Patent Publication Number: US-7718913-B2

Title: Actuation by cylindrical CAM of a circuit-breaker for an alternator

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION OR PRIORITY CLAIM 
     This application claims the benefit of a French Patent Application No. 06-52628, filed on Jun. 23, 2006, in the French Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     FIELD OF THE INVENTION 
     The invention relates to the field of electrical apparatus equipping devices for delivering energy from alternators in power stations. The invention relates to actuating the various switch elements so that the alternator circuit-breakers are of simpler structure. 
     More particularly, the invention relates to an alternator circuit-breaker coupled to a disconnector, in which circuit-breaker the various relative movements of the contacts take place by means of a cylindrical cam making it possible to optimize the synchronization and the speed of separation of the contacts, while also maintaining the compactness of the circuit-breaker. 
     STATE OF THE PRIOR ART 
     At the outlet of the power station, e.g. for each alternator, one safety option is to dispose a circuit-breaker making it possible to isolate the circuit in question before the transformer connected to a power line. That type of switchgear, under a voltage in the range approximately 15 kilovolts (kV) to approximately 36 kV, then performs the functions of passing high permanent current (of the order of a few thousand amps) and of breaking high fault current (of the order of a few tens of thousands of amps), while isolating the circuit. 
     In view of the magnitude of the rated nominal current in the circuit, the circuit-breaking is performed in two stages by means of two switches in parallel, one of which passes the rated permanent current and the other of which breaks the short-circuit current, thereby defining a “main circuit” and an “auxiliary circuit”. 
     The contacts of the switch of the main circuit for such alternator circuit-breakers are heavy enough to withstand high rated currents without overheating, and they define a relatively large volume. The circuit-breaker switch conventionally comprises a small-size chamber disposed inside said volume and having arcing contacts that are mounted to move relative to each other and that, de facto, withstand only the circuit-breaking current of the circuit-breaker. 
     Usually, firstly the main contacts move apart and travel sufficiently before the current switches over to the arcing contacts, which then open and cause the current to be broken. 
     It is usual for the alternator circuit-breaker to be associated with a disconnector, which has no circuit-breaking power: the disconnector opens only when the circuit-breaker is open and thus when current is no longer passing through the circuit. It is known that such a disconnector can be incorporated into the power station circuit-breaker that is described, for example, in Document EP 0 877 405. 
     The various breaking elements of such a disconnector circuit-breaker must be actuated in the above-mentioned order, while optimizing the separation speeds. Unfortunately, in view of the overall size and weight, not all solutions are feasible. 
     In particular, in the state of the art, actuation usually (EP 0 877 405) takes place via levers provided with springs, thus posing the problem of dimensioning the springs, and above all of fatigue and ultimate deterioration thereof. 
     Another option concerns implementing linkage guide systems (Document EP 0 878 817), which are, however, very difficult to design and very voluminous. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to make alternator circuit-breakers more compact and more simple to make by means of a novel, common-control actuation system. 
     More particularly, in one of its aspects, the invention provides an alternator disconnector circuit-breaker comprising a change-over switch in parallel with a circuit-breaker switch, e.g. a vacuum chamber; each of the switches has a pair of contacts that are mounted to move relative to each other along a respective axis, by being actuated by actuator means. The circuit-breaker further comprises a disconnector switch advantageously in series in with the circuit-breaker switch, which disconnector switch comprises a pair of contacts that are mounted to move relative to each other, advantageously in translation, by being actuated by actuator means. 
     Preferably, the three axes along which the contacts move coincide. Usually, only one contact of each pair is a moving contact, the other contact being a stationary contact. 
     The actuator means for actuating one or more of the switches may be coupled to the corresponding contact via a connection rod, in order to leave a certain distance between the contacts. 
     The circuit-breaker further comprises synchronization means making it possible, while breaking, for the contacts to separate successively in the following order: the contacts of the change-over switch, then the contacts of the circuit-breaker switch, and then the contacts of the disconnector; the synchronization means also make it possible for the contacts to be re-closed in the reverse order. It is possible to make provision for the circuit-breaker switch to be closed at the end of the opening operation, in particular if it is a vacuum chamber. Advantageously, the synchronization means are coupled to the actuator means and make it possible, via common control means, to implement each of the switching operations. 
     In accordance with the invention, in order to make the circuit-breaker compact and in order to make the control simple, the actuation and synchronization means of at least the first and second switches comprise a cylindrical cam, i.e. a cylinder provided with slots that co-operate with slider elements making it possible to actuate the contacts. Preferably, the cylinder also actuates the disconnector. The cylinder is caused to move in rotation by an appropriate system, e.g. a transmission chain or a linkage actuated by a lever. 
