EP2223308A1

EP2223308A1 - Weakly conducting nozzle for a gas circuit breaker and ptfe based material therefore

Info

Publication number: EP2223308A1
Application number: EP07866307A
Authority: EP
Inventors: Felix Greuter; Martin Seeger; Lutz Niemeyer; Dieter Stoll; Stéphane Schaal
Original assignee: ABB Research Ltd Switzerland
Current assignee: ABB Research Ltd Switzerland
Priority date: 2007-12-21
Filing date: 2007-12-21
Publication date: 2010-09-01
Also published as: CN101946288B; WO2009080123A1; CN101946288A

Abstract

Provided is a nozzle for a gas circuit breaker and a material or a gas circuit breaker nozzle made of a composition comprising PTFE and at least one additive which leads to a weak dielectric conductivity of the PTFE-based material, wherein the composition comprises PTFE as a main substance, a first pigment-like additive giving the PTFE the necessary optical properties for a circuit breaker nozzle and a second additive giving the PTFE a controlled dielectric conductivity, wherein the amounts of the additives are selected in amounts, so that the material shows a core-shell like structure, wherein the core of the core-shell like structure is mainly formed by the PTFE and/or the PTFE with the first pigment like additive, and wherein the shell of the core-shell like structure is mainly formed by the second additive causing a dielectric conductivity of the sintered product in the range of 1*10 -14 S/m < < 1*10-8 S/m by forming the shell of the core-shell like structure.

Description

Weakly Conducting Nozzle for a Gas Circuit Breaker and PTFE based Material therefore

Description

The invention relates to a nozzle of a gas circuit breaker and a material for a gas circuit breaker nozzle made of a composition comprising polytetrafluoroethylene (PTFE) and at least an additive which leads to a weak dielectric conductivity of the nozzle.

The gas for the insulation and interruption in the gas circuit breaker can be for example air, SF6, CO2, N2 or mixtures thereof.

State of the art

Nozzles in gas circuit breakers used in medium voltage systems and high voltage systems have to meet a lot of different requirements. A material suitable for those nozzles therefore has to provide a lot of different material properties which are at least partially seem to be contradictory to each other. For example a nozzle material has to have a high dielectric withstand, a low dielectric permittivity and low dielectric losses, excellent ablation properties when exposed to an arc during switching operation, no soot production, uncritical toxically and chemically decomposition products, good mechanical, optical and thermal properties etc.. It has been shown that polytetrafluoroethylene (PTFE) or PTFE with a small amount of pigment is a very suitable material for nozzles in gas circuit breakers, because it has a unique combination of material properties meeting the requirements of this application. However, due to the insulating nature of PTFE, nozzles in circuit breakers made of PTFE can charge up electrically, which can be a serious limitation in the dielectric field design and can lead to unexpected breakdowns if not taken properly care of. Flashover can be triggered if the charges deposited on the insulating nozzle surface significantly distort the electrical field distribution. This imposes additional limitations in the design of circuit breakers.

In the past one tried to avoid nozzle charging by using various conducting / semiconducting materials for the nozzles of gas circuit breakers. Thereby it has been figured out by the inventors that the required conductivity of the material has to be in the range of the borderline of insulating and antistatic properties, which to obtain is technically very difficult, especially if the needed mechanical, thermal and optical properties, which are met by PTFE, have to remain.

In DE 3025042 for example, a sintered PTFE with metal filler is given as material for a circuit breaker, wherein the metal filler is formed preferably by one or more of the following metals: wolfram, aluminium, copper, iron. The amount of the conductive filler is in the range of 5w.-% to 30w.-% and is mixed with the PTFE before the sintering process. The high content of filler was necessary to reach the percolation threshold. However, it has been shown that the high content of filler leads to difficulties in controlling the conductivity in the required range right at the onset of percolation. It reduces the quality of the mechanical properties of the PTFE, changes the optical properties of the material completely and decreases the interruption performance.

In WO2005015574 problems regarding electromagnetic shielding and electrostatic dissipation are considered in connection with chip carriers, photocopier components, computers, printers and so on. Besides al lot of other polymers PTFE has been proposed to be blended with carbon nano-tubes, in order to solve the problem. Thereby, the carbon nano-tubes should be present in the composition of the organic polymer in form of a network and the electrical conductive composition is described with a bulk volume resistivity less or equal to about 1*10² to 1*10⁸ Ohm cm. As manufacturing method blending has been supposed. The blending comprises melt blending and/or solution blending.

