WO2014187940A1

WO2014187940A1 - Electrical apparatus comprising a contamination-reducing component

Info

Publication number: WO2014187940A1
Application number: PCT/EP2014/060630
Authority: WO
Inventors: Axel Kramer; Denis Tehlar; Navid Mahdizadeh; Thomas Alfred Paul
Original assignee: ABB Technology AG
Current assignee: ABB Technology AG
Priority date: 2013-05-23
Filing date: 2014-05-23
Publication date: 2014-11-27
Anticipated expiration: 2015-11-23

Abstract

The present invention relates to an electrical apparatus (2) for the generation, the distribution and/or the usage of electrical energy, the electrical apparatus (2) comprising a housing (4) enclosing an electrical apparatus interior space (5), at least a portion of the electrical apparatus interior space (5) forming an insulation space (6), in which an electrical component (8) is arranged and which contains an insulation medium surrounding the electrical component (8). The electrical apparatus (2) further comprises a contamination-reducing component (10) for reducing or eliminating at least one contaminant from the insulation space (6). According to the invention, the contamination-reducing component (10) is arranged in a contamination-reduction space (12) which is separated from the insulation space (6) by a semipermeable membrane (14).

Description

Electrical apparatus comprising a

contamination-reducing component

The present invention relates to an electrical apparatus for the generation, the distribution and/or the usage of electrical energy and to a method for reducing contaminations in such an electrical apparatus according to the preamble of the independent claims .

In a wide variety of electrical apparatuses, such as switchgears, gas-insulated substations (GIS) , gas-insulated lines (GIL) or transformers, a dielectric insulation media in liquid or gaseous state is conventionally used for the insulation of the electrical component comprised therein.

In medium or high voltage metal-encapsulated switchgears, for example, the electrical component is arranged in a gas-tight housing, which encloses an insulating space, the insulation space comprising an insulation gas and separating the housing from the electrical component without letting electrical current to pass through from the electrical component to the housing. For interrupting the current in high voltage switchgear or switches, the insulating gas further functions as an arc-extinguishing or arc-quenching gas.

The electrical apparatus can further be provided with a contamination-reducing component to reduce or eliminate the presence of contaminants, in particular moisture (i.e. water), decomposition products and/or any other component or components, the presence of which is not desired.

In theory, adsorbers can be used as contamination-reducing component . However, choosing the right adsorber for a given insulation medium is not an easy task: A zeolite, for example, has a selectivity that is primarily driven by its pore size. Therefore, the use of zeolite is only feasible, if the kinetic diameter of the insulation medium molecule (s) is significantly different from the one of the contaminant ( s ) . If the kinetic diameter of the insulation gas molecule (s) is similar, co-adsorption of the insulation gas molecules can occur.

This problem is particularly evident, if the insulation medium is a mixture of gases, more particularly if this mixture comprises insulation gas molecules of a relatively small kinetic diameter, such as CO2 and/or 0₂ and/or N2, similar to the kinetic diameter of the contaminant to be removed and thus to the pore size of the molecular sieve or zeolite.

When using a zeolite, there is thus always a trade-off between the integrity of the insulation medium and an efficient removal of contaminants, in particular when using gas mixtures comprising CO2 and/or O2 and/or N₂.

Further, there is evidence that adsorbers, such as a molecular sieve, and in particular a zeolite, can support heterogeneous- ly catalysed reactions that accelerate decomposition of insulation gas molecules. In particular in view of an organofluorine compound to be used in the insulation medium, a hydrolytic degradation of the compound cannot be excluded.

However, an adsorption and/or degradation of components of the insulation medium goes along with a decrease in its insulation and arc extinction performance.

Considering these drawbacks, the problem of the present invention is thus to provide an electrical apparatus using a dielectric insulation medium, the apparatus allowing a reduction or elimination of contaminants from the insulation medium without negatively interfering with the integrity of the insulation medium and, in particular, its insulation and arc extinction performance. This problem is solved by the subject matter according to the independent claims. Preferred embodiments are given in the dependent claims and in any claim combinations.

The present invention thus relates to an electrical apparatus for the generation, the distribution and/or the usage of electrical energy, the electrical apparatus comprising a housing enclosing an electrical apparatus interior space. At least a portion of the electrical apparatus interior space forms an insulation space, in which an electrical component is arranged and which contains an insulation medium surrounding the electrical component. The electrical apparatus of the present invention further comprises a contamination-reducing component for reducing or eliminating at least one contaminant, in particular moisture (i.e. water), from the insulation space.

According to the invention, the contamination-reducing component is arranged in a contamination-reduction space which is separated from the insulation space by a semipermeable membrane .

Due to the contamination-reducing component being arranged in a contamination-reduction space, which is separated from the insulation space by a semipermeable membrane, the contamination-reducing component is not in direct contact with the insulation medium, but only with molecules that are able to pass the semipermeable membrane. The semipermeable membrane functions as a "pre-filter" . Thus, even in the case that a molecular sieve is used as contamination-reducing agent, this has no negative impact on the integrity of the insulation medium itself, since only the permeate of the pre-filtration is allowed to contact the molecular sieve, and ultimately to be adsorbed by the molecular sieve, in particular zeolite.

The term "housing" as used in the context of the present invention is to be understood broadly as any at least approximately closed system. In particular, the term "housing" can encompass a plurality of chambers interconnected with each other. More particularly in embodiments, "housing" can encompass a chamber, which encloses the insulating space, and a recycling system, the chamber being interconnected with the recycling system through which the insulation medium is removed, processed (e.g. cleaned) and reintroduced into the insulating space. Alternatively or in addition, "housing" can comprise a chamber, which encloses the insulating space and a pre-treatment room, the chamber being interconnected with the pre-treatment room for pre-treating the insulation medium prior to introduction into the insulating space of the chamber .

In particular, the term "insulation medium" refers to an insulation fluid and encompasses any dielectric fluid. More particularly, it refers to an insulation gas and particularly to an insulation gas mixture.

The term "adsorption" or "adsorbed" as used in the context of the present invention shall encompass any type of adsorption, such as for example physisorption and/or chemisorption .

According to an embodiment, the semipermeable membrane is selectively permeable for at least one contaminant. Such contaminant may be present in the electrical apparatus a priori or may occur or be generated during operation of the electrical apparatus.

In particular, the term "semipermeable membrane" as used in the context of the present invention shall encompass any two- or three-dimensional material formation allowing the passage of a certain constituent while retaining another constituent. More particularly, it encompasses a polymer layer or a filter amp for this purpose. More preferably, the semipermeable membrane is selectively permeable for water, and even more preferably is at least approximately exclusively or even exclusively permeable for water.

