Abstract:
A low-voltage multipole circuit breaker with high electrodynamic strength comprises a case made of insulating material, subdivided into a front compartment housing an operating mechanism commanding opening and closing of the circuit breaker and a rear compartment separated from the front compartment by an intermediate wall. The rear compartment is itself subdivided into individual compartments by separating partitions, each individual compartment housing one of the poles of the circuit breaker. The operating mechanism is linked to a pole shaft common to all the poles. The pole shaft is located in the rear compartment and supported by bearings passing through the separating partitions.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a high-current, low-voltage multipole circuit breaker with high electrodynamic strength. In the past, high-current circuit breakers (for indication purposes between 630 A and 6300 A) acting as base switchgear apparatuses for the incomers and feeders in large power installations, were formed by composite elements assembled on a metal frame, whence them being given the name of “open” power circuit breakers. But progressively the equipment of this range inherited of part of the technology of lower power circuit breakers, called “molded case” circuit breakers because they are characterized by an insulating protective enclosure, generally molded in reinforced polyester, housing the poles with their extinguishing chambers, and an operating mechanism and trip devices. The protective enclosure, by contributing to ensuring confinement of breaking and limitation of its external effects, integral partitioning between poles and a better insulation between the power circuit and the auxiliaries, in return enabled the overall dimensions of these apparatuses to be reduced. 
     The document EP-A-0,322,321 describes a circuit breaker of this type, whose case is formed by assembly of an intermediate case, of the cover forming the circuit breaker front panel, and of a rear panel. The front face of the intermediate case divides the case into a front compartment bounded by this face and by the cover, and a rear compartment designed for housing the poles and electrically insulated from the front compartment. The front compartment houses an operating mechanism acting on a transverse switching shaft common to all the poles, called the pole shaft. This shaft is supported by bearings fitted on the front face of the intermediate case. The rear compartment is for its part subdivided by insulating separating partitions into individual compartments for housing the poles. The front wall of the intermediate case comprises in addition, for each pole, an aperture for access to the corresponding individual compartment. Each pole comprises a pair of separable contacts with a stationary contact and a movable contact, and an arc extinguishing chamber. Each movable contact is mechanically linked to the transverse shaft by means of a connecting rod passing through the front wall of the intermediate case via the corresponding access aperture. 
     Each rod connecting one of the movable contacts to the transverse shaft is arranged in such a way that in the closed position of the contacts, and in a plane of straight cross-section perpendicular to the pivoting axis of the pole shaft, the distance between a straight line passing through the rotation axes of the connecting rod and the pivoting axis of the shaft is small. In other words, the leverage of the resultant of the forces exerted by the contacts on the pole shaft is small which guarantees that the connecting rod, when it transmits large electrodynamic forces, only generates a low torque at the level of the shaft. At static equilibrium in the closed position of the contacts, the operating mechanism exerts on the shaft a torque opposing the electrodynamic forces transmitted by the connecting rods. This torque only generates low forces at the level of the operating mechanism. Moreover, the resultant of the reaction forces at the level of the guide bearings of the shaft is great and opposes the forces transmitted by the connecting rod and by the operating mechanism. 
     This architecture is characteristic of circuit breakers with high electrodynamic strength. These circuit breakers must in fact by definition, in order to achieve time selectivity in the electrical installation, be able to withstand the flow of established fault currents which generate large electrodynamic forces tending to separate the contacts. The relative arrangement of the pole shaft, of the connecting rods with the movable contacts and of the connecting rod to the operating mechanism must be such that these forces do not give rise to separation of the contacts or to opening of the operating mechanism. In this case, the arrangement chosen enables these forces to be transmitted to the case by means of the shaft bearings so that the operating mechanism is not subjected to too great forces or torques. 
