Abstract:
A protective device for an electrical installation, having at least two electrodes between which an elastic arc can electric arc can form, and a device for interrupting ( 6 ) the arc, formed by an assembly of divider plates ( 7 ) and extending between an upstream end ( 6 A) and a downstream end ( 6 B), with an entry region (E) for the arc at the upstream end ( 6 A) thereof. The interrupter device ( 6 ) has an insulation means ( 10 ), formed by caps ( 13 ) that form a partial insulating barrier between the electrodes and the upstream end ( 6 A), the caps ( 13 ) are provided with teeth ( 16 ) housed between two adjacent plates ( 7 ). The invention further relates to overload and short-circuit protection devices.

Description:
PRIORITY CLAIM 
       [0001]    This patent application is a U.S. National Phase of International Application No. PCT/FR2005/001888, filed Jul. 21, 2005, which claims priority to French Patent Application No. 0408095, filed Jul. 21, 2004, the disclosures of which are incorporated herein by reference in their entirety. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to devices for protecting electrical equipment or installations against overvoltages, notably transient overvoltages due to lightning, overloads or short circuits. 
         [0003]    This invention more particularly relates to a device for protecting an electrical installation against overvoltages, overloads or short circuits, including at least two main electrodes between which an electric arc may form, and a device for breaking the electric arc formed from an assembly of splitting plates and extending along the direction of propagation of the electric arc, between an upstream end and a downstream end, and with an entry area for the arc at its upstream end, at which the electric arc penetrates inside the breaker device, the breaker device including at its upstream end, insulating means against the return of the electric arc, structurally designed and arranged so as to allow the electric arc to enter the breaker device while forming an obstacle against the exit of the electric arc, preventing the electric arc from escaping from the inside of the breaker device once the electric arc is inside the breaker device. 
       BACKGROUND OF THE INVENTION 
       [0004]    There are different categories of devices that may interrupt a current, particularly high intensity current at a conventional frequency (50 Hz). A distinction is made between devices, such as circuit breakers designed to protect an electrical installation against overloads or short circuits, and devices used to protect an electrical installation against overvoltages, such as lightning arresters or surge suppressors. 
         [0005]    Such protection devices are usually provided with a current breaking device (or a breaking chamber). In the case of circuit breakers, this breaker device is intended to provide breaking of short circuit currents. In spark gap lightning arresters, the breaker device is intended to provide breaking of follow currents. 
         [0006]    The breaker device is generally formed by a plurality of metal splitting plates mounted in parallel so as to break the electric arc down into small elementary arcs so as to increase the arc voltage and to provide breaking of the current. Known breaker devices intrinsically have a predetermined breaking capacity corresponding to the maximum value of current that they are able to extinguish. 
         [0007]    Thus, it is found that when the current intensity values are greater than the recommended values for a given breaker device, the electric arc may escape from the breaker device after having penetrated therein and then form again outside the breaker device, for example following the shortest path between one of the main electrodes and the end of the splitting plates. 
         [0008]    Such a phenomenon is particularly detrimental to the protection device insofar that its effect is to make the attempt to cut off the current fail. Further, this phenomenon may occur several times within a fairly short period. The electric arc may thus enter the breaker device and then exit from the breaker device and enter the breaker device once again, until the unit is destroyed without having been able to cut off the follow or short circuit current. 
         [0009]    It is known that when higher breaking capacities are required, these drawbacks may be overcome by increasing the number of splitting plates, putting several protection devices in series or in parallel, or using additional mechanisms for physically breaking the electric arc. Nevertheless, all these solutions have a number of drawbacks particularly related to their application, which is often difficult, and due to the fact that they lead to a significant increase in the size of the protection devices. 
       SUMMARY OF THE INVENTION 
       [0010]    Consequently, the features provided by the present invention provide a solution to the various drawbacks listed above and propose a new device for protecting an electrical installation against overvoltages, overloads or short circuits, with improved current breaking capacity. 
         [0011]    Another feature of the present invention proposes a new device for protecting an electrical installation against overvoltages, overloads or short circuits, with limited bulkiness. 
