Abstract:
A high voltage switch contact structure capable of interrupting high voltage, high current AC and DC circuits. The contact structure confines the arc created when contacts open to the thin area between two insulating surfaces in intimate contact. This forces the arc into the shape of a thin sheet which loses heat energy far more rapidly than an arc column having a circular cross-section. These high heat losses require a dramatic increase in the voltage required to maintain the arc, thus extinguishing it when the required voltage exceeds the available voltage. The arc extinguishing process with this invention is not dependent on the occurrence of a current zero crossing and, consequently, is capable of rapidly interrupting both AC and DC circuits. The contact structure achieves its high performance without the use of sulfur hexafluoride.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/374,495 filed Apr. 23, 2002. 

   This invention was made with Government support under Contract No. DE FG02-99ER52915 awarded by the Department of Energy. The Government has certain rights in this invention. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to contact structures of high voltage circuit breakers. More specifically, contact structures using an interposed solid nonconductor to extinguish the arc. 
   The interruption of DC high voltage, high current circuits is particularly difficult due to the lack of periodically occurring current zero crossings. Arcs exhibit a negative resistance characteristic in that the arc voltage decreases with increasing current. Consequently, switch contact arcs of more than a few amperes require little voltage to maintain, and, without an arc quenching means, will continue to quickly destroy the switch contacts. The arc is extinguished by using techniques that cause a momentary current zero or techniques that raise the voltage required to maintain the arc above the voltage available or by breaking the arc into a series of short arcs. 
   Conventional devices use different methods for accomplishing one or more of these basic arc quenching techniques. However, most of the high voltage high current switches now in use require the use of sulfur hexafluoride, a potent greenhouse gas considered nearly 25,000 times more damaging to the environment than carbon dioxide. 
   Contact structures can be found in Harton et al., U.S. Pat. No. 3,053,945, and Fisher, U.S. Pat. No. 3,026,396. However, neither of those devices is intended to open active high current circuits, only to reliably isolate circuits after an additional breaker has interrupted the main load circuit. 
   SUMMARY OF THE INVENTION 
   The present invention uses a novel technique to dramatically increase the voltage required to maintain a contact arc thus significantly raising the maximum voltage interrupting capability of any switch using the contact structure without requiring the use of sulfur hexafluoride. Holding the insulating surfaces in intimate contact significantly increases the voltage interrupting capability. The arc&#39;s required maintenance voltage can be increased by lengthening the arc path, increasing the arc&#39;s heat losses, and interposing a nonconductor in the arc path. 
   It is the object of the present invention to provide a simple switch contact structure that is capable of rapidly interrupting high voltage, high current, DC or AC circuits. 
   The strategy of increasing the rate of heat transfer between the contact arc and its surrounding environment, thus increasing the voltage required to sustain the contact arc, is of particular relevance to this invention. Although the heat transfer is difficult to accurately predict, the increase in arc voltage due to the increase in heat losses is easy to understand. An arc loses heat energy by radiation, conduction, and convection, and any arc in thermal equilibrium absorbs electrical energy at a rate equal to these losses. 
   At any given current, if measures are taken that increase the arc&#39;s losses, there must be a corresponding increase in arc voltage to supply the additional energy or the arc will continually cool and extinguish. Consequently, the key to quenching an arc is to increase its losses until the voltage required to maintain it is greater than the available voltage. 
   The present invention dramatically increases the voltage required to maintain a switch contact arc by forcing the arc to assume the shape of a very thin sheet. A thin sheet has a high ratio of surface area to cross-sectional area, thus maximizing the arc&#39;s heat losses and, consequently, the arc&#39;s required maintenance voltage. 
   These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view of a contact structure using plane surfaces. 
       FIG. 2  is a perspective view of the contact structure of  FIG. 1  in the closed position. 
       FIG. 3  is a perspective view of the contact structure of  FIG. 1  just as the contacts begin to open. 
       FIG. 4  is a perspective view of the contact structure of  FIG. 1  with the contacts completely open. 
       FIG. 5  is a perspective view of an armature for the contact structure of FIG.  1 . 
       FIG. 6  is a perspective view of the contact structure using cylindrical surfaces. 
