Patent Publication Number: US-6337449-B1

Title: Limiting circuit breaker comprising an auxiliary energy storage means

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a low-voltage limiting circuit breaker, and more particularly to a low-voltage limiting circuit breaker of high rating. 
     The document GB-A-1,564,412 describes a low-voltage limiting circuit breaker of high rating comprising 
     a case; 
     an opening mechanism comprising at least one energy storage means; 
     one or more poles each comprising: 
     a stationary contact part fixed with respect to the case; 
     a stop fixed with respect to the case; 
     a movable contact part comprising: 
     a support movable relatively to the case between a closed position and an open position; 
     at least one movable contact finger movable relatively to the support between a non-repelled position and a repelled position; 
     at least one bistable mechanism comprising a spring arranged between the support and the finger in such a way that it passes via a maximum potential energy when the finger and support are situated in a dead point position relatively to one another, that it tends to urge the finger to its repelled position when the finger is situated relatively to the support between its repelled position and the dead point position, and that it tends to urge the finger to its non-repelled posit ion when the finger is situated relatively to the support between its non-repelled position and the dead point position; 
     the stop being arranged in such a way that when the finger is positioned in its repelled position and the support moves from its closed position to its open position, the finger, once in contact with the stop, remains in contact therewith until the support passes beyond an intermediate rocking position relatively to the case, corresponding to the relative dead point position with respect to the finger, 
     the opening mechanism being kinematically linked to the support in such a way as to urge the support to its open position when the support is in its closed position. 
     The spring of the bistable device performs several functions. It is first of all designed to provide a contact pressure between the stationary contact part and the contact finger when the circuit breaker is closed which pressure is relatively independent from the state of wear and the manufacturing tolerances of the circuit breaker. This contact pressure is moreover determinant for the repulsion threshold beyond which the electromagnetic forces will drive the finger to its repelled position. When the finger has pivoted beyond the dead point, the spring also serves the purpose of confirming repulsion and/or of preventing the finger from rebounding, since it prevents the finger from returning to a non-repelled position. Before the circuit breaker can be closed again, the energy storage means of the opening mechanism has to be released, which drives the bar and, with said bar, the support of the movable contact part to the open position, and which enables the finger to pivot to the non-repelled position by cooperation with the stop. 
     In such a device, the energy storage means of the opening mechanism has to overcome the resistance of the spring of the bistable device. However this passage should preferably take place at the beginning of opening travel in order to limit the dimensions of the circuit breaker compartment where the contacts are located. The support for its part has to pivot at sufficiently high speed, when passing the intermediate rocking position, for the return force of the spring of the bistable device not to give rise to too great a movement of the finger and the stationary contact towards one another after the dead point has been passed. 
     Consequently, the spring of the opening mechanism has to simultaneously speed up the support and compress the spring of the bistable device. In energy terms, it has to simultaneously supply the spring of the bistable device with the energy necessary for the latter to reach its maximum potential energy state, and supply the support with the kinetic energy necessary for high-speed movement thereof to the open position. Let us also recall that the spring of the opening mechanism also has to achieve on its own high-speed opening of the circuit breaker in the event of tripping on a weak current surge. 
     To reconcile these requirements, a powerful opening energy storage means is generally provided. However this solution is not without drawbacks since the energy released on opening has to be dissipated in the end of opening travel stops so that the power of the spring is determinant for the cost and dimensions of the circuit breaker. Furthermore, different opening mechanisms have to be provided depending on the number of poles of the circuit breaker. Let us recall that not only single-pole, three-pole and four-pole circuit breakers are encountered, but also, for high ratings where each phase is connected to two poles in parallel or serially, six-pole or even eight-pole circuit breakers. 
     The dimensioning problem is even more complicated when identical movable contact parts of the identical fingers and bistable devices, using supports, are designed to equip circuit breakers whose opening mechanisms are of different kinds. It is in fact desirable to be able to equip a range of circuit breakers indifferently with a first type of mechanism in which the energy storage means of the opening mechanism also releases the energy required for closing of the circuit breaker, and with a second type of mechanism, called O-C-O (for open, closed, open) in which a closing energy storage means is loaded independently from the position of the contacts and performs loading of the opening energy storage means simultaneously when closing takes place. However the two types of mechanism have different opening kinematics. We thus generally consider that, for a given opening energy, i.e. for a given opening spring, the O-C-O mechanism operates at lower speed at the beginning of opening travel and at higher speed at the end of opening travel. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to overcome the shortcomings of the prior art and in particular to enable movable contact parts with identical bistable mechanisms to be used for limiting circuit breakers whose opening mechanisms have variable characteristics in particular at the beginning of opening travel. Its object is also to enable the opening mechanism of a limiting circuit breaker to be dimensioned regardless of the number of poles. Another object of the invention is to make speeding-up of the support of a movable contact part at the beginning of opening travel relatively independent from the type of opening mechanism implemented. Another object of the invention is to limit the energy to be dissipated at the end of opening travel, without notably increasing either the opening travel or the dimensions of the apparatus. Another object is to reduce the energy required on opening to a minimum. 