The reduction or elimination of water is of particular relevance, since water can - apart from reducing the insulation performance - also lead to corrosion of the electrical apparatus, in particular of the housing or the electrical component ( s ) . Furthermore, water can open reaction pathways for the formation of toxic and/or corrosive decomposition products, in particular resulting from partial discharge or arcing in the presence of high moisture content. This is of particular relevance when using an insulation medium which comprises an organofluorine compound, in particular in gaseous phase, since one decomposition product of the organofluorine compound is hydrogen fluoride (HF) , which is highly corrosive and extremely toxic.

In this regard, it is further preferred that the semipermeable membrane is made of an ionomer, and more preferably is made of a sulfonated tetrafluoroethylene based fluoropolymer- copolymer .

In embodiments, the semipermeable membrane can be made of a polymer of the chemical formula C7HF13O5S · C2F4, and more particularly is made of tetrafluoroethylene-perfluoro-3 , 6- dioxa-4-methyl-7-octenesulfonic acid copolymer.

This material, also known under the trade name Nation®, allows compounds having a hydroxyl group, in particular water, to pass through selectively. This is due to the side chains of the (tetrafluoroethylene) backbone being terminated with a sulfonic acid (-SO3H) group, which essentially provides an H- bonding channel for the hydroxyl-group containing compound through the membrane. In the case of water, for example, migration through the membrane is driven by the water concen- tration gradient between the two sides of the membrane, i.e. the insulation space and the contamination-reduction space.

In more detail, water molecules are adsorbed onto the surface of the membrane facing the insulation space and are passed onto underlying sulfonic acid groups, until the water reaches the opposite side, i.e. the contamination-reduction space. There, water evaporates and is ultimately adsorbed by the contamination-reducing component. By way of adsorption, water is removed from the gas phase and the concentration gradient is upkept.

In addition, the ionomer described above is extremely resistant to chemical attack and operable up to 150°C, which further contributes to its suitability in an electrical apparatus according to the present invention.

Alternatively, in particular additionally, to a semipermeable membrane made of an ionomer, it is possible to use any other semipermeable membrane suitable for the described purposes, in particular a semipermeable membrane selectively permeable for water and/or any degradation product of the insulation gas components. For example, zeolite sheets having a pore size of 5 A or less can be used alternatively or additionally to the ionomer .

According to an embodiment, the semipermeable membrane forms at least one closed container, preferably in tubular shape. The at least one closed container encloses at least partly, preferably fully, the contamination-reduction space. Thus, the interior of the at least one closed container corresponds to the contamination-reduction space in which the contamination- reducing component is held. The container (s) being in tubular shape allows easy manufacture and at the same provides a large surface of semipermeable membrane per mass of contamination- reducing component enclosed, ultimately allowing for a very efficient per-filtration and contamination reduction. The membrane, and in particular the tube, can be arranged on a supporting scaffold.

According to a further embodiment, the contamination-reduction space is arranged within the electrical apparatus interior space. This means that the semipermeable membrane with the contamination-reducing component enclosed is fully surrounded by the insulation medium. The semipermeable membrane is thus in direct contact with the insulation medium and presents a large area for the pre-filtration of the insulation medium, which ultimately allows an efficient reduction of contaminants .

According to another embodiment and in accordance with the embodiment comprising a semipermeable membrane selectively permeable for water, the contamination-reducing component is a moisture-reducing component. In this regard, the term "moisture-reducing component" is equivalent to the term "water-reducing component".

In exemplary embodiments to be discussed in detail further below, the contamination-reducing component can also be a liquefaction device and/or a solidification device, which by condensation, solidification and/or deposition (desubli- mation) , respectively, reduces the amount of contaminant, in particular water, from the gas phase.

In embodiments, the contamination-reduction space comprises a molecular sieve as contamination-reducing component, in particular a zeolite.

According to an embodiment, the contamination-reducing component is a molecular sieve, more preferably a zeolite, i.e. a micro-porous aluminosilicate mineral that has undergone cation exchange to achieve a desired pore size. In embodiments, the molecular sieve has a pore size from 3 A to 13 A, preferably from 5 A to 13 A, more preferably from 6 A to 12 A, even more preferably from 7 A to 11 A, most preferably from 9 A to 11 A. A respective molecular sieve has been found to have a particularly high adsorption capacity.

Suitable zeolites include e.g. ZEOCHEM® molecular sieve 5Ά (having a pore size of 5 A) and ZEOCHEM® molecular sieve 13X (having a pore size of 9 A) .

As mentioned, the term "adsorption" or "adsorbed" encompasses both physisorption and/or chemisorption . Physisorption can, in particular, be determined or be influenced by the relationship between the size of molecules of the insulation medium and the pore size of the molecular sieve. Chemisorption can, in particular, be determined or be influenced by chemical interactions between molecules of the insulation medium and the molecular sieve .

Additionally or alternatively to the molecular sieve, the electrical apparatus can comprise a desiccant selected from the group consisting of: calcium, calcium sulphate, calcium carbonate, calcium hydride, potassium carbonate, potassium hydroxide, copper (II) sulphate, calcium oxide, magnesium, magnesium oxide, magnesium sulphate, magnesium perchlorate, sodium, sodium sulphate, aluminium, lithium aluminium hydride, aluminium oxide, montmorrilonite, phosphorpentoxide, silica gel, a cellulose filter, and mixtures or combinations thereof.

According to exemplary embodiments, a liquefaction device for liquefying and/or a solidification device for solidifying the at least one contaminant, in particular water, is or are arranged in the contamination-reduction space.

By removing vapour from the gas contained in the contamination-reduction space, be it by a desiccant or by a liquefaction device or by a solidification device, the water concentration gradient between the gas in the insulation space and the gas in the contamination-reduction space is maintained. This results in a continuous, concentration- gradient-driven transport of water from the insulation space through the semipermeable membrane into the contamination- reduction space. In such embodiments, the contamination- reduction space thus forms a water collection space.

According to specific embodiments, the liquefaction device and/or solidification device comprises a cooling area which is cooled to a temperature below the dew point of the at least one contaminant, in particular water. For this purpose, the liquefaction device and/or solidification device can be or can comprise a thermoelectric cooler (TEC) .

In particular, embodiments can be encompassed by the present invention in which two or more liquefaction and/or solidification devices, in particular thermoelectric coolers, are arranged in the contamination-reduction space, whereby a first of the devices is preferably designed for liquefaction of water and a second of the devices is preferably designed for solidification of the liquid water obtained from the first device. This cascade or series of liquefaction and/or solidification devices, in particular thermoelectric coolers, allows for a very efficient removal of vapour, since at least some of the cooling areas where liquefaction occurs can be readily freed from water occupying these areas and the solidification rate on the cooling area of the second device is relatively high.

