electrical energy The present invention relates to a method for reclaiming at least one substance from an insulation medium of an electrical apparatus for the generation, transmission, distribution and/or usage of electrical energy. The invention further relates to a substance reclaiming device as well as to an assembly comprising an electrical apparatus and the substance reclaiming device.

Dielectric insulation media in liquid or gaseous state are conventionally applied for the insulation of an electrical component in a wide variety of apparatuses, such as for example switchgears, gas-insulated substations (GIS) , gas-insulated lines (GIL), or transformers.

In medium or high voltage metal-encapsulated switchgears, for example, the electrical component is arranged in a gas-tight housing, the interior of which defines an insulating space, said insulation space comprising an insulation gas and separating and electrically insulating the housing from the electrical component. For interrupting the current in a high voltage switchgear, the insulating gas further functions as an arc extinction gas.

Recently, the use of organofluorine compounds in an insulating gas has been suggested. Specifically, WO 2010/142346 discloses a dielectric insulation medium comprising a fluoroketone having 4 to 12 carbon atoms. A dielectric insulation medium of particular relevance is further disclosed in WO 2012/080246, relating to a medium comprising a dielectric insulation gas, which comprises a fluoroketone containing exactly 5 carbon atoms in a mixture with a dielectric insulation gas component different from said fluoroketone. Still further, WO 2012/080222 discloses a dielectric insulation medium comprising a hydrofluoromonoether .

The fluoroketones according to WO 2010/142346 and WO 2012/080246 as well as the hydrofluoromonoethers according to WO 2012/080222 have been shown to have high insulation capabilities, in particular a high dielectric strength, as well as high arc extinction capabilities. At the same time, they have a very low Global Warming Potential (GWP) and very low toxicity. The combination of these characteristics renders these organofluorine compounds highly suitable as a substitute for SF ₆ (sulphur hexafluoride) , which is commonly used as a dielectric insulation medium, but which is known to have a high GWP.

Notwithstanding their low GWP and toxicity, it would be highly desirable to keep the amount of organofluorine compound to be used during long term operation of the apparatus to a minimum for both ecological and economic reasons.

However, in particular during e.g. a switching operation, which is accompanied by a high temperature increase in the insulation space, organofluorine compounds can be subject to decomposition. Contrary to SF ₆ , the decomposed organofluorine compounds usually do not recombine.

In order to keep the insulation space essentially free from harmful decomposition products, WO 2014/053661 suggests an apparatus for the generation, distribution and/or usage of electrical energy comprising a molecular sieve arranged such as to come into contact with the insulation gas, the molecular sieve having an average pore size greater than the molecular size of at least one decomposition product of the organofluorine compound generated during operation of the apparatus.

During decommissioning and maintenance activities (e.g. reconditioning after a heavy short circuit event) it may be required to reduce the pressure in the insulation space to a safe level proper for handling.

When applying conventional evacuation techniques using a pump, problems regarding the removal of the insulation medium are particularly pronounced, since the boiling point of the organofluorine compound comprised in the insulation medium is typically relatively high.

In order to provide an electrical apparatus which allows to minimize the amount of organofluorine compound to be used and which at the same time allows for a safe overall operability, international patent application No. PCT/EP2014/060300 (not yet published) suggests an electrical apparatus comprising a separator, which is or comprises a liquefaction device, specifically a cooler for cooling the initial gas mixture down to a temperature below the dew point of the organofluorine compound. Despite of the favourable effects achievable by the technology according to international patent application No. PCT/EP2014/060300, the cooler must provide a very high cooling efficiency in order to achieve a sufficient condensation rate of the organofluorine compound. This is owed to the fact that the initial gas mixture enters the cooler with the pressure present in the insulation space of the electrical apparatus.

In order to achieve an acceptable condensation rate of the high-boiling organofluorine compound, the insulation space of the electrical apparatus is typically evacuated, i.e. down to a pressure of less than 0.1 bar, and the extracted gas mixture is cooled to very low temperatures. With the aid of standard cooling media, minimum temperatures of about -38 °C are achievable. If lower temperatures shall be reached, alternative cooling media should be used. However, these alternative cooling media are expensive and thus not desirable. Also, the evacuated housing is subject to a very high differential pressure, i.e. about 1 bar, requiring that the housing walls have a minimum thickness in order to safely withstand the pressure difference between the ambience and the interior space .

In consideration of this, the problem to be solved by the present invention is to provide a method for the efficient reclaiming of at least one substance from an insulation medium, in particular of an organofluorine compound, and at the same time allowing for a safe overall operability of the electrical apparatus in which the insulation medium is used.

With regard to the technology described in international patent application PCT/EP2014/060300, the present invention shall in particular allow for a high reclaiming yield of the organofluorine compound and liquefaction of this compound at relatively low efforts.

More particularly, a high reclaiming yield shall be allowed also in the case where the insulation space of the apparatus is not thoroughly evacuated, ultimately allowing for relatively thin housing walls of the electrical apparatus.

