%. In fact, it has been found that adding a few percent of oxygen to a mixture containing heptafluoroisobutyronitrile and CO2 makes it possible to obtain a synergistic effect on the insulating properties of the entire gas mixture.

[0017] General Electric claims it has 98% less GWP than SF6. -70 mole percent (mol%) to 97 mole% CO2; -3 mol% to 10 mol% of (CF3)2CF-CN; -0 mol% to 20 mol% O2 g (which stands for "green gas for the grid"), including and in particular consisting of 3The company sells an electrical insulating gas mixture called

[0018] The inventors seek to find an insulation system comprising at least a gas or mixture of gases that is sufficient for applications in the field of medium or high voltage equipment and that in particular exhibits electrical insulating or electric arc quenching properties comparable to those of SF6 equipment, while also having a low environmental impact in terms of GWP and LCA.

[0019] The inventors also seek to provide an insulation system, and in particular a gas or mixture of gases contained in said system, that is non-toxic to humans and the environment.

[0020] The inventors further seek to provide an insulation system, particularly a gas or mixture of gases, whose manufacturing or purchase costs are compatible with use on an industrial scale.

[0021] The inventors further seek to provide medium or high voltage equipment based on said insulation system, in particular a gas or mixture of gases, having a size and pressure close to that of comparable equipment insulated with SF6 and which does not exhibit liquefaction at the lowest operating temperature without the addition of an external heat source. [Prior art documents] [Patent documents]

[0022] [Patent Document 1] US Patent Application Publication No. 2022 / 359138 Summary of the Invention

[0023] These and other objectives are achieved by the present invention, which proposes the use of a specific gas mixture that allows obtaining medium- or high-voltage equipment with a low environmental impact in terms of GWP and LCA. In fact, this specific gas mixture does not require the insulated equipment to be larger than comparable equipment insulated with SF6 and / or to present an external heat source.

[0024] Thus, an insulating system implemented in the context of the present invention is based on a gaseous medium comprising heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone in a mixture with a diluent gas for use as a gas for electrical insulation and / or for electric arc quenching in medium or high voltage equipment.

[0025] In the present invention, the expressions "gas mixture", "gaseous mixture", "gaseous medium" and "gaseous medium" are equivalent and may be used interchangeably.

[0026] In general, the present invention provides medium or high voltage equipment comprising a leak-tight enclosure in which an electrical component is disposed, and a gaseous medium for providing electrical insulation and / or for quenching electrical arcs that may occur within said enclosure, said gaseous medium comprising heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone in a mixture with a diluent gas.

[0027] In the device of the present invention, the gas insulator implements a gas medium comprising heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone.

[0028] As already explained, heptafluoroisobutyronitrile of formula (I): (CF3)2CFCN(I) (hereinafter referred to as i-C3F7CN) corresponds to 2,3,3,3-tetrafluoro-2-trifluoromethylpropanenitrile, CAS number: 42532-60-5. This compound is (i) a boiling point of -4.7°C at 1013 hectopascals (hPa) (as determined in accordance with ASTM D1120-94, "Standard Test Method for Boiling Point of Engine Coolants"); (ii) Molar mass 195 g.mol -1 and, (iii) GWP2750 (calculated for 100 years according to the 2022 IPCC method); and (iv) Ozone Depletion Potential (ODP) 0 and Shows.

[0029] Table I below compares the dielectric strength of heptafluoroisobutyronitrile having formula (I) with that of N2, as normalized to the gas it is desired to replace, i.e., SF6, as measured at atmospheric pressure with a DC voltage between two steel electrodes having a diameter of 2.54 centimeters (cm) and spaced 0.1 cm apart.

[0030] [Table 1]

[0031] Heptafluoroisopropyl(trifluoromethyl)ketone of formula (II): CF3C(O)CF(CF3)2(II) corresponds to 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)butan-2-one, CAS number: 756-12-7. (i) a boiling point of 26.9°C at 1013 hectopascals (hPa) (as determined in accordance with ASTM D1120-94, "Standard Test Method for Boiling Point of Engine Coolants"); (ii) Molar mass 266 g.mol -1 and, (iii) GWP<1 (calculated over 100 years according to the 2022 IPCC methodology); and (iv) Ozone Depletion Potential (ODP) 0 and Shows.

