Patent Publication Number: US-9412541-B2

Title: Circuit breaker with fluid injection

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of high-voltage technology, and more specifically to a circuit breaker, to a switchgear, and to a method for improved circuit breaker operation. 
     BACKGROUND OF THE INVENTION 
     In conventional circuit breakers, the arc formed during a breaking operation is normally extinguished using compressed gas. The arc extinction or interruption performance is thereby mostly defined by the blow pressure and the physical properties of the medium, e.g. the dielectric strength, the heat capacity as a function of temperature, the electronegativity and the thermal conductivity. For large ratings, compressed sulphur hexafluoride (SF 6 ) is generally used. 
     Typically, the arc interruption performance is improved by increasing the blow pressure of the gas using the self-blast or puffer principle. Although up to a certain rating the required interruption performance can be achieved, compressed-gas circuit breakers have intrinsic limitations that make it impossible to increase the performance without affecting product cost constraints. 
     Aiming at a reduction in the size, circuit breakers employing a liquefied gas, in particular SF 6 , as the interruption medium have been proposed, e.g. in U.S. Pat. No. 3,150,245. However, the design according to U.S. Pat. No. 3,150,245 has inter alia the drawback that given the low critical temperature of SF 6  the respective storage vessel has to be designed for extremely high pressures. 
     In consideration of the drawbacks of this design, further circuit breaker using SF 6  have been proposed in U.S. Pat. No. 4,288,668, U.S. Pat. No. 4,307,274 and U.S. Pat. No. 4,736,080. 
     All these circuit breakers have in common that a relatively sophisticated ejection device is required for building up a pressure that is high enough for the insulation liquid to be ejected with the required blow pressure. For example, U.S. Pat. No. 4,307,274 discloses an operator for pumping liquid SF 6  and in this context mentions a typical pressure of 2′500 psi (about 170 bar). 
     It is clear that for these circuit breakers not only a complex pressure build-up mechanism is required, but that also the walls of the pre-injection chamber have to be designed in a manner to withstand such high pressures. Ultimately, this leads to a relatively large size and high cost of the circuit breakers. 
     SUMMARY OF THE INVENTION 
     In consideration of the above drawbacks, the objective of the present invention is to provide a circuit breaker which has improved interruption capability and which at the same time allows for a simple and economic construction and operation. This objective is achieved by the subject matter of the independent claims. More specific embodiments of the invention are given in the dependent claims. 
     The present invention relates to a circuit breaker comprising an ejection device, i.e. at least one ejection device, said ejection device comprising a compartment in which an arc-extinction medium and/or exhaust-cooling medium for improving circuit breaker operation, and in particular an arc-extinction medium for improving extinction of an arc formed during a breaker operation, is contained and which has an ejection orifice, i.e. at least one ejection orifice, through which the arc-extinction medium and/or exhaust-cooling medium is to be ejected. According to the invention, the ejection orifice opens out into an injection zone of the circuit breaker, in which injection zone the pressure is lower than in an arcing zone when an arc is present and the arc-extinction medium and/or exhaust-cooling medium is at least partially present in liquid form, when it is contained in the ejection device. 
     This allows for a very straightforward and economic design of the ejection device, since the counter-pressure against which the arc-extinction medium is to be ejected is relatively low. In particular, neither electrical means, such as an electrical power supply, nor external mechanical components are needed to pressurize and eject the arc-extinction medium. 
     Preferably, the ejection orifice opens out into a heating volume and/or a compression chamber of the circuit breaker for improving extinction of an arc formed during a breaker operation. Alternatively or in addition, the ejection orifice opens out into an exhaust volume of the circuit breaker for improving exhaust cooling during a breaker operation. 
     According to a further preferred embodiment, the arc-extinction medium is present in fully liquid form, when it is contained in the ejection device. 
     For clarity, the arc-extinction medium and/or exhaust-cooling medium is present in the ejection device at least partially or fully in liquid form under operating conditions of the circuit breaker, in particular under operating temperatures and/or operating pressures of the circuit breaker. Such operating conditions may depend, inter alia, on the type of circuit breaker and the currents and/or voltages to be interrupted. Such operating conditions shall encompass at least intermediate times between circuit breaker operations and/or time intervals of active circuit breaker operations, such as contact-opening and/or contact-closing, for example as occurring in a typical O—C—O sequence according to the IEC or ANSI international standard. In this context, operating temperatures shall be within a rated operating temperature range and operating pressures shall be within a rated operating pressure range of the circuit breaker. 
     Due to the fact that according to the present invention a liquid arc-extinction medium is ejected which instantly evaporates in the injection zone, the blow pressure present in the injection zone readily increases, which ultimately contributes to a high arc-extinction performance. 
