Patent Publication Number: US-8530774-B2

Title: High voltage circuit breaker with improved gas exhaust

Description:
CROSS REFERENCE TO RELATED APPLICATIONS OR PRIORITY CLAIM 
     This application claims priority to French Patent Application No. 07 59228, filed Nov. 22, 2007. 
     TECHNICAL FIELD AND PRIOR ART 
     This invention relates to the field of high voltage circuit breakers, having a metal outer tank and being either of the gas insulated switchgear (GIS) or of the dead tank type. Such circuit breakers may be part of a metalclad switch. 
     More particularly, the invention relates to a method of evacuating hot gases produced in a current-breaking operation by such a circuit breaker, and to the structure of the circuit breaker itself. 
     In this type of circuit breaker, for certain values of short-circuit current that correspond to a maximum fault current, the hot gases (that is to say the plasma and exhaust gases) that are generated can lead to restriking between the various high voltage current breaking components and the components connected to ground, such as the metal outer tank. 
     In metalclad circuit breakers available commercially at the present time, various kinds of evacuation or exhaust systems are provided. 
     A first type of system, which is for example to be found in Japanese types of circuit breaker, such as the system described in Patent Application JP 2003 217411, includes a short tube fitted at the outlet of the hot gas blow-out nozzle, this tube also permitting the gas to be blown directly into the metal outer tank. Dielectric insulation is obtained by keeping long distances between the evacuation crown, constituted by the tube and the metal outer tank. 
     A second type of system, which is for example provided in “dead tank” switches such as published Patent Application EP 1 806 760, makes it possible to have present in the metal part of the exhaust a volume of dielectric gas that is large enough to absorb all the hot gases generated during the longest arcing period of the maximum short-circuit current. This exhaust arrangement includes lateral ports on the side through which the hot gases escape into the interior of the metal outer tank. 
     The first above-described type contains volumes of insulating gas that are by construction smaller than the quantity of hot gases blown out during a current breaking operation. That is why the metal outer tank has overall dimensions that are larger than in the second type, due to the fact that the hot gases are evacuated in a controlled way, and consequently dimensional safety margins are needed in order to ensure that the outer tank has the necessary dielectric strength. 
     The closing operation performed in the system of the second type involves a large enough volume to conserve the hot gases inside the metal part of the exhaust. In addition, the dimensional safety margin between the outside of the exhaust and the metal outer tank can be reduced. 
     Documents U.S. Pat. No. 4,236,053, DE 9 314 779, and DE 2 947 957, teach means for cooling the hot gases by passing them through heat exchangers including solids. Heat exchanges are limited to the single exposed surface of the components and necessarily take time to perform their function. 
     Finally, the document EP 1 185 996 B1 teaches an exhaust structure with means arranged in alternation for varying the section through which the stream of hot gases passes in the exhaust path, and accordingly for cooling the gas stream before it leaves via the longitudinal end of the contact tube surrounding the fixed arcing contact. 
     It is not recommended to use the variations in section described in that document if satisfactory purging of the current-breaking gases between the arcing contacts is to be obtained. 
     An object of the invention is to reduce further the overall dimensions for the exhaust or evacuation of the hot gases, and also to reduce further the dimensions of the metal outer tank. 
     Another object of the invention is to propose a way of evacuating the hot gases that gives satisfactory cooling while maintaining satisfactory purging of the current-breaking gases between the arcing contacts. 
     DISCLOSURE OF THE INVENTION 
     To that end, the invention provides a method of evacuating hot gases produced in a current breaking operation by a high voltage circuit breaker which comprises a metal outer tank filled with insulating gas, a casing having gas outlet ports and arranged inside the metal outer tank, with which it is in communication via the said ports. 
     According to the invention, insulating gas is aspirated from inside the casing in a direction parallel to the flow of the hot gases produced by the current breaking operation, so as to mix the gases inside the casing before they are evacuated, through the said gas outlet ports of the casing, into the interior of the metal outer tank. 
