It is known that medium- and high-voltage circuit breakers comprise an insulating casing in which there is an interruption chamber with interruption mechanisms constituted by at least one fixed contact and at least one moving contact. Opening/closure maneuvers of the circuit breaker are performed by engaging/disengaging the fixed contacts with respect to the moving contacts by using known actuation devices.

Generally, during opening the mutual separation of the moving contact and of the fixed contact is accompanied by the generation of an electric arc between the two contacts; these arcs are quenched by using known kinds of dielectric fluid whose use. in the current state of the art, entails various drawbacks and disadvantages.

For example, one of the most common fluids used to quench the electric arc in medium Lind/oi- hi-h-voltace circuit breakers is constituted by a mineral oil : mineral oils, however, in addition to being dangerously flammable, can sometimes lead to unacceptable drawbacks, such as the generation of hydrogen, methane and carbon residuals.

Many applications commonly use gaseous substances such as nitrogen, noble gases, compressed air, sulfur hexafluoride (SF6) and mixtures thereof. With these substances it is indispensable to use devices for monitoring the pressure of the gas used and for replenishing it in order to maintain the dielectric performance of the system.

Another drawback is due to the fact that both when using gaseous fluids and

when using liquid fluids it is necessary to adopt particular refinements and to use safety systems in order to avoid and/or indicate any losses and leaks of said fluid : in this case, the losses and consequent leaks of the fluid might in fact cause malfunctions of the circuit breaker and environmental contamination problems. This obviously affects the constructive complexity of the circuit breaker and its overall reliability.

It is also known in the technical literature to use non-flammable liquids, such as for example mixtures of chlorofluorocarbons (CFC) or of perfluorocarbons (PFC) : these liquids are highly limited in their use because in the presence of electric arcs they undergo a decomposition which produces reactive and toxic by-products. Since these reactive substances are unacceptable from the point of view of environmental impact, they require the adoption of disposal procedures typical of toxic waste.

The main aim of the present invention is to provide a medium and/or high- voltage circuit breaker (i. e. for voltages greater than 1000V) which contains, as an arc quenching means, a dielectric fluid in which the decomposition products generated as a consequence of electric arcs have an extremely low environmental impact, thus allowing to avoid the disposal problems typical of known circuit breakers.

Within the scope of this aim, an object of the present invention is to provide a medium and/or high-voltage circuit breaker which is compact and has a total volume which is comparable to the volume of known types of circuit breaker.

Another object of the present invention is to provide a medium and/or high- voltage circuit breaker in which it is possible to minimize the use of the associated safety systems while increasing its overall reliability.

Another object of the present invention is to provide a medium and/or high- voltage circuit breaker which is highly reliable and relatively easy to manufacture at competitive costs.

This aim. these objects and others which will become apparent hereinafter are achieved by a medium and/or high-voltage circuit breaker, comprising an insulating casing inside which there is at least one interruption chamber which contains at least one fixed contact and at least one moving contact and a dielectric fluid for quenching electric arcs, characterized in that said dielectric fluid comprises a fluoridized dielectric fluid which contains dissolved oxygen and in that it comprises at least one first active filter located in the volume occupied by the fluoridized dielectric fluid, said first active filter being suitable to neutralize the chemically reactive species that originate from the decomposition/recombination of the fluoridized dielectric fluid following an electric arc.

It has in fact been found experimentally that the fluoridized dielectric fluid, following an electric arc, decomposes producing both reactive gaseous substances and, to a larger extent, stable gaseous substances; the latter, being nonreactive, cannot be neutralized chemically. Advantageously, the presence of oxygen dissolved in the fluoridized dielectric liquid allows to alter the recombination reaction of the gases produced by the decomposition of the fluoridized fluid so as to avoid producing the stable compounds and produce only the reactive ones. In this manner one has the avantage of obtaining compounds which can be neutralized chemically by the provided active filter very simply and effectively, in the manner described in greater detail hereinafter.

Further characteristics and avantages of the invention will become apparent from the description of preferred but not exclusive embodiments of the circuit breaker according to the invention, illustrated only by way of nonlimitative example in the accompanying drawing, which is a schematic view of a high- voltage circuit breaker according to the invention.

The circuit breaker according to the invention is described with particular

reference to the use of a perfluoropolyether as fluoridized liquid: as an alternative, and in a fully equivalent manner, it is possible to use a perf ! uorocarbon or a mixture of perfluoropolyether/perfluorocarbon.

Furthermore, reference is made specifically to a high-voltage circuit breaker in the description that follows without thereby limiting the scope of its application in any way.