     A further reason for the high arc-extinction performance lies in the fact that part of the arc energy is absorbed for vaporisation of the extinction liquid leading to improved cooling of the arc. As well, when the liquid is used for exhaust gas cooling, it readily evaporates after ejection and thus very efficiently cools the exhaust gases. 
     In order to safeguard that the required blow pressure can be built up, the ejection orifice is preferably a valve which only opens when a predetermined threshold pressure is reached in the compartment. 
     According to a particularly preferred embodiment, the circuit breaker comprises a floating piston which is designed to transmit a compressing force onto the interior of the compartment during a breaker operation. In particular, the floating piston is useful for smoothing out pressure peaks in the compression force. 
     As will be shown in detail below, pressure increase forcing the floating piston to move relatively to the compartment and thus transmitting the compressing force onto the compartment, can be obtained by mechanical means and/or by a pressure rise in the heating volume or compression chamber or exhaust volume due to the heating by the arc. Such compressing force can also be obtained by pressure present in a compression chamber or puffer volume, or in an exhaust volume of the circuit breaker. 
     According to a preferred embodiment, the ejection device is connected to a moving part of the circuit breaker such that a movement of the moving part during a breaker operation is translated into a movement of the floating piston relative to the compartment for compressing the compartment. 
     It is thereby particularly preferred that the ejection device further comprises an auxiliary compartment which contains a compressible medium, in particular gas, the compartment and the auxiliary compartment being separated from each other by the floating piston. In particular, the floating piston is freely floating between the compartment and the auxiliary compartment such that it is only driven by a differential pressure between the compartment and the auxiliary compartment. 
     In further embodiments, the circuit breaker comprises a piston for compressing the interior of the auxiliary compartment, wherein a moving part of the circuit breaker causes a relative movement between the piston and the auxiliary compartment. In particular, the auxiliary compartment can be connected to the moving part. Then the piston increases the pressure in the auxiliary compartment which in turn drives the floating piston and causes ejection of arc-extinction liquid and/or exhaust-cooling liquid from the compartment containing the arc-extinction and/or exhaust-cooling medium into the injection zone of the circuit breaker. 
     When the piston is moved relatively to the auxiliary compartment, the auxiliary compartment thus functions as a compressible force transmitter or gas cushion that allows smoothing out pressure peaks in the compression force to be transmitted to the floating piston, and consequently to the compartment containing the arc-extinction medium and/or exhaust-cooling. Ultimately, this allows controlling the dosing of the arc-extinction medium and/or exhaust-cooling as well as of the timeliness, duration and rate of its ejection in a very accurate manner. 
     The compartment containing the arc-extinction medium and/or exhaust-cooling and the auxiliary compartment functioning as a gas cushion can be arranged axially displaced from each other and/or can be arranged coaxially. Coaxial arrangement, also in combination with some axial displacement, is preferred as it allows a very simple and straightforward design of the ejection device. Thus, the circuit breaker can comprise a housing comprising the compartment and the auxiliary compartment, said housing having a cylindrical shape. 
     The effect of smoothing out pressure peaks is particularly pronounced when the area of the piston for compressing the interior of the auxiliary compartment is smaller than an area of the floating piston, as it is the case in a further preferred embodiment. 
     Additionally or alternatively to the above mechanism using a moving part of the circuit breaker, increase of the pressure acting on the floating piston can also be achieved by the heating of the gas, and thus by the pressure increase, e.g. in the heating volume or compression chamber or exhaust volume, caused by the arcing heat. 
     In a preferred embodiment, the floating piston is therefore designed such that its compressing force is increased when an arc is present, in particular wherein the increase is at least partially caused by an increase of the pressure in the heating volume due to the heating by the arc. 
     In this embodiment, the floating piston preferably comprises a primary floating piston facing the heating volume and a secondary floating piston facing the compartment, which contains the arc-extinction and/or exhaust-cooling medium, said primary floating piston and said secondary floating piston being rigidly connected to each other. 
     In order to avoid the building up of a counterproductive pressure between the primary floating piston and the secondary floating piston, appropriate means such as an outflow valve can be provided. Additionally or alternatively, the volume between the primary floating piston and secondary floating piston can be connected to a low pressure volume. 
     According to a particularly preferred embodiment, both concepts for increasing the compressing force of the floating piston, i.e. the concept of using a moving part of the circuit breaker as well as the concept of using the pressure increase in e.g. the heating volume caused by the arcing heat, can be combined with each other. 
     A same or similar construction as described above with a floating piston, and in particular with an auxiliary compartment as compressible force transmitter, may be present to transmit an additional compressing force onto an additional compartment, which may be present for storing and ejecting an auxiliary compound (as disclosed hereinafter). 