Various other experiments with PTFE and conductive or semi-conductive fillers have been carried out. US 2006186567 for example discloses a tape or rod, preferably with a single layer structure with a thickness of 30 μm to 500 μm, formed by lubricated extrusion of a mixture of PTFE powder and a filler selected from carbon black, carbon nano-tubes or carbon nano-fibres, whereby the filler-content lies at about 3w.-% to 6w.-% and the obtained material shows a surface resistivity of less than 1 * 10⁸ Ohms per square.

In another example HDPE has been sintered with a small amount of carbon black, forming a conductive network with amounts of filler < lw.-%. During the sintering process a kind of core-shell structure was formed. The core was mainly formed by the HDPE, the shell- network by the filler. (K. -H. Mόbius: Fϋllstoffhaltige elektrisch leitfahige Kunststoffe 78 (1), 1988, page 53-57, Carl Hanser Verlag, Mϋnchen 1988) .

EP 1655739 discloses a composition with quite good chemical and mechanical properties and a dielectric resistivity of about 1*10 ³ Ohm m at 20 ⁰C, having a continuous polymeric phase of fluoropolymer and a dispersed phase of conductive particles. Said dispersed phase comprising a plurality of conductive particles dispersed in the continuous polymeric phase. The conductive particles are selected from the group consisting of: graphite, steel, iron, copper, silver, aluminium, nickel, wolfram, gold, copper-manganese, each of the selected as fibre or powder. Or the particles are selected from the group consisting of: carbon black, carbon-nano-tubes or carbon-fibre, bronze fibre, and combinations thereof. The composition contains 20w.-% to 90w.-% of the fluoropolymers. A main aspect in the method of manufacturing the composition is vulcanization and a combination of vulcanization and copolymerisation.

In US2004262581 electrical conductive articles with a minimized inhomogeneity of mechanical and electric properties should be achieved. This goal should be obtained using a composition out of a polymeric resin, carbon nano-tubes and possible other conductive fillers together with a plasticizer creating the desired articles out of this composition by using the method of injection moulding. Besides a lot of other polymeric resins a PTFE resin has been proposed as base material of the composition.

Description of the invention

However, none of the materials given above show the material properties needed for a gas circuit breaker, either due to the high amount of fillers, which reduces the mechanical, optical and thermal quality of the composition, or due to an uncontrollable conductivity, which can not be adjusted to the necessities of the gas circuit breaker. Thus, the research and development departments around the world are still searching for a suitable composition combining all the different properties necessary for the nozzle of a gas circuit breaker, which can be produced for a reasonable price and which is durable and easy to maintain. Thus, object of the current invention is to provide a nozzle for a circuit breaker and a material for a circuit breaker nozzle fulfilling the abovementioned attributes and particularly having a well controlled conductivity, while keeping all other essential mechanical, thermal, optical and other necessary properties of the circuit breaker nozzle and the material of the circuit breaker nozzle largely unchanged.

This is achieved by a nozzle for a circuit breaker according to claim 1 and a material for a circuit breaker according to claim 16.

The requirements of a circuit breaker nozzle are met by PTFE in such a broad range as by no other material known by now. Therefore, PTFE has been the basis of the current invention regarding a nozzle for a circuit breaker and particularly a material for a circuit breaker nozzle.

The inventive nozzle for a circuit breaker and the material for a circuit breaker nozzle are made of PTFE with small amounts of a first additive giving the PTFE its necessary optical properties and with small amounts of a second additive, a so called filler. The first additive is a pigment or pigment-like substance. The second additive is a substance or composition with dielectric conductive properties or a substance or composition that at least leads to a determined dielectric conductivity of the resulting material during operation of a circuit breaker nozzle. Due to the high ionisation potential of its elements, which are selected particularly higher or equal to e.g. 6 eV, the second additive does not detonate the thermal and dielectric interruption capability of the circuit breaker respectively.