       FIG. 7  is a cross-sectional view of a preferred embodiment of the contact structure of FIG.  6 . 
       FIG. 8  is an end view of the embodiment of FIG.  7 . 
       FIG. 9  is a detailed and enlarged view of the armature used in the embodiment of FIG.  7 . 
       FIG. 10  is a part cross-sectional, part schematic view of a preferred embodiment of a contact structure suitable for high voltages. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A basic form of the invention is shown in  FIGS. 1-4 . A preferred embodiment includes at least a pair of electrodes  1  and  2  in a pair of insulating blocks  3  and  4  forming a pair of sliding surface assemblies  101 ,  103 , preferably in intimate contact  105  with each other. Preferably, blocks  3 ,  4  and surfaces  107 ,  109 , respectively, have holes  111 ,  117  which receive electrodes  1 ,  2 . The ends  113 ,  115  of electrodes  1  and  2  form conductive metallic contacts within the nonconductive insulating areas of the contact-surrounding nonconducting surface areas  119 ,  121  of insulating blocks  3  and  4 . When the metallic contacts  115 ,  113 , are mutually aligned and contacting each other 123 as depicted in  FIG. 2 , the switch is closed. Conversely, when the metallic contacts are moved out of alignment and are no longer touching each other, the switch is open, as shown in FIG.  4 . As these contacts just begin to break connection, as shown in  FIG. 3 , any arc created is forced to assume the shape of a thin sheet between the two insulating blocks  3  and  4 , which are held in intimate contact. 
   The losses of such an arc are usually extremely high due to the large surface area of a thin sheet relative to its cross-sectional area. Consequently, a much higher voltage is required to maintain this arc compared to one of the same current that is free to assume the normally circular cross-section. At low currents, the arc may form a number of thin filamentary arcs rather than a thin sheet but will still have greater losses than a single arc column conducting the same current. 
   It is important that both the conductive areas  115 ,  113  and nonconductive areas  119 ,  121 , of the sliding surfaces  107 ,  109 , are in intimate contact. The insulating surfaces fit together tightly so as to minimize the thickness of the sheet arc, thus maximizing its heat losses. The metallic contact areas are also in intimate contact with each other when closed so as to minimize the contact resistance. This is essential when using the contacts to conduct and interrupt high currents. Springs or interference fits or the like may be used to ensure intimate contact between both insulating and conductive surfaces. 
   The insulating portions  119 ,  121  of the sliding surfaces  107 ,  109  need not totally surround the metallic contact areas, as is shown in  FIGS. 1-4 . The insulating portions  119 ,  121  may be limited only to areas near the points where electrical connection is finally broken. The surface contours may be of any form that allows opposing surfaces to slide against each other while remaining in intimate contact over a substantial area. This includes, but is not limited to, plane, triangular, quadrilateral, polygonal, cylindrical, and spherical surfaces, or any surface of revolution. 
   The addition of a nonconductive armature  6 , shown in  FIG. 5 , between the insulating blocks,  3  and  4 , allow these blocks to remain stationary. The contact structure is opened and closed by sliding the armature relative to the blocks  3 ,  4  shown in  FIGS. 1-4 . The contact structure is closed when the conductive section  5 , which extends through the insulating armature block  6 , is in contact with the electrodes  1  and  2  and is open when the conductive section is not in contact with the electrodes. 
   A cylindrical surface is a particularly useful form of the present invention.  FIG. 6  shows a cylindrical insulating rod or armature  9  containing a short conductive segment  11  inserted into a tight fitting hole in a stationary insulating block  8 . The conductive segment  11  makes an electrical connection between partially cylindrical contact surfaces of a pair of radially opposing electrodes  7  or resilient contact structures held against the armature. The electrical connection is opened by moving the armature  9  until the electrodes  7  are resting on the armature&#39;s insulating segments  10  some distance away from the conductive segment  11 . As the connections open, the arcs created assume the form of thin curved sheets on opposite sides of the armature, between its cylindrical surface and the inner surface of the hole in the insulating block. This arrangement breaks two connections, one at each electrode  7  contact point with the armature&#39;s conductive segment  11 , forming two arcs in series, thus doubling the voltage interrupting capability compared to breaking a single connection. 