     Each of the actuation and synchronization slots has a helical portion whose winding direction depends on the direction of the movement in translation of the contact in question, and whose slope depends on the relative separation speed of the contacts. In order to generate latencies between opening the contacts of the switches, the helical portions of the slots are offset relative to one another by the presence of zero-slope portions (i.e. portions extending around the cylinder orthogonally to the axis) or shallow-slope portions. 
     It is advantageous for the moving contact of at least one switch or preferably of all the switches to be actuated via a plurality of slider elements distributed around its periphery, e.g. two diametrically opposite elements; said slider elements can be coupled to the contact via rods, each having one end fastened to the contact and the other end carrying the slider element. Each slider element co-operates with a corresponding slot in the cylinder, the slots that make it possible to actuate a single contact being of similar shape but being offset around the periphery of the cylinder. If rods between slider element and contact are present, it is preferred for the plurality of actuating rods for actuating the same contact to be coupled together via a part guaranteeing that they remain in the correct geometrical positions, e.g. a bar. 
     In a preferred embodiment, the actuator means are guided in translation by the presence of studs co-operating with rectilinear grooves situated in the casing of the circuit-breaker. In particular, the slider elements are extended perpendicularly to the axis of movement by said studs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The characteristics and advantages of the invention will be better understood on reading the following description with reference to the accompanying drawings, which are given by way of non-limiting illustration, and in which: 
         FIG. 1  diagrammatically shows the circuit-breaking principle of a disconnector circuit-breaker of the invention. 
         FIGS. 2A and 2B  show a preferred embodiment of the circuit-breaker of the invention, in the fully-open position and in the fully-closed position. 
         FIGS. 3A and 3B  diagrammatically show two elements that are part of actuation and synchronization means of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 
     The operating principle of a circuit-breaker, and in particular of an alternator circuit-breaker  1  of the invention, is shown diagrammatically in  FIG. 1 , with a main circuit in which a current I 0  close to the rated current I flows when in operation, and an auxiliary circuit that is used for breaking a short-circuit. 
     For an alternator circuit-breaker, passing a current I of rated magnitude greater than a few thousand amps require a switch  10  whose contacts are particularly conductive, e.g. made of copper, to be used on the main circuit; the breaking power of those contacts is, however, limited due to electric arcs striking. A circuit-breaker second switch  20  is put in parallel with the first switch  10  in order to perform the circuit-breaking function proper. The first switch  10  opening causes, de facto, the current I to be switched over from the main circuit to the auxiliary circuit; the contacts of said second switch  20  that are, for example, made of tungsten, are of limited performance as regards passing the rated current I, but have high breaking power. 
     Thus, the functions of passing the permanent current and of breaking short-circuit current are separated: when such circuit-breaking is necessary, firstly the first switch  10  is activated, all of the current I then going over to the auxiliary circuit and causing the second switch  20  to be opened so as to obtain the circuit-breaking function. In addition, a third switch  30  is then opened: its function is mainly a safety function, its association on the auxiliary circuit making it possible to avoid a reduction in the dielectric strength of the second switch  20  that might accidentally allow current to pass into the associated branch. 
     In order to re-close such a circuit-breaker, the reverse order applies: firstly the disconnector  30  is re-closed, then the circuit-breaker switch  20  is re-closed, and finally the first switch  10  is re-closed. 
     Each of the switches  10 ,  20 ,  30  has a pair of contacts that are mounted to move relative to each other; advantageously, the first contact  12 ,  22 ,  32  of each pair is stationary, and the second contact  14 ,  24 ,  34  is a moving contact that is mounted to move relative to the first contact. 
     In particular, the first switch  10  can be of the gas type; it can also, if the rated current is very high, itself be switchgear comprising two switches put in parallel with each other. Preferably, however, as shown in  FIGS. 2 , the first switch  10  is an air-insulated switch having a stationary first contact  12  that is tubular about an axis AA and into which a second contact  14  that is also tubular can be inserted. 
     The second switch  20  can be a gas-insulated circuit-breaker containing a gas, e.g. the sulfur hexafluoride (SF 6 ); preferably, since the current I-I 0  passing through it is low under normal operating conditions, it is a vacuum chamber: this makes it possible to avoid using SF 6 , thereby improving ecological performance and reducing costs. 
     Finally, the third switch  30  can have a stationary contact  32  into which another moving contact  34  of the rod type can be inserted along the opening/closure axis AA. 
     Preferably, the first and second switches have a common axis; such a common axis for the electrical circuits is favorable to switching over the current from the main circuit to the secondary circuit; the contacts of both switches thus extend along the same longitudinal axis and are moved in translation parallel to said axis AA. In the preferred embodiment, the contacts of the third switch  30  also move in translation and all three axes along which the contacts  14 ,  24 , and  34  move coincide. 