     According to a particularly preferred embodiment, the arc-extinction liquid comprises an organofluorine compound having a boiling point T b  at 1 bar higher than −60° C. 
     According to recent findings, organofluorine compounds, and in particular fluoroketones, are able to provide arc-extinguishing performance and/or high exhaust-gas-cooling performance required for a circuit breaker. 
     By employing an organofluorine compound having a boiling point T b  at 1 bar higher than −60° C. and thus higher than the one of SF 6 , the arc-extinction and/or exhaust-cooling medium can be stored and ultimately ejected in liquid form without requiring sophisticated cooling and pressurizing means. This not only allows for a reduction in size of the whole design, but also leads to an increase in the interruption performance, since part of the arc energy is absorbed for vaporisation of the extinction medium which leads to improved circuit breaker operation, and in particular to improved cooling of the arc. As well, when the liquid is used for exhaust cooling, it readily evaporates after ejection and thus very efficiently cools the exhaust gases. 
     A further reason for improved interruption performance lies in the increased blow pressure which is generated due to the vaporisation and potentially the further decomposition of the arc extinction liquid, in particular the organofluorine compound, using the arc energy. Since several of the by-products generated by the decomposition of the organofluorine compound, and in particular the fluoroketone, are electronegative, they have good arc quenching capabilities, which further contribute to the excellent interruption performance achieved according to the present invention. 
     It is understood that the expression “that the arc-extinction medium comprises an organofluorine compound” is to be interpreted such that it encompasses embodiments in which a single organofluorine compound is comprised as well as embodiments in which a mixture of different organofluorine compounds is comprised. 
     According to a preferred embodiment, the arc-extinction liquid and/or exhaust-cooling liquid has a boiling point T b  at 1 bar higher than −40° C., preferred higher than −20° C., more preferred higher than −10°, even more preferred higher than +5° C., most preferred higher than +20° C. In further embodiments, the boiling point can also be higher than +40° C., preferred higher than +65° C., most preferred higher than +90° C. This allows storage of the medium in liquid form by means of very simple cooling and/or pressurisation means or without such means at all. 
     The term “organofluorine compound” as used in the context of the present invention is to be understood broadly and means a compound containing at least one carbon atom and at least one fluorine atom. It is understood that these compounds can optionally comprise further atoms, in particular at least one atom selected from the group consisting of oxygen, hydrogen, nitrogen, and iodine, in addition to carbon and fluorine. The present invention encompasses both embodiments where the arc-extinction liquid is at least essentially consisting of the organofluorine compound as well as embodiments comprising further components. 
     Specifically, the arc-extinction and/or exhaust-cooling liquid comprises as organofluorine compound preferably at least one compound selected from the group consisting of: a fluorocarbon, in particular C 2 F 6  and C 3 F 8 ; a hydrofluorocarbon; a fluoroether; a fluoroamine; a fluoroketone; and mixtures thereof. 
     Herein, the term “fluoroether”, “fluoroamine” and “fluoroketone” refer to at least partially fluorinated compounds. In particular, the term “fluoroether” encompasses both hydrofluoroethers and perfluoroethers, the term “fluoroamine” encompasses both hydrofluoroamines and perfluoroamines, and the term “fluoroketone” encompasses both hydrofluoroketones and perfluoroketones. 
     It is thereby preferred that the fluorocarbon, the fluoroether, the fluoroamine and the fluoroketone are fully fluorinated, i.e. perfluorinated. They are thus devoid of any hydrogen which—in particular in view of the potential by-products, such as hydrogen fluoride, generated by decomposition—is generally considered unwanted in circuit breakers. 
     According to a particularly preferred embodiment, the arc-extinction liquid comprises as organofluorine compound a fluoroketone or a mixture of fluoroketones, in particular a fluoromonoketone. 
     Fluoroketones have recently been found to have excellent dielectric insulation properties. They have now been found to have also excellent interruption properties. 
     The term “fluoroketone” as used in the context of the present invention shall be interpreted broadly and shall encompass both perfluoroketones and hydrofluoroketones. The term shall also encompass both saturated compounds and unsaturated 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 and can optionally form a ring. 
     The term “fluoroketone” shall encompass compounds that may comprise in-chain heteroatoms. In exemplary embodiments, the fluoroketone shall have no in-chain hetero atom. The term “fluoroketone” shall also encompass fluorodiketones having two carbonyl groups or fluoroketones having more than two carbonyl groups. In exemplary embodiments, the fluoroketone shall be a fluoromonoketone. 
     According to a preferred embodiment, the fluoroketone is a perfluoroketone. It is preferred that the fluoroketone has a branched alkyl chain. It is also preferred that the fluoroketone is fully saturated. 
     Preferably, the fluoroketone contains from 5 to 15 carbon atoms, preferably from 5 to 9, more preferably exactly 5, exactly 6 or exactly 7 or exactly 8 carbon atoms. The respective fluoroketones have a relative high boiling point and thus allow storage of the medium in liquid form by means of very simple cooling and/or pressurisation means or no such means at all. 
     According to a particularly preferred embodiment, the fluoroketone has exactly 5 carbon atoms and is 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: 
     