According to a particularly preferred embodiment, the insulation medium comprises carbon dioxide (CO2) ·

By the term "comprises" embodiments are encompassed in which the insulation medium consists or essentially consists of carbon dioxide. In this embodiment, carbon dioxide is thus the sole component of the insulation medium. Alternatively, the insulation medium can comprise carbon dioxide apart from other constituents and can thus form a gas mixture, which is an often preferred embodiment. It is particularly preferred that the insulation medium comprises - apart from carbon dioxide - air or at least one air component, in particular selected from the group consisting of; oxygen, nitrogen, and mixtures thereof.

In particular, in the frame of the present invention, that is based on arranging the contamination-reducing component in a contamination-reducing space which is separated from the insulation space by a semipermeable membrane, the insulation medium may initially, i.e. in its uncontaminated form, comprise solely one molecular species or may be or comprise a gas mixture of several components, wherein the semipermeable membrane is selectively impermeable for at least one of the components, preferably for all components, of the insulation medium in its uncontaminated form. The at least one contaminant may be present in the insulation gas from the beginning or may occur over time or during operation of the electrical apparatus, for example by outgassing, by decomposition of the insulation medium or of one of its components, or by other processes. The at least one contaminant is then prefiltered by the semipermeable membrane and is reduced or eliminated by the contamination-reducing component .

According to a preferred embodiment, the insulation medium comprises carbon dioxide and oxygen. According to an embodiment, the ratio of the amount of carbon dioxide to the amount of oxygen can thereby range from 50:50 to 100:1. In particular in view of interrupting the current in a high voltage switchgear, it is a further embodiment that the ratio of the amount of carbon dioxide to the amount of oxygen ranges from 80:20 to 95:5, more preferably from 85:15 to 92:8, even more preferably from 87:13 to less than 90:10, and in particular is about 89:11. In this regard, it has been found on the one hand that oxygen being present in a molar fraction of at least 5% allows soot formation to be prevented even after repeated current interruption events with high current arcing. On the other hand, oxygen being present in a molar fraction of at most 20%, more particularly of at most 15%, reduces the risk of degradation of the material of the electrical apparatus by oxidation.

According to a further preferred embodiment, the insulation medium comprises an organofluorine compound, in particular in gaseous phase, in particular wherein the semipermeable membrane is selectively impermeable for the organofluorine compound. As mentioned, the advantages achievable by the present invention are of particular relevance in this embodiment, since water, which might otherwise open reaction pathways with the organofluorine compound to generate decomposition products, such as hydrogen fluoride, is efficiently removed. The generation of harmful decomposition products, such as hydrogen fluoride, which in the presence of water might occur, can efficiently be avoided.

In particular, the organofluorine compound is selected from the group consisting of fluoroethers , in particular hydro- fluoromonoethers , fluoroketones, in particular perfluoro- ketones, and fluoroolefins , in particular hydrofluoroolefins , and mixtures thereof.

These classes of compounds have been found to have very high insulation capabilities, in particular a high dielectric strength (or breakdown field strength) , and at the same time a low GWP and low toxicity.

The invention encompasses both embodiments in which the dielectric insulation gas comprises . either one of a fluoro- ether, in particular a hydrofluoromonoether, a fluoroketone and a fluoroolefin, in particular a hydrofluoroolefin, as well as embodiments in which it comprises a mixture of at least two of these compounds . The term "fluoroether" as used in the context of the present invention encompasses both perfluoroethers , i.e. fully fluorinated ethers, and hydrofluoroethers , i.e. ethers that are only partially fluorinated. The term "fluoroether" further encompasses saturated compounds as well as unsaturated compounds, i.e. compounds including double and/or triple bonds between carbon atoms. The at least partially fluorinated alkyl chains attached to the oxygen atom of the fluoroether can, independently of each other, be linear or branched.

The term "fluoroether" further encompasses both non-cyclic and cyclic ethers. Thus, the two alkyl chains attached to the oxygen atom can optionally form a ring. In particular, the term encompasses fluorooxiranes . In a specific embodiment, the organofluorine compound according to the present invention is a perfluorooxirane or a hydrofluorooxirane, more specifically a perfluorooxirane or hydrofluorooxirane comprising from three to fifteen carbon atoms.

It is preferred that the dielectric insulation gas comprises a hydrofluoromonoether containing at least three carbon atoms. Apart from their high dielectric strength, these hydrofluoromonoethers are chemically and thermally stable up to temperatures above 140 °C. They are further non-toxic or have a low toxicity level. In addition, they are non-corrosive and non-explosive.

The term "hydrofluoromonoether" as used herein refers to a compound having one and only one ether group, the ether group linking two alkyl groups, which can be, independently from each other, linear or branched, and which can optionally form a ring. The compound is thus in clear contrast to the compounds disclosed in e.g. US-B-7128133 , which relates to the use of compounds containing two ether groups, i.e. hydrofluorodiethers, in heat-transfer fluids. The term "hydrofluoromonoether" as used herein is further to be understood such that the monoether is partially hydrogenated and partially fluorinated. It is further to be understood such that it may comprise a mixture of differently structured hydrofluoromonoethers . The term "structurally different" shall broadly encompass any difference in sum formula or structural formula of the hydrofluoromonoether .

As mentioned above, hydrofluoromonoethers containing at least three carbon atoms have been found to have a relatively high dielectric strength. Specifically, the ratio of the dielectric strength of the hydrofluoromonoethers according to the present invention to the dielectric strength of SF6 is greater than about 0.4.

As also mentioned, the GWP of the hydrofluoromonoethers is low. Preferably, the GWP is less than l'OOO over 100 years, more specifically less than 700 over 100 years.

The hydrofluoromonoethers mentioned herein have a relatively low atmospheric lifetime and in addition are devoid of halogen atoms that play a role in the ozone destruction catalytic cycle, namely CI, Br or I. Their Ozone Depletion Potential (ODP) is zero, which is very favourable from an environmental perspective .

The preference for a hydrofluoromonoether containing at least three carbon atoms and thus having a relatively high boiling point of more than -20 °C is based on the finding that a higher boiling point of the hydrofluoromonoether generally goes along with a higher dielectric strength.