[0032] Table II below shows the relative dielectric strength of heptafluoroisopropyl(trifluoromethyl)ketone of formula (II) normalized to the gas it is desired to replace, i.e., SF6, said dielectric strength being measured according to ASTM D877 using disk electrodes with a gap of 2.5 mm.

[0033] [Table 2]

[0034] Heptafluoroisopropyl(trifluoromethyl)ketone gas is sold under the trade name 3M™ Novec™ 5110 by 3M™ Company.

[0035] Thus, the above-mentioned heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone, which are non-toxic, non-corrosive and non-flammable and exhibit a GWP significantly lower than that of SF, are mixed with a diluent gas to be endowed with suitable electrical insulating and arc quenching properties to enable them to replace SF as a gas for electrical insulation and / or arc quenching in medium or high voltage equipment.

[0036] However, the GWP of heptafluoroisobutyronitrile is lower than that of SF6 but higher than that of heptafluoroisopropyl(trifluoromethyl)ketone. It is therefore appropriate to minimize the presence of this heptafluoroisobutyronitrile in the gas mixture and to determine its amount as a function of the target GWP of the gas mixture.

[0037] In this regard, it should be noted that the inventors have identified a synergistic effect between heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone in the gaseous medium according to the invention, which makes it possible to improve the dielectric and extinction properties while using lower amounts of heptafluoroisobutyronitrile than those implemented in prior art gas mixtures.

[0038] In fact, heptafluoroisopropyl(trifluoromethyl)ketone in an amount of 5 mol % or less was used. 3 Addition of heptafluoroisopropyl(trifluoromethyl)ketone to the mold mixture allows for an increase in the dielectric resistance of the resulting mixture by approximately 20%. Furthermore, if the amount of heptafluoroisobutyronitrile in the mixture implemented in the present invention is reduced to 0.9 mol % or less, the loss in dielectric performance can be at least partially compensated for by the addition of the above-specified amount of heptafluoroisopropyl(trifluoromethyl)ketone.

[0039] In a specific embodiment, the gaseous medium implemented in the device of the invention contains heptafluoroisopropyl(trifluoromethyl)ketone in an amount of 5 mol% or less. Advantageously, in the gas mixture implemented in the device of the invention, the amount of heptafluoroisopropyl(trifluoromethyl)ketone is comprised between 0.1 mol% and 5 mol%, in particular between 0.5 mol% and 3 mol%, and more particularly between 1 mol% and 2 mol%. In a more specific embodiment, the amount of heptafluoroisopropyl(trifluoromethyl)ketone is about 1.5 mol% (i.e., 1.5 mol% ± 0.3 mol%).

[0040] In another specific embodiment, the gaseous medium implemented in the device of the invention contains heptafluoroisobutyronitrile in an amount of 0.9 mol% or less. Advantageously, in the gas mixture implemented in the device of the invention, the amount of heptafluoroisobutyronitrile is comprised between 0.001 mol% and 0.9 mol%, in particular between 0.01 mol% and 0.5 mol%, and more particularly between 0.05 mol% and 0.2 mol%. In a more specific embodiment, the amount of heptafluoroisobutyronitrile is about 0.1 mol% (i.e., 0.1 mol% ± 0.03 mol%).

[0041] More specifically, the present invention provides a gas insulator with low environmental impact that combines a gas mixture with low environmental impact (low GWP compared to SF6 or lower GWP than prior art gas mixtures containing heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone), that is compatible with the minimum operating temperature of the equipment, and that has dielectric, dissipation, and heat dissipation properties that are superior to those of conventional gases such as CO2, air, or nitrogen.