     However, guiding of the pole shaft and transmission of the forces to the circuit breaker case are not completely satisfactory. The transverse shaft must in fact be dimensioned, disposed and supported in such a way that deformation thereof is limited and does not hinder its operation. Furthermore, the pole shaft bearings need to be well secured in the case as the large forces transmitted to them tend to tear them away from the front face of the intermediate case to which they are fixed. Making the assembly rigid imposes the use of costly and bulky fixing parts and bearings and of complementary arrangements on the case. Assembly of the circuit breaker requires a large number of parts resulting in a high cost price and fastidious fitting. This architecture moreover limits miniaturization of the circuit breaker. 
     Moreover, the numerous openings for passage of the connecting rods between the pole shaft and each of the poles are detrimental to the tightness of the extinguishing chambers. However the electrical arc and the endothermal vaporizations generated by this arc at the level of certain elements of the extinguishing chamber partitions give rise to an overpressure and of a gas flow which has to be channeled towards the outlet orifices provided with suitable filters. In order not to hamper inlet of the arc to the extinguishing chamber, it is judicious to place these outlet orifices at the bottom of the extinguishing chambers. The presence of the openings for passage of the connecting rods, situated just above the contacts at the inlet of the chambers, therefore considerably hampers the flow of the gases to the outlet orifices. It allows an uncontrolled gas flow through the front compartment and the openings of the front face, directly to the outside, without any protective filter. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to overcome the drawbacks of the prior art and in particular to increase the rigidity of the mechanism of a circuit breaker with high electrodynamic strength, at low cost. 
     According to the invention, this problem is solved by means of a low-voltage circuit breaker of high electrodynamic strength with a case made of insulating material, comprising an operating mechanism linked to a pole shaft supported by bearings securedly affixed to the case, a plurality of poles, each pole comprising at least one pair of separable contact parts, one at least of the contact parts of each pair, called the movable contact part, being mechanically linked to the pole shaft, the pole shaft, operating mechanism and movable contact part being able to move between an open position corresponding to separation of the contact parts of each pair, and a closed position corresponding to contact between the contact parts of each pair, the case of the circuit breaker comprising a front compartment housing the operating mechanism and a rear compartment separated from the front compartment by an intermediate wall and subdivided into individual compartments by separating partitions, each individual compartment housing one of the poles of the circuit breaker, a circuit breaker whose rotation axis of the pole shaft is located in the rear compartment. 
     In state of the technique devices whose pole shaft was situated in the front compartment, a minimum distance had to be provided between the pole shaft and the movable contact parts in the open position. The link between the movable contact parts and the shaft was in fact made through the intermediate wall between the front compartment and the rear compartment. The configuration according to the invention to enables this distance to be considerably reduced and even eliminated, as there is no longer any part placed between the shaft and the contact parts. The overall dimensions of the device can thus be reduced. 
     This arrangement also enables the electrodynamic forces exerted on the contacts to be taken up by the case, without giving rise to large deformations of the intermediate parts. It in fact becomes possible to place the support bearings in the rear compartment. If these bearings are scheduled to be secured at least partially to the intermediate wall, it is then easy to make the securing parts work in compression instead of working in tear, in response to the electrodynamic forces exerted on the movable contact parts. 
     Furthermore, this arrangement enables the orifices for passage of the connecting rods between the pole shaft and each movable contact part to be eliminated. Pollution of the front compartment is thereby reduced and flow of the breaking gases to the outlet orifices of the base of the extinguishing chamber is improved. 
     Assembly is made easier by the fact that it is no longer necessary to fit the link between the pole shaft and each connecting rod via orifices of the intermediate partition. 
     Each of the separating partitions preferably supports one of said bearings and the pole shaft passes through each partition at the level of one of said bearings. This arrangement enables the bearings to be multiplied and to be distributed regularly along the pole shaft, without increasing the overall dimensions of the assembly. Alternatively, it is also possible to provide for the bearings to be arranged between the separating partitions of the chambers, on autonomous supports. Advantageously, each of the separating partitions comprises a partition element molded with the intermediate wall, in an edge of which there is formed a semi-cylindrical sector forming a part of the corresponding bearing. A multifunctional part is thus obtained which makes assembly easier and reduces costs. 