The problem of the present invention is solved by the subject matter of the independent claims. Preferred embodiments are defined in the dependent claims and claim combinations. According to claim 1, the present invention relates to a method for reclaiming at least one substance from an insulation medium of an electrical apparatus for the generation, transmission, distribution and/or usage of electrical energy, the insulation medium comprising an organofluorine compound and at least one further component in gaseous phase, said method comprising the subsequent steps of: a) transferring an initial gas mixture containing the organofluorine compound and at least one further component of the insulation medium out of an insulation space of the electrical apparatus into a substance reclaiming device, b) liquefying the organofluorine compound in the substance reclaiming device by bl) compressing the initial gas mixture, and

b2) cooling the compressed initial gas mixture down to a temperature where the organofluorine compound liquefies, and c) separating the liquefied organofluorine compound from the remaining gas comprising the at least one remaining component of the initial gas mixture.

The term "initial gas mixture" as used in the context of the present invention is to be interpreted broadly and encompasses any possible gas mixture containing the organofluorine compound and at least one further component of the insulation medium.

This at least one further component can in particular be a background gas (or "carrier gas") or a background gas component, as will be discussed in further detail below, but can also be a decomposition product generated from the organofluorine compound . According to one specific embodiment, the initial gas mixture is at least essentially identical to the insulation medium. In this regard, the term "insulation medium" relates to the insulation medium to be replaced, i.e. the insulation medium (or its composition) present in the insulation space at the time directly prior to reconditioning. It is understood that the composition of the insulation medium can change over time, specifically due to the mentioned decomposition phenomena. For example, partial decomposition of the organofluorine compound can occur during a switching operation of a switching component. Thus, the insulation medium to be replaced has in comparison to the insulation medium used for filling the insulation space a lower amount of organofluorine compound and a higher amount of decomposition products. Alternatively, the term "insulation medium" can also relate to the insulation medium used for filling the insulation space, i.e. the fresh mixture, provided that it contains apart from the organofluorine compound a further component, typically the background gas. The fresh mixture is typically devoid of any decomposition products.

As mentioned, reclaiming of the substance is according to the invention obtained by liquefaction. Specifically, the terms "liquefying" or "liquefaction" as used in the context of the present invention is to be interpreted as a phase transition of the respective substance, particularly the gaseous organo- fluorine compound, to the liquid phase. More specifically, a phase separation is achieved by the liquefaction, which allows the substances of the respective phases to be separated in very simple manner, e.g. by draining the liquid phase. After liquefaction and separation of the organofluorine compound, the remaining gas is preferably at least essentially devoid of organofluorine compound. More preferably, the remaining gas at least essentially corresponds to the background gas of the insulation medium. Of course, minor amounts of the organoflourine compound can still be contained in the remaining gas, but these amounts are in any case lower than the amounts contained in the initial gas mixture, as will be discussed in further detail below.

The concept of separating the organofluorine compound from the remaining components by phase separation is in any respect different from the concept suggested in WO 2014/053661 which aims at removing gaseous decomposition products from the insulation gas by means of a molecular sieve: first of all, WO 2014/053661 relates to a mere purification of the insulation gas by removing gaseous decomposition products therefrom, but nowhere mentions or suggests a phase separation of components each of which having the potential to be re-used in the electrical apparatus. In more concrete terms, WO 2014/053661 nowhere mentions or suggests a separation of an organofluorine compound from a background gas, but merely the removal or separation of gaseous decomposition products from an insulation gas containing an organofluorine compound and a background gas. Secondly, the means that are applied are completely different, in that according to WO 2014/053661 a molecular sieve and hence a separation on the basis of the kinetic diameter of the molecules is applied, whereas according to the present invention a separation on the basis of the different boiling points of the substances is performed.

In aiming at a high reclaiming yield of the organofluorine compound in pure form, the present invention is further completely different from the concept of US 5,701,761 which does not deal with the reclaiming of a substance, least of all a dielectric compound, but which aims at simplifying a process for liquefying a natural gas and in this regard suggests to mix a liquid fraction with a vapour fraction. The present invention allows the organofluorine compound to be reclaimed in high yields, which is not only highly advantageous from an economic point of view. Since disposal of the organofluorine compound can be omitted, the present invention also brings an ecologic benefit. In particular, the present invention allows high yields of the reclaimed organofluorine compound to be achieved in a very simple and fast manner. This is owed to the fact that by compressing the initial gas mixture, relatively moderate cooling temperatures are sufficient for obtaining a high condensation rate of the organofluorine compound. Therefore, standard cooling media are sufficient for obtaining a high reclaiming yield.

Typically, the remaining gas, which directly after step c) has a relatively high pressure due to its prior compression in step bl), is expanded via a balancing valve. After expansion, the remaining gas or a portion thereof is preferably reintroduced back into the insulation space. Alternatively or additionally, the remaining gas or a portion thereof can be released into the atmosphere. This applies in particular to the case where the remaining gas is non-hazardous to the environment.