     According to the invention, these objects are achieved by means of a circuit breaker of the above-mentioned type, wherein each pole further comprises an auxiliary mechanism comprising one or more energy storage means urging the support to its open position over all or part of the travel of the support between its closed position and the intermediate rocking position, but no longer urging the support to its open position beyond the intermediate rocking position. The speeding-up at the beginning of opening travel can thus be adjusted by choosing the power of the second energy storage means judiciously. 
     Preferably the energy storage means of the auxiliary mechanism do not act on the support when the latter is located between its intermediate rocking position and its open position. Beyond the rocking position, the support does not require much energy to reach its open position, so that the energy provided by the second energy storage means is no longer necessary. 
     Alternatively, an energy storage means can be provided supplying energy to the support over a part of its travel at least between the closed position and the intermediate rocking position and storing energy over at least a part of the travel of the support between the intermediate position and the open position. This energy storage means may for example comprise a spring whose rest position corresponds to the relative rocking position, acting in compression before this position and in traction beyond it. This enables the energy remaining to be dissipated in the end-of-travel stops of the opening mechanism at the end of opening travel to be limited even further. 
     Preferably, the energy storage means of the auxiliary mechanism of each pole are such that when movement of the movable support of the pole involved takes place, they release an energy greater than or equal to that necessary to move the bistable mechanism(s) of the pole involved to their maximum potential energy. This arrangement is particularly advantageous for a multipole circuit breaker comprising an operating mechanism common to all the poles. It is then in fact easier to dimension the opening spring independently from the number of poles, while limiting the power of said spring. 
     According to one embodiment, the circuit breaker comprises in addition latching means. This arrangement fosters movement from the intermediate rocking position to the open position. It therefore enables the kinetic energy required for movement from the intermediate rocking position to be limited. This consequently enables the power of the auxiliary mechanism to be limited and furthermore limits the energy to be dissipated in the end of opening travel stops. 
     According to a preferred embodiment, the energy storage means of the auxiliary mechanism each comprise a spring arranged between the case and the support. Alternatively, it would naturally be possible to make the auxiliary energy storage means act indirectly on the support, for example on an intermediate part of the kinetic transmission system linking the energy storage means of the opening mechanism to the support. However, the preferred embodiment provides the advantage of limiting the stresses on this kinematic transmission system. Advantageously the case comprises polar compartments each containing one of said poles, the spring of each energy storage means of the auxiliary mechanism of each pole being located in the corresponding polar compartment. 
     According to one embodiment, the spring is a compression spring arranged inside a cylinder closed by a piston head designed to come into contact with the support and to transmit the force of the compression spring thereto. Alternatively, other types of springs can be envisaged, for example torsion or flexion springs. 
    
    
     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 cross-sectional view of a circuit breaker according to the invention, in the closed non-repelled position; 
     FIG. 2 represents in cross-section the circuit breaker of FIG. 1, in the closed, partially repelled position, when a dead point is passed; 
     FIG. 3 represents in cross-section the circuit breaker of FIG. 1, in the closed, repelled position; 
     FIG. 4 represents in cross-section the circuit breaker of FIG. 1, in an intermediate rocking position; 
     FIG. 5 represents in cross-section the circuit breaker of FIG. 1, in the open position; and 
     FIG. 6 represents in a cross-sectional plane parallel to that of FIG. 1, a latching mechanism in a position corresponding to the closed repelled position of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIGS. 1 to  5 , a multipole low-voltage limiting circuit breaker of high rating  10  comprises a case  12  divided into a front compartment  14  and a rear compartment  16  by an intermediate partitioning wall  18 . A window  20  made in the intermediate partitioning wall enables communication between the front and rear compartments. 
     The front compartment  14  acts as housing for an operating device  22  which comprises an energy storage closing mechanism  24  and an opening mechanism  26 . This device is known as such and reference should be made to the document FR-A-2,589,626 for further details thereon. It will merely be recalled here that the opening mechanism  26  comprises a toggle device comprising two rods  28 ,  30  articulated on one another by a pivoting spindle  32 , the bottom transmission rod  30  being coupled to a crank  34  of a switching bar  36 . An opening spring  38  is secured between the crank  34  and a fixed securing pin  40 . 
