Patent Publication Number: US-2007119819-A1

Title: Axial current interrupter

Description:
FIELD OF THE INVENTION  
      Embodiments of the present invention are generally related to circuit arc quenching, or current interruption, devices, and, more particularly, to an axial circuit arc quenching, or current interrupter, including an arc constrictive zone.  
     BACKGROUND OF THE INVENTION  
      A variety of devices are known and have been developed for interrupting current between a source and a load. Circuit breakers are one type of device designed to trip upon occurrence of heating or over-current conditions. Other circuit interrupters trip either automatically or by implementation of a tripping algorithm, such as to limit current to desired levels, limit power through the device in the event of phase loss or a ground fault condition. In general, such devices include one or more moveable contacts, which separate from mating contacts to interrupt a current carrying path. The devices may be single phase or include multiple phase sections for interrupting current through parallel current paths, such as in three phase applications.  
      Performance of a circuit interrupter is typically dictated by a peak let through current, which is in turn controlled by a rate of arc voltage development across the contacts as the contacts are moved away from one another during a circuit interruption event. Accordingly, improvement of circuit interrupter performance has focused on more rapidly increasing arc voltage development to limit a peak let though current. A wide range of techniques has been employed for improving interruption times to limit the let-through energy, such as by providing faster contact separation. The voltage investment in an arc may be made to rise very quickly to cause a corresponding rapid interruption of the current. Another technique used to limit the let-through energy is to provide arc dissipating structures, such as conductive plates arranged with air gaps between each plate, commonly known as an arc chute. Entry of the arc into such structures may assist in extinguishing the arc and thereby limit the let-through energy during circuit interruption.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a partial cross sectional schematic view of an example embodiment of a circuit interrupter in a current conducting mode.  
       FIG. 2  shows a partial cross sectional schematic view of the example embodiment of the circuit interrupter of  FIG. 1  at a beginning of a current interruption mode.  
       FIG. 3  shows a partial cross sectional schematic view of the example embodiment of the circuit interrupter of  FIG. 1  at an end of a current interruption mode.  
       FIG. 3A  shows a partial cross sectional schematic view of another example embodiment of the circuit interrupter of  FIG. 1 .  
       FIG. 3B  shows a partial cross sectional schematic view of another example embodiment of the circuit interrupter of  FIG. 1 .  
       FIG. 4  shows another example embodiment of a circuit interrupter.  
       FIG. 5  shows another example embodiment of a circuit interrupter.  
       FIG. 6  shows another example embodiment of a circuit interrupter including an enclosure.  
       FIG. 7  shows an example circuit breaker including an example embodiment of a circuit interrupter.  
       FIG. 7A  shows an example three phase circuit breaker including an example embodiment of a circuit interrupter.  
       FIG. 8  is a graph showing circuit interruption performance for the example circuit interrupter of  FIG. 1 .  
       FIG. 9  is a graph showing circuit interruption performance for an example conventional-type circuit interrupter that does not include an arc constrictive zone.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The inventors of the present invention have innovatively realized that a portion of the energy in an arc produced in a circuit interrupter may be harnessed to provide a force acting to separate contacts of the circuit interrupter, thereby providing faster contact separation and correspondingly faster arc voltage development resulting in improved circuit interruption performance compared to conventional circuit interrupters. By confining the arc to an arc constriction zone between the contacts and disposing an ablative material in the zone, an arc voltage development rate has been demonstrated to be increased compared to that of a circuit interrupter having no constrictive zone, resulting in a lower peak let through current. In another advantageous aspect of the invention, an ablation-formed vapor, generated as a result of the arc interacting with the ablative material, acts to cool the arc, resulting in a cooler gas emission and improved performance of the interrupter.  
       FIG. 1  shows a partial cross sectional schematic view of an example embodiment of an improved axial circuit interrupter  10  in a current conducting mode. The circuit interrupter  10  may include a first conducting element, or first contact  12 , having a contacting end portion  14 , and a second conducting element, or second contact  16 , having a respective contacting end portion  18 . When the contacts  12 ,  16  are positioned in electrical contact with one another, such as when the contacting end portions are abutting, an electrical current may be conducted between the elements  12 ,  16 . The first  12  and second contacts  16  may be separable away from one another to interrupt an electrical current flowing between them. For example, the second contact  16  may be movable out of electrical contact with the first contact  12  to interrupt the electrical current, the first contact  12  may be movable out of electrical contact with the second contact  16  to interrupt the electrical current, or both contacts  12 ,  16  may be movable out of electrical contact with each other to interrupt the electrical current.  