In this regard, it is particularly preferred that the method of the present invention comprises the further step of d) expanding the remaining gas via a balancing valve and reintroducing at least a portion of the remaining gas, specifically the background gas, back into the insulation space .

If - as according to this embodiment - the remaining gas is reintroduced into the insulation space, the absolute pressure in the insulation space will never drop below the partial pressure of the background gas. Due to the lower differential pressure that the housing enclosing the insulation space has to withstand, the housing walls can be designed thinner as it would be the case for a housing which has to withstand thorough evacuation and thus a differential pressure of e.g. about 1 bar . Specifically, the reintroduced remaining gas corresponds to the background gas of the insulation medium. It is understood that the reintroduced remaining gas can also contain a minor amount of organofluorine compound, since the separation according to step c) is typically not perfect due to physical and/or technical reasons. However, it has been found that by repeated recycling, i.e. by repeatedly performing steps a) to d) , the amount of organofluorine compound in the reintroduced remaining gas is continuously decreased until reaching a minimum value. At the same time, the yield of organofluorine compound reclaimed is increased.

The concept of reintroducing the remaining gas, i.e. the gas from which the liquefied organofluorine compound has been separated, is in any respect different from the concept according to WO 2015/177149 having a publication date after the priority date of the present application, since WO 2015/177149 teaches the separated organofluorine compound to be re ^¬ introduced into the insulation space, but not the remaining component .

It is further preferred that in step b2) only the organofluorine compound is liquefied in order to allow for a high purity of the organofluorine compound reclaimed. Thus, it is possible to reclaim the organofluorine without any contaminants, such as decomposition products, which might have been generated during operation of the apparatus. Specifically, reclaiming is particularly straightforward in embodiments, in which the difference in the dew point of the organofluorine compound and the at least one further component, particularly the background gas or background gas component, is large.

The method of the present invention thus differs from the technology according to yet unpublished PCT/EP2014/060300 in that in step bl) the initial gas mixture is compressed before it is cooled in step b2) . Step bl) of the method according to the present invention is preferably carried out such that the temperature increase resulting from the compression does not reach the decomposition temperature of the organofluorine compound, leaving the integrity of the organofluorine compound unaffected, which further contributes to a high yield of the organofluorine compound reclaimed.

Specifically, in step bl) the initial gas mixture is preferably compressed up to a pressure in the range from 2 bar to 20 bar, more preferably from 5 bar to 10 bar, and most preferably to about 9 bar, since the temperature increase resulting from such pressures lies well below the decomposition temperature of the organofluorine compound.

In step b2) the initial gas mixture is preferably cooled down to a temperature below 0°C, preferably below -10°C, more preferably below -20°C, even more preferably below -30°C, and most preferably of about -38°C, thus allowing for a high reclaiming yield of the organofluorine compound from the compressed initial gas mixture. As mentioned above, standard cooling media, which fully comply with the pertinent safety requirements, can be used to reach these temperatures. Given the fact that by the compression the initial gas mixture is heated, the initial gas mixture is preferably pre-cooled after step bl) and before step b2) . Thus, the heating effect of the compression is at least partially compensated for by the pre-cooling, such that the initial gas mixture, which is subjected to the cooling step b2), has a temperature that is manageable for achieving liquefaction of the organofluorine compound, even if a condenser with moderate cooling efficiency is used. According to a further preferred embodiment, the initial gas mixture is purified from liquid and/or solid impurities by a filter before being transferred to the separator, in which liquefaction and separation according to step b) and c) are performed. Thus, the risk of the separator being harmed by impurities, e.g. due to clogging, can efficiently be reduced.

According to a still further embodiment, the method comprises the further step of: e) collecting the condensed organofluorine compound by an organofluorine compound collecting device. Further embodiments comprise after step c) or optionally step d) and/or e) the further step of: f) conveying the organfluorine compound to an organofluorine compound reservoir tank for being stored, as will be discussed in further detail below. In embodiments, in order not to introduce into the insulation space of the electrical apparatus any impurities, such as decomposition products or residual water, the remaining gas or the background gas is preferably purified before being reintroduced into the insulation space. This contributes further to a safe operability of the apparatus.

In embodiments, heat, which is generated during compressing the initial gas mixture according to step bl) , is used for heating the remaining gas prior to being reintroduced into the insulation space. This can be of particular relevance as the background gas is cooled during expansion when passing through the balancing valve, which might result in high-boiling residues, that are still contained in the background gas, to become liquid. This can efficiently be counteracted by using the compression heat generated upstream.

According to a further aspect, the present invention also relates to a substance reclaiming device for reclaiming at least one substance of an initial gas mixture contained in the insulation space of an electrical apparatus, the substance reclaiming device comprises a separator for separating an organofluorine compound from at least one remaining component of the initial gas mixture.

In analogy to the above description of the method of the present invention, the separator comprises a compressor in combination with a cooling device comprising a condenser for liquefying the organofluorine compound. Looking in direction of transfer of the initial gas mixture, the compressor is arranged upstream of the condenser and is designed to compress the initial gas mixture before it is transferred to the condenser.