         [0012]    Another feature of the present invention proposes a new device for protecting an electrical installation against overvoltages, overloads or short circuits, with a structure particularly well adapted to the case of strong intensity currents. 
         [0013]    Another feature of the present invention proposes a new device for protecting an electrical installation against overvoltages, overloads or short circuits that is particularly easy to manufacture. 
         [0014]    The features provided by the present invention are achieved by a device for protecting an electrical installation against overvoltages, overloads or short circuits including at least two main electrodes between which an electric arc is able to form, and an electric arc breaker device formed by an assembly of splitting plates and extending, considering the direction of propagation of the electric arc, between an upstream end and a downstream end, and with an entry area for the arc at its upstream end, at which the electric arc penetrates inside the breaker device, the breaker device including at its upstream end, insulating means against the return of the electric arc, structurally designed and arranged so as to allow the electric arc to enter the breaker device while forming an obstacle against the exit of the electric arc, so as to prevent the electric arc from escaping from the inside of the breaker device once the electric arc is inside the breaker device, wherein the insulating means consist of caps arranged so as to form a partial insulating barrier between the electrodes and the upstream end, the caps having teeth positioned at a distance from each other and adapted to fit between two consecutive splitting plates. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Other features and advantages of the present invention will become more apparent after reading the following description made with reference to the figures, given as purely illustrative and non-limiting, wherein: 
           [0016]      FIG. 1  is a sectional view of one exemplary embodiment of an overvoltage protection device according to the present invention; 
           [0017]      FIG. 2  is a side view of a first exemplary embodiment of a breaker device according to the present invention; 
           [0018]      FIG. 3  is a front view of the breaker device of  FIG. 2 ; 
           [0019]      FIG. 4  is a top view of the breaker device of  FIG. 2 ; 
           [0020]      FIG. 5  is a front view of another exemplary embodiment of a breaker device for the protection device according to the present invention; 
           [0021]      FIG. 6  is a side view of another exemplary embodiment of a breaker device for the protection device according to the present invention; and 
           [0022]      FIG. 7  is a side view of another exemplary embodiment of a breaker device for the protection device according to the present invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0023]    The device according to the present invention for protecting an electrical installation against overvoltages, overloads or short circuits, is designed to protect an electrical piece of equipment or installation. The expression “electrical installation” refers to any type of apparatus or network subject to voltage perturbations, notably transient overvoltages due to lightning or even overloads, notably overload or short circuit currents. Such devices may consist of spark gap lightning arresters or surge suppressors provided with a follow current breaking device or circuit breakers fitted with a short circuit current breaking device. 
         [0024]    In this description, we are more particularly interested in a spark gap type lightning arrester type device for protection against overvoltages, but the invention obviously applies to circuit breakers. 
         [0025]      FIG. 1  illustrates a protection device  1  according to the present invention, advantageously formed by a spark gap lightning arrester. The protection device  1  comprises at least a first and second electrode  2 ,  3  that may form the two main electrodes of the spark gap lightning arrester, within an insulating casing  20 , as illustrated in  FIG. 1 . These two electrodes  2 ,  3  are held at a distance from each other and separated by a lamella  4  in a dielectric material which may improve and better control striking of an electric arc between the electrodes  2 ,  3 . This so-called upstream end part of the device is the area for striking the electric arc  5 . 
         [0026]    In the case of a circuit breaker, the electrodes are formed by two contacts, for example, a fixed contact and a mobile contact, held in physical contact with each other so as to provide the electrical connection. In this case, the electric arc is formed between both contacts when the mobile contact separates from the fixed contact to provide electrical disconnection. 
         [0027]    According to the present invention and as illustrated in  FIG. 1 , the protection device  1  includes a device  6  for breaking the electric arc  5 . 
         [0028]    In a particularly advantageous way, the breaker device  6  is formed by an assembly of splitting plates  7  made of electrically conducting material, for example, in metal, positioned in parallel and at a distance from each other. The splitting plates  7  are advantageously kept at a distance from each other by supporting strips  8  made of an electrically insulating material. 