     Advantageously, the intermediate wall comprises a window for passage of a mechanical link part between the pole shaft and the operating mechanism. 
     Preferably, the external surface of the pole shaft is made of electrically insulating material, in particular of thermosetting polyester plastic. This arrangement enables the electrical insulation both between the poles and with the operating mechanism to be obtained. The thermosetting material provides the advantage of a good dielectric strength after breaking. In practice, the shaft can be made of bulk thermosetting material. Alternatively, the shaft can have a metallic body covered with an insulating material. 
     The circuit breaker advantageously comprises at least one connecting rod between the pole shaft and each movable contact part, linked to the pole shaft by a pivot in such a way that in a certain relative position of the shaft and of the rod, called the assembly position, the rod can be freely moved in a direction parallel to the axis of the pivot, and that once the rod has been fitted and moved from its fitting position, a positive link is achieved preventing translational motion of the rod in a direction parallel to the axis of the pivot, the assembly position being such that in the operating state, the pole shaft and rod never take this position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and features of the invention will become more clearly apparent from the following description of an embodiment of the invention, given as a non-restrictive example only and represented in the accompanying drawings in which: 
     FIG. 1 represents a perspective view of a circuit breaker according to the invention, cut away at the level of a pole, 
     FIG. 2 represents an exploded view of a pole shaft and of a part of a case of the circuit breaker according to the invention, 
     FIG. 3 represents a cross section of the circuit breaker of FIG. 1, in the closed position, 
     FIG. 4 represents a cross section of the circuit breaker of FIG. 1, in the open position, 
     FIG. 5 represents a perspective view of the pole shaft and of a connecting rod to one of the poles in a position preceding their assembly, 
     FIG. 6 represents a perspective view of the pole shaft and of a connecting rod for connection to one of the poles in a respective position called the assembly position, 
     FIG. 7 represents a perspective view of the pole shaft on which the connecting rod is fitted, in their positioning with respect to one another when the circuit breaker is open, 
     FIG. 8 represents a perspective view of the pole shaft on which the connecting rod is fitted, in their positioning with respect to one another when the circuit breaker is closed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIGS. 1 to  3 , a low-voltage non-limiting circuit breaker  10  with high electrodynamic strength is arranged in a molded case comprising a front compartment  12  and a rear compartment  14 . The front compartment  12  is limited by a front panel  16 , side panels  18  cast with the front face, and an intermediate wall  20  separating it from the rear compartment. It comprises openings on the front panel for passage of a pivoting handle  22  for performing resetting of an operating mechanism  24  of the circuit breaker, an opening pushbutton and a closing pushbutton. The operating mechanism  24  is housed in the front compartment  12 . 
     The rear compartment  14  is limited by the intermediate wall  20 , by a back plate  26  constituting a rear panel, and by side panels  28  a part of which is cast with the back plate and another part of which is molded with the intermediate wall. The back plate  26  supports connecting strips  30  for connection of the circuit breaker  10  to an external electrical circuit. The back plate  26  and intermediate wall  20  are fixed to one another by means of fixing screws  32  dimensioned so as to be able to withstand high shear stresses. A window  34 , visible in particular in FIG. 2, is arranged in the intermediate wall  20  and allows communication to take place between the front compartment  12  and the rear compartment  14 . The rear compartment  14  is sub-divided into individual compartments  36  by separating partitions  38 . Each partition  38  comprises two lateral parts arranged on each side of a central part. Each lateral part comprises a partition element  40  molded with the back plate and a partition element  42  molded with the intermediate wall, the partition elements  40 ,  42  being joined on the assembled unit. The central part comprises a partition element  44  molded with the back plate of a larger height than the adjacent lateral elements  40 . This partition element  44  comprises ribs  46  cooperating when assembly is performed with complementary grooves  48  of the lateral partition elements  42  securedly united to the intermediate wall  20 . The central partition element  44  of the back plate comprises a smooth semi-cylindrical surface  50 . The intermediate wall  20  comprises a complementary central partition element  52  of smaller height which also comprises a smooth semi-cylindrical surface  54  facing that of the element securedly united to the back plate. 