       
         
         
             
             
         
       
     
     Compared to fluoroketones having a lower chain length with less than 5 carbon atoms, fluoroketones containing 5 carbon atoms have the advantage of a relatively high boiling point, allowing to maintain it in liquid form by means of very simple cooling and/or pressurisation means or no such means at all. Fluoroketones containing exactly 5 carbon atoms have the further advantage that they are generally non-toxic. 
     In a particularly preferred embodiment, the fluoroketone has the molecular formula C 5 F 10 O, i.e. is fully saturated without any double or triple bond. The fluoroketone may more preferably be selected from the group consisting of 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)butan-2-one (also named decafluoro-3-methylbutan-2-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, 1,1,1,4,4,5,5,5,-octafluoro-3-bis(trifluoromethyl)-pentan-2-one; and most preferably is 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)butan-2-one. 
     Among the fluoroketones containing exactly 5 carbon atoms, 1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)butan-2-one, here briefly cited by the generic term “C5-ketone” (=fluoroketone containing exactly 5 carbon atoms), with molecular formula CF 3 C(O)CF(CF 3 ) 2  (or sum formula C 5 F 10 O), has been found to be particularly preferred because it has the advantages of a high dielectric insulation performance, in particular in mixtures with a dielectric carrier gas component, a very low GWP and a low boiling point. It has an ozone depletion potential of 0 and is practically non-toxic. 
     1,1,1,3,4,4,4-heptafluoro-3-(trifluoromethyl)butan-2-one can be represented by the following structural formula (I): 
     
       
         
         
             
             
         
       
     
     According to a further preferred embodiment, the fluoroketone has exactly 6 carbon atoms and 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: 
     
       
         
         
             
             
         
       
     
     According to a further preferred embodiment, the fluoroketone has exactly 7 carbon atoms and 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: 
                                           
named dodecafluoro-cycloheptanone.
 
     The present invention encompasses each compound or combination of compounds selected from the group consisting of the compounds according to structural formulae Ia to Id, IIa to IIg, IIIa to IIIn. 
     A fluoroketone containing exactly 6 carbon atoms is particularly preferred for the purpose of the present invention due to its relatively high boiling point. Also, fluoroketones having exactly 6 carbon atoms are non-toxic with outstanding margins for human safety. 
     In particular, the fluoroketone has the molecular formula C 6 F 12 O. More preferably, the fluoroketone is 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), 1,1,1,3,4,4,4-heptafluoro-3-bis-(trifluoromethyl)butan-2-one (also named dodecafluoro-3,3-(dimethyl)butan-2-one), dodecafluorohexan-2-one and dodecafluorohexan-3-one, and particularly is the mentioned 1,1,1,2,4,4,5,5,5-nonafluoro-2-(trifluoromethyl)pentan-3-one. 
     1,1,1,2,4,4,5,5,5-Nonafluoro-2-(trifluoromethyl)pentan-3-one (also named dodecafluoro-2-methylpentan-3-one or perfluoro-2-methyl-3-pentanone) can be represented by the following structural formula (II): 
     
       
         
         
             
             
         
       
     