     The rear compartment  16  acts as housing for the switching bar  36  and for a plurality of poles  42  arranged side by side along a pivoting axis  44  of the switching bar  36  in individual compartments separated by tight partitions appreciably parallel to the plane of FIGS. 1 to  5 . Each pole  42  comprises a stationary contact part  46  connected to a connection strip  48 , a movable contact part  50  connected to a connection strip  52  and an arc extinguishing chamber  54  equipped with metallic separators  56 . The movable contact part  50  comprises a movable support  58  mounted pivoting around a fixed geometric axis  60  with respect to the case, and a contact finger  62  pivoting around a geometric axis  64  fixed with respect to the case and eccentric with respect to the axis  60 . A connecting rod  66  couples the support  58  to the switching bar  36 . One end of the finger  62  supports a contact pad  68  designed to perform contact with a contact pad  70  supported by the stationary contact part  46 . The other end of the finger  62  forms a cam  72  with two ramps  74 ,  76  on each side of a top dead point  78 . Between the support  58  and the finger  62  there is arranged a flexible energy storage means comprising a spring  82  guided in a cage  84  and repelling therefrom a rod  86  supporting a rotating roller  88 . The roller  88  is thus permanently in contact with the cam  72 . The flexible energy storage means forms a bistable mechanism  80  with the cam  72 . 
     Between the case  12  and support  58  there is arranged an auxiliary flexible energy storage means  90 , able to be seen in its relaxed state in FIG. 5, and comprising a compression spring  92  tending to repel in the direction of the support  58  a head  94  guided in translation in a cylinder  96  fixed with respect to the case  12 . The front part of the head  94  comprises a pad  98  designed to cooperate radially with the cylinder to perform guiding and axially with a flange  100  partially closing the cylinder and forming an end-of-travel stop. 
     A latching device  102 , able to be seen in detail in FIG. 6, comprises an arm  104  pivoting around a fixed spindle  106  and flexibly urged in the clockwise direction in the figure by a torsion spring  108 . A movable stop  110  is situated at the end of the arm  104  and cooperates with a stepped surface  112  of the finger  62 . The arm has in addition a spigot  114  designed to cooperate with a cam  116  situated on the support  58 . 
     The intermediate wall  18  supports an end-of-travel stop  118  made of elastomer material. 
     Operation of the device is as follows: 
     In the closed position of FIG. 1, the contact pads  68 ,  70  are in contact with one another and perform closing of the electrical circuit between the connection strips  48 ,  52 . The spring  82  of the bistable mechanism  80  is compressed and the roller  88  cooperates with the ramp  74  so as to provide a contact pressure between the pads  68 ,  70 . In the presence of a current surge, the electromagnetic forces tend to make the finger  62  pivot around its axis in the clockwise direction in the figures, and the bistable mechanism  80  tends to oppose this pivoting. When the current intensity exceeds a limiting threshold corresponding to the calibration of the spring  82 , the finger  62  pivots and passes the dead point  78  of the bistable mechanism  80 , represented in FIG.  2 . Once this dead point has been passed, the roller  88  cooperates with the ramp  76  and contributes to repelling the finger  62  towards the end-of-travel stop  118 , to the position of FIG.  3 . The stop  118  acts as a damper and, by absorbing the excess kinetic energy, prevents the finger  62  from rebounding. The stop  110  of the latching device  102  pivots urged by its return spring  108  and remains in contact with the stepped surface  112  of the finger  62 , so that the latching mechanism  102  prevents the finger  62  from returning to the down position. 
     To be able to reclose the circuit breaker, an opening operation has to be performed previously by the operating mechanism. An opening latch, actuated by an operator or a trip device, releases the connecting rod system  28 ,  30 ,  32 . The opening spring  38 , assisted by the springs  92  of the auxiliary energy storage means  90  of each pole, moves the switching bar  36  in counterclockwise rotation and, by means of the connecting rod  66 , makes the support  58  pivot clockwise around its axis  60  from the position of FIG. 3 to the position of FIG. 4 then continues on its own to urge the bar  36  until the position of FIG. 5 is reached. 
     Between the position of FIG.  3  and that of FIG. 4, the roller  88  cooperates with the ramp  76  and applies on the finger  62  a force whose moment tends to make the finger  62  rotate clockwise around the axis  64 . The damper.  118  then acts as an end-of-travel stop so that the finger  62  remains immobile; it is therefore the roller  88  that is retracted by compressing the spring  82 . In this phase, the auxiliary energy storage means  80  of each pole repels the corresponding support  58 . The head  94  of the auxiliary energy storage means  80  reaches its end-of-travel position when the support  58  reaches the intermediate rocking position of FIG. 4, so that contact between the head of the auxiliary energy storage means and the support ceases. 