      In an aspect of the invention shown in  FIG. 2 , the circuit interrupter  10  includes an arc constrictive zone  20  disposed around the contacts  12 ,  16 , such as around respective end portions  14 ,  18  of the contacts  12 ,  16 . The arc constrictive zone  20  may confine an arc  32  generated between the contacts  12 ,  16  during a separation of the contacts  12 ,  16 , such as occurs at a beginning of a current interruption mode of the circuit interrupter. The arc constrictive zone  20  may be defined by wall  22  of an aperture  26  (as shown in  FIG. 3 ) formed in an insulator  24 , such as, but not limited to, a ceramic plate a polymer plate, a plastic composite plate or combination of these material, disposed around the around the contacts  12 ,  16 . The constrictive zone  20  receives at least the end portions  14 ,  18  of the contacts  12 ,  16  when the contacts  12 ,  16  are positioned in electrical contact so that end portions  14 ,  18  remain within the constrictive zone  20  during at least an initial period of a current interruption mode. It should be understood that an arc created between the contacts  12 ,  16  is not limited to being located within the constrictive zone  20 , and may extend outside of the zone  20 , such as when one or more of the contacts  12 ,  16  are moved out of the constrictive zone  20 , as shown in  FIG. 3   
      Referring now to  FIG. 3 , a geometry of the aperture  26  may be selected to conform to a geometry of the contacts  12 ,  16 . For example, a cylindrical aperture defining the constrictive zone  20  may be used for cylindrical contacts operating reciprocally with respect to constrictive zone  20 . It should be understood that other geometries may be used, such as a square geometry, a rectangular geometry, a triangular geometry, or any other desired geometrical shape. In an aspect of the invention, a height, H, of the constrictive zone  20  may range from about 1 to about 24 millimeters (mm), and preferably from about 3 to about 10 mm, and even more preferably, from about 5 to about 7 mm. In an example embodiment shown in  FIG. 3A , respective opening portions  27 ,  29  of the aperture  26  may be curved or tapered away from a central region  31  of the aperture  26 . The aperture  26  may be defined by a single insulating layer  24 , or, in another example embodiment shown in  FIG. 3B , the aperture  26  may be defined by two or more spaced apart layers, such as multiple spaced apart insulators  24 .  
      Returning to  FIG. 2 , an ablative material  28  may be disposed in the arc restrictive zone  20  for producing an increased pressure in the arc constrictive zone  20  forcing separation of the contacts  12 ,  16 . The increased pressure may be generated in response to the arc  32  formed between the contacts  12 ,  16 . When the contacts  12 ,  16  are initially separated from being in electrical contact as shown in  FIG. 2 , an arc  32  formed in the constrictive zone  20  there between generates vapors in the constrictive zone in part by the heat and/or radiation generated by the arc  32  acting on the ablative material  28  lining the walls  22 . The vapor generated by the ablating process in turn causes a pressure increase in the constrictive zone  20  resulting in force acting on the contacts  12 ,  16  to move at least one of the contacts (e.g.,  16 ) away from the other contact  12  and out of the constrictive zone  20  at an end of a current interruption mode as shown in  FIG. 3 . Accordingly, at least one of the contacts  16  may be with-drawable from the arc constrictive zone  20  to allow the arc  32  to be dissipated. For example, the interrupter may further include an optional arc dissipation structure  34 , such as a plate, ring or an array of plates forming an arc chute, to which the arc  32  is drawn from the arc constrictive zone  20 .  
      As shown in  FIG. 2 , the ablative material  28  may be configured to line a wall  22  of the constrictive zone  20  around the end portions  14 ,  18  of the contacts  12 ,  16 . The ablative material  28  may abut the sides  19  of the contacts  12 ,  16 , or may be spaced away a sufficiently small clearance distance, D, to achieve a desired reduced let-through current limiting performance. For example, a desired spacing between the ablative material  28  and the sides  19  of the contacts  12 ,  16 , or clearance distance D, may be in the range of about 0.1 mm to about 5 mm, more preferably, about 0.2 mm to about 2 mm, even more preferably, about 0.3 mm to about 1 mm, and even more preferably about 0.4 mm to about 0.7 mm. In an aspect of the invention, the ablative material  28  may include polymers such as polytetrafluoroethylene (PTFE), polyethylene, polyimide, polyamide, or poly-oxymethylene (POM), epoxide, polyester, polypropylene, poly methyl-methacralate, poly acetal, polysulphones, phenolic resin, phenolic resin composite, polyetherimide, polyether ketone, polypropylene sulphide-based polymers. Such polymers may also include organic and/or inorganic fillers and/or additives to achieve, for example, desired ablating properties. In an embodiment, the ablative material  28  may comprise a tubular insert disposed in the aperture  26 .  
      In embodiments of the invention depicted in  FIGS. 4 and 5 , the circuit interrupter  10  may include multiple contact pairs  36 , each pair  36  comprising a first contact  12  and a second contact  16 . The contacts pairs  36  may be disposed in a common constrictive zone  20  as shown in  FIG. 4 , the ablative material  28  forming a vapor in the constrictive zone  20  may line the wall  22  of the constrictive zone  20  and may also be disposed in spaces  38  between the contact pairs  36 . In another embodiment, each contact pair  36  may be disposed in separate constrictive zones  20  as shown in  FIG. 5 . Each contact pair  36  may be wired in parallel or series to serve a common electrical circuit. While two contact pairs  36  are shown in  FIGS. 4 and 5 , it should be appreciated that two or more contact pairs  36  may be used, thereby providing two or more paths for current to flow through the interrupter  10 .  