         [0029]    According to the present invention, the breaker device  6  extends, considering the direction of propagation F of the electric arc  5 , between an upstream end  6 A and a downstream end  6 B. As shown in  FIGS. 3-5 , the breaker device  6  has at its upstream end  6 A, an entry area for the electric arc E at which the electric arc  5  penetrates inside the breaker device  6 . Thus, before penetrating into the breaker device  6 , the electric arc  5  propagates along the direction of propagation F within a divergent space  9  extending between the striking area of the electric arc and the breaker device  6 . The divergent space  9  is advantageously delimited by electrodes  2 ,  3 , and preferably filled with air. 
         [0030]    According to one essential feature of the present invention, the breaker device  6  includes at its upstream end  6 A, insulating means  10  against the return of the electric arc  5 . 
         [0031]    These insulating means  10  are structurally designed and arranged so as to allow the electric arc  5  to enter the breaker device  6  while forming an obstacle against the exit of the electric arc  5 , in order to prevent the electric arc  5  from escaping from the breaker device  6  once the electric arc is inside the breaker device. 
         [0032]    The insulating means  6  are adapted to prevent the electric arc  5  from returning backwards along a direction opposite to its normal direction of propagation F, in such a way that once the electric arc  5  has been broken down into a plurality of elementary arcs within the breaker device  6 , the electric arc may no longer form again outside the breaker device  6 , notably in the divergent space  9 . 
         [0033]    Therefore, the non-return insulating means  10  operate as a ground and are built and positioned relative to the splitting plates  7  on the one hand and to the electrodes  2 ,  3 , on the other hand, so as to significantly reduce the likelihood that the electric arc  5  escapes from the breaker device  6 . Therefore, the design of the protection device  1  according to the present invention may significantly improve its short circuit current breaking capacity. 
         [0034]    The insulating means  10  according to the present invention must provide an answer to a new problem which is that of letting the electric arc  5  penetrate into the inside of the protection device  6  while limiting the likelihood that the electric arc escapes and forms again outside the breaker device  6 . 
         [0035]    Advantageously, the insulating means  10  are arranged so as to form a partial insulating barrier between the electrodes  2 ,  3  and the upstream end  6 A of the breaker device  6 . The expression “partial insulating barrier” refers not only to physical barriers made of electrically insulating material, but also to not necessarily physical barriers which may be electrically insulating barriers, capable of preventing the formation of an electric arc between the electrodes  2 ,  3  and the upstream end  6 A of the breaker device  6 . 
         [0036]    Advantageously, the splitting plates  7  extend along the direction of propagation F of the electric arc  5 , between a front end  7 A and a distal end  7 B. The front end  7 A and the distal end  7 B are located at substantially the same level as the upstream end  6 A and the downstream end  6 B of the breaker device  6 . In a particularly advantageous way, the splitting plates  7  are each provided with a notch  11 , at least partially separating each splitting plate  7  into two separate branches  7 C,  7 D. Thus, when the splitting plates  7  are assembled so as to form the breaker device  6 , the notches  11  form a groove  12 , the shape of which, for example a V-shape, is specifically designed to attract the electric arc  5  towards the inside of the breaker device  6 . In this way, the entry area E for the electric arc  5  substantially coincides with the groove  12 . 
         [0037]    According to a first exemplary embodiment of the present invention, the insulating means  10  are arranged so as to at least partially physically close off the upstream end  6 A of the breaker device  6 , thus forming a physical insulating barrier between the electrodes  2 ,  3  and the upstream end  6 A of the breaker device  6 . 
         [0038]    Even more preferably, the insulating means  10  are arranged so as to entirely cover the upstream end  6 A of the breaker device located around the entry area E for the electric arc  5 , for example, on either side of it. The insulating means  10  may be positioned on either side of the groove  12 , as illustrated in  FIG. 3 , so as to cover the front end  7 A of the branches  7 C,  7 D of the splitting plates  7 . 
         [0039]    According to a another exemplary embodiment of the present invention, the insulating means  10  may be formed from one or several rigid strips (not shown), for example, positioned on either side of the groove  12  so as to cover the front end  7 A of the splitting plates  7 . The rigid strips then preferably extend along a plane approximately perpendicular to the direction of propagation F of the electric arc  5 , and coplanar with the plane formed by the front ends  7 A of the splitting plates  7 . 