     FIGS. 7-9  show further details of the contact structure of FIG.  6 . The armature details are shown in  FIG. 9. A  split insulated contact block  12  surrounds the armature  15 . The contact ends  22  of the electrodes  24  are electrically connected together by the armature&#39;s conductive ring  26  when the contacts are in the closed position as shown in FIG.  7  and FIG.  9 . Suitable washers such as, but not limited to, spring washers  19  hold the contacts  22  tightly against the conductive ring  26 . 
   The contact assembly housing  13  holds the split contact blocks  12  together and serves to mount the contact assembly to a switch actuator housing  21  with connectors, for example, screws  20 . A pair of insulators  14  hold the electrodes  10  centered as they pass through holes in the housing  13 . The armature  15  is attached to the end of the actuating rod  18  using the armature&#39;s cap screw or bolt  29 . 
   As shown in  FIG. 9 , the armature  15  consists of an insulating segment  25 , the conducting ring segment  26 , both mounted on an insulating tube  27 , and tightly sandwiched between a pair of insulating end caps  28  using the bolt  29 . The contact assembly is opened by the actuating rod  18 , pushing the armature&#39;s conducting ring  26  deep into the insulating seal ring  16 . 
   As the insulating ring segment  26  breaks the electrical connection between the electrode contacts  22 , any arc created is confined by the inner surface of the seal ring  16  and the armature&#39;s insulating ring  25 . Either a precise fit or a slight interference fit, depending on the choice of insulating materials, between the insulating ring  25  and the seal ring  16  leaves virtually no space for the arc, forcing it to assume the shape of a thin curved sheet on opposite sides of the insulating ring  25 . A slight interference fit works well when a plastic is used for either the insulating ring  25  or the seal ring  16  (or both). A precision fit is needed when both are hard, rigid insulating materials such as, but not limited to, ceramic. The insulating seal ring  16  is held in place by plate  17  and screws  19 . The insulating seal ring  16  is thus easily replaced by removing the screws  19  and the plate  17 . The armature components are also easily replaced. 
   Another configuration of the present invention is shown in  FIG. 10. A  rod armature  42  electrically connects a pair of resilient contact structures  30  and  33 . Suitable resilient contact structures may consist of a cylindrical array of highly conductive metallic fingers making electrical contact with the cylindrical surface of another good electrical conductor. A puffer type interrupter showing a typical finger structure is shown, for example, in Meyer et al., U.S. Pat. No. 5,654,532. 
   The connection is made by a pair of conductive segments  37  and  38  of the armature  42 , connected to each other with conductive rod  39  under the surface of an insulating segment  40  placed between the two conductive segments  37  and  38 . Tight fitting insulating blocks  32  and  35  are immediately adjacent to the resilient contact structures  30  and  33 . Conductors  31  and  34  are connected to the contact structures  30  and  33 . The electrical connection between the resilient contact structures  30  and  33  is opened by moving the armature  42  until the resilient contacts  30  and  33  are resting on insulated segments  36  and  40  of the armature. The conductive segments  37  and  38  are some distance into the insulating blocks  32  and  35 , confining the arcs between the insulating surfaces as previously described. Precision fits in lieu of tight fit may be used with rigid insulating materials as described earlier. 
   The invention comprises, but is not limited to, the following features:
         1. A switch contact structure comprised of two sliding surface assemblies in intimate contact, where at least one part of each sliding surface assembly is an electrical conductor and the remaining part or parts are an electrical insulator, forming a closed switch when the electrical parts on opposing surfaces are in mutual contact, which, when sliding apart to open, confine any arc created to the area between the surfaces of two opposing insulating parts in intimate contact, thus forcing this arc to assume the form of a very thin sheet or a multiplicity of very thin filaments.       

   2. The switch contact structure where the opposing surfaces are planar, triangular, quadrilateral, polygonal, cylindrical, spherical in shape or any figure of revolution or any combination of these shapes capable of sliding against each other while maintaining intimate contact over a significant area. 
   3. The switch contact structure where the insulating surfaces and the conductive surfaces are held in mutual intimate contact using one or more springs, elastic components, or by interference or precision fits or by any combination of springs, elastic components, and precision or interference fits. 
   While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is defined in the following claims.