     In the invention, therefore, use is made of the insulating gas that is present in the exhaust structure of the circuit breaker before the current is broken, this gas being by definition colder than the hot gases that are given off by the current breaking operation, and this colder gas is mixed with the said hot gases before they are exhausted into the interior of the outer tank. In the circuit breaker structures of the prior art, the cold insulating gas that is already present in the exhaust is merely pushed towards the interior of the metal outer tank by the hot gases, which therefore do not undergo any cooling by mixing with the insulating gas. 
     The invention has particular relevance in relation to maximum fault currents, with the longest arcing times. 
     The invention also provides to a high voltage circuit breaker that is, in particular, adapted to perform the method of the invention. 
     According to the invention, such a circuit breaker comprises: 
     a metal outer tank filled with an insulating gas; 
     a casing having gas outlet ports, the casing being arranged inside the metal outer tank, with which it is in communication via the ports; 
     a pair of arcing contacts, at least one of which is movable in straight line motion along an axis and which is fixed to an insulating nozzle for blowing out hot gases generated in the separating of the contacts; and 
     means for aspirating insulating gas from inside the casing, in a direction parallel to the flow of hot gases blown out in the separating of the contacts, whereby to mix the gases inside the casing before they are evacuated, through the gas outlet ports of the casing, into the interior of the metal outer tank. 
     In one embodiment of the invention, the circuit breaker comprises, as the means for aspirating insulating gas: 
     a sheath surrounding the fixed contact and arranged inside the casing to define an open passage; and 
     at least one deflector element arranged inside the sheath and being such that the hot gases aspirate insulating gas from the open passage, with the or each deflector diverting the aspirated insulating gas in a direction parallel to the hot gas flow, and the insulating gas thus aspirated and diverted mixing with the hot gases inside the casing. 
     The or each deflector so provided within the framework of the invention therefore forces the insulating gas aspirated from the open-ended passage to be completely deflected, and to be caused to flow parallel to the stream of hot gases generated by the blowing-out operation, before they are subsequently mixed inside the casing, to leave via the ports provided. 
     In an advantageous modified version, the gas outlet ports are formed at one of the longitudinal ends of the casing. 
     The open passage may have a plurality of holes spaced apart uniformly at the periphery of the sheath. In this version, where the gas outlet ports are formed at the periphery of the casing, the hot gases leaving the nozzle that is blowing gas out at high velocity are able to aspirate the colder insulating gas from the outer part of the exhaust (that is to say the part lying between the sheath and the casing), and through the gas return portion of the passage (that is to say from the base to the ports), and through the open holes. 
     In one advantageous embodiment, there are provided two deflectors that are coaxial on the axis of the straight line motion of the movable contact, one of the two deflectors having at least one notch formed at one of its longitudinal ends, and the said casing, sheath, and two deflectors together defining a baffle for directing insulating gas through the said notch. 
     In one embodiment, one of the two arcing contacts is fixed to the casing, and the other one is movable in straight line motion along the said axis. 
     Alternatively, both arcing contacts are movable in straight line motion along an axis. 
     Finally, the invention provides to a circuit breaker module of the kind set forth above, which comprises the casing, the sheath and the deflectors. 
     According to the invention, this module may be made from five metal components that are assembled together and that consist of: 
     two cast members, of which:
         one cast member is a cover member in which the gas outlet ports are formed; and   the other cast member comprises a body portion to which the fixed arcing contact can be fixed, and which defines one part of the sheath and one of the two deflectors, the body portion further including a portion in which the insulating nozzle can slide; and       

     three tubular members constituting, respectively, the casing, the remaining part of the sheath, and the other deflector, each of the said tubular members being made from rolled metal sheet. 
     The module of the invention may also be made from six metal components that are assembled together and that consist of: 
     three cast members, of which:
         one cast member is a cover member in which the gas outlet ports are formed;   a further cast member defines a portion of the sheath and a portion of one of the two deflectors, the said further cast member comprising a body portion on which the fixed arcing contact may be secured; and   a final said cast member, which includes the remaining portion of the said one deflector, in which the insulating nozzle is able to slide; and       

     three tubular members constituting, respectively, the casing, a part of the sheath, and the other part of the sheath, each of the said tubular members being made from rolled metal sheet. 