[0042] In the context of the present invention, when heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone are contained within medium- or high-voltage equipment, they exist exclusively or almost exclusively in a gaseous state within the equipment under all temperature conditions to which the gaseous medium is intended to be subjected. To achieve this, heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone should be present in the equipment at partial pressures selected as a function of the respective saturated vapor pressures exhibited by these compounds at the equipment's lowest operating temperature. The term "lowest operating temperature" is used in the equipment to refer to the lowest temperature at which the equipment is designed to be used.

[0043] Taking into account the common recommended filling pressure levels for medium and high voltage equipment, which are typically a few bar, and taking into account, firstly, the liquefaction temperature of heptafluoroisopropyl(trifluoromethyl)ketone at normal atmospheric pressure (1013.25 hPa) and, secondly, the GWP of heptafluoroisobutyronitrile, heptafluoroisobutyronitrile is most often used diluted with at least one other gas to obtain the recommended filling pressure level for the equipment in question, while ensuring that the heptafluoroisopropyl(trifluoromethyl)ketone is maintained in a gaseous state over the entire range of temperatures used in the equipment.

[0044] According to the invention, said other gas, known as a diluent gas or vector gas or buffer gas, if present, is selected from gases that meet the following four criteria: (1) A boiling point that is very low, below the minimum operating temperature of the device, typically below -50°C at standard pressure; (2) exhibit a dielectric strength equal to or greater than that of carbon dioxide under test conditions identical to those used to measure the dielectric strength of carbon dioxide (i.e., the same equipment, same geometric configuration, same operating parameters, etc.); (3) non-toxic to humans and the environment; and (4) Since the GWP of a gas mixture is a weighted average of the sum of the weight fractions of each compound in the mixture multiplied by its corresponding GWP, it exhibits a lower GWP than the GWP of the heptafluoroisobutyronitrile and heptafluoroisopropyl (trifluoromethyl) ketone mixture, such that diluting this mixture with a diluent gas also has the effect of reducing the environmental impact of the mixture.

[0045] The diluent gases typically used are neutral gases with a very low GWP, typically a GWP of 1 or less.

[0046] Gases that exhibit this set of properties are, for example, air, advantageously dry air (GWP 0), nitrogen (GWP 0), helium (GWP 0), carbon dioxide (GWP 1) and dioxygen (GWP 0). Consequently, any one of these gases or a mixture thereof may be used as a diluent gas in the present invention. In particular, the diluent gas implemented in the present invention comprises or consists of a mixture of either CO and O, or N and O.

[0047] In the context of the present invention, in order to avoid liquefaction of heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone at the lowest operating temperature of the equipment, the partial pressures of the different components of the gas mixture according to the invention should be selected so that the following formula (III) is satisfied: A+B+C<1(III) (In the formula, A=P i-C3F7CN / PVS i-C3F7CN B=P CF3C(O)CF(CF3)2 / PVS CF3C(O)CF(CF3)2 C=P dilution / PVS dilution P i-C3F7CN = partial pressure of heptafluoroisobutyronitrile at the lowest temperature of use, P CF3C(O)CF(CF3)2 = partial pressure of heptafluoroisopropyl(trifluoromethyl)ketone at the lowest temperature of use, P dilution= partial pressure of diluent gas at minimum operating temperature, PVS i-C3F7CN = saturated vapor pressure of heptafluoroisobutyronitrile at the lowest use temperature, PVS CF3C(O)CF(CF3)2 = saturated vapor pressure of heptafluoroisopropyl(trifluoromethyl)ketone at the lowest temperature of use, and PVS dilution = saturated vapor pressure of the diluent gas at the lowest operating temperature).

[0048] In certain embodiments, when the diluent gas is a mixture of CO and O, C=P CO2 / PVS CO2 +P O2 / PVS O2 is.

[0049] In another embodiment, when the diluent gas is a mixture of N2 and O2, C=P N2 / PVS N2 +P O2 / PVS O2 is.

[0050] Advantageously, in the context of the present invention, the minimum use temperature T min is selected from 0°C, -5°C, -10°C, -15°C, -20°C, -25°C, -30°C, -35°C, -40°C, -45°C and -50°C, in particular selected from 0°C, -5°C, -10°C, -15°C, -20°C, -25°C, -30°C, -35°C and -40°C.