     1,1,1,2,4,4,5,5,5-Nonafluoro-4-(trifluoromethyl)pentan-3-one, here briefly cited by the more generic term “C6-ketone” (=fluoroketone comprising exactly 6 carbon atoms), with molecular formula C 2 F 5 C(O)CF(CF 3 ) 2  (or sum formula C 6 F 12 O) has been found to be particularly preferred. 
     It has a boiling point of 49.2° C. at 1 bar and can thus be kept in liquid form by means of very simple cooling and/or pressurisation means or without such means at all. 
     1,1,1,2,4,4,5,5,5-Nonafluoro-4-(trifluoromethyl)pentan-3-one has further been found to have high insulating properties and an extremely low GWP. It has an ozone depletion potential of 0 and is non-toxic (LC50 of about 100′000 ppm). Thus, the environmental impact is much lower than with conventional insulation gases, and at the same time outstanding margins for human safety are achieved. 
     As will be discussed in detail below, the present invention encompasses embodiments of the circuit breaker comprising an improved ejection device which allows for an accurate control of the dosing of the medium as well as of the timeliness, duration and rate of its ejection. In this regard, the ejection device is preferably designed such that the arc-extinction medium and/or exhaust-cooling medium is ejected at a rate in a range from 0 ml/ms, in particular 0.1 ml/ms, to 15 ml/ms, preferably from 1 ml/ms to 10 ml/ms, more preferably from 3 ml/ms to 6 ml/ms. 
     It is further preferred that the ejection device is designed such that the arc-extinction medium and/or exhaust-cooling medium is ejected during an ejection time shorter than 25 ms (milliseconds), preferably during an ejection time in a range from 5 ms to 15 ms, more preferably during an ejection time of about 10 ms. 
     According to a further preferred embodiment the circuit breaker comprises a dielectric insulation medium comprising an organofluorine compound which is at least partially in gaseous state at operational conditions. Specifically, the dielectric insulation medium is comprised outside the ejection device. Thus, increased insulating properties can be achieved. The term dielectric insulation medium here also encompasses arc-extinction capability of the medium. 
     In particular, the organofluorine compound comprised in the dielectric insulation medium corresponds to the organofluorine compound comprised in the arc-extinction liquid and/or exhaust-cooling liquid and more particularly stems therefrom. Again, it is understood that the expression “comprising an organofluorine compound” is to be interpreted such that it encompasses embodiments in which a single organofluorine compound is comprised as well as embodiments in which a mixture of different organofluorine compounds is comprised. 
     According to a further preferred embodiment at least one background gas is present in the circuit breaker selected from the group consisting of: CO 2 , N 2 , O 2 , SF 6 , CF 4 , a noble gas, in particular Ar, and mixtures thereof. When using an arc-extinction liquid comprising a fluoroketone as in the above described preferred embodiment in combination with a background, in particular a background gas as defined above, also the insulation performance of the background gas can be improved due to the high dielectric strength of the gaseous fluoroketone obtained by vaporization of the arc-extinction liquid using the arc energy and/or due to the high dielectric strength of its decomposition products. As well, when the arc-extinction liquid and specifically the fluoroketone liquid is used for exhaust cooling, it readily evaporates after ejection, possibly decomposes and thus very efficiently cools the exhaust gases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is further illustrated by the following examples, in combination with the figures which show exemplarily and schematically in: 
         FIG. 1  a circuit breaker with an outside ejection device or inside ejection device; 
         FIG. 2  an outside ejection device with a compression mechanism according to a first embodiment of the invention; 
         FIG. 3  an inside ejection device with a compression mechanism according to a second embodiment of the invention; 
         FIG. 4 a , 4 b , 4 c    three operating states of the outside ejection device of  FIG. 2 ; 
         FIG. 5  an outside ejection device with another compression mechanism according to a third embodiment of the invention; 
         FIG. 6  an inside ejection device with yet another compression mechanism according to a fourth embodiment of the invention, and 
         FIG. 7 a , 7 b , 7 c    an ejection device comprising an auxiliary chamber for injection of an auxiliary injection compound. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows schematically an exemplary circuit breaker  1  having a central axis  1   a , an enclosure  1   b , nominal contacts  2 , arcing contacts  30 ,  31 , in particular a plug  30  and tulip  31  which provide in opened state between them an arcing zone  32  (see  FIG. 2, 3 ), and an insulating material nozzle  4 . The circuit breaker  1  has further a puffer volume or compression chamber  6  and optionally, if it is a self-blast circuit breaker  1 , a heating volume or heating chamber  5 . It also has an exhaust tube  70  which leads exhaust gases into an exhaust volume  71 . The exhaust volume  71  can also be present on the side of the arcing pin or plug  30 .  FIG. 1  also indicates that the circuit breaker  1  has a novel ejection device outside  8  or inside  9  the circuit breaker enclosure  1   b.    
       FIG. 2  shows a first embodiment of an outside ejection device  8  with a compression mechanism  14  comprising a compartment  14   a  for arc-extinction medium  18 ;  18   a ,  18   b , in particular arc-extinction liquid  18 ;  18   a ,  18   b . The arc-extinction medium  18 ;  18   a ,  18   b  contained in compartment  14   a  comprises or is for example an organofluorine compound having a boiling point T b  at 1 bar higher than −60° C. 