     Such modules, for performing the method of the invention have the advantage of reduced manufacturing cost, which results in particular from the reduction in casting of components and from the fact that assembly of the various parts is simplified. 
     The module consisting of six metal parts has the advantage of simplified castings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and features appear more clearly from a reading of the following detailed description, which is made with reference to the attached drawings, in which: 
         FIG. 1  is a diagrammatic view in longitudinal section showing a circuit breaker in one embodiment of the invention; 
         FIG. 2  is a front view of a circuit breaker module in an advantageous embodiment of the invention; 
         FIGS. 2A ,  2 B,  2 C and  2 D are views in longitudinal section taken on the planes AA, BB, CC and DD respectively in  FIG. 2 ; 
         FIG. 3  is a front view of a circuit breaker module in another advantageous embodiment of the invention; 
         FIGS. 3A to 3E  are perspective views which show various components of the embodiment shown in  FIG. 3 ; 
         FIG. 3F  is a scrap view in longitudinal section taken on the plane FF in  FIG. 3 ; and 
         FIG. 4  is a diagrammatic view in longitudinal section showing a circuit breaker in one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 
       FIG. 1  is a view, seen in longitudinal section, of a metalclad (gas insulated switchgear or GIS) circuit breaker. This high voltage circuit breaker includes a metal outer tank  2  filled with an insulating gas GI, and a casing  3  that has gas outlet ports  30 . The casing is arranged in the interior of the metal outer tank, with which it is in communication through the gas outlet ports for the purpose of evacuating insulating gases GI or hot gases GC, as represented by the respective arrows. More precisely, in the embodiment of  FIG. 1 , the gas outlet ports are formed at the periphery of the casing  3  close to its longitudinal end  3   b , which is the end nearest to the current breaking zone. 
     The circuit breaker  1  also includes a pair of arcing contacts, of which only the fixed contact  40  is shown in  FIG. 1 , this contact being fixed to the casing  3 . The other contact, which is movable in straight line motion along the axis XX′, is fixed to an insulating nozzle  41 , the purpose of which is to blow out the hot gases which are generated as the contacts move apart. 
     In accordance with the invention, means are provided for aspirating insulating gas GI from the interior of the casing  3 , in a direction parallel to the stream of hot gases CC blown out as the contacts are separated, so that the gases GI and GC are mixed together inside the casing before being evacuated, through the gas outlet ports in the casing  3 , into the interior of the metal outer tank  2 . 
     In the embodiment of  FIG. 1 , the aspirating means,  5 , comprise a sheath  50  surrounding the fixed contact  40 , the sheath being arranged inside the casing  3  to define a passage  6  which is open through a plurality of through holes  500  that are spaced uniformly around the periphery of the sheath  50 . The aspirating means also include a single deflector in the form of a tubular portion  51 , arranged inside the sheath in such a way that the hot gases GC aspirate gas GI from the holes  500 , that is to say exclusively from the interior of the casing  3 , and the deflector  51  diverts the insulating gas GI in a direction parallel to the stream of hot gases. The arrangement of the deflector  51  in the sheath  50  is therefore such that only the insulating gas GI originating in the interior of the casing  3  is aspirated, and not, for example, the gases at the periphery of the nozzle  41 . The aspirated and diverted insulating gas is then mixed with the hot gas in the interior of the casing  3 . 
     Thus, in the embodiment shown in  FIG. 1 , the hot gases GC leaving the nozzle  41  at a high velocity are able to aspirate the cooler insulating gas from the outer part of the exhaust (that is to say the part lying between the sheath  50  and casing  3 ), through a part of the gas return passage (that is to say from the closed end  3   a  towards the lateral openings), and then through the through holes  500 . 