The very small amounts of the additives are selected in a range that the nozzle-material shows a core-shell like structure. The shell of the core-shell like structure is mainly formed by the first and the second additive or more or less solely by the second additive. The core of the core-shell like structure is mainly formed by PTFE or PTFE and the first additive respectively. The resulting nozzle of a circuit breaker and the resulting material for a circuit breaker have a dielectric conductivity in the range of 1*10 ¹⁴ S/m < σ < 1*10 ⁸ S/m, which is caused by the second additive forming essentially the shell of the core-shell structure.

PTFE and the circuit breaker nozzle made of PTFE have exceptional optical properties, which moreover can be adjusted to the foreseen ablation behaviour during switching operation in the circuit breaker by adopting the suitable amount of the first additive or all additives, respectively. Due to the small amount of the second additive the behaviour of ablation and radiation withstand is very similar to the known PTFE based materials of circuit breakers. No critical soot is formed and decomposition products are uncritical. In addition the mechanical and dielectric strength are sufficient.

The first additive is preferably selected in a range of 0.005v.-% to 0.5v.-%, preferably 0.01v-% to 0.2v.-% ("v.-%" is used as abbreviation for "% by volume"). However, the actually used amount of the first additive depends on the chemical characteristics of the first additive and its particle size. The range of the particle size lies at the scale of nm to μm. The smaller the particle size the smaller is the amount of the first additive which has to be added. Based on its chemical characteristics and the particle size the first additive disperses more or less easily. The more easily the particle is dispersed the higher the homogeneity and the smaller the amount of the first additive to be added to the composition. A high homogeneity further improves the ablation properties and hence increases the lifetime of the inventive circuit breaker nozzle and the inventive material for a circuit breaker nozzle. The first pigment-like additive is selected from the group of MoS₂ and/or doped or undoped fluoride, e.g. CaF₂, SnF₂, etc., and/or doped or undoped oxides of aluminium (e.g. Al₂CoO₄) and/or of zinc and/or of copper and/or titanium and/or magnesium. The first additive often gives the PTFE a grey colour. Therefore, it is often called "grey-PTFE".

The amount of the second additive, the filler, is selected smaller than 2v.-%, preferably smaller than lv.-%, with respect to the sintered composition. The amount depends on the particle size, the shape of the particles and their chemical and physical characteristics, particularly on the conductivity and the capability of the second additive to build up a network. The lower limit of the amount of the second additive lies at about 0.001v.-%.

Selecting the amounts of the additives in the above-mentioned ranges, causes a controllable dielectric conductivity σ of the circuit breaker nozzle and the material of a circuit breaker nozzle in a range of 1*10 ¹⁴ S/m < σ < 1*10 ⁸ S/m , particularly in the range of l*10^~13 S/m < σ < l*10^~9 S/m. The second additive belongs to the group of conducting and/or semi-conducting fillers or substances developing conductive properties under the conditions in a gas circuit breaker under operation and particularly during and/or immediately after exposition to an arc during switching operation. In a first embodiment the second additive is selected from a group of nano and/or micro sized semi-conductive fillers with a low conductivity in the range of l*10^~9 S/m to l*10^~2 S/m, preferably in the range of l*10^~8 S/m to l*10^~4 S/m. This has the advantage of an easy reproducibility in the electrical conductivity. The nano and/or micro sized semi-conductive filler, or combination of fillers, can be selected from doped and/or undoped oxides like ZnO, SnO₂, TiO₂, NiO, Fe-oxides, e.g. Fe₃O₄, and/or sulfides like CuS, FeS₂, NiS and so on, and/or sulphates/sulphids, e.g. BaSO₄, MoS₂, and/or antimonides, e.g. Ag₃Sb, and/or tellurides and/or selenides and/or semi-conductive coated particles like mica (e.g. Minatec® micro mica from Merck®) and/or coated nano-silicates and/or electro-conductive powders like Zelec® ECP from Zelec®. Further, doped or intercalated carbon nano particles and/or micro or nano sized silicates can be a good selection to be used as a second additive, depending on their specific chemical and electrical properties. These fillers with reduced conductivity can be added at filler levels well above the percolation limit of the core-shell-material. The percolation threshold depends among others on the particle size of the PTFE, the aspect ratio of the filler and the ability of the filler of building agglomerations and/or a network. High aspect ratio means a high ratio of length to diameter or length to thickness of a particle. Particles with a high aspect ration are, e.g. nano-tubes, carbon black and other additives with a two dimensional structure like nano-sheets, e.g. graphene and carbon nano-cones.