     The ejection device further comprises an auxiliary compartment  14   b  separated from and mechanically connected to the compartment  14   a  by a floating piston  15 , and a mechanically driven piston  11  of the auxiliary compartment  14   b . The compression mechanism  14  according to  FIG. 2  is arranged outside the circuit breaker enclosure  1   b . The compartment  14   a  serves for receiving, storing and ejecting the arc-extinction medium  18 ;  18   a ,  18   b  under pressure. As shown, the piston  11  can e.g. be fixedly supported on a wall  13  while the compression mechanism  14 , in particular the auxiliary compartment  14   b , is moveable, typically along the operating axis  1   a  of the circuit breaker. 
     Preferably, the ejection device  8 , in particular the compression mechanism  14 , is mechanically connected to a moving part  16  of the circuit breaker  1 . During a breaker operation a movement of the moving part  16  is translated into a relative movement between the auxiliary compartment  14   b  and the piston  11  for compressing the auxiliary compartment  14   b  such that a volume of the auxiliary compartment  14   b  is reduced. Thus the pressure inside the auxiliary compartment  14   b  increases. This increased pressure is applied via the floating piston  15  onto the liquid ejection compartment  14   a  so that there the pressure rises, as well. 
       FIG. 3  shows a second embodiment of an inside ejection device  9  with a compression mechanism  14  comprising a compartment  14   a  for the arc-extinction medium  18 ;  18   a ,  18   b , in particular the arc-extinction liquid  18 ;  18   a ,  18   b , an auxiliary compartment  14   b  separated from and mechanically connected to the compartment  14   a  by a floating piston  15 , and a mechanically driven piston  11  of the auxiliary compartment  14   b . The ejection device  9  and in particular the compression mechanism  14  is now arranged inside the circuit breaker enclosure  1   b . The functions of the elements, in particular the moveable mechanism  14 , the preferably fixed piston  11 , the liquid compartment  14   a  and the auxiliary compartment  14   b  are as described above for  FIG. 1 . 
     In both embodiments of  FIGS. 1 and 2 , the pressure in the compartment  14   a  filled with the incompressible arc-extinction medium  18 ;  18   a ,  18   b , typically a liquid  18 ;  18   a ,  18   b , is increased by the compressive force exerted onto the interior of the compartment  14   a  via the externally driven piston  11 . As a result the arc-extinction medium is ejected through the ejection orifice  17  out of the compartment  14   a  into an injection zone  5 ,  6 ,  71 . 
     The injection zone can be any zone of the circuit breaker  1  in which the pressure is lower than in an arcing zone  32  when an arc is present. In particular, the injection zone  5 ,  6 ,  71  can be a heating volume  5 , a puffer volume  6  or an exhaust volume  71 . 
     In both  FIGS. 1 and 2 , the auxiliary compartment  14   b  is filled with a compressible medium, in particular a gas, and serves for transmitting a compression force to the compartment  14   a  and thereby to pressurize and eventually eject arc-extinction liquid  18 ;  18   a ,  18   b  into an injection zone  5 ,  6 ,  71  or possibly arcing zone  32  of the circuit breaker  1 . The auxiliary compartment  14   b  as disclosed herein functions as a compressible force transmitter or gas cushion that allows to smoothen out pressure peaks in the compression force to be transmitted to the liquid compartment  14   a . Thus the timeliness, amount and dosing of the arc-extinction medium or liquid  18 ;  18   a ,  18   b  is improved considerably over previously known ejection devices. 
       FIG. 4 a , 4 b , 4 c    show three operating states of the circuit breaker  1  and of the ejection devices  8 ,  9  here shown for the outside ejection device  8 . With increasing contact separation an arc forms, the pressure in the auxiliary compartment  14   b  is increased by the advancing decrease of the volume of the auxiliary compartment  14   b  due to the breaker movement of circuit breaker  1  and is smoothly transmitted to the liquid compartment  14   a . Continuously or upon traversing a pressure limit, if the ejection orifice is or has a valve  17 , arc-extinction fluid  18 ;  18   a ,  18   b  is ejected and is injected into any or several of the aforementioned injection zones  5 ,  6 ,  71 , in the shown embodiment, particularly into the heating volume  5 . After release out of the liquid compartment  14   a , the arc-extinction medium  18 ;  18   a ,  18   b  vaporizes and then improves the extinguishing performance of the breaker with highest efficiency. 
       FIG. 5  shows another variant of an outside ejection device  80  of a circuit breaker  1  having an axis  1   a , an enclosure  1   b , arcing contacts, in particular a plug (not shown) and a tulip  31 , which provide in opened state between them an arcing zone  32 . In analogy to the embodiment shown e.g. in  FIG. 1 , also the embodiment shown in  FIG. 5  comprises an insulating material nozzle  4   a  and an exhaust tube  70  which leads exhaust gases into an exhaust volume  71 . Generally, the exhaust volume  71  may also exist on the side of the plug  30 , and the exhaust gas may be guided into the exhaust volume  71  by passing through the main nozzle  4  or through a hollow plug  30 . 
     According to the variant shown in  FIG. 5 , floating piston  21 , which is acting on and is compressing compartment  140   a  containing the arc-extinction medium, is driven by gas pressure present in the circuit breaker  1  during a breaker operation, and in particular is driven by gas pressure present in the heating volume  5  of a self-blast circuit breaker  1 . To this end, ejection device  80  is connected to the heating volume  5  via a pressure opening  50 . 
     If due to the compressing force exerted on compartment  140   a  a pressure limit is exceeded, valve  17  opens such that arc-extinction medium  18 ;  18   a ,  18   b , in particular arc-extinction liquid  18 ;  18   a ,  18   b , is ejected out of liquid compartment  140   a  and is injected into the heating volume  5 . 