     A pole  56  of the circuit breaker is housed in each individual compartment  36 . Each pole  56  comprises an arc extinguishing chamber  58  and a separable contact device. The latter comprises a stationary contact part  60  electrically connected to a connecting strip  30  of the circuit breaker passing through the back plate  26  of the insulating case, and a movable contact part  61 . The latter is provided with a plurality of contact fingers  62  in parallel mounted pivoting on a first transverse axis  64  supported by a support tunnel  66 . The heel of each finger is connected by a flexible conductor  68  formed by a metallic braided strip to a second connecting strip  30  of the circuit breaker. Each finger  62  comprises a contact pad  70  cooperating with a pad  72  of the stationary contact part  60  in the closed position of FIG.  3 . The tunnel  66  is U-shaped (cf. FIG.  5 ). Its end situated near to the second connecting strip is equipped with an axis  74  housed in a bearing securedly united to the insulating case, so as to enable pivoting of the tunnel  66  between a closed position of the pole  56 , represented in FIG. 3, and an open position, represented in FIG. 4. A contact pressure spring device  76  is arranged in a notch of the tunnel  66  and urges the contact fingers  62  to pivot in a counterclockwise direction around the first axis  64 . 
     The arc extinguishing chamber  58  comprises a stack of deionization plates of the electrical arc drawn when separation of the poles takes place, and also orifices for outlet of the extinguishing gases. Further details on the structure of the poles  56  can be found in the document FR-A-2,650,434, the description of which is on this point incorporated herein by reference. 
     A pole shaft  78  is placed between the semi-cylindrical sectors  50 ,  54  which, once assembled, form tight bearings supporting the shaft  78  in rotation around its axis  79 . The shaft  78  is molded from thermosetting polyester. Each of the tunnels  66  is coupled to the pole shaft  78  by a pair of parallel transmission rods  80  which pivot around a geometrical axis which is the same as the axis  64 . Each rod  80  is linked to the pole shaft  78  by a pivot  81 . 
     The operating mechanism  24  comprises an energy storage closing device and an opening device. This mechanism is known as such and for further details reference should be made to the document FR-A-2,589,626 which is on this point incorporated herein by reference. It will merely be recalled here that the opening device comprises a toggle device which comprises two rods  82 ,  84  articulated on one another by a pivoting axis  86 , the lower transmission rod  82  being mechanically coupled to the pole shaft  78  by a pivoting axis  88  operating in conjunction with a bearing made in crank  90  securedly united to the shaft  78 . An opening spring  92  is secured between the axis  88  and a fixed securing spigot. FIG. 3 shows that in the closed position the window  34  made in the intermediate wall  20  serves the purpose of allowing the lower transmission rod  82  and the opening spring  92  to pass through. In the closed position, the leverage of the rods  80  on the pole shaft  78  is appreciably lower than that of the transmission rod  82 . In other words, the distance between the axis  79  of the pole shaft  78  and the plane which contains the axes  64 ,  81  of the pivots of the rods  80  is smaller than the distance between the axis  79  of the pole shaft  78  and the plane which contains the axes  86 ,  88  of the pivots of the lower transmission rod  82 . In practice, the ratio of the two distances is less than 0.3. 