In order to realize a core-shell microstructure, the particle size of the filler is selected smaller than the particle size of PTFE. In an advantageous embodiment the particle size of PTFE is e.g. 20μm to 40μm and particle size of the semi-conductive filler is less than 4μm. A further advantage is realized adding a filler with a high aspect ratio, e.g. with an aspect ratio higher than 3, and/or a nano sized filler forming a network.

In a further embodiment the second additive is selected from the group of carbon nano particles, wherein the nano particles can be added per se or in form of a premixed compound. The group of carbon nano particles comprises: nano-sized carbon black and/or single wall nano-tubes and /or multiwall nano-tubes and/or carbon nano-sheets e.g. graphene and/or carbon nano-cones. In order to impede a high impact on the mechanical, optical and thermal properties and so on, the selection of the second additive is selected so, that a net like structure in the nozzle and the material respectively results comprising a very small number of particles and having a sufficient electric conductivity for a circuit breaker nozzle.

Single wall nano-tubes and /or multiwall nano-tubes have a diameter of about 5nm to lOOnm and a length in the range of some μm up to about lcm. That means the aspect ratio can be up to a range of 1*10⁹. But, typical values are diameters about IOnm with a length of 20μm, which results in an aspect ratio of 2000. These high aspect ratios are very advantageous, because a high aspect ratio of the filler leads to a low percolation threshold for the conductivity down to well below Iv. -% of filler in the nozzle and the material respectively, making use of the combined effects of a high aspect ratio of the filler and the core-shell structure of the nozzle and the material respectively. Carbon black is the name for clusters of primary carbon particles often in a prolonged or spherical form with typical diameters of IOnm up to some lOOnm. Graphene are sheets of carbon with a lateral dimension of lOOnm up to some lOμm and a thickness down to less than lnm-2nm. Carbon-cones or -discs are available with diameters of about 3μm and a layer thickness of about 20nm to 50nm and a resulting aspect ratio of about 10 to 200.

Generally it can be stated, that due to the core-shell structure of the nozzle or the material according to the invention, the percolation threshold of the obtained inventive nozzle or the inventive material is reduced from a typical bulk volume of 10v.-% to 20v.-%, to a volume typically less than lv.-%. If in addition the second filler has a high aspect ratio (e.g. fϊbre- or platelet-shaped fillers) and/or has a tendency to form networks (as often observed for nano sized powders like carbon black etc. ), then it is possible to further reduce the percolation threshold to values much below lv.-%, e.g. to values as low as 0.001v.-%.

In a further embodiment the carbon nano particles are added in form of a compound having an amount of carbon nano particles typically in the range of 0.5v.-% up to 5v.-% of the compound, rest polymer. In dependence on the aspect ratio of the carbon nano particle the percolation limit is in the range of 0.005v.-% up to 0.05v.-%. That means, the nozzle of the gas circuit breaker and the material for a gas circuit breaker nozzle made of PTFE according to the invention with a carbon nano sized compound as a second additive, the percolation threshold of the core-shell like structure lies at about 0.05v.-% with higher or lower values depending on the aspect ration of the filler. In contrary to this, known three dimensional structures with soot or soot agglomerations show a percolation threshold in a range of lv.-% to 5v.-% and in a range of 20v.-% to 50v.-% for spherical micro-sized fillers like Fe₃O₄.

In a further modified embodiment the second additive can also comprise metallic nano particles in very low concentrations. The metallic particles are e.g. selected from Ag and/or Au and/or Sn and/or Pd and/or In and/or Ti and/or TiB2 and/or TiC and/or TiOx (with x<2) and/or RuO₂ and/or Ag-Cu and/or Ag-Pd. The size of the metallic particles is about 5nm up to 500nm. Their aspect ratio is in the range of 1 to higher than 100. The amount of metallic particles added as second additive depends mainly on the aspect ratio of the selected metallic particles and is the less the higher the aspect ratio is. The added amount of metallic nano particles typically lies in a range of 0.001 v.-% up to lv.-%. The amount of metallic particles can even be less than 0.001v.-%, in case the aspect ratio of the particles is higher than 100.