[0051] Specific examples of gas mixtures for use in the present invention are: -0.001 mol% to 0.9 mol% of i-C3F7CN; -0.1 mol% to 5 mol% of CF3C(O)CF(CF3)2, - 94.1 mol % to 99.899 mol % of the diluent gas defined above; It comprises or consists of:

[0052] More specific examples of gas mixtures for use in the present invention include: -0.001 mol% to 0.9 mol% of i-C3F7CN; -0.1 mol% to 5 mol% of CF3C(O)CF(CF3)2, a diluent gas that is either a mixture of 94.1 mol% to 99.899 mol% CO2 and O2 or a mixture of N2 and O2; It comprises or consists of:

[0053] More specific examples of gas mixtures for use in the present invention include: -0.001 mol% to 0.9 mol% of i-C3F7CN; -0.1 mol% to 5 mol% of CF3C(O)CF(CF3)2, -1 mol% to 25 mol% O2; -69.1 mol% to 98.899 mol% of either CO2 or N2 It comprises or consists of:

[0054] As a result, the gas mixture implemented in the present invention may be a four-component mixture (i-C3F7CN + CF3C(O)CF(CF3)2 + O2 + CO2 or i-C3F7CN + CF3C(O)CF(CF3)2 + O2 + N2).

[0055] To improve the overall dielectric strength, in a hybrid insulation system, a gas mixture containing i-C3F7CN, CF3C(O)CF(CF3)2, and a diluent gas as defined above may be used in combination with a solid insulator, particularly one with a low dielectric constant, which is applied as a solid insulating layer to conductive components that are respectively subjected to electric fields greater than the breakdown field of medium- or high-voltage equipment without the solid insulator. In other words, a portion of an electrical component located within an enclosed container of medium- or high-voltage equipment is covered by the solid insulating layer.

[0056] These solid insulating layers can be of various thicknesses, such as those disclosed in WO 2014 / 037566, or the insulating layers in medium or high voltage equipment must be present at a thickness of less than 1 mm, such as those disclosed in WO 2017 / 114862.

[0057] According to the invention, the device may firstly be a gas-insulated transformer, for example a power transformer or a measuring transformer.

[0058] It may also be an overhead or buried gas insulated wire or a series of busbars for transporting or distributing electricity.

[0059] There may be elements for connecting to other equipment in the network, for example overhead lines or partition bushings.

[0060] Finally, the equipment may also be a circuit breaker, such as a "dead tank, live tank or GIS" type circuit breaker, a "puffer" or "self-blasting" type circuit breaker, a puffer type circuit breaker with double acting arcing contacts, a heat effect puffer type circuit breaker with single acting arcing contacts, a heat effect puffer type circuit breaker with partially moving contact pins, a switch, a disconnector such as an air insulated switchgear (AIS) or gas insulated switchgear (GIS), a combined switch and fuse unit, an earthing switch or a contactor.

[0061] As already explained, the present invention can be applied to low or high voltage, medium or high voltage equipment, and in particular to high voltage equipment.

[0062] The present invention also provides the use of a gaseous medium comprising i-C3F7CN, CF3C(O)CF(CF3)2 and a diluent gas as defined above as a gas for electrical insulation and / or electric arc quenching in medium or high voltage equipment, in which equipment some of the electrical components may further be covered with a solid insulating layer as defined below.

[0063] Other characteristics and advantages of the invention may become more apparent from the following further description, given as an illustrative and non-limiting example. DETAILED DESCRIPTION OF THE INVENTION

[0064] The present invention is based on the use of specific gas mixtures that combine heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone as defined above with a diluent gas, which have a low environmental impact and improved destructive capabilities.

[0065] In the present invention, the expressions "diluent gas", "neutral gas" or "buffer gas" are equivalent and may be used interchangeably.