       FIG. 6  shows a further variant similar to the one shown in  FIG. 5  but with an inside ejection device  90  which operates as described above. 
     According to both embodiments shown in  FIGS. 5 and 6 , the floating piston  21  is guided in a piston guidance  140   b  and comprises a primary floating piston  19  which transmits compressing force from the heating chamber  5  onto a secondary floating piston  20 , said secondary floating piston  20  transmitting compressing force to the compartment  14   a  containing the arc-extinction medium  18 ;  18   a ,  18   b  in particular the arc-extinction liquid  18 ;  18   a ,  18   b . The primary floating piston  19  is rigidly connected to the secondary floating piston  20 . Given the design of the primary floating piston having a larger area than the secondary floating piston  20  a high injection pressure can also be achieved even if the movement of the primary floating piston is relatively small. The blow pressure in the heating volume  5  is further increased by evaporation of the arc-extinction liquid  18 ;  18   a ,  18   b  upon release into the heating volume  5 . 
     When an arc is present, the pressure in the heating volume  5  is increased due to the heating of the gas by the burning arc. Since the ejection device  80  is connected to the heating volume  5  via the pressure opening  50 , the floating piston moves from a remote position in relation to the compartment  140   a , thereby compressing the interior of the compartment  140   a . Continuously, or upon traversing a pressure limit if the ejection orifice is or has a valve  17 , arc-extinction fluid  18  is ejected and is injected into any or several of the aforementioned injection zones  5 ,  6 ,  71 , in the shown embodiment, particularly into the heating volume  5 , as shown in  FIG. 1-6 . After release out of the liquid compartment  140   a , the arc-extinction medium  18  vaporizes and then improves the extinguishing performance of the circuit breaker  1  with highest efficiency. 
     The circuit breaker  1  can be, e.g., a high voltage circuit breaker, a generator circuit breaker, a medium voltage circuit breaker, or any other electrical switch which requires active arc extinction, as e.g. a load break switch. 
     In embodiments, an ejection device  8 ,  9 ;  80 ,  90 —as disclosed in  FIG. 1-6  and in the description thereof for an arc-extinction medium  18 ;  18   a ,  18   b  which serves for improving extinction of an arc burning temporarily in the arcing zone  32  of the circuit breaker  1 —can also be used when being arranged close to or inside of or outside of the exhaust volume  71  of the circuit breaker, as indicated in  FIG. 1 , and when containing an exhaust-cooling medium  18 ;  18   a ,  18   b . Please note that the arc-extinction medium  18  may also serve as the exhaust-cooling medium  18 ;  18   a ,  18   b  and vice versa, and both media  18 ;  18   a ,  18   b  can be or can comprise the same compound or compounds and, in particular, can be identical. Herein, exhaust volume is any volume of the circuit breaker that is connected downstream of the arcing zone and is for outflowing exhaust gases. 
     A further aspect of the invention is disclosed in connection with  FIGS. 7 a , 7 b  and 7 c   . Embodiments relate to a circuit breaker  1 , in particular a circuit breaker  1  as disclosed above, with the circuit breaker  1  comprising an ejection device  8 ,  9 ;  80 ,  90  comprising an arc-extinction medium  18 ;  18   b  for improving extinction of an arc formed during a breaker operation, wherein the arc-extinction medium  18 ;  18   b  contained in the ejection device  8 ,  9 ;  80 ,  90  comprises an auxiliary injection compound  18   b  selected from the group consisting of: O 2 , CO 2 , N 2 , CF 4 , a noble gas, in particular argon, and mixtures thereof. This allows to create a locally increased concentration of the auxiliary injection compound  18   b  in the arcing zone  32  and to enhance the thermal and/or dielectric interruption capability of the circuit breaker. 
     In a preferred embodiment the arc extinction medium  18  contained in the ejection device  8 ,  9 ;  80 ,  90  is or comprises oxygen  18   b . This may serve for boosting an arc-blowing pressure in the arcing zone  32 . The auxiliary injection compound  18   b  and in particular oxygen  18   b  as an example can namely trigger additional effects between the components of the gas mixture in the arcing zone  32  which leads to an increased pressure build-up and enhances the extinction capability of the circuit breaker  1 . 
     In an embodiment, and as exemplarily shown in  FIG. 7 a -7 c   , the ejection device  8 ,  9 ;  80 ,  90  can comprise an additional compartment  14   c  in which the arc-extinction medium  18 ;  18   b  is contained and which has an ejection orifice  17  through which the auxiliary injection compound  18   b , in particular oxygen  18   b , is to be ejected. The additional compartment  14   c  may also be pressurized indirectly via an or the above mentioned auxiliary compartment (not shown in  FIG. 7 a -7 c   ), in particular for smoothening out pressure peaks in the compression force to be transmitted to a or the above mentioned floating piston and for accurately controlling the dosing of the auxiliary injection compound  18   b , in particular oxygen  18   b , and the timeliness, duration and rate of its ejection. 
       FIG. 7 a    shows an embodiment, in which the auxiliary injection compound  18   b , in particular oxygen  18   b , is to be injected directly into an arcing zone  32  of the circuit breaker  1  via an auxiliary injection channel  24 . In particular, the auxiliary injection channel  24  can be arranged in close proximity to the arcing zone  32  such that temperatures of the auxiliary compound  18   b  above 2000 K are achievable when the auxiliary compound  18   b  is injected into the auxiliary injection channel  24  during a contact-opening operation of the circuit breaker  1 . 