In a further embodiment the second additive comprises additives for static dissipative compounds, such as the commercial products Eonomer 700 ® and Pelestat ®, which are polymerised and deposited intrinsically conductive polymers (ICP) with carbon black or other particles, particularly semi-conducting or metallic nano particles, with intermediate resistivities and a processability up to 360⁰C or higher for these dissipative compounds.

Another embodiment comprises one or several fine powders of a melt processable, conducting fluoropolymer, which melt during the production process , e.g. sintering, of the nozzle or nozzle-material respectively and thereby form the thin conducting shell-structure of the formed core-shell structure. The particle size of the powder thereby is preferably much smaller than the particle size of the used PTFE, e.g. particle size of the powder is about lμm to lOμm and the particle size of the PTFE is about 20μm to 40μm. The conducting fluoropolymer is preferably selected from polyvinylidene difluoride (PVDF)/carbon nano-tube composites, e.g. RTP 3300 from RTP-Company and/or FIBRIL masterbatches from Hyperion Catalysis International, which are compositions with a high amount of fillers, provided to be mixed by the end-user with his/her unfilled composition in order to create a composition of a finite amount of filler. Those masterbatches are e.g. compositions comprising semi-conductive or conducting nano-tubes and PVDF or ethylene tetrafluoroethylene (ETFE) or perfluoroalkoxy (PFA) as a matrix where the content of nanoparticles in the masterbatch is in the range of 5v.-% to 25v.-%.

A special effect can be obtained using insulating fillers, like nano sized and/or micro sized silicate or SiO₂ as the second additive. Said second additive forms an insulating nozzle, but during the application in a circuit breaker, the formerly insulating filler interacts at the surface region with the chemical decomposition products of the arc and thereby forming a surface region with conductivity high enough to prevent electrostatic charging.

As PTFE, in particular sintered PTFE has small pores, very good results can be obtained by filling the small pores with a dielectric liquid of a finite conductivity. In order to fill the pores, high pressure infiltration can be used. The conductive liquid can be selected for example from aromatics and/or alcohols and/or castor oil or combinations thereof having a relative permittivity ε of preferably at least 5. These liquids form an internal conductive network and/or diffuse within a period of time and/or diffuse during/after an arcing event from the pores to the surface, which results in a reduction of the surface charge. Examples for those dielectric liquids are: Cumylalcohol (relative permittivity ε ~ 8, conductivity σ ~ l*10^~10 Ω^'W¹); Acetophenone (ε = 17, σ ~ 5*10^~9 Ω^"1 cm^"1) ; Amide (e.g. Propanamide C₇Hi₅NO or Butanamide C₆Hi₃NO); Nitroaniline C₆H₆N₂O₂; Maleicanhydride C₄H₂O₃; Glycerol C₃H₈O₃; Dimethylsulfone C₂H₆O₂S; wherein usually it has to be considered that the higher ε of the organic material the higher the conductivity. Another option is to use a material for infiltration, which is solid at room temperature, but having a melting point lower than 360⁰C, and is a metal or semimetal, e.g. In, Se, Sn, or a hot wax, e.g. wax with conductive particles and/or organic wax and/or carbowax containing up to 60v.-% linitrate.

The preferred method of manufacturing the inventive material for a gas circuit breaker nozzle and an inventive circuit breaker nozzle is powder processing. The powder processing routes have to be adjusted to the type of additives and particularly to the type of added fϊller(s). Possible methods are: dry mixing; hot mixing with masterbatch; predispersing the filler e.g. in a lubricant, which can be evaporated, or in an organic solvent etc.. The nanofillers can be provided with a surface compatibilizer, which reduces agglomeration and simplifies the mixing process. The mixed powders are then processed following standard techniques of pressing and sintering or hot-pressing. Basically, powder injection moulding followed by sintering is also feasible, analogous to what is being used in powder metallurgy or injection moulding of ceramics. This opens up the possibility of (near) netshaping the nozzles, which is very attractive compared to today's machining process.