According to other embodiments, the hydrofluoromonoether contains exactly three or four or five or six carbon atoms, in particular exactly three or four carbon atoms, most preferably exactly three carbon atoms. More particularly, the hydrofluoromonoether is thus at least one compound selected from the group consisting of the compounds defined by the following structural formulae in which a part of the hydrogen atoms is each substituted by a fluorine atom:

(Oa) ,

(Oc) ,

(Od) ,

(Of) ,

(Og) ,

^■cr (Oh) ,

!Oi) ,

By using a hydrofluoromonoether containing three or four carbon atoms, no liquefaction occurs under typical operational conditions of the apparatus. Thus, a dielectric insulation medium, every component of which is in the gaseous state at operational conditions of the apparatus, can be achieved. Considering flammability of the compounds, it is further advantageous that the ratio of the number of fluorine atoms to the total number of fluorine and hydrogen atoms, here briefly called "F-rate", of the hydrofluoromonoether is at least 5:8. It has been found that compounds falling within this definition are generally non-flammable and result in an insulation medium complying with highest safety requirements. Thus, safety requirements of the electrical insulator and the method of its production can readily be fulfilled by using a corresponding hydrofluoromonoether .

According to other embodiments, the ratio of the number of fluorine atoms to the number of carbon atoms, here briefly called "F/C-ratio", ranges from 1.5:1 to 2:1. Such compounds generally have a GWP of less than l'OOO over 100 years and are thus very environment-friendly. It is particularly preferred that the hydrofluoromonoether has a GWP of less than 700 over 100 years.

According to other embodiments of the present invention, the hydrofluoromonoether has the general structure (0)

CaHbFc-O-CdHeFf (0) wherein a and d independently are an integer from 1 to 3 with a + d = 3 or 4 or 5 or 6, in particular 3 or 4, b and c independently are an integer from 0 to 11, in particular 0 to 7, with b + c = 2a + 1, and e and f independently are an integer from 0 to 11, in particular 0 to 7, with e + f = 2d + 1, with further at least one of b and e being 1 or greater and at least one of c and f being 1 or greater.

It is thereby a preferred embodiment that in the general structure or formula (0) of the hydrofluoromonoether : a is 1, b and c independently are an integer ranging from 0 to 3 with b + c = 3, d = 2, e and f independently are an integer ranging from 0 to 5 with e + f = 5, with further at least one of b and e being 1 or greater and at least one of c and f being 1 or greater.

According to a more particular embodiment, exactly one of c and f in the general structure (0) is 0. The corresponding grouping of fluorines on one side of the ether linkage, with the other side remaining unsubstituted, is called "segregation". Segregation has been found to reduce the boiling point compared to unsegregated compounds of the same chain length. This feature is thus of particular interest, because compounds with longer chain lengths allowing for higher dielectric strength can be used without risk of liquefaction under operational conditions.

Most preferably, the hydrofluoromonoether is selected from the group consisting of pentafluoro-ethyl-methyl ether (CH3-0- CF2C F3 ) and 2, 2, 2-trifluoroethyl-trifluoromethyl ether ( CF3-O-CH2CF3 ) .

Pentafluoro-ethyl-methyl ether has a boiling point of +5.25°C and a GWP of 697 over 100 years, the F-rate being 0.625, while 2 , 2 , 2-trifluoroethyl-trifluoromethyl ether has a boiling point of +11°C and a GWP of 487 over 100 years, the F-rate being 0.75. They both have an ODP of 0 and are thus environmentally fully acceptable.

In addition, pentafluoro-ethyl-methyl ether has been found to be thermally stable at a temperature of 175°C for 30 days and therefore to be fully suitable for the operational conditions given in the apparatus. Since thermal stability studies of hydrofluoromonoethers of higher molecular weight have shown that ethers containing fully hydrogenated methyl or ethyl groups have a lower thermal stability compared to those having partially hydrogenated groups, it can be assumed that the thermal stability of 2 , 2 , 2-trifluoroethyl-trifluoromethyl ether is even higher. Hydrofluoromonoethers in general, and pentafluoro-ethyl-methyl ether as well as 2 , 2 , 2-trifluoroethyl-trifluoromethyl ether in particular, display a low risk of human toxicity. This can be concluded from the available results of mammalian HFC (hydrofluorocarbon) tests. Also, information available on commercial hydrofluoromonoethers do not give any evidence of carcinogenicity, mutagenicity, reproductive/developmental effects and other chronic effects of the compounds of the present application.

Based on the data available for commercial hydrofluoro ethers of higher molecular weight, it can be concluded that the hydrofluoromonoethers , and in particular pentafluoro-ethyl- methyl ether as well as 2 , 2 , 2-trifluoroethyl-trifluoromethyl ether, have a lethal concentration LC 50 of higher than 10' 000 ppm, rendering them suitable also from a toxicological point of view.

The hydrofluoromonoethers mentioned have a higher dielectric strength than air. In particular, pentafluoro-ethyl-methyl ether at 1 bar has a dielectric strength about 2.4 times higher than that of air at 1 bar.

Given its boiling point, which is preferably below 55°C, more preferably below 40°C, in particular below 30°C, the hydrofluoromonoethers mentioned, particularly pentafluoro- ethyl-methyl ether and 2 , 2 , 2-trifluoroethyl-trifluoromethyl ether, respectively, are normally in the gaseous state at operational conditions. Thus, a dielectric insulation medium in which every component is in the gaseous state at operational conditions of the apparatus can be achieved, which is advantageous.

Alternatively or additionally to the hydrofluoromonoethers mentioned above, the dielectric insulation gas comprises a fluoroketone containing from four to twelve carbon atoms. The term "fluoroketone" as used in this application shall be interpreted broadly and shall encompass both perfluoroketones and hydrofluoroketones, and shall further encompass both saturated compounds and unsaturated compounds, i.e. compounds including double and/or triple bonds between carbon atoms. The at least partially fluorinated alkyl chain of the fluoroketones can be linear or branched, or can form a ring, which optionally is substituted by one or more alkyl groups. In exemplary embodiments, the fluoroketone is a perfluoroketone . In further exemplary embodiment, the fluoroketone has a branched alkyl chain, in particular an at least partially fluorinated alkyl chain. In still further exemplary embodiments, the fluoroketone is a fully saturated compound .

According to another aspect, the present invention also relates to a dielectric insulation medium comprising a fluoroketone having from 4 to 12 carbon atoms, the at least partially fluorinated alkyl chain of the fluoroketone forming a ring, which is optionally substituted by one or more alkyl groups .

It is particularly preferred that the insulation medium comprises a fluoroketone containing exactly five and/or exactly six carbon atoms.

Compared to fluoroketones having a greater chain length with more than six carbon atoms, fluoroketones containing five or six carbon atoms have the advantage of a relatively low boiling point. Thus, problems which might go along with liquefaction can be avoided, even when the apparatus is used at low temperatures.