With reference to the figure, the circuit breaker according to the invention comprises a shed insulating casing 5 inside which there is an interruption chamber)) which contains interruption mechanisms constituted by at least one fixed contact 3 and by a corresponding moving contact 14. In the embodiment shown in the figure, the insulating casing 5 is constituted by an insulator which is formed monolithically : as an alternative, and according to an embodiment which is widely known in the art, the casing 5 can be made of two parts which are mutually connected by a metallic flange : a first base part which acts as a support and a second part which contains the interruption chamber, the fixed contact and the moving contact. Said casing 5 can be constituted, for example, by a shed tubular body made entirely of porcelain, or by a tube made of composite material, for example fiberglass-reinforced plastic, on the outer surface of which there are sheds made of silicone rubber.

The moving contact 14 is operatively connected to an actuation rod 4 which runs. inside the insulating casing 5, from the moving contact 14 to the base of said casing and slides in a guide 6. The opening/closure maneuver of the circuit breaker is performed by appropriately moving the rod 4 and accordingly engaging/disengaging the fixed contact 3 with respect to the moving contact ) 4. In particular, the actuation of the rod 4 occurs by means of kinematic systems 7 located in a housing 8 which is fixed to the base of the insulating casing 5 : said kinematic systems 7 are operatively connected by means of a shaft 9 to an actuation device which is not shown in the figure. The actuation

device that can be used in the circuit breaker according to the invention can be, for example, of the mechanical or hydraulic or electric type. according to solutions which are widely known in the art and accordingly are not described further.

Generally, during the opening of the circuit breaker, the separation between the moving contact 14 and the fixed contact 3 is accompanied by the generation of an electric are which forms between the contacts ; accordingly, a dielectric fluid suitable to quench said electric arcs is provided in the insulating casing 5.

Advantageously, in the embodiment of the circuit breaker according to the invention, the dielectric fluid comprises a fluoridized dielectric fluid, preferably a perfluoropolyether (PFPE) in liquid form of the family having the tollowin c : hemical formula : endcap-O-(C3F6O)n-(CF2O)m-endcap; (a) or endcap-O-(CF4O)n-(CFO)m-endcap. (b) In the figure, the reference numerals 13 and 10 schematically designate the volume in which the dielectric liquid is placed and its free surface, respectively.

The endcaps can be constituted by HCF (one or both) or CF. (preferably no more than one) : in particular, the presence of the HCF, endcap (hydrogen- endcapped perfluoropolyether) is highly important for environmental impact, since it makes the molecule reactive in the upper atmosphere and therefore does not contribute to the greenhouse effect. In general, perfluoropolyethers can be chosen from a wide range of molecular weights; for example. for motecuiar weight 2. 000 it is possible to have m and n equal to approximately 1 t. or m and n can be chosen in a ratio of 1 : 3.

In the presence of an electric arc, the perfluoropolyether (PFPE) decomposes and produces various species of gas which can be classified into two main

types : - part of the generated gases is constituted by reactive gases, mainly carbonyl fluoride (COF,) ; - a predominant part is constituted by gases which are chemically stable and therefore nonreactive, mainly carbon tetrafluoride (CF4) and to a lesser extent C, F (,, C, F-1. etcetera.

Advantageously, the reactive gases can be eliminated chemically, as described in greater detail hereinafter, by using at least one active filter, arrange in the volume 13 occupied by the perfluoropolyether and designated by the reference numeral 12 : said active filter 12 can be fixed to an internal wall of the casing 5 or can be arranged on a supporting element located inside said casing. The stable gases, being chemically nonreactive, could neither be eliminated by the active filter 12 nor be fully dissolved in the liquid : moreover, since they are rreellllouse gases, they cannot be released into the atmosphere.

Advantageously, in the circuit breaker according to the invention the presence of dissolved oxygen in the dielectric liquid allows to alter the recombination reaction of the gases produced by the decomposition of the liquid during the electric arc. It has in fact been found experimentally that the presence of oxygen alters the main reaction from the formation of CF4 to the formation of reactive gases, such for example COR,, as preferential reaction ; in this way only gaseous substances are produced that can be neutralized chemically by the active filter 12.

The oxygen contained in the circuit breaker must be present in an amount which is at least stoichiometrically sufficient to ensure the exclusive formation of reactive gases throughout the life of the circuit breaker. For this purpose, the circuit breaker according to the invention uses a tank, designated by the reference numeral 1 (which contains the oxygen. In the embodiment shown in the figure, the tank 1 is arrange at the top of the insulating casing 5 and is

connected thereto by means of a coupling flange 15.