As discussed above, the substance reclaiming device of the present invention allows a high yield of the reclaimed organo- fluorine compound to be achieved in a very simple, fast and economic manner. As also discussed above, the remaining gas can then be expanded again by means of a balancing valve and reintroduced into the insulation space of the apparatus.

The separator used according to the present invention generally functions in a manner to allow the obtained liquid organo- fluorine compound to flow or fall down, thus allowing to consolidate and collect liquid organofluorine compound. The separator is thus in any respect different from a filter through which the insulation gas is pumped and which requires the organofluorine compound to remain in gaseous phase. In addition to what is taught in yet un-published international patent application No. PCT/EP2014/060300, the substance reclaiming device of the present invention comprises a compressor in combination with a cooling device comprising a condenser for liquefying the organofluorine compound, said compressor being arranged upstream of the condenser, when seen in direction of transfer of the initial gas mixture, and being designed to compress the initial gas mixture, before it is transferred to the condenser.

According to embodiments, the compressor is designed to com- press the initial gas mixture up to a maximum pressure p _max , said maximum pressure p _max being chosen such that the maximum temperature T _max resulting from the compression lies below the decomposition temperature of the organofluorine compound. As discussed above, the compressing is in other words carried out such that the temperature increase resulting from the compression does not reach the decomposition temperature of the organofluorine compound, leaving the integrity of the organofluorine compound unaffected, which further contributes to a high yield of the organofluorine compound reclaimed. Preferably, the compressor is designed to compress the initial gas mixture up to a pressure in the range from 2 bar to 20 bar, more preferably from 5 bar to 10 bar, and most preferably to about 9 bar, in analogy to the above. According to embodiments, the liquefaction device is specifi ^¬ cally adapted for liquefying the organofluorine compound only. Thus, the pressure increase obtained by compressor and the temperature decrease obtained by cooling device are specifically adapted to liquefy the organofluorine compound only.

In further analogy to the above, the condenser is designed to cool the initial gas mixture down to a temperature below 0°C, preferably below -10°C, more preferably below -20°C, more preferably below -30°C, and most preferably of about -38°C, thus allowing for high reclaiming yield of the organofluorine compound from the compressed initial gas mixture. Thus, standard cooling media which fully comply with the pertinent safety requirements can be used to reach these temperatures.

In embodiments, the condenser further comprises a heating element to raise the temperature above 0°C. The temperature raise aims particularly at de-icing the condenser in case that any residual moisture in the initial gas mixture is detected, which, if left in the condenser, could lead to icing and ultimately to failure of the condenser. Given the fact that by the compression the initial gas mixture is heated, it is particularly preferred that the cooling device further comprises a heat exchanger for pre-cooling the initial gas mixture before it is transferred to the condenser. As discussed above, the heating effect of the compression is thus at least partially compensated for by the pre-cooling, such that the initial gas mixture entering the condenser has a temperature that is manageable for achieving liquefaction, even if a condenser with moderate cooling efficiency is used. For pre-cooling the initial gas mixture, a plate heat exchanger is particularly preferred.

In embodiments, the substance reclaiming device additionally comprises an organoflourine compound collecting device for collecting the organofluorine compound separated by the separator. In further embodiments, the substance reclaiming device comprises at least one organofluorine compound reservoir tank for storing the organofluorine compound separated by the separator. Thus, the organofluorine compound is collected, e.g. by means of a vessel into which the liquid organofluorine compound falls or flows, and is ultimately directed to the organofluorine compound reservoir tank in which the organofluorine compound is held under storage conditions. In this regard, it is for example thinkable that the organofluorine compound collecting device is equipped with a float valve which, once a threshold amount of organofluorine compound is collected, activates a pump for transferring the organofluorine compound into the organofluorine compound reservoir tank. By storing only the organofluorine compound in its liquid form, much less space and much less sophisticated reservoir tanks are required compared to the case where the whole gas mixture including the background gas would have to be stored at high pressures .

In embodiments, the substance reclaiming device further comprises a filter designed such to remove solid or liquid impurities from the flow of the initial gas mixture before it enters the compressor. In particular, the filter can be allocated to a primary gas channel adapted to be connected to an outlet opening of the housing of the electrical apparatus by means of a connecting piece, as will be discussed below. By a pre-removal of solid or liquid impurities from the initial gas mixture prior to its entering into the compressor, the risk of clogging of the compressor, and ultimately of a failure of the substance reclaiming device, can efficiently be reduced.

According to embodiments, a flow of initial gas mixture out of the housing of the apparatus is generated by means of a suction force generated by the compressor. Additionally or alternatively, the substance reclaiming device can comprise a pump designed to purge the insulation space.

The substance reclaiming device is typically an individual device. It is preferably connected to the housing of an electrical apparatus, e.g. a transformer tank, once the insulation medium needs reconditioning.