[0066] Advantageously, heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone are present in the device exclusively or almost exclusively in gaseous form over the entire range of temperatures used in the device. Therefore, the partial pressures of heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone in the device are desirably selected as a function of the saturated vapor pressure (PVS) exhibited by these compounds at the lowest temperature used in the device.

[0067] However, since the equipment is usually gas-filled at ambient temperature, e.g., 20°C, the inequality (III) defined above must first be verified at the lowest use temperature, and then the partial pressures of the gases implemented in the mixture at the lowest use temperature must be brought to the filling pressures at 20°C of all gases implemented in the mixture by using the equations of state of each gas.

[0068] Depending on the equipment, the recommended total filling pressure for filling the gaseous medium varies, however, the pressure is typically a few bars, i.e., a few hundred kilopascals (kPa).

[0069] In the context of the present invention, heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone are implemented with the addition of a diluent gas (or vector gas or buffer gas) to make it possible to obtain the recommended level of filling pressure.

[0070] Preferably, the dilution gas is selected from gases that, firstly, have a very low boiling point below the minimum operating temperature of the equipment, and secondly, exhibit a dielectric strength equal to or greater than that of carbon dioxide under the same test conditions (same equipment, same geometric configuration, same operating parameters, etc.) as those used to measure the dielectric strength of carbon dioxide.

[0071] Furthermore, since the GWP of a gas mixture is proportional to the partial pressure of each of its components, it is preferred that the diluting gas be non-toxic and exhibit low or zero GWP, so that dilution of heptafluoroisobutyronitrile with the diluting gas also has the effect of reducing the environmental impact of said compound.

[0072] Also, the diluent gas implemented in the present invention is preferably carbon dioxide with a GWP equal to 1, nitrogen with a GWP equal to 0, oxygen or air, advantageously dry air, or a mixture thereof. In a specific embodiment, the diluent gas implemented in the present invention comprises or consists of a mixture of CO and O. In another specific embodiment, the diluent gas implemented in the present invention comprises or consists of a mixture of N and O.

[0073] Because heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone have higher dielectric strengths than gases that may be used as diluents, it is desirable to optimize the filling of the device with heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone. Therefore, the device should be filled with heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone at the filling temperature, preferably at a partial pressure in the range of 95% to 100%, more preferably 98% to 100%, of the pressure corresponding to the saturated vapor pressure exhibited by these compounds at the device's lowest operating temperature.

[0074] Table III below provides different examples of gas mixtures that can be implemented in the present invention (amounts in the table are given as mole %).

[0075] [Table 3]

[0076] A first specific example quaternary gas mixture for use in the present invention at a minimum temperature of -30°C is: -0.075 mol% i-C3F7CN; -1.2 mol% CF3C(O)CF(CF3)2, -13 mol% O2, -85.73 mol% CO2 and It consists of:

[0077] Such mixtures make it possible to reduce the carbon equivalent of pure SF6 by at least 99.95% (Table IV).

[0078] [Table 4]

[0079] A second specific example quaternary gas mixture for use in the present invention at a minimum temperature of -25°C is: -0.075 mol% i-C3F7CN; -1.75 mol% CF3C(O)CF(CF3)2, -13 mol% O2, -85.18 mol% CO2 and It consists of:

[0080] Such mixtures make it possible to reduce the carbon equivalent of pure SF6 by at least 99.95% (Table V).

[0081] [Table 5]

[0082] From a practical point of view, after generating a vacuum with an oil vacuum pump, a commercially available 5 bar (500 kPa) device for use at -30 °C can be filled with a gas mixer that allows the ratio between the pressure of heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone and the pressure of the diluent gas to be controlled, and this ratio is kept constant during filling by using a precision mass flow meter: 0.075% for heptafluoroisobutyronitrile and 1.2% for heptafluoroisopropyl(trifluoromethyl)ketone. The vacuum (0 kPa to 0.1 kPa) is preferably prepared beforehand inside the device.