According to embodiments, the fluoroketone is at least one compound selected from the group consisting of the compounds defined by the following structural formulae in which at least one hydrogen atom is substituted with a fluorine atom:

:ih)

Fluoroketones containing five or more carbon atoms are further advantageous, because they are generally non-toxic with outstanding margins for human safety. This is in contrast to fluoroketones having less than four carbon atoms, such as hexafluoroacetone (or hexafluoropropanone) , which are toxic and very reactive. In particular, fluoroketones containing exactly five carbon atoms, herein briefly named fluoroketones a) , and fluoroketones containing exactly six carbon atoms are thermally stable up to 500°C.

In embodiments of this invention, the fluoroketones, in particular fluoroketones a) , having a branched alkyl chain are preferred, because their boiling points are lower than the boiling points of the corresponding compounds (i.e. compounds with same molecular formula) having a straight alkyl chain.

According to embodiments, the fluoroketone a) is a perfluoroketone, in particular has the molecular formula C₅F₁₀O, i.e. is fully saturated without double or triple bonds between carbon atoms. The fluoroketone a) may more preferably be selected from the group consisting of 1,1,1,3,4,4,4- heptafluoro-3- (trifluoromethyl ) butan-2-one (also named decafluoro-2-methylbutan-3-one) , 1,1,1,3,3,4,4,5,5,5- decafluoropentan-2-one, 1,1,1,2,2,4,4,5,5, 5-decafluoropentan- 3-one and octafluorocylcopentanone, and most preferably is 1,1,1,3,4,4, 4-heptafluoro-3- (trifluoromethyl) butan-2-one .

1,1,1,3,4,4, -heptafluoro-3- (trifluoromethyl ) butan-2-one can be represented by the following structural formula (I):

1,1,1,3,4,4, 4-heptafluoro-3- (trifluoromethyl) butan-2-one, here briefly called "C5-ketone", with molecular formula CF₃C (0) CF (CF₃) 2 or C5F10O, has been found to be particularly preferred for high and medium voltage insulation applications, because it has the advantages of high dielectric insulation performance, in particular in mixtures with a dielectric carrier gas, has very low G P and has a low boiling point. It has an ODP of 0 and is practically non-toxic.

According to embodiments, even higher insulation capabilities can be achieved by combining the mixture of different fluoroketone components. In embodiments, a fluoroketone containing exactly five carbon atoms, as described above and here briefly called fluoroketone a) , and a fluoroketone containing exactly six carbon atoms or exactly seven carbon atoms, here briefly named fluoroketone c) , can favourably be part of the dielectric insulation at the same time. Thus, an insulation medium can be achieved having more than one fluoroketone, each contributing by itself to the dielectric strength of the insulation medium.

In embodiments, the further fluoroketone c) is at least one compound selected from the group consisting of the compounds defined by the following structural formulae in which at least one hydrogen atom is substituted with a fluorine atom:

(Ila) ,

O (Ilf), and

as well as any fluoroketone having exactly 6 carbon atoms, in which the at least partially fluorinated alkyl chain of the fluoroketone forms a ring, which is substituted by one or more alkyl groups (Ilh); and/or is at least one compound selected from the group consisting of the compounds defined by the following structural formulae in which at least one hydrogen atom is substituted with a fluorine atom:

o

(IHj) ,

and

(ΙΙΙη), e.g. dodecafluoro-cycloheptanone, as well as any fluoroketone having exactly 7 carbon atoms, in which the at least partially fluorinated alkyl chain of the fluoroketone forms a ring, which is substituted by one or more alkyl groups (IIIo) .

According to another aspect, the present invention relates to a dielectric insulation medium comprising a fluoroketone having exactly 6 carbon atoms, in which the at least partially fluorinated alkyl chain of the fluoroketone forms a ring, optionally substituted by one or more alkyl groups.

Furthermore, such dielectric insulation medium can comprise a background gas, in particular selected from the group consisting of: air, air component, nitrogen, oxygen, carbon dioxide, nitrogen oxides, and mixtures thereof. Furthermore, an electrical apparatus comprising such a dielectric insulation medium is disclosed. In particular, the semipermeable membrane is selectively impermeable for the background gas.

According to still another aspect, the present invention relates to a dielectric insulation medium comprising a fluoroketone having exactly 7 carbon atoms, in which the at least partially fluorinated alkyl chain of the fluoroketone forms a ring, optionally substituted by one or more alkyl groups. Furthermore, such dielectric insulation medium can comprise a background gas, in particular selected from the group consisting of: air, air component, nitrogen, oxygen, carbon dioxide, nitrogen oxides, and mixtures thereof. Furthermore, an electrical apparatus comprising such a dielectric insulation medium is disclosed. The present invention encompasses each compound or each combination of compounds selected from the group consisting of the compounds according to structural formulae (la) to (Ii) , (Ila) to (Ilh), (Ilia) to (IIIo), and mixtures thereof; as well as in additional embodiments compounds ' according to structural formulae (Oa) to (Or) and mixtures thereof with any of the foregoing compounds.

Depending on the specific application of the apparatus of the present invention, a fluoroketone containing exactly six carbon atoms (falling under the designation "fluoroketone c) " mentioned above) may be preferred; such a fluoroketone is nontoxic, with outstanding margins for human safety.

In embodiments, fluoroketone c) , alike fluoroketone a) , is a perfluoroketone, and/or has a branched alkyl chain, in particular an at least partially fluorinated alkyl chain, and/or the fluoroketone c) contains fully saturated compounds. In particular, the fluoroketone c) has the molecular formula C6F12O, i.e. is fully saturated without double or triple bonds between carbon atoms. More preferably, the fluoroketone c) can be selected from the group consisting of 1,1,1,2,4,4,5,5,5- nonafluoro-2- (trifluoromethyl) pentan-3-one (also named dodecafluoro-2-methylpentan-3-one) , 1, 1, 1, 3,3,4, 5, 5, 5- nonafluoro-4- (trifluoromethyl) pentan-2-one (also named dodecafluoro-4-methylpentan-2-one) , 1,1,1,3,4,4,5, 5, 5- nonafluoro-3- (trifluoromethyl ) pentan-2-one (also named dodecafluoro-3-methylpentan-2-one) , 1,1,1,4,4, 4-hexafluoro-

3 , 3-bis- (trifluoromethyl ) butan-2-one (also named dodecafluoro- 3, 3- (dimethyl) butan-2-one) , dodecafluorohexan-2-one, dodecafluorohexan-3-one and decafluorocyclohexanone, and particularly is the mentioned 1, 1, 1, 2, 4 , 4 , 5, 5, 5-nonafluoro-2- (trifluoromethyl) pentan-3-one . 1,1,1,2,4,4,5,5, 5-Nonafluoro-2- (trifluoromethyl) pentan-3-one (also named dodecafluoro-2-methylpentan-3-one) can be represented by the following structural formula (II):

(ID

1,1,1,2,4,4,5,5, 5-Nonafluoro-2- (trifluoromethyl ) pentan-3-one (here briefly called "C6-ketone", with molecular formula C2F5C (0) CF (CF3) 2) has been found to be particularly preferred for high voltage insulation applications because of its high insulating properties and its extremely low GWP. Specifically, its pressure-reduced breakdown field strength is around 240 kV/ (cm*bar) , which is much higher than the one of air having a much lower dielectric strength (E_cr = 25 kV/ (cm*bar) . It has an ozone depletion potential of 0 and is non-toxic (LC50 of about 100' 000 ppm) . Thus, the environmental impact is much lower than when using SF₆, and at the same time outstanding margins for human safety are achieved.