Advantageously, the oxygen is placed in the tank 1 under pressure, so as to reduce the volume required. For example, a tank with a volume of no more than 30 liters is sufficient to contain 300 liters of oxygen at a pressure of 10 bar. In this manner one has a very compact tank which does not entail excessive constructive complications and allows to have a circuit breaker with an overall volume comparable to that of known kinds of circuit breaker. In order to check the pressure of the oxygen, the tank 1 can be provided with a "and with a tap 16 for optional replenishment of said oxygen.

Furthermore, the casing 5 of the circuit breaker, which contains the interruption chamber, and the tank 1 are sealed hermetically : in this manner, in addition to seating the pressurized oxygen, losses and external leaks of the fluids contained therein are avoided. in a preferred embodiment, the active filter 12 is constituted by granules of soda lime contained in a containment means made of inert and gas-permeable material.

In a second embodiment, the active filter 12 comprises a supporting means and chemically active means for the chemical neutralization of the products generated by the decomposition/recombination of the perfluoropolyether. Said chemically active means comprise a primary or secondary amine, for example a substance of the Jeffamine family adsorbed on the supporting means, or a zeolite resistant to an acid environment associated with the substance of the Jeffamine family : the supporting means can be constituted, for example, by Chromosorb or alumina or a zeolite resistant to an acid environment.

Merely by way of example, the substance of the Jeffamine family can be the one known commercially as T 403, produced by the Texaco Chemical Company.

The substance of the Jeffamine family that is used is in liquid form and once

supported on Chromosorb, alumina or zeolite it assumes the form of granules whose diameter depends on the supporting means chosen and is generally of few millimeters : in this case also, the filter is inserted in a containment means.

By way of example, the containment means, in the case of a filter comprising an amine and in the case of a filter made of soda lime. can be constituted by a bau maze of an ethylene-chlorotrifluoroethylene copolymer (Halar) ; as an ulternative. it is possible to use a box-like container made of thermoplastic material or thermosetting material or sheet metal provided with gas passage openings.

In practice. in the presence of an electric arc the reactive gas species are generated as described above ; the reactive by-products that originate directly from the decomposition of the perfluoropolyether and those produced by recombination by the reaction between the oxygen and the perfluoropolyether decomposition gases react with the active filter, depositing on its surface and producing granules; this produces solid compounds which, as such, do not produce overpressures. These products are fully inert and non-toxic and therefore allow to completely avoid the disposal problems that are typical of known kinds of circuit breaker.

Another advantage is the fact that inside the tank 1 it is possible to use a second active filter 12, not shown in the figure, also suitable to neutralize the reactive species produced by the decomposition of the fluoridized dielectric liquid. In this manner, the efficiency and performance of the circuit breaker are further improved. The reactive species in fact tend to remain dissolved in the perfluoropolyether and slowly reach equilibrium in the gaseous phase passing into the tank 1 ; accordingly, the part of the reactive substances that has not reacted with the first filter 12 located in the volume of liquid is neutralized by the second filter arranged in the tank 1. In order to accelerate the direct passage ot the (lases into the tank 1 which contains the oxygen and accordingly

facilitate their faster neutralization, in the circuit breaker according to the invention it is possible to provide a suitable preferential duct for the passage of the gases from the interruption chamber 11 to the tank 1; for example, said duct can be provided by appropriately perforating the fixed contact 3, obtaining a through channel. If necessary due to particular requirements and/or needs of the application, it is possible to arrange a phase separator, not shown in the figure, at the surface 10 of the fluoridized liquid. The phase separator can be constituted, for example, by a plurality of disks made of metal or plastics which are perforated and arrange mutually adjacent with staggered holes ; this prevents sprays of tluoridized fluid from directly entering, as a consequence of the arc. the tank I where the second active filter is located. tn practice it has been found that the circuit breaker according to the invention allows to achieve the intended aim and objects, since it allows to achieve optimized electric arc quenching with dielectric fluid decomposition products which have an extremely low environmental impact.

The fact is noted that the circuit breaker according to the invention has a compact structure and an overall volume which can be compared to that of known circuit breakers ; furthermore, according to specific requirements and/or various applications the concepts described above can be effectively applied to various kinds of circuit breaker, such as for example circuit breakers with an interruption chamber of the axial- or transverse-blast type or of the mixed transverse-axial blast type, and also to circuit breakers of the type having a large oil volume and to those having a large oil volume with an open interruption chamber.

The circuit breaker thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept ; thus, for example, it is possible to use multiple active filters both inside the volume occupied by the dielectric liquid and in the tank. All the details may furthermore be replaced with other technically equivalent elements.

In practice, the materials used, so long as they are compatible with the specific use. as wel ! as the dimensions, may be any according to the requirements and the state of the art.