       FIGS. 7 b  and 7 c    show embodiments, in which the auxiliary injection compound  18   b , in particular oxygen  18   b , is to be injected indirectly via a or the heating volume  5  and/or compression volume  6  and/or via an auxiliary volume  22 . In particular, the auxiliary volume  22  can be arranged in close proximity to the arcing zone  32  such that temperatures of the auxiliary compound  18   b  above 2000 K are achievable when the auxiliary compound  18   b  is injected into the auxiliary volume  22  during a contact-opening operation of the circuit breaker  1 . 
     The auxiliary volume  22  for temporarily receiving and transmitting the auxiliary injection compound  18   b  has the following advantages: When there is high current arcing, as may occur during severe short-circuits (such as T60 and higher) in a circuit breaker  1 , for example a self-blast and/or puffer circuit breaker  1 , the arcing zone  32  may mainly be filled with ablated PTFE (C 2 F 4 , Teflon) that displaces the gas mixture with which the circuit breaker  1  is filled. In this case, direct injecting of oxygen is likely to be less efficient and not to the full extent to create the additional effect that result in increased pressure build-up. Therefore, indirect injection into the heating volume  5  and/or compression volume  6  and/or auxiliary volume  22  is done. 
     In particular, the auxiliary volume  22  is fluidly connected via an auxiliary intermediate channel (not explicitly shown in  FIG. 7 c   ), an auxiliary opening  23  or an auxiliary valve  23  to a or the heating volume  5  and/or compression chamber  6  for transmitting the auxiliary compound  18   b  to the arcing zone  32 . 
     In an embodiment, timing means for timed injection of the auxiliary compound  18   b , in particular oxygen  18   b , into the arcing zone  32  can be present such that a or the boosting of the arc-blowing pressure occurs close to current-zero, in particular in a time window of less than 15 ms, preferably less than 10 ms, more preferably less than 5 ms, and most preferred less than 3 ms, around the time instant when current-zero occurs. Such timed injection allows to create the boost in pressure in close time-relationship to current-zero when the high pressure is most beneficial. The timing means may for example comprise an timing control for operating an ejection orifice valve  17  and/or an auxiliary valve  23  for the auxiliary volume  22 . 
     Such valve timing control may comprise valves  17 ,  23  that are actively operated, for example based on information about operational timing or operational conditions of the circuit breaker, or that are passively operated, for example by the pressures and/or temperatures present under operating conditions in the circuit breaker. Alternatively or in addition, the timing means may for example also comprise other passive timing control, such as a time-delaying injection channel  17   a , and/or a time-delaying auxiliary intermediate channel between auxiliary volume  22  and heating volume  5  or compression chamber  6 , and/or a time-delaying auxiliary injection channel (to be present at position  23  in  FIG. 7 c   ). 
     While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may otherwise variously be embodied and practised within the scope of the following claims. Therefore, terms like “preferred”, “preferably”, “in particular”, “particularly” or “advantageously” signify optional and exemplary embodiments only. As well, reference numerals are not meant to be limiting but exemplary only. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               1  circuit breaker 
               1   a  axis (of circuit breaker) 
               1   b  enclosure (of circuit breaker), chamber wall, heating chamber wall, compression chamber wall 
               2  nominal contacts 
               30 ,  31  arcing contacts 
               30  plug 
               31  tulip 
               32  arcing zone 
               4  nozzle 
               5 ,  6 ,  71  injection zone 
               5  heating volume, heating chamber 
               50  pressure opening 
               6  puffer volume, compression chamber 
               70  exhaust tube 
               71  exhaust volume 
               8 ,  9 ;  80 ,  90  ejection device 
               8 ,  80  outside ejection device 
               9 ,  90  inside ejection device 
               11  piston, mechanically driven piston 
               12  rod, mechanical connection 
               13  support 
               14 ,  140  compression mechanism 
               14   a ,  140   a  compartment, liquid compartment 
               14   b , auxiliary compartment, gas compartment, gas cushion compartment 
               140   b  piston guidance 
               14   c  additional compartment of ejection device  8 ,  9 ;  80 ,  90  for auxiliary injection compound 
               15 ,  21  floating piston 
               16  moving part of interrupter, movement transmitter 
               17  ejection orifice; valve, outlet valve, ejection valve, injection nozzle, spray nozzle 
               17   a  injection opening, injection channel 
               18  arc-extinction medium, arc-extinction liquid 
               18   a  fluoroketone, mixture of fluoroketones, fluoromonoketone 
               18   b  auxiliary injection compound; O 2 , CO 2 , N 2 , CF 4 , a noble gas 
               19  primary piston, primary floating piston 
               20  secondary piston, secondary floating piston 
               22  auxiliary volume for receiving auxiliary compound, pre-heating-up volume for the auxiliary compound 
               23  auxiliary intermediate channel, auxiliary opening, auxiliary valve 
               24  auxiliary injection channel. 
             T b  boiling point (at 1 bar), boiling temperature of arc-extinction liquid, boiling temperature of exhaust-cooling liquid