In order to further guarantee for the integrity of the insulation medium, the housing preferably encloses the insulation space in a gas-tight manner.

According to a further preferred embodiment, the electrical component is a high voltage or medium voltage apparatus.

Preferably, the electrical apparatus is a switchgear, in particular a gas-insulated switchgear (GIS) or a part and/or component thereof, a busbar, a bushing, a cable, a gas- insulated cable, a cable joint, a gas-insulated line (GIL) , a transformer, a current transformer, a voltage transformer, a surge arrester, an earthing switch, a disconnector, a combined disconnector and earthing switch, a load-break switch, a circuit breaker, gas-insulated switch, a convertor building and/or any type of gas-insulated space or room. Room is to be understood as a space into which a person can enter, typically through a door.

Another aspect of the present application relates to a method for reducing contamination in an electrical apparatus, in particular as disclosed herein, the electrical apparatus comprising an insulation space containing an electrical component and an insulation medium for providing electrical insulation for the electrical component, with the electrical apparatus further comprising a contamination- reducing component for reducing or eliminating at least one contaminant from the insulation space, with the contamination- reducing component being arranged in a contamination-reduction space which is separated from the insulation space by a semipermeable membrane, and the method comprising the method elements of: pre-filtering the insulation medium present in the insulation space by means of the semipermeable membrane such, that at least one contaminant present in the insulation medium is at least partially extracted from the insulation medium, and immobilizing an amount of the extracted contaminant by means of the contamination-reducing component. Immobilizing shall mean reducing the amount or concentration of the extracted contaminant present in a gas phase, in particular in a contamination-reduction space.

Thus, the method step of filtering is performed before the step of immobilizing the amount of contaminant in the gas phase. Further embodiments are disclosed in the dependent method claims and claim combinations. In embodiments of the apparatus or method, the electrical apparatus comprises a housing enclosing an electrical apparatus interior space, at least a portion of the electrical apparatus interior space forming the insulation space containing the electrical component and the insulation medium.

In additional or alternative embodiments of the apparatus or method, the electrical apparatus comprises a room that can be entered by a person, in particular through a door, which room encloses an electrical apparatus interior space, at least a portion of the electrical apparatus interior space forming the insulation space containing the electrical component and the insulation medium.

In the apparatus and method, it is preferred that the semipermeable membrane is selectively impermeable for at least one component of the uncontaminated insulation medium. Preferably, the semipermeable membrane is selectively impermeable at least for all those components of the uncontaminated insulation medium, that can be subject to co-adsorption by the contamination-reducing component and the reduction or removal of which reduces the integrity, in particular dielectric insulation strength and/or arc-extinguishing performance, of the insulation medium.

Throughout this application, the term "contaminant" is to be understood broadly to encompass any substance (s) or component ( s ) , the presence of which negatively affects the integrity, in particular the dielectric insulation strength and/or arc-extinguishing performance, of the insulation medium or the integrity of materials the electrical apparatus is made of, independent of the origin of such contaminating substance (s) or component ( s ) . Such contaminating substance (s) or component (s) may for example be present in the electrical apparatus a priori, from transportation, mounting, installation, operation or maintenance, and for example may be stemming from filling, out-gasing, ageing, arcing, decomposition, recombination, chemical reaction of any type, adsorption, desorption, leakage in or leakage out, or any other source. Such contaminant may for example comprise moisture, water, and/or decomposition products of an insulation medium comprising, for example, perfluoromonoketones comprising exactly 5 or exactly 6 or exactly 7 carbon atoms.

A further advantage of the disclosed apparatus and method is that the combined effect of pre-filtering by semipermeable membrane and immobilizing by the contamination-reducing component reduces or eliminates also toxic contaminants. Thereby, the environmental impact and exposure of personnel e.g. during maintenance and decommissioning are reduced.

The invention is further illustrated by way of the attached figures, of which

Fig. 1 shows a purely schematic representation of an electrical apparatus according to the present invention in the form of a switchgear in a longitudinal cross-section;

Fig. 2 shows a perspective view of an array of closed containers as used in the embodiment shown in Fig. 1, the containers being formed by a semipermeable membrane and enclosing a contamination-reduction space; and

Fig. 3 shows a purely schematic representation of further embodiments of the present invention comprising a contamination-reduction space in which a solidification device is arranged as a contamination-reducing component .

In the embodiment in Fig. 1, the electrical apparatus 2, more particularly the switchgear, comprises a housing 4 enclosing an interior space 5 of the electrical apparatus 2. In the embodiment shown, the electrical apparatus interior space 5 forms an insulating space 6, in which an electrical component 8 is arranged and which contains an insulation medium surrounding the electrical component 8.

The electrical apparatus 2 further comprises a contamination- reducing component 10 (schematically illustrated as dots) for reducing or eliminating at least one contaminant from the insulation space 6.

According to the invention, the contamination-reducing component 10 is arranged in a contamination-reduction space 12, which is separated from the insulation space 6 by a semipermeable membrane 14. In the embodiment shown, a plurality of closed containers 16a, 16b, 16c is formed by the semipermeable membrane 14, each container 16a, 16b, 16c enclosing a respective part of the contamination-reduction space 12.

The containers 16a, 16b, 16c are arranged within the electrical apparatus interior space 5, and the semipermeable membrane 14 with the contamination-reducing component 10 enclosed is fully surrounded by the insulation medium.

Fig. 2 shows an array of nine containers 16a, 16b, 16c formed by the semipermeable membrane 14 and holding the contamination-reducing component 10. The containers 16a, 16b, 16c are closed, but for illustrative purposes are shown in a longitudinal cross-section.

The containers 16a, 16b, 16c are exemplarily shown to be evenly arranged in three rows of three containers, with the three containers 16a, 16b, 16c of the first row corresponding to the ones shown in Fig. 1. In the embodiment shown, the containers are in tubular shape. Of course, any other shape or number of container (s) 16a, 16b, 16c is possible and can be adapted to the actual need. In the exemplary embodiment shown in Fig. 3, the housing 4 comprises an extension 41, the interior of which forming the contamination-reduction space 12, which is separated from the insulation space 6 by a semipermeable membrane 14, here in the form of a filter running co-planar to the housing wall 18 on which the extension 41 is mounted. In the contamination- reduction space 12, a solidification device 20 for solidifying water is arranged as the contamination-reducing component 10.

