Abstract:
A self-pressurized arc diverter includes a vessel configured to enclose a fusible member disposed in a conductor and a pressure-activated arc diverter. The pressure-activated arc diverter is configured to provide access to a preferred arc path when actuated by pressure in the vessel caused by an arc that is created when the fusible member opens.

Description:
BACKGROUND 
     Arc resistant switchgear includes features that mitigate the effects of arcing within an electrical switchgear enclosure. These features are designed to reduce pressure caused by arcing that may result in hot gases escaping the enclosure. In addition, some features function to redirect an arc away from areas that are likely to be accessed by personnel. 
     SUMMARY 
     One example embodiment of a self-pressurized arc diverter includes a vessel and a pressure-activated arc diverter. The vessel encloses a fusible member spliced into a conductor. The pressure-activated arc diverter is configured to provide access to a preferred arc path when actuated by pressure in the vessel caused by an arc that is created when the fusible member opens. 
     In an example embodiment, the vessel includes a cylindrical insulator tube that encloses the fusible link and has end caps through which the conductor passes. The arc diverter includes at least one slot in the cylindrical insulator tube and an insulating cover on the slot. The cover is configured to be dislodged from the slot when the insulator tube becomes pressurized by the arc across the fusible link. 
     In another example embodiment, the arc diverter includes one or more plugs inserted into holes in one of the end caps of the insulator tube. The one or more plugs are configured to be dislodged from the sealed end when the insulator tube becomes pressurized by the arc across the fusible link. 
     The preferred arc path may include a ground plane or a conducting plate that routes an arc to an adjacent phase conductor. The preferred arc path may be oriented perpendicular to a flow of current through the conductor to shorten a length of the arc to minimize an amount of pressure created by the arc. 
     According to another embodiment, a bus assembly includes a bus and a preferred arc path component disposed proximate to the bus that provides a conductive ground path. A fusible link is spliced into the bus that is configured to conduct a rated current of the bus and to vaporize in response to current above the rated current. A vessel encloses the fusible link. A pressure-activated arc diverter provides access to the preferred arc path when actuated by pressure in the vessel caused by an arc that is created when the fusible link opens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various example systems, methods, and other example embodiments of various aspects of the invention. It will be appreciated that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the figures represent one example of the boundaries. One of ordinary skill in the art will appreciate that in some examples one element may be designed as multiple elements or that multiple elements may be designed as one element. In some examples, an element shown as an internal component of another element may be implemented as an external component and vice versa. Furthermore, elements may not be drawn to scale. 
         FIG. 1  is an isometric view of a prior art electrical enclosure exhibiting an uncontrolled electrical arc. 
         FIG. 2  is an isometric view of an electrical enclosure that includes one example embodiment of self-pressurized arc diverters. 
         FIGS. 3 and 3   a  are cross section views of a self-pressurized arc diverter of  FIG. 2 . 
         FIG. 4  is an isometric view of the self-pressurized arc diverters shown in  FIG. 2 . 
         FIG. 5  is schematic side view of one example embodiment of a self-pressurized arc diverter. 
         FIG. 6  is schematic side view of the self-pressurized arc diverter shown in  FIG. 5 . 
         FIG. 7  is schematic rear view of the self-pressurized arc diverter shown in  FIG. 5 . 
         FIG. 8  is schematic rear view of another example embodiment of a self-pressurized arc diverter. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an interior view of a prior art electrical switchgear enclosure  10 . The enclosure  10  is divided by a wall  17  into a main compartment  14  and an auxiliary compartment  12 . The main compartment  14  typically houses primary buses (not shown) that are connected to a power source. The auxiliary compartment  12  typically holds transformers or other components that are connected between the power source and the load by way of secondary buses  25   a ,  25   b ,  25   c . The auxiliary compartment  12  is usually accessed more often by personnel who work on the load-related components. The auxiliary compartment  12  may include vents in exterior walls (not shown) for cooling and ventilation purposes. 