      The circuit interrupter  10  may be vented to a surrounding environment, or, optionally, may be disposed in an enclosure, or bottle  40 , as depicted in  FIG. 6 . The bottle  40  may confine ablation emissions  42  generated, for example, during ablation of the ablating material  28 . The bottle  40  may be filled with air or other gas such as, but not limited to, nitrogen or sulphur hexafluoride. The bottle  40  may optionally include one or more vents for venting emissions  42  from the bottle  40 . In another aspect, two or more contact pairs  36 , such as the contact pair configurations shown in  FIGS. 4 and 5 , may be housed within a bottle  40 . In another example embodiment, multiple bottles  40  may be used with venting to emit cooler and/or safer emissions from the bottle(s)  40 .  
       FIG. 7  shows an example circuit breaker  66 , depicted in a circuit interrupting mode, including an embodiment of the circuit interrupter  10 . The circuit breaker  66  includes a circuit interrupter  10  comprising a stationary contact  12  and a movable contact  16  disposed in an interruption chamber  62  of the breaker  66 . The movable contact  16  is movable into and out of electrical contact with stationary contact  12 , so that when the contacts  12 ,  16  are positioned in electrical contact, electrical power is provided to an electrical circuit via load strap  46  and line strap  82 . An arc constrictive zone  20  of the circuit interrupter  10  is defined by an aperture  26  through an insulator  24 , such as a ceramic plate, being lined with an ablative material  28 , such as PTFE or other ablative material described previously. The insulator  24  may be formed from the polymers previously described. The movable contact  16  is moveable into and out of the zone  20  to provide improved circuit interrupting performance as described previously. A gas path  64  in communication with the interruption chamber  62  may be provided to conduct emissions generated by the ablative material  28  during a circuit interruption event out of the interruption chamber  62 .  
      The circuit breaker  66  includes a current overload sensor  50 , that may comprise a current sensing coil  48  disposed proximate the load strap  46  for sensing an electrical current level being conducted through the load strap  46 . The sensor  50  may further include an electronic trip unit  44  in communication with the current sensing coil  48  for detecting an overload condition of the electrical circuit in response to a sensed load strap current level. A magnetic latch  52  in communication with the sensor  50  may be operable to provide a force on the movable contact  16  to move the contact  16  out of electrical contact with the fixed contact  12  when an overload condition is detected. The magnetic latch  52  may include coils  54  and magnets  56  for selectively moving an actuating shaft  58  to act on an interfacing lever  60  to selectively move the movable contact  16  into and out of electrical contact with the fixed contact  12 . It should be understood that the above description of the circuit breaker  66  is example only, and other types of circuit breaker configurations may be used with the invention without departing form the spirit and scope of the invention. For example, a mechanical latch may be used instead of the magnetic latch  52 , and the fixed contact  12  may be movable, while the movable contact  16  may be fixed fixed, or both contacts  12 ,  16  may be movable away from each other.  
       FIG. 7A  shows an example three phase circuit breaker  68  including an embodiment of the circuit interrupter  10 . The three phase circuit breaker  68  may include three separate circuit interrupters  10 , each circuit interrupter  10  connected to a respective phase  70 ,  72 ,  74  of a three phase circuit  76 . It should be understood that a multiple circuit interrupter circuit breaker embodiment is not limited to three interrupters, and may include two or more interrupters used in the circuit breaker. In an embodiment, each circuit interrupter  10  may be housed within a respective bottle  40 . An activation of the circuit breaker  68  may be controlled by an arc sensing system  80 , for example, sensing arcs  78  on the three phase circuit  76 .  
       FIG. 8  shows a performance graph for an example embodiment circuit interrupter having an arc constrictive zone during a circuit interruption event for a prospective current of 10.5 kilo amps (kA). For comparison,  FIG. 9  shows a performance graph of an example conventional-type circuit interrupter having no arc constrictive zone for a prospective current of 10.5 kA. As can be seen by examining the performance graphs depicted in  FIGS. 8 and 9 , the arc voltage develops at a much faster rate (beginning at about 3.6 milliseconds) for the circuit interrupter including an arc constrictive zone than for a circuit interrupter without an arc constrictive zone. In addition, the circuit interrupter including an arc constrictive zone displays a relatively higher arc voltage [about 323 volts (V) and allows a let through current of about 4.4 kA for about a 40% reduction from the prospective current of 10.5 kA. In contrast, the circuit interrupter having no arc constrictive zone exhibits a lower arc voltage 145 V and allows a higher let through current of 8.9 kA for only a 15% reduction of the prospective current.  
      While certain embodiments of the present invention have been shown and described herein, such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.