[0083] Furthermore, at the end of its life or after a circuit breaker test, the gaseous medium can be recovered by conventional recovery techniques using compressors and vacuum pumps. Heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone can then be separated from the diluent gas using zeolites capable of capturing only smaller diluent gases. Alternatively, since heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone have a larger molar mass than the diluent gas, a selective separation membrane can be used that allows the diluent gas to escape while retaining heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone. Naturally, any other option may be envisioned.

[0084] Thus, the present invention proposes a gas mixture with a significant (approximately 99.95%) CO₂ equivalent reduction factor, resulting in low environmental impact; compatible with the minimum operating temperature of the equipment; and improved dielectric properties compared to typical gases such as CO₂, air, or nitrogen, resulting in dielectric properties approaching those of pure SF₆, while improving its breakdown capacity. This gaseous medium can advantageously replace the SF₆ currently used in equipment, with little or no change to the equipment design, allowing the same production line to be used while only changing the gaseous medium used for filling. Furthermore, thanks to its higher dielectric strength, equipment implemented with the present invention can be made smaller, thus reducing cost and LCA.

[0085] To obtain dielectric properties equivalent to SF6 (up to 100% of the strength of SF6) without reducing performance at low temperatures or increasing the total pressure, the gas mixtures presented above are used in combination with solid insulators of low dielectric constant, which are applied to conductive components each subjected to an electric field greater than the breakdown field of a system without solid insulators.

[0086] Solid insulators implemented in the context of the present invention may be such as those disclosed in WO 2014 / 037566 or WO 2017 / 114862.

Claims

1. 1. Medium or high voltage equipment comprising a leak-tight enclosure in which an electrical component is disposed, and a gaseous medium for providing electrical insulation and / or for quenching electrical arcs that may occur within said enclosure, said gaseous medium comprising heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone in a mixture with a diluent gas; A medium- or high-voltage appliance, wherein the amount of heptafluoroisobutyronitrile in the gas medium is 0.9 mol % or less.

2. 2. Medium or high voltage equipment according to claim 1, wherein the amount of heptafluoroisopropyl(trifluoromethyl)ketone in the gas medium is not more than 5 mol %.

3. 3. Medium or high voltage equipment according to claim 1 or 2, wherein the amount of heptafluoroisopropyl(trifluoromethyl)ketone in the gas medium is comprised between 0.1 mol % and 5 mol %.

4. 4. Medium or high voltage equipment according to any one of claims 1 to 3, wherein the amount of heptafluoroisobutyronitrile in the gas medium is comprised between 0.001 mol % and 0.9 mol %.

5. The diluent gas is CO ２ and O ２ 5. Medium or high voltage equipment according to any one of claims 1 to 4, comprising or consisting of a mixture of

6. The diluent gas is N ２ and O ２ 5. Medium or high voltage equipment according to any one of claims 1 to 4, comprising or consisting of a mixture of

7. The gas medium is 0.001 mol % to 0.9 mol % of heptafluoroisobutyronitrile; - 0.1 mol % to 5 mol % of heptafluoroisopropyl(trifluoromethyl)ketone; 1 mol % to 25 mol % O ２ and, -69.1 mol% to 98.899 mol% CO ２ or N ２ and 7. Medium or high voltage equipment according to any one of claims 1 to 6, comprising or consisting of:

8. 8. Medium or high voltage equipment according to any one of claims 1 to 7, wherein a part of the electrical components arranged inside the enclosure of the equipment is covered by a solid insulating layer.

9. 9. Medium or high voltage equipment according to any one of claims 1 to 8, wherein the equipment is a gas-insulated electrical transformer, an overhead or buried gas-insulated line, a series of busbars for transporting or distributing electricity, an element for connecting to other equipment in a network, or a connector / disconnector.

10. 1. Use of a gaseous medium comprising heptafluoroisobutyronitrile and heptafluoroisopropyl(trifluoromethyl)ketone in a mixture with a diluent gas as a gas for electrical insulation and / or electric arc quenching in medium or high voltage equipment, in which some electrical components may further be covered with a solid insulating layer, and in which the amount of heptafluoroisobutyronitrile in the gaseous medium is not more than 0.9 mol %.

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