     Pole operation of the disconnector circuit-breaker  1  is such that the contacts of each switch  10 ,  20 ,  30  are preferably driven by a common control coupled to the poles via a synchronization set of moving parts making it possible to guarantee that the operating sequence takes place in the proper order. 
     According to the invention, each moving contact  14 ,  24 ,  34  is actuated via an actuation and synchronization device using a rotary cam system located in a casing  5  of the circuit-breaker  1 . This solution makes it possible to determine the movement of each switch  10 ,  20 ,  30  in a common-axis construction which facilitates compactness, which is easy to design, and which is robust over time; the cam system  40  is located inside the existing circuit-breaker  1  without reducing its compactness. 
     In particular, the actuation and synchronization means comprise a cylinder  40  that is preferably circularly symmetrical about the axis AA of movement in translation of the contacts  14 ,  24 ,  34  of the circuit-breaker  1 . 
     Slots  42  are machined in the wall of the cylinder  40 , at least one slot being provided for each contact to be actuated: a first slot  42   1  serves to actuate opening and/or closing of the main first switch  10 , a second slot  42   2  serves to actuate opening and/or closing of the secondary second switch  20 , and a third slot  42   3  serves to actuate the disconnector switch  30 . The shapes of the slots  42  make it possible to synchronize the movements, and to determine the relative speeds of the movements in translation. 
     Each of the switches is actuated via an element  44  suitable for sliding in the corresponding slot  42  in the cylinder  40  and secured firmly to the contact; if the contact is remote from the cylinder  40 , the slider element  44  can be coupled at one end to a connection rod  46  which is firmly secured via its other end to the contact; for reasons of clarity, it is this embodiment that is shown in  FIG. 3A , but it should be understood that, in most cases and for reasons of compactness, the connection rod  46  is absent and the slider elements  44  are integral parts of the contact to be moved. 
     Thus, while the cylinder  40  is moving in rotation (arrow R), due to the shape of the slot  42 , the slider element  44  moves in the slot  42  and the contact is driven in translation (arrow T), e.g. via the rod  46 . 
     Preferably, the contact, the slider elements  44  and/or the connection rods  46  are located inside the actuation and synchronization rotary cylinder  40 : the shape of each of the slots  42  can thus be more precise in view of the larger diameter of the cylinder  40 , which is also more robust. 
     In order to avoid any torsion force on the contact, and in particular any interference rotation from a rod  46 , the slider element  44  itself is preferably guided in translation, or the connection rod  46  is guided longitudinally. Advantageously, the guidance is achieved by co-operation between a stud  48  that is integral with the slider element  44  and/or with the rod  46 , and a groove  50  parallel to the axis of movement in translation AA of the contact, e.g. located in the casing  5  of the circuit-breaker  1 . In particular, the slider element  44  mounted to slide in the slot  42  in the cylinder  40  can be extended outwards by a stud  48  mounted to slide in a groove  50  in the casing  5 . 
     The actuation and synchronization slots are shaped so as to control the characteristics of speed and of synchronization between the movement of each of the switches  10 ,  20 ,  30 . 
     Thus, for example, in a preferred example that is shown, the cylinder  40  is located between the first and second contacts  14 ,  24  which move in opposite directions, the disconnector  30  being moved similarly to the first switch  10 . One configuration for the slots  42  is shown in  FIG. 3B , in an “unrolled” version of the cylinder  40 . 
     The first slot  42   1  of the cylinder  40  comprises an initial end portion  42   1i  which is helical in a first direction: as soon as the cylinder  40  is actuated R, the first contact  14  of the first switch  10  is urged to move in translation for separation purposes so as to break the current as quickly as possible. The slope of the first slot  42   1  depends on the relative speed T to be obtained as a function of the rotation speed R imparted to the cylinder  40  by its control means  52 . 
     Once the contacts of the first switch  10  are open, it is no longer necessary to actuate them, and advantageously the first slot  42   1  includes a final end portion  42   1f  which is rectilinear, and normal to the axis AA. It is also possible to make provision for a slower movement in translation by changing the slope, or for a reverse movement. 
     The second slot  42   2  has an initial end portion  42   2i  which is not sloping but rather it is linear along a perimeter of the wall: during a first stage after actuation, the second switch  20  is not switched; on the contrary, it remains closed so that the current passes from the main circuit to the auxiliary circuit. By means of the shape of the initial end portion  42   2i  of the second slot, the cylinder moving in rotation does not, in a first stage, cause any movement in translation of the slider element  44  and thus of the second contact  24 . 