Specifically, the substance reclaiming device comprises means for fluidly connecting the separator with the insulation space of the electrical apparatus. More specifically, the substance reclaiming device comprises a connecting piece for connecting it to the outlet opening of the housing and for receiving the initial gas mixture containing the substance (s) to be reclaimed. In particular, the substance reclaiming device further comprises a secondary connecting piece for connecting it to the inlet opening of the housing for allowing reintroducing the remaining gas, specifically via a balancing valve for reducing the pressure again to the pressure present in the insulation space.

In embodiments, at least one gas recycling channel branches off from the separator of the substance reclaiming device, the gas recycling channel being fluidly connected to a gas inlet opening arranged in the housing for reintroducing the remaining gas, in particular the background gas, into the insulation space. As mentioned, the remaining gas, and specifically the background gas, is at least essentially devoid of the organofluorine compound which has been separated off in the separator .

As mentioned, the substance reclaiming device can further comprise a balancing valve arranged downstream of the condenser, said balancing valve being designed to expand the remaining gas after the initial gas mixture has passed the condenser. In other words, the pressure of the remaining gas, specifically the background gas, is reduced before it is reintroduced into the insulation space. Thus, the relatively high pressure of the background gas resulting from the initial gas mixture having been compressed upstream in the process cycle is reduced, in particular to the pressure present in the insulation space, more particularly to a pressure between the partial pressure of the background gas and the initial total pressure, i.e. (e.g. in a gas-insulated transformer) between 0.8 bar and 1.3 bar absolute pressure.

In embodiments, a background gas treatment device is arranged upstream of the inlet opening, in particular for removing impurities from the background gas to be reintroduced into the insulation space. More particularly, the background gas treatment device is or comprises a zeolite able to adsorb the organofluorine compound or decomposition products thereof. This background gas treatment device is preferably linked to the gas recycling channel.

According to a still further aspect, the present invention further relates to an assembly of A) an electrical apparatus for the generation, transmission, distribution and/or usage of electrical energy, and

B) a substance reclaiming device as described above.

The electrical apparatus comprises a housing enclosing an electrical apparatus interior space, at least a portion of said electrical apparatus interior space comprising at least one insulation space, in which an electrical component is arranged and which contains an insulation medium surrounding the electrical component. In analogy to the description above, the insulation medium comprises an organofluorine compound and at least one further component in gaseous phase.

The substance reclaiming device is arranged downstream of the outlet opening, with regard to the direction of transfer of the initial gas mixture.

In further analogy to the disclosure above, an outlet opening for transferring an initial gas mixture out of the insulation space is arranged in the housing of the electrical apparatus, with the initial gas mixture containing the organofluorine compound and at least one further component of the insulation medium. As mentioned above, the initial gas mixture is preferably at least essentially identical to the insulation medium present in the insulation space at the time directly prior to reconditioning. In order to reintroduce the background gas back into the insulation space after separating off the organoflourine compound, it is preferred that at least one gas recycling channel branches off from the separator of the substance reclaiming device, the gas recycling channel being fluidly connected to a gas inlet opening arranged in the housing for reintroducing the background gas of the initial gas mixture into the insulation space e.g. via a balancing valve, said background gas being at least essentially devoid of organo- fluorine compound. Specifically, said balancing valve is designed to expand the background gas before being reintroduced into the insulation space. As mentioned above, a background gas treatment device can be arranged upstream of the gas inlet opening, in particular for purifying the background gas to be reintroduced into the insulation space, and more particularly is a zeolite able to adsorb the organofluorine compound or decomposition products thereof.

In embodiments, the organofluorine compound used according to the present invention has a boiling point higher than 0°C. Throughout this disclosure, the term "boiling point" relates to the standard boiling point, i.e. the temperature at which boiling occurs under a pressure of 1 bar.

According to embodiments, the organofluorine compound is selected from the group consisting of: fluoroethers , in parti ^¬ cular hydrofluoromonoethers , fluoroketones , fluoroolefins , in particular hydrofluoroolefins , and fluoronitriles , in particular perfluoronitriles , as well as mixtures thereof, since 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 lower GWP and toxicity. The invention encompasses both embodiments, in which the respective insulation medium comprises either one of a fluoro- ether, in particular a hydrofluoromonoether, a fluoroketone and a fluoroolefin, in particular a hydrofluoroolefin, and fluoronitriles , in particular perfluoronitriles , as well as embodiments in which it comprises a mixture of at least two of these compounds. The background gas is preferably selected from the group consisting of: air, an air component, nitrogen, oxygen, carbon dioxide, a nitrogen oxide and mixtures thereof. Thus, at least one of the remaining components of the initial gas mixture, i.e. the initial gas mixture without the organofluorine compound, is preferably selected from the group consisting of: air, an air component, nitrogen, oxygen, carbon dioxide, a nitrogen oxide and mixtures thereof.

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.