The solidification device 20 is in the form of a thermoelectric cooler 201 which comprises a heat exchanger 22. On its upper side, the thermoelectric cooler 201 comprises a cooling area 24 which is cooled down below the dew point of the at least one contaminant, in particular water. The thermoelectric cooler 201 is supplied with power e.g. from a power supply 26, which is connected to the thermoelectric cooler 201 e.g by an electrical feedthrough 28. At the power supply 26, a temperature controller (not shown) can be arranged which is connected with respective temperature sensors (not shown) of the thermoelectric element 201.

After having passed through the semipermeable membrane 14, vapour contained in the contamination-reduction space 12 condenses on the cooling area 24 and upon further cooling solidifies to an ice layer 30, as schematically shown in Fig. 3.

By the condensation (or "liquefaction") and ultimately the solidification, vapour is removed from the gas contained in the contamination-reduction space 12, and the water concentration gradient between the gas in the insulation space 6 and the gas in the contamination-reduction space 12 is maintained, thus resulting in a continuous, concentration- gradient-driven transport of water from the insulation space 6 through the semipermeable membrane 14 into the contamination- reduction space 12. Since the semipermeable membrane 14 is exclusively permeable for water, other constituents of the insulation medium, such as organofluorine compounds, in particular C5-ketone, do not pass the membrane and do therefore not come into contact with the contamination-reducing component 10, particularly the solidification device 20.

List of reference ntunerals

2 electrical apparatus

4 housing

5 electrical apparatus interior space

6 insulation space

8 electrical component

10 contamination-reducing component

12 contamination-reduction space

14 semipermeable membrane

16a, 16b, 16c closed containers

18 housing wall

0; 201 solidification device; thermoelectric cooler 2 heat exchanger

4 cooling area

6 power supply

8 electrical feedthrough

0 ice layer

1 extension of housing

Claims

1. Electrical apparatus (2) for the generation, the distribution and/or the usage of electrical energy, the electrical apparatus (2) comprising a housing (4) enclosing an electrical apparatus interior space (5), at least a portion of the electrical apparatus interior space (5) forming an insulation space (6), in which an electrical component (8) is arranged and which contains an insulation medium surrounding the electrical component ( 8 ) , the electrical apparatus (2) further comprising a contamination-reducing component (10) for reducing or eliminating at least one contaminant from the insulation space ( 6) , wherein the contamination-reducing component (10) is arranged in a contamination-reduction space (12) which is separated from the insulation space (6) by a semipermeable membrane (14).

2. Electrical apparatus (2) according to claim 1, wherein the semipermeable membrane (14) is selectively permeable for at least one contaminant present in the insulation space ( 6) .

3. Electrical apparatus (2) according to any of the preceding claims, wherein the semipermeable membrane (14) is selectively permeable for water, which in particular is or is comprised by the at least one contaminant, and is preferably at least approximately exclusively permeable for water; and/or the semipermeable membrane (14) is selectively impermeable for at least one component, preferably all components, of the uncontaminated insulation medium.

Electrical apparatus (2) according to any of the preceding claims, wherein the semipermeable membrane (14) is made of an ionomer.

Electrical apparatus (2) according to any of the preceding claims, wherein the semipermeable membrane (14) is made of a sulfonated tetrafluoroethylene based fluoropolymer-copolymer .

Electrical apparatus (2) according to any of the preceding claims, wherein the semipermeable membrane (14) is made of a polymer of the chemical formula C₇HFi₃0₅S · C₂F₄.

Electrical apparatus (2) according to any of the preceding claims, wherein the semipermeable membrane (14) is made of tetrafluoroethylene-perfluoro-3 , 6-dioxa-4- methyl-7-octenesulfonic acid copolymer.

Electrical apparatus (2) according to any of the preceding claims, wherein the semipermeable membrane (14) forms at least one closed container (16a, 16b, 16c), preferably in tubular shape, which at least one closed container (16a, 16b, 16c) encloses at least partly, preferably fully, the contamination-reduction space (12).

Electrical apparatus (2) according to any of the preceding claims, wherein the contamination-reduction space (12) is arranged within the electrical apparatus interior space (5).

Electrical apparatus (2) according to any of the preceding claims, wherein the electrical apparatus (2) , in particular the contamination-reduction space (12), comprises a molecular sieve as the contamination-reducing component ( 10 ) .

Electrical apparatus (2) according to claim 10, wherein the molecular sieve is a zeolite.

Electrical apparatus (2) according to claim 10 or 11, wherein the molecular sieve has an average pore size from 3 A to 13 A, preferably from 5 A to 13 A, more preferably from 6 A to 12 A, even more preferably from 7 A to 11 A, most preferably from 9 A to 11 A.

Electrical apparatus (2) according to any of the preceding claims, wherein the electrical apparatus (2), in particular the contamination-reduction space (12), comprises a desiccant selected from the group consisting of: calcium, calcium sulphate, calcium carbonate, calcium hydride, potassium carbonate, potassium hydroxide, copper (II) sulphate, calcium oxide, magnesium, magnesium oxide, magnesium sulphate, magnesium perchlorate, sodium, sodium sulphate, aluminium, lithium aluminium hydride, aluminium oxide, montmorrilonite, phosphorpentoxide, silica gel, a cellulose filter, and mixtures or combinations thereof.

Electrical apparatus (2) according to any one of the preceding claims, wherein in the contamination-reduction space (12) a liquefaction device for liquefying and/or a solidification device (20) for solidifying the at least one contaminant, in particular water, is or are arranged.

Electrical apparatus (2) according to claim 14, wherein the liquefaction device and/or solidification device comprises a cooling area (24) which is cooled to a temperature below the dew point of the at least one contaminant, in particular water, present in the insulation space (6) .

Electrical apparatus (2) according to claim 14 or 15, wherein the liquefaction device and/or solidification de^¬ vice (20) is or comprises a thermoelectric cooler (201).

Electrical apparatus (2) according to any one of the preceding claims, wherein the insulation medium in its uncontaminated form is or comprises a gas mixture of several components, and the semipermeable membrane (14) is selectively impermeable for at least one of the components, preferably for all components, of the insulation medium in its uncontaminated form.

Electrical apparatus (2) according to any of the preceding claims, characterized in that the insulation medium comprises a background gas, in particular selected from the group consisting of: air, at least one air component, nitrogen (N₂) , oxygen (0₂) , nitrogen oxides, and mixtures thereof, in particular wherein the semipermeable membrane (14) is selectively impermeable for the background gas.