     Beyond this intermediate rocking position, the roller  88  solicits the ramp  74 . The counterclockwise movement of the finger  62  is however counteracted by the stop  110  of the latching means  102 , so that the finger  62  remains relatively immobile, with exception made for its assembly clearance. The action of the opening spring  38  and that of the spring  82  of the bistable mechanism are combined and move the support  58  clockwise to its up position of FIG.  5 . In an intermediate position between the position of FIG.  4  and that of FIG. 5, very close to the latter position, the cam  116  of the support  58  repels the spigot  114  of the arm  104  so that the latter pivots counterclockwise and releases the stop  110 . However, this releasing does not lead to any notable counterclockwise pivoting of the finger  62 , as the movement of the support  58  is then practically completed. 
     From the position of FIG. 6, closing can be triggered by action on a closing latch which releases a closing spring, making the switching bar pivot from its position of FIG. 6 to its closed position of FIG.  1 . The bar  36  drives the support  58  counterclockwise and the finger  62 , urged only by the roller  88  which follows the movement of the support  58 , is also driven. The support  58  compresses and reloads the spring  92  of the auxiliary energy storage means  90  at the end of closing travel. This accessorily enables the impact at the end of closing travel to be limited. 
     For simplification purposes, the invention has been described considering each pole to comprise a single contact finger  62 , a single bistable mechanism  80  and a single auxiliary energy storage means  90 . In practice, it may be advantageous to provide a plurality of fingers per pole, for example three or five identical fingers pivoting around a common axis  64 . Each finger must then be biased by a bistable mechanism, which may be common to several fingers or independent for each finger, so that each finger is biased by a different spring. A single support  58  is however still provided for each pole. According to the size of the support  58 , in particular its width in a direction perpendicular to the plane of the figures, it may be advantageous to provide an auxiliary energy storage means  90  comprising several springs arranged in parallel. In practice, three springs arranged in parallel and each acting on a different head enable interesting dimensional characteristics to be obtained. 
     In practice, it is advantageous to dimension the auxiliary energy storage means in such a way that when relaxation thereof takes place they together release a greater energy than that required to compress the spring of the bistable mechanism. 
     The invention is naturally not limited to the embodiment described above. Various modifications are possible within the scope of the invention. 
     In the foregoing example, the latching mechanism  102  performs two functions: it acts on the one hand as a debounce device in the sense that, in the event of a short-circuit of very high intensity generating large electrodynamic forces, it prevents the finger, which has reached the position of FIG.  3  and comes and strikes the damper  118  violently, from rebounding and closing the contact; moreover it prevents pivoting of the finger  62  on opening when the support  58  has just passed the intermediate rocking position. However, depending on the circuit breaker rating and the dimensioning of the mechanical parts, it can be envisaged to eliminate this latching mechanism. The debounce function is then performed exclusively by the bistable mechanism  80 , which may be assisted by the end-of-travel damper  118 . The movement beyond the intermediate rocking position can for its part be limited in amplitude so as to become imperceptible, if the speed of the support  58  when passing the rocking position is sufficient. 
     In the described embodiment, the stop  118  performs two functions: it acts firstly as a debounce device since it absorbs a part of the kinetic energy at the end of travel of the finger  62  to its repelled position; it moreover enables the finger  62  to be immobilized when the support  58  pivots from its closed position to its intermediate rocking position. According to an alternative embodiment, these two functions can be performed by different parts. An end of repulsion travel stop of the finger can for example be arranged on the support  58  and an independent stop be arranged on the case. This arrangement enables the support  58  and the repelled finger  62  to be raised together in a first part of the travel of the support  58  to its open position before the finger  62  encounters the case stop and is immobilized with respect to the latter. 
     The invention has been described with reference to a limiting circuit breaker whose fingers pivot around a geometric axis  64  fixed with respect to the case. It is however also applicable to a limiting circuit breaker as for example described in the document GB-A-1,564,412 whose fingers pivot around an axis fixed with respect to the support itself pivoting around an axis fixed with respect to the case and offset with respect to the latter. 
     The switching bar  36  and support  58  may form a single part, in which case the connecting rod  66  disappears and the operating mechanism connecting rod system  28 ,  30 ,  32  is directly articulated via one of its ends on the support. This configuration corresponds to the mechanism of the document GB-A-1,564,412. 
     The invention is also applicable regardless of the type of opening and closing mechanism of the circuit breaker.