In embodiments, the respective insulation medium comprises a hydrofluoromonoether containing at least three carbon atoms. Apart from their high dielectric strength, these hydrofluoro- monoethers 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, said 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 SF ₆ 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:

By using a hydrofluoromonoether containing three or four carbon atoms, no liquefaction occurs under typical operational conditions of the apparatus. Thus, a dielectric insulation fluid, every component of which is in the gaseous state at operational conditions of the apparatus, can be achieved. Nevertheless, the boiling point of this hydrofluoromonoether is still high enough to allow liquefaction by means of the liquefaction device of the present invention.

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 thus 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 (O) C _a H _b F _c -O-C _d H _e F _f (O) 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.

Most preferably, the hydrofluoromonoether is selected from the group consisting of pentafluoro-ethyl-methyl ether (CH ₃ -O- CF ₂ CF ₃ ) and 2 , 2 , 2-trifluoroethyl-trifluoromethyl ether (CF ₃ -0-CH ₂ CF ₃ ) . 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 or 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, an 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 respective insulation medium 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 insulation medium according to the present invention can comprise 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 or exactly six carbon atoms or mixtures thereof. 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, allowing to avoid liquefaction under operational conditions. Nevertheless, the boiling point of this fluoroketone is still high enough to allow liquefaction by means of the liquefaction device of the present invention.

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:

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.

According to a specific embodiment, the insulation medium according to the present invention, in particular comprising a fluoroketone having exactly 5 carbon atoms, can further comprise a background gas, in particular selected from the group consisting of: air, air component, nitrogen, oxygen, carbon dioxide, a nitrogen oxide (including but not limited to O ₂ , NO, ₂ O) , and mixtures thereof. 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 perfluoro- ketone, in particular has the molecular formula C ₅ F ₁₀ O, i.e. is fully saturated without double or triple bonds between carbon atoms. The fluoroketone a) may 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, 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 CF ₃ C (0) CF (CF ₃ ) 2 or C ₅ Fi ₀ O, 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 GWP 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:

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:

(ΙΙΙη), in particular 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) .

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.

According to another aspect, the insulation medium according to the present invention can comprise 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.

As mentioned, such insulation medium can comprise a background gas, in particular selected from the group consisting of: air, air component, nitrogen, oxygen, carbon dioxide, a nitrogen oxide (including but not limited to O ₂ , NO, ₂ O) , and mixtures thereof. Furthermore, an electrical apparatus comprising such an insulation medium is disclosed.

According to still another aspect, the insulation medium according to the present invention can comprise 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 an insulation medium can comprise a background gas, as mentioned above, in particular selected from the group consisting of: air, air component, nitrogen, oxygen, carbon dioxide, a nitrogen oxide (including but not limited to O ₂ , NO, ₂ O) , and mixtures thereof. Furthermore, an electrical apparatus comprising such a dielectric insulation fluid is disclosed . The insulation medium according to the present invention encompasses any insulation medium comprising each compound or each combination of compounds selected from the group consisting of the compounds according to structural formulae (la) to (Ii), (Ha) to (Ilh), (Ilia) to (IIIo), and mixtures thereof, and with the insulation medium further comprising a background gas, in particular selected from the group consisting of: air, air component, nitrogen, oxygen, carbon dioxide, a nitrogen oxide (including but not limited to NO ₂ , NO, N ₂ O) , and mixtures thereof. Furthermore, an electrical apparatus comprising such an insulation medium is disclosed.

Depending on the specific application of the electrical component 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 for the respective insulation space compartment; such a fluoroketone is non-toxic, 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 C ₆ F ₁ 2O, 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 (with sum formula C ₆ F ₁₀ O) , 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- (also named dodecafluoro-2-methylpentan-3-one) can represented by the following structural formula (II) :

1,1,1,2,4,4,5,5, 5-Nonafluoro-4- (trifluoromethyl) pentan-3-one (here briefly called "C6-ketone", with molecular formula C ₂ F ₅ C (0) CF (CF ₃ ) 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. Thus, the environmental impact is much lower than when using SF ₆ , and at the same time outstanding margins for human safety are achieved.

As mentioned above, the organofluorine compound can also be a fluoroolefin, in particular a hydrofluoroolefin . More particularly, the fluoroolefin or hydrofluorolefin contains exactly three carbon atoms.

According to an embodiment, the hydrofluoroolefin is thus selected from the group consisting of: 1 , 1 , 1 , 2-tetrafluoro- propene (HFO-1234yf) , 1, 2, 3, 3-tetrafluoro-2-propene (HFO- 1234yc) , 1, 1, 3, 3-tetrafluoro-2-propene (HFO-1234zc) , 1,1,1,3- tetrafluoro-2-propene (HFO-1234ze) , 1 , 1 , 2 , 3-tetrafluoro-2- propene (HFO-1234ye) , 1 , 1 , 1 , 2 , 3-pentafluoropropene (HFO- 1225ye) , 1 , 1 , 2 , 3 , 3-pentafluoropropene (HFO-1225yc) , 1,1,1,3,3- pentafluoropropene (HFO-1225zc) , ( Z ) 1 , 1 , 1 , 3-tetrafluoropropene (HFO-1234zeZ) , ( Z ) 1 , 1 , 2 , 3-tetrafluoro-2 -propene (HFO-1234yeZ) , (E) 1, 1, 1, 3-tetrafluoropropene (HFO-1234zeE) , (E)l, 1,2,3- tetrafluoro-2-propene (HFO-1234yeE) , ( Z ) 1 , 1 , 1 , 2 , 3- pentafluoropropene (HFO-1225yeZ) , (E) 1 , 1 , 1 , 2 , 3- pentafluoropropene (HFO-1225yeE) and combinations thereof.