     Once the contacts of the first switch  10  are separated, it is necessary to open the secondary switch  20 : after the initial end portion  42   2i , the second slot  42   2  is extended by a helical middle portion  42   2m  whose slope depends on the relative speed of opening of the switch  20 . In the context shown, the winding direction of the second slot  42   2m  is the reverse of the winding direction of the initial end portion  42   1i  of the first slot, the two contacts  14 ,  24  moving in opposite directions; this is merely an example given by way of illustration. The length of the initial end portion of the second slot  42   2i  depends on the latency time before the second switch  20  is actuated; preferably the sector covered by the second initial end portion  42   2i  is smaller than the sector covered by the first initial end portion  42   1i , sufficient opening of the main switch  10  being just defined to enable the vacuum chamber  20  to be opened without a risk of an electrical arc striking. In addition, in view of the dimensions when a vacuum chamber  20  is used, it should be noted that the length of the middle portion  42   2m  of the slot is very small, the distance of separation of the contacts  22 ,  24  being small. 
     In the same way, actuation of the third contact  34  is offset relative to the movement of the second contact  24 : the third slot  42   3  has a linear initial end portion  42   3i  that is longer than the initial end portion  42   2i  of the second slot and than the middle portion  42   2m  of said second slot, de facto determined to be greater than the distance corresponding to the maximum arcing time; it is naturally possible instead to impart a “slow” movement in translation. Helical winding of the third slot  42   3f  is then provided, in the direction of winding of the first slot  42   2i  for this embodiment in which the disconnector  30  and first switch  10  operate “in the same direction” even though the reverse would be possible. In this example too, it is advantageous for the final end portion 42 2f  of the second slot to be linear and for the contacts  22 ,  24  to cease moving (at least for a certain time) once opening is achieved. 
     Through the choice of the slope of each of the windings  42   1i ,  42   2m ,  42   3f  it is possible to adjust the speed of separation of the contacts without modifying the speed of rotation of the cylinder  40 ; the control means can thus be simplified, and the cylindrical cam  40  can be moved in rotation by any suitable system  52 , e.g. by insulating links mounted on a lever, or by a system of drive chains. 
     Through the choice of the shapes for the slots  42 , it should be noted that the closure sequence is also complied with. 
     It is possible to adapt the shapes to the desired sequences, and, for example, to provide opening in two stages, or to design more than two or three portions for each of the slots  42   1 ,  42   2 ,  42   3 . In particular, and as shown in  FIG. 3B , it is possible, in order to protect it, to re-close the vacuum chamber  20  once the disconnection has been performed. To this end, the “final” end portion  42   2f  of the second slot is de facto extended by a second middle portion  42   2m′ , of direction opposite from the direction of the middle portion  42   2m , and which makes it possible to re-close the contacts  22 ,  24  of the vacuum chamber; a second final linear portion  42   2f  can also be provided. 
     In addition, the cam-driven control and synchronization can be chosen to actuate the first two switches  10 ,  20  only, if, for example, a “knife-switch” disconnector  30  is chosen. 
     In an advantageous embodiment (shown in a particular configuration in  FIG. 3A ) in order to balance the forces on a contact, two slider elements  44 ,  44 ′ are secured thereto in diametrically opposite manner, and they slide in a corresponding slot of the cylinder  40 : the cylinder then has a pair of first, of second and/or of third slots  42 ,  42 ′, each slot of the pair being identical and offset by 180° relative to the other slot in the pair. In which case, and preferably, each slider element  44 ,  44 ′ is provided with a guide stud  48 ,  48 ′ for guiding in a slot  50 ,  50 ′ opposite from the casing  5  of the circuit-breaker  1 . 
     In particular, if the contact is remote from the actuator cylinder  40 , each slider element  44 ,  44 ′ can be connected to the contact via a rod  46 ,  46 ′. Advantageously, the ends of the rods  46 ,  46 ′ that are provided with the slider elements  44 ,  44 ′ are connected together, inside the cylinder  40 , by an orthogonal bar  54  that keeps them apart and holds them in position in order to limit the forces. 
     It is understood that the embodiment with two slider elements  44 ,  44 ′ is given by way of example, and that is possible, for example, to design a plurality of elements distributed uniformly or otherwise, over the periphery of the contact. 
     Preferably, every one of the switches or each of only some of them can be provided with two slider elements. In an advantageous embodiment, only one of the switches, e.g. the vacuum chamber, is actuated via the actuator rods, which are optionally interconnected by bars. 
     By means of the actuation of the invention, it is possible to control the various opening/closure movements of the switches  10 ,  20 ,  30  independently from one another. In addition, unlike the spring, this control is not degraded over time. The cam-driven actuation  40  also makes it possible to keep the pole of the circuit-breaker  1  compact, the cylinder  40  lying within the usual circuit-breaker  1 . The circuits can thus continue to have a common axis, even though it is possible, in particular by implementing an actuator rod  46  external to the cylinder  40 , to use a disconnector circuit-breaker having intersecting axes, as presented in Application EP 0 878 817.