Examples

In the following a few examples for the inventive material for a gas circuit breaker nozzle and an inventive circuit breaker nozzle as well as the process of their manufacturing are given:

Example 1

A homogeneous mixture of PTFE with particle size of lOμm to 40μm, a first additive of MoS₂ with a particle size of lμm to 5μm, and a second additive in the form of multiwall carbon nano-tubes is achieved via dispersion in alcohol and subsequent evaporation of the solvent under agitation. The dried powder is isostatically pressed to a cylindrical shape and sintered at 375°C for 4 hours. The resulting inventive PTFE nozzle material has a core- shell structure according to the invention and comprises a first additive of MoS₂, with a concentration of 0.15v.-%, and a second additive of multiwall carbon nanotubes with a concentration of 0.1 v.-%.

Example 2

To a PTFE powder with particle size of 10μm-40μm the pigment ZnO, doped with 1 mol-% MnO and 0.5 mol-% MgO, is added as a first additive in an amount of about 0.1 v-% and with a particle size in the range of O.lμm to lμm. As a second additive nanosized indium doped with SnO₂ (nano-ITO) of 30nm average particle size, concentration 0.25v.-%, is added. The mixture is realized as a homogeneous ethanol-based dispersion. The further process is carried out like in example 1.

Example 3

As a first additive 0.05v.-% Of MoS₂ with an average particle size of 150nm is added. As a 2^nd additive 2v.-% of a masterbatch is added, which consists of 5v.-% of carbon nano-tubes mixed in an ETFE-matrix. The masterbatch is granulated to a particle size average of less then lOμm and then dry-mixed with PTFE of a particle size of lOμm to 40μm and MoS₂- pigment. The mixture is isostatically pressed in cylindrical form and sintered at 360⁰C for 2 hours.

Example 4

PTFE powder is mixed with 0.15v.-% of MoS₂ of a particle size in the range of lμm to 5μm and then isostatically dry-pressed to a cylindrical preform. In a first step the preform is sintered to 96% of theoretical density. In a second step the pores of the semimanufactured product are filled up with castor oil via vacuum pressure infiltration.

Generally speaking the nozzle for a gas circuit breaker and the material for a gas circuit breaker nozzle made of a PTFE, in particular made of sintered PTFE, provided by the current invention shows a very low percolation threshold and a controllable conductivity as well as the optical and mechanical properties necessary for the use in a gas circuit breaker. Thereby the optical properties are obtained by a small amount of a first additive in form of a pigment or pigment-like substance and the controllable conductivity is achieved by a small addition of a second additive. The second additive is selected form a dielectric liquid pressed into the pores of a semi-manufactured product according to the invention or from a substance or component added to the first component PTFE and the first additive before starting pressing and or sintering. The last mentioned second additive causes a core-shell like structure and leading to a continuous percolation network. Due to the special selection of the first and second additive it becomes possible to build up this percolation network in the sintered PTFE with a very low number of filler particles, thus a low and controllable conductivity can be obtained for the material for a gas circuit breaker and the nozzle for a gas circuit breaker. In case of using fillers with a high aspect ratio the amount of the needed material decreases, which decrease results in an increase of quality of the sintered product.

Instead of a sintering process to produce the nozzle and the material for a gas circuit breaker respectively, also a different process could be used known to a person skilled in the art. Such a process is for example an injection molding process.

Claims

1. Nozzle for a gas circuit breaker made of a composition comprising PTFE and at least one additive which leads to a weak dielectric conductivity of the nozzle, wherein the composition comprises PTFE as a main substance, a first pigment- like additive giving the PTFE the necessary optical properties for a circuit breaker nozzle and a second additive giving the PTFE a controlled dielectric conductivity, wherein the additives are selected in amounts, so that the nozzle- material shows a core-shell like structure, wherein the core of the core-shell like structure is mainly formed by the PTFE and/or the PTFE with the first pigment- like additive, and wherein the shell of the core-shell like structure comprises the second additive causing a dielectric conductivity σ of the nozzle in the range of 1*10 ¹⁴ S/m < σ < 1*10 ⁸ S/m by forming the shell of the core-shell like structure.

2. Nozzle according to claim 1, wherein the first pigment like additive is selected from the group of MoS₂ and/or doped or undoped fluoride, particularly CaF₂, SnF₂, and/or doped or undoped oxides of aluminium, particularly Al₂CoO₄, and/or zinc and/or copper and/or titanium and/or magnesium and, in particular, wherein the particle size is in the range of nm to μm.

3. Nozzle according to claim 1 or 2, wherein the first pigment- like additive is added in the amount of 0.005v.-% to 0.5v.-%, preferably 0.01v-% to 0.2v.-%.