As mentioned above, the organofluorine compound can also be a fluoronitrile, in particular a perfluoronitrile . In particular, the organofluorine compound can be a fluoronitrile, specifically a perfluoronitrile, containing two carbon atoms, three carbon atoms or four carbon atoms .

More particularly, the fluoronitrile can be a perfluoro- alkylnitrile, specifically perfluoroacetonitrile, perfluoro- propionitrile (C ₂ F5CN) and/or perfluorobutyronitrile (C3F7CN) .

Most particularly, the fluoronitrile can be perfluoro- isobutyronitrile (according to the formula (CF3) ₂ CFC ) and/or perfluoro-2-methoxypropanenitrile (according to the formula CF ₃ CF (OCF3) CN) . Of these, perfluoroisobutyronitrile is particu- larly preferred due to its low toxicity.

Preferably, the electrical apparatus of the present invention or the electrical component thereof is a high voltage or medium voltage apparatus, or is a high voltage or medium voltage component, respectively. Specifically, the electrical apparatus is selected from the group consisting of: 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, any type of gas-insulated switch, a high voltage apparatus, a medium voltage apparatus, a low voltage apparatus, a direct-current apparatus, an air-insulated insulator, a gas-insulated metal- encapsulated insulator, sensors, a capacitor, an inductance, a resistor, a current limiter, a high voltage switch, a gas circuit breaker, a vacuum circuit breaker, a generator circuit breaker, a medium voltage switch, a ring main unit, a recloser, a sectionalizer, a low voltage switch, a distribution transformer, a power transformer, a tap changer, a transformer bushing, a power semiconductor device, a power converter, a converter station, a convertor building, a computing machine, and components and/or combinations of such devices. According to a particularly preferred embodiment, the electrical apparatus is a transformer with the transformer tank forming the housing of the apparatus.

According to a further embodiment, the remaining gas or a portion thereof is reintroduced back into the insulation space separately from any other component to be reintroduced, in particular from any organofluorine compound to be reintroduced. According to this embodiment, there is prior to the reintroduction no mixing of the remaining gas with the separated organofluorine compound. According to a still further embodiment, only the remaining gas is reintroduced back into the insulation space. According to this embodiment, the organofluorine compound separated from the remaining gas in step c) is not reintroduced into the insulation space . According to these specific features of the process of the present invention, the electrical apparatus of the present invention comprises a gas recycling channel designed to be fluidly connected to a gas inlet opening arranged in the housing for reintroducing the remaining gas into the insulation space. Specifically, said gas recycling channel is preferably devoid of any inlet connection for the supply of the separated organofluorine compound.

The electrical apparatus according to these embodiments is therefore in even clearer distinction from the teaching of US 5,701,761 according to which a low-temperature mixture of a light fluid mainly consisting of a vapour phase is mixed with a heavy fluid mainly consisting of a liquid phase, where said mixture is then used in a device for the cooling of natural gas . The present invention is further illustrated by way of the attached

Fig. 1 showing schematically an assembly comprising an electrical apparatus and a substance reclaiming device according to an exemplary embodiment of the present invention.

As shown in Fig. 1, the electrical apparatus 10 of the assembly according to the present invention comprises a housing 12 enclosing an electrical apparatus interior space.

The electrical apparatus interior space forms or comprises an insulation space 16, in which an electrical component 14 is arranged. The electrical component 14 can for example be connected to respective conductors 18a, 18b which are insulated from the material of the housing 12 by means of respective bushings. The electrical component 14 is surrounded by an insulation medium 22 which comprises an organofluorine compound and a background gas and hence separates and electrically insulates the housing 12 from the electrical component 14.

In the housing 12, an outlet opening 26 is arranged for transferring an initial gas mixture out of the insulation space 16. The initial gas mixture contains the organofluorine compound and at least one further component. This further component can in particular be the background gas or a background gas component, but can also be a decomposition product generated from the organofluorine compound. The apparatus 10 further comprises a substance reclaiming device 30. The substance reclaiming device 30 is linked to the housing 12 by means of respective connecting pieces (not shown) . The outlet opening 26 opens out into a primary gas channel 28 of the substance reclaiming device 30. The primary gas channel 28 fluidly connects the insulation space 16 with a separator 34 of the substance reclaiming device 30, said separator 34 being intended to separate the organofluorine compound from the at least one remaining component of the initial gas mixture, specifically from the background gas.