         [0040]    The rigid strips may advantageously be perforated with a plurality of orifices so as to provide air flow between the divergent space  9  and the breaker device  6 . 
         [0041]    Preferably, the rigid strips, through one of their faces, come into contact with the front ends  7 A of the splitting plates  7 , and preferably bear on them in a sealed manner. 
         [0042]    Even more preferably, the insulating means  10  are formed by caps  13  arranged so as to form a partial insulating barrier between the electrodes  2 ,  3  and the upstream end  6 A positioned on either side of the groove  12  and designed in such a way that, in their functional position, they will also cover the front end  7 A of one or several splitting plates  7 . 
         [0043]    Advantageously, the caps  13  are arranged so as to entirely cover the upstream end  6 A of the breaker device  6  located around the entry area E for the arc. 
         [0044]    As illustrated in  FIGS. 3 and 4 , the caps  13  are preferably formed by a substantially elongated strip  14 , designed to cover the front end  7 A of several splitting plates  7 , and from which a lip  15  is arranged and oriented such that when the cap  13  is in its functional position, the lip  15  will naturally cover the upper edge  12 A of the groove  12 . 
         [0045]    Preferably, the edge  15  of the cap  13  is adapted to substantially penetrate inside the groove  12  when the cap  13  is in its functional position ( FIG. 3 ). 
         [0046]    Even more preferably, and as illustrated in  FIG. 3 , the cap  13  has a substantially U-shaped section so as to cover the end of the splitting plates  7 , notably of branches  7 C,  7 D, approximately conforming to the shape of the branches  7 C,  7 D. 
         [0047]    According to one exemplary embodiment illustrated in  FIG. 2 , the caps  15  include teeth  16  positioned at a distance from each other, preferably at regular intervals, and adapted to fit in between two consecutive splitting plates  7  when the cap  13  is in its functional position. With the teeth  16 , it is possible to prevent the splitting plates  7  at their front ends  7 A from deforming and notably moving closer to each other, while improving the insulation properties of the caps  13 . 
         [0048]    According to one exemplary embodiment of the present invention (not shown in the figures), the insulating means  10  are advantageously made from the same material as the casing  20  of the protection device  1 , the casing  20  including the main electrodes  2 ,  3  on the one hand and the breaker device  6  on the other hand. 
         [0049]    In this case, the shape of the inner surface of the casing  20  is adapted, for example, at the time when the casing  20  is moulded, to exhibit structures in relief capable of forming the insulating means  10 . 
         [0050]    The insulating means  10  and/or the casing  20  may advantageously be made from a rigid material able to withstand the arc temperature, for example, injected plastic with good temperature resistance, and even more preferably an epoxy resin or ceramic. 
         [0051]    According to another exemplary embodiment of the present invention illustrated in  FIG. 5 , the insulating means  10  are advantageously formed by one or several preferably flexible and adhesive strips  17 . As illustrated in  FIG. 5 , the strips  17  advantageously cover the front ends  7 A of the branches  7 C,  7 D of the splitting plates  7 , thus forming caps, similar to the exemplary embodiments described above. 
         [0052]    Advantageously, the strips  17  are made in a high-temperature-resistant insulating material, and notably resistant to the temperature of the arc. Preferably, the strips  17  are made from fiberglass, coated on one of its faces with a thermosetting type silicone adhesive so as to provide excellent thermal and mechanical strength. 
         [0053]    In a particularly advantageous way, the sticky portion of the strips  17  will conform to the upstream end  6 A of the breaker device  6 , so as to fix the ribbons  17  onto the latter end. 
         [0054]    According to another exemplary embodiment of the present invention illustrated in  FIGS. 6 and 7 , the insulating means  10  do not form a physical barrier between the electrodes  2 ,  3  and the upstream end  6 A of the breaker device  6 , but the insulating means  10  form an immaterial electrically insulating barrier instead. 