     Insulator tubes  30   a ,  30   b ,  30   c  surround the connection between the primary buses (not shown) and the secondary buses  25   a ,  25   b ,  25   c  and prevent the buses from shorting to the enclosure wall  17 . An uncontrolled arc fault is shown occurring between the secondary buses  25   a ,  25   b ,  25   c . The uncontrolled arc has significant length, meaning that it will generate significant pressure and tend to cause damage and burn-through of the enclosure, allowing hot gases to escape from the enclosure. In addition, the arc is occurring between electrical phases in the auxiliary enclosure  12 , where it may reach an exterior wall or be inadvertently contacted by personnel. 
       FIG. 2  is an isometric view of an auxiliary compartment  112  that includes one example embodiment of self-pressurized arc diverters  150   a ,  150   b ,  150   c . The auxiliary compartment  112  is a voltage transformer drawer that houses three transformers, one for each electrical phase. A secondary bus  125  connects each transformer to a corresponding primary bus  120  (not visible in  FIG. 2 , see  FIGS. 3 ,  3   a ) located in a main compartment  114 . 
     A fusible link (not visible in  FIG. 2 , see  FIGS. 3 ,  3   a ) is spliced into the primary bus near its connection to the secondary bus  125 . The fusible link  132  has a rating in the range of normal current for the load. The normal current draw of the load is typically much lower than the rated current for the circuit breakers used to protect the circuit. When an arc fault occurs the increased current draw may not be sufficient to trip the circuit breaker. However, the fusible link can be selected so that it will vaporize in the presence of an arc fault current. While a fusible link is described herein, any device that vaporizes in response to current draw over its rated value may be utilized. 
     The self-pressuring arc diverters  150   a ,  150   b ,  150   c  form part of a vessel that encloses the fusible link in the primary bus. The self-pressuring arc diverter  150  is actuated by pressure within the vessel to provide access to a preferred arc path. The pressure is caused by arcing between the primary and secondary conductors when the fusible link vaporizes in response to high current draw due to an arc fault condition. The preferred arc path includes a ground plane  160  that is electrically connected to an enclosure ground  165  with a ground bracket  163 . 
       FIG. 3  is a cross section view of a self-pressurized arc diverter  150 . The self-pressurized arc diverter  150  encloses the connection of a secondary bus  125  in an auxiliary compartment  112  to a primary bus  120  in a main compartment  114 . The secondary bus  125  rests on an insulator  121 . The secondary bus  125  includes a connector post  123  that is used as a connection point for load related devices in the auxiliary compartment. The self-pressurized arc diverter  150  includes a slotted insulator tube  152  surrounding the connection between the primary bus  120  and the secondary bus  125 . The slotted insulator tube  152  includes upper and lower slots  153  that have removable covers  155  (shown in  FIGS. 2 and 4 ). The ground plane  160  is aligned with the slots  153  and is connected to the enclosure ground  165  ( FIG. 3 ) by way of the ground bracket  163 . A mounting flange  156  is integrally molded at one end of the insulator tube  152 . A mounting bracket  167  is used to connect the mounting flange  156  to the ground plane  160  to fix their relative locations. 
       FIG. 3   a  is a cross sectional view of the self-pressurized arc diverter  150 . In  FIG. 3   a , the secondary bus  125  is shown disconnected from the primary bus  120 . A set of contacts  127  is connected at an end of the secondary bus  125 . The contacts  127  are configured to receive an end of the primary bus  120  and to form an electrical connection between the secondary bus and the primary bus. The fusible link  132  is spliced into the primary bus  120 . A seal  154  seals around the primary conductor  120  to the insulator tube  152  on the auxiliary compartment ( 112 ) side of the fusible link  132 . The interior seal  158 , which is molded as part of the insulator tube mounting flange  156 , seals around the primary conductor  120  to the insulator tube  152  on the main compartment side ( 114 ) of the fusible link  132 . 
     Thus, the fusible link  132  is enclosed within a vessel  190  made up of the slotted insulator tube  152  (with the cover installed) and end caps in the form of the seals  154 ,