     In the embodiment of  FIGS. 2 to 2D , and in that shown in  FIGS. 3 to 3F , the gas outlet ports are formed at one of the longitudinal ends,  3   a , of the casing  3 , and the aspirating means include two deflectors  51  and  52 , which are coaxial relative to the axis XX′ along which the straight movement of the movable contact and nozzle  41  takes place, with one of the two deflectors,  52 , having a plurality of notches  520  formed at one of its longitudinal ends  52   a , and the arrangement of the casing, and sheath with the two deflectors  51  and  52  defines a baffle  7  for guiding insulating gas through the notches  520  (see the curved arrows in  FIGS. 2A and 2C  for example). 
     More precisely, in the two embodiments shown, one of the two deflectors, the deflector  51 , consists of two wall portions  510  and  511  parallel to each other. The other deflector  52  is arranged between these two parallel wall portions  510  and  511 , in such a way that the baffle for guiding insulating gas, or aspiration baffle  7 , is configured in the form of a Z with the interior of the sheath  50  parallel to the wall portion  511  (see for example  FIG. 2A ). 
     In the embodiment shown in  FIGS. 2A to 2D , the module  8  of the invention is made from six metal parts, telescoped and screwed together. Three of the six parts are castings. One of these is a cover member  80 , in which the gas outlet ports  30  are formed. A further cast part  81  constitutes one part of the sheath  50 , and has a body portion  50   a , to which the fixed arcing contact may be secured, and a portion  511  of one of the deflectors, namely the deflector  51 . The final cast component comprises another portion  510  of the deflector  51  in which the nozzle  41  is arranged to slide. Finally, three tubular members are, respectively, the casing  3 , the other part of the sheath  50  and the other deflector  52 , each of which is made in rolled sheet metal. 
     In the embodiment shown in  FIGS. 3 to 3F , the module  8 ′ of the invention is made from five metal components that are telescoped and screwed together. Two of these are castings ( FIG. 3A  and  FIG. 3B ). One of the castings is a cover member  80 ′ in which the gas outlet ports  30  are formed. The other cast member  81 ′ defines a portion of the sheath  50 , with a body portion  50   a  to which the fixed arcing contact  40  may be secured. The member  81 ′ includes, integral with it, one of the deflectors, namely the deflector  51 , in a portion  510  of which the insulating nozzle is able to slide. Finally, three tubular members consist, respectively, of the casing  3  ( FIG. 3C ), the other portion of the sheath  50  ( FIG. 3D ), and the other deflector  52  ( FIG. 3E ), each of which is made from rolled sheet metal. 
     Referring to  FIG. 4 , during a breaking operation of the circuit-breaker  1  according to the invention, the displacement of mutual separation between arcing contacts is given by the another arcing contact (not shown on  FIG. 4 ). This arcing contact is mechanically linked to the nozzle  41 . The means for achieving the double movement, i.e, transmission for transmitting the movement to the other arcing contact  40 , includes a first connecting rod  401  which is mechanically connected to the nozzle  41 ; a return lever  402  with two arms, mounted pivoting on the casing  3 , and which is coupled to the first connecting rod  401 ; and, a second connecting rod  403  with one end connected to the return lever and with the other end connected to a tube part  400  of the second arcing contact  40 . When the nozzle linked to the first arcing contact (not shown) is moving towards the left, the first connecting rod  401  is also moving towards the left and thanks to the return lever  402 , the second connecting rod  403  is moving on the right together with the second arcing contact  40 . In other words, both arcing contacts are movable in a straight motion along an axis. 
     Calculations have shown that the use of the method of the invention in a circuit breaker is effective. In particular, it has been calculated that the static pressure in the interior of the exhaust that guides the hot gases from the insulating nozzle is lower than the pressure prevailing between the exhaust (the casing) and the metal outer tank. 
     By means of the invention, the length of the exhaust of a high voltage circuit breaker is shortened, which leads to a reduction in the overall length of the associated metal outer tank. This is of particular importance in relation to transport requirements, prior to on-site installation, for “dead tank” outer tanks.