4. Nozzle according to one of the previous claims, wherein the second additive is added in an amount of less or equal to 2v.-%, particularly less than lv.-%.

5. Nozzle according to one of the previous claims, wherein the conductivity σ of the nozzle is in the range of 1 * 10 ¹³ S/m < σ < 1 * 10 ⁹ S/m.

6. Nozzle according to one of the previous claims, wherein the second additive is a nano or micro sized semi-conductive filler with a low conductivity in the range of 1*10 ⁹ S/m to 1*10 ² S/m, particularly selected from doped and/or undoped SnO₂, and/or doped and/or undoped ZnO, and/or doped and/or undoped TiO₂, and/or various oxides and/or sulfides and/or sulfates and/or antimonides and/or tellurides and/or selenides and/or semi-conductive coated particles like mica and/or coated nano-silicates and/or electro-conductive powders.

7. Nozzle according to one of the claims 1 to 5, wherein the second additive is selected form carbon nano particles or a compound comprising carbon nano particles, and wherein the carbon nano particles are carbon black particles and/or single wall nano-tubes and /or multi-wall nano-tubes and/or carbon nano- sheets and/or carbon nano-cones and/or graphene.

8. Nozzle according to one of the claims 1 to 5, wherein the second additive comprises metallic nano particles, wherein the metallic particles are selected from Ag and/or Au and/or Sn and/or Pd and/or In and/or Ti and/or TiB₂ and/or TiC and/or TiO_x and/or RuO₂ and/or Ag-Cu and/or Ag-Pd.

9. Nozzle according to one of the claims 1 to 5, wherein the second additive comprises additives for static dissipative compounds, particularly deposited ICP on carbon black or other particles.

10. Nozzle according to one of the claims 1 to 5, wherein the second additive comprises fine powder of a melt processable, conducting fluoropolymer, which melts during the production process, in particular during a sintering process and thereby forms the thin conducting shell-structure of the core-shell structure.

11. Nozzle according to one of the claims 1 to 5, wherein the second additive comprises an insulating filler, which interacts at the surface region with the decomposition products of the arc and thereby forms a surface region with a conductivity high enough to prevent electrostatic charging, selecting the second additive preferably from nano sized or micro sized SiO₂ and/or a silicate.

12. Nozzle according to one of the claims 1 to 5, wherein the PTFE, particularly sintered PTFE, having small pores, and the second additive is a dielectric liquid of a finite conductivity which is filled in the small pores, whereby the liquid is selected preferably from aromatics and/or alcohols and/or castor oil and/or an organic wax and/or a metal or semimetal having a melting point lower than 360⁰C.

13. Nozzle according to one of the previous claims, wherein the elements of the second additive have a high ionisation potential, which is selected particularly higher or equal to 6eV.

14. Nozzle according to one of the claims 1 to 5, wherein the second additive is selected as a combination of two or more of the second additives given in claims 6 to 13.

15. Nozzle according to one of the previous claims, wherein the composition is sintered to produce the nozzle or the nozzle-material respectively.

16. Material for a gas circuit breaker made of a composition comprising PTFE and a at least one additive which leads to a weak dielectric conductivity of the PTFE material, wherein the composition comprises a first pigment-like additive in the range of 0.005v.-% to 0.5v.-% and a second additive in the range less or equal to 2v.-% of the composition, wherein the material shows a core-shell like structure, and wherein the core of the core-shell like structure is mainly formed by the PTFE and or the PTFE and the first additive and the shell of the core- shell like structure is mainly formed by the second additive, and wherein the dielectric conductivity of the material is in the range of 1*10 ¹⁴ S/m < σ < 1*10 ⁸ S/m and is caused by the additive forming the shell of the core-shell like structure.

17. Material for a gas circuit breaker according to claim 16, wherein the second additive of the composition is selected from one of the second additives given in claims 6 to 13 or a combination of two or more of the second additives given in claims 6 to 13.

18. Material for a gas circuit breaker according to claim 16, wherein the first pigment like additive of the composition is selected from one of the first additives given in claims 2 and/or 3.

9. Material for a gas circuit breaker according to one of the claims 16 to 18, wherein the composition is sintered to produce the material.