Between the outlet opening 26 and the separator 34, a filter 32 can be arranged, which is designed such to remove solid or liquid impurities from the flow of the initial mixture prior to entering the separator 34. The separator 34 comprises the compressor 25 mentioned above which apart from functioning as flow generating device is designed for compressing the initial gas mixture. The separator 34 further comprises a cooling device 35 fluidically connected with and located downstream of the compressor 25. The cooling device 35 comprises a heat exchanger 36 and a condenser 37. The heat exchanger 36 is fluidically connected to the condenser 37 and is intended to pre-cool the initial gas mixture heated as a result of the compression in the compressor 25 before it is transferred to the condenser 37. In the separator 34, the liquefied organofluorine compound is separated from the remaining gas containing the background gas of the insulation medium by phase separation. For collecting the organofluorine compound separated by the separator 34, the separator 34 further comprise an organofluorine compound collecting device 38. The organofluorine compound collecting device 38 can e.g. be in the form of a funnel, as schematically indicated in Fig. 1, and leads in the embodiment shown to an organofluorine compound reservoir tank 40 for storing the organofluorine compound. From the separator 34 of the substance reclaiming device 30, a gas recycling channel 46 branches off. The gas recycling channel 46 is designed to guide the background gas, which at this stage contains only minor amounts of the organofluorine compound, to a gas inlet opening 50 arranged in the housing 12 for reintroducing the background gas into the insulation space 16. For this purpose, a balancing valve 48 is allocated to the separator 34 designed to expand the remaining gas. Downstream of the expansion valve 48 and upstream of the gas inlet opening 50 a background gas treatment device 49 in the form of a secondary filter 491 is arranged for purifying the background gas before it is reintroduced into the insulation space 16, thereby closing the recycling cycle.

In more concrete terms, the specific embodiment according to Fig. 1 relates to an electrical apparatus 10, the insulating space 16 of which has a volume of about 20 m ³ and contains an insulation medium comprising 1, 1, 1, 3, 4, 4, 4-heptafluoro-3- (trifluoromethyl) butan-2-one ("C5-ketone") in mixture with air. The total filling pressure is about 1.2 bar at 20°C with the content of C5-ketone being about 30%. Thus, the partial pressure of C5-ketone inside the housing is about 360 mbar.

By means of the compressor 25, a flow of the initial gas mixture is generated by suction, the gas flow entering the primary gas channel 28 and being regulated by means of a valve 27 allocated to the primary gas channel 28. The initial gas mixture thus corresponds to the insulation medium 22 present in the insulation space 16 at the time directly before refurbishment. During the refurbishment, the pressure in the insulation space 16 is reduced to a pressure of about 850 mbar.

The extracted initial gas mixture passes the filter 32, which is arranged downstream of the valve 27, before it enters the compressor 25. By means of the compressor 25, the gas is compressed, in the specific case to a pressure of about 7.4 bar. Thus, the partial pressure of C5-ketone is increased to 2.2 bar at this stage, i.e. at the beginning of the reclaiming process . From there, the compressed initial gas mixture is transferred to the heat exchanger 36 by means of which the compressed gas is pre-cooled to moderate temperatures, i.e. to about ambient temperature. Thus, the temperature increase due to adiabatic compression of the initial gas mixture is at least partly compensated by the heat exchanger 36.

The pre-cooled initial gas mixture is then transferred to the condenser 37 for liquefying the organofluorine compound. The condenser is designed to actively cool the initial gas mixture according to the principles of a cold trap. Ideally, cooling of the initial gas mixture down to a temperature of about -38°C is thereby achieved. At -38°C, only around 40 mbar of the C5- ketone contained in the compressed gas stays in gaseous phase, if a perfect heat transfer is achieved. In other words, the partial pressure of the C5-ketone is reduced by about 2.16 mbar because about 97% of the C5-ketone vapour liquefies under optimal conditions. The liquefied C5-ketone is collected by the organofluorine compound collecting device 38 and then transferred via an organofluorine compound storing line 39 to a reservoir tank 40 for storing. The background gas, which after having passed the condenser 37 is at least approximately devoid of organofluorine compound, is guided into the gas recycling channel 46 and is expanded by means of the balancing valve 48 to the pressure present in the insulation space 16. Prior to entering the insulation space, the background gas is guided through another valve 51 to regulate the gas recycling flow.

List of reference numerals

10 electrical apparatus

12 housing

14 electrical component

16 insulation space

18a, 18b conductors

22 insulation medium

25 compressor

26 outlet opening

27 valve allocated to primary gas channel

28 primary gas channel

30 substance reclaiming device

32 filter

34 separator

35 cooling device

36 heat exchanger

37 condenser

38 organofluorine compound collecting device

39 organofluorine compound storing line

40 organofluorine compound reservoir tank

46 gas recycling channel

48 expansion valve, balancing valve

49; 491 background gas treatment device; secondary filter 50 gas inlet opening for reintroducing background gas

51 valve allocated to gas recycling channel