     In the closed position represented in FIG. 3, it can be observed that for each pole  56  that the contact pads  70  of the contact fingers  62  are pressing on the pad  72  of the stationary contact part  60 . The contact pressure is provided by the spring device  76  which enables any possible play of the mechanism and wear of the pads  70 ,  72  to be compensated. The electrodynamic forces exerted on the contact fingers  62  are taken up at the level of the tunnel  66  by the bearing surfaces of the springs  76  and by the axis  64 , and generate a moment around the pivoting axis  74  of the tunnel  66  tending to make the tunnel  66  pivot in the direction of separation of the contacts. This moment is compensated by an opposite moment exerted by the rods  80  on the tunnel  66  at the level of their relative pivoting axis  64 . At dynamic equilibrium, the rods  80  are therefore subjected at the level of their link pivot  64  connecting them to the tunnel  66  to a force directed towards their link pivot  81  connecting them with the pole shaft  78 . This force, transmitted to the pivot  81 , generates a moment around the axis  79  of the pole shaft  78 . The same phenomenon occurs for each of the poles. A moment generated by the lower transmission rod  82  of the opening device toggle is opposed to the sum of the moments of the forces exerted by all the rods  80  and by the opening spring  92  on the shaft  78 . Due to the relative position of the rods  80 , the transmission rod  82  and the pole shaft  78 , i.e. to the weakness of the leverage of the rods  80  compared with that of the transmission rod  82 , the resultant at the level of the transmission rod  82  remains moderate. The characteristics of a circuit breaker of high electrodynamic strength are therefore to be found here, as the electrodynamic forces on the contact parts only generate limited stresses on the operating mechanism so that the latter can oppose them. At equilibrium, the pole shaft  78  exerts pressure forces at the level of the support bearings the resultant of which forces is a reaction force opposing the sum of the forces exerted by the rods  80  and the transmission rod  82 . These relatively high pressure forces are exerted mainly on the semi-cylindrical sector  54  formed in the intermediate wall  20 . 
     When opening of the circuit breaker takes place, the rod  82  stops opposing counter-clockwise rotation of the pole shaft. This rotation, generated jointly by the opening spring  92  and the resultant of the electrodynamic forces at the level of the link pivots  81  of the rods  80  and of the shaft  78 , drives all the tunnels  66  to the open position represented in FIG.  4 . In this position, the crank  90  of the pole shaft  78  emerges slightly from the window  34 . 
     FIGS. 5 to  8  describe the assembly mode of the link by pivot between the pole shaft  78  and the connecting rods  80  with each tunnel  66 . The pole shaft  78  comprises, for each pole, an arm  94  bearing two coaxial pivots  81  eccentric with respect to the pivoting axis  79  of the pole shaft  78 . These pivots  81  are each situated on a notch  98  of the side face  100  of the arm. A tab  102  overhanging the notch  98  materializes a groove  104 . 
     Each rod  80  comprises, on the side designed to operate in conjunction with the shaft  78 , a cylindrical bore  108  designed to form a bearing for one of the pivots  81 , and a flat part  110 . When assembly takes place, the rod  80  is presented in such a way that the flat part  110  is parallel with the bottom edge of the tab  100 , in the relative assembly position represented in FIG.  6 . It is then possible to insert the pivots  81  in the bores  108 . Once assembled, the assembly formed by the rods  80  and the pole shaft  78  is placed in the case, where it oscillates between two extreme positions: a position corresponding to opening of the contacts and represented in FIG. 7 and a position corresponding to closing of the contacts and represented in FIG.  8 . In both of these positions, as well as in all the intermediate positions, the rods  80  operate in conjunction with the corresponding grooves  104  of the pole shaft  78 , which form a guide preventing any movement of the rods  80  in a direction parallel to the pivoting axis  81 . A simple positive link is thus achieved which does not require the use of any additional intermediate part. 
     Naturally, the invention is not limited to the example described above. It is clear for example that the pivoting axis of the rods  80  on the tunnels  66  is not necessarily the same as the pivoting axis of the fingers  62 . There may moreover be only one rod  80  per pole. Furthermore, arrangements can be made to increase the tightness at the level of the bearings passing through the partitions. A bearing can thus be provided having a zigzag profile with a central annular groove operating in conjunction with a complementary asperity of the shaft. Additional bearings can also be provided at the level of the external side walls of the case. The circuit breaker described in the example comprises an energy storage mechanism. However, within the scope of the invention, the operating mechanism of the pole shaft can be of any kind. The mechanism described can therefore be replaced by any other known mechanism, whether it be a mechanism with manual or motor-driven resetting.