         [0055]    According to a first exemplary embodiment illustrated in  FIG. 6 , the insulating means  10  are advantageously formed by an electrically insulating coating  18  deposited over substantially the entire surface of the terminal portion  7 E, located towards the front end  7 A of one or several splitting plates  7 . The coating  18  is advantageously positioned so as to cover the terminal portion  7 E. The coating  18  may notably increase the distance to be travelled by the electric arc to form again outside the breaker device  6 . Therefore, the presence of the coating  18  may reduce the likelihood that the electric arc may form again between both main electrodes  2 ,  3  outside the breaker device  6 . 
         [0056]    According to another exemplary embodiment of the present invention illustrated in  FIG. 7 , the insulating means  10  are formed by insulating plates  19  positioned on either side of the groove  12  and inserted between two successive splitting plates  17  so as to extend towards the outside of the breaker device  6 , beyond the front end  7 A of the splitting plates  7 . The insulating plates  19  may also prevent the electric arc from escaping outside the breaker device  6  by increasing the distance that the electric arc needs to travel to form again outside the breaker device  6 , between the main electrodes  2 ,  3 . 
         [0057]    According to another more preferred exemplary embodiment of the present invention, the breaker device  6  includes, at its downstream end  6 B, an insulating screen  30  positioned so as to at least partially cover the downstream end  6 B of the breaker device  6  so as to prevent the electric arc  5  from escaping from the breaker device  6  after the electric arc has passed through the breaker device, for example once ( FIG. 1 ). 
         [0058]    In this preferred exemplary embodiment, the insulating means  10  have a crucial role in that, after passing through the breaker device  6  along the direction of propagation F, the electric arc  5  “rebounds” on the insulating screen  30  and then continues in a direction substantially opposite the direction of propagation F, towards the upstream end  6 A of the breaker device  6 . In such a configuration, the applicant has observed that the electric arc  5  preferably returns along the branches  7 C,  7 D of the splitting plates  7  and much more rarely to the central portion  12 B of the groove  12 . 
         [0059]    Consequently, in this exemplary embodiment, the insulating barrier formed by the insulating means  10  may notably reduce the likelihood that the electric arc escapes at the upstream end  6 A of the breaker device  6 , thereby preventing the electric arc  5  from forming again between the main electrodes  2 ,  3 . 
         [0060]    Operation of the protection device  1  according to the invention will now be described, with reference to  FIGS. 1-7 . 
         [0061]    During operation, when an overvoltage exceeding a predetermined threshold value occurs, notably as a result of a lightning strike, an electric arc  5  is established between one of the two main electrodes  2 ,  3  allowing the lightning current to flow to ground. This electric arc  5  then moves up to the breaker device  6  into which the electric arc penetrates at the entry area E, located in approximately the same plane as the groove  12 . The electric arc  5  is then broken down into a plurality of elementary arcs so as to increase the arc voltage of the current above the mains voltage and limit the intensity of the current drained by the protection device. The elementary electric arcs move towards the downstream end  6 B of the breaker device  6  until they reach the insulating screen  30 . A “rebound” phenomenon then occurs and the elementary electric arcs leave in the direction opposite to the initial direction of propagation F of the electric arc  5 , towards the downstream end  6 A of the breaker device  6 . According to the most likely operating mode, the elementary electric arcs move towards the branches  7 C,  7 D and more specifically along these branches as far as their front end  7 A. 
         [0062]    They are then trapped by the insulating means  10  which prevent the electric arc  5  from forming again outside the breaker device  6 . 
         [0063]    Therefore, the protection device  1  according to the present invention has a better short circuit current or follow current breaking capacity than the current breaking capacity for devices according to the prior art, while limiting the likelihood that the electric arc, once inside the breaker device and broken down into a plurality of elementary arcs, escapes from the breaker device to form again outside the breaker device between the main electrodes. 
         [0064]    By the presence of the insulating means  10 , the protection device according to the present invention has a current-breaking power multiplied by at least two as compared with devices from the prior art. 
         [0065]    The invention finds one aspect of its industrial application in the design, the manufacturing and the use of protection devices against overvoltages, overloads, or short circuits.