Electrical apparatus (2) according to any of the preceding claims, characterized in that the insulation medium comprises carbon dioxide (C0₂) .

Electrical apparatus (2) according to any of the preceding claims, wherein the insulation medium comprises carbon dioxide (C0₂) and oxygen (0₂) .

Electrical apparatus (2) according to claim 20, wherein the ratio of the amount of carbon dioxide (C0₂) to the amount of oxygen (0₂) ranges from 50:50 to 100:1, preferably from 80:20 to 95:5, more preferably from 85:15 to 92:8, even more preferably from 87:13 to less than 90:10, and in particular is about 89:11.

Electrical apparatus (2) according to any of the preceding claims, wherein the insulation medium comprises an organofluorine compound, in particular in gaseous phase, in particular wherein the semipermeable membrane (14) is selectively impermeable for the organofluorine compound.

Electrical apparatus (2) according to claim 22, wherein the organofluorine compound is selected from the group consisting of: fluoroethers , in particular hydrofluoro- monoethers, fluoroketones , in particular perfluoro- ketones, and fluoroolefins , in particular hydrofluoro- olefins, and mixtures thereof.

Electrical apparatus (2) according to any of the preceding claims 22 to 23, characterized in that the insulation medium comprises a hydrofluoromonoether containing at least three carbon atoms.

Electrical apparatus (2) according to any of the preceding claims 22 to 24, characterized in that the insulation medium comprises a fluoroketone containing from four to twelve carbon atoms, preferably containing exactly five and/or exactly six carbon atoms.

Electrical apparatus (2) according to any of the preceding claims, characterized in that the housing (4) encloses the insulation space (6) in a gas-tight manner.

Electrical apparatus (2) according to any of the preceding claims, characterized in that the electrical component (8) is a high voltage or medium voltage apparatus ( 8 ) .

Electrical apparatus (2) according to any of the preceding claims, wherein the electrical apparatus (2) is a switchgear, in particular a gas-insulated switchgear (GIS) or a part and/or component thereof, a busbar, a bushing, a cable, a gas-insulated cable, a cable joint, a gas-insulated line (GIL) , a transformer, a current transformer, a voltage transformer, a surge arrester, an earthing switch, a disconnector, a combined disconnector and earthing switch, a load-break switch, a circuit breaker, gas-insulated switch, a convertor building and/or any type of gas-insulated space or room.

Method for reducing contamination in an electrical apparatus (2), in particular in an electrical apparatus (2) of any of the preceding claims, the electrical apparatus (2) comprising an insulation space (6) containing an electrical component (8) and an insulation medium for providing electrical insulation for the electrical component (8), the electrical apparatus (2) further comprising a contamination-reducing component (10) for reducing or eliminating at least one contaminant from the insulation space ( 6) , wherein the contamination-reducing component (10) is arranged in a contamination-reduction space (12) which is separated from the insulation space (6) by a semipermeable membrane (14), the method comprising the method steps of: pre-filtering the insulation medium present in the insulation space (6) by means of the semipermeable membrane (14) such, that at least one contaminant present in the insulation medium is at least partially extracted from the insulation medium, and immobilizing an amount of the extracted contaminant by means of the contamination-reducing component (10) .

Method according to claim 29, wherein the electrical apparatus (2) comprises a housing (4) enclosing an electrical apparatus interior space (5), at least a portion of the electrical apparatus interior space (5) forming the insulation space (6) containing the electrical component (8) and the insulation medium; and/or wherein the electrical apparatus (2) comprises a room that can be entered by a person, in particular through a door, which room encloses an electrical apparatus interior space (5) , at least a portion of the electrical apparatus interior space (5) forming the insulation space (6) containing the electrical component (8) and the insulation medium.

Method according to any one of the claims 29 to 30, wherein the semipermeable membrane (14): is selectively permeable for water, and/or is selectively impermeable for at least one component, preferably all components, of the uncontaminated insulation medium, and/or is made of an ionomer, and/or is made of a sulfonated tetrafluoroethylene based fluoropolymer-copolymer, and/or is made of a polymer of the chemical formula C7HF13O5S · C2F4, and/or is made of tetrafluoroethylene-perfluoro-3 , 6-dioxa-4- methyl-7-octenesulfonic acid copolymer.

Method according to any of the claims 29 to 31, the semipermeable membrane (14) forming at least one closed container (16a, 16b, 16c), preferably in tubular shape, which encloses at least partly, preferably fully, the contamination-reducing component (10).

Method according to any of the claims 29 to 32, comprising selecting the contamination-reducing component (10) from the group consisting of: a molecular sieve, a zeolite, a desiccant, calcium, calcium sulphate, calcium carbonate, calcium hydride, potassium carbonate, potassium hydroxide, copper (II) sulphate, calcium oxide, magnesium, magnesium oxide, magnesium sulphate, magnesium perchlorate, sodium, sodium sulphate, aluminium, lithium aluminium hydride, aluminium oxide, montmorrilonite, phosphorpentoxide, silica gel, a cellulose filter, and mixtures or combinations thereof.

Method according to any one of the claims 29 to 33, wherein the insulation medium in its uncontaminated form is or comprises a gas mixture of several components, and the semipermeable membrane (14) is selectively impermeable for at least one the components, preferably for all components, of the insulation medium in its uncontaminated form.

Method according to any of the claims 29 to 34, selecting the insulation medium to comprise: a background gas, in particular selected from the group consisting of: air, at least one air component, nitrogen (N2) , oxygen (0₂) , carbon dioxide (CO2) , nitrogen oxides, and mixtures thereof; and/or an organofluorine compound, in particular being selected from the group consisting of: fluoroethers, in particular hydrofluoromonoethers , fluoroketones , in particular perfluoroketones , and fluoroolefins, in particular hydrofluoroolefins , and mixtures thereof.

Method according to any of the claims 29 to 35, selecting the insulation medium to comprise: a hydrofluoromonoether containing at least three carbon atoms, and/or a perfluoroketone containing from four to twelve carbon atoms, preferably containing exactly five and/or exactly six carbon atoms.

37. Method according to any of the claims 29 to 36, the electrical apparatus (2) being a switchgear, in particular a gas-insulated switchgear (GIS) or a part and/or component thereof, a busbar, a bushing, a cable, a gas- insulated cable, a cable joint, a gas-insulated line (GIL) , a transformer, a current transformer, a voltage transformer, a surge arrester, an earthing switch, a disconnector, a combined disconnector and earthing switch, a load-break switch, a circuit breaker, gas- insulated switch, a convertor building and/or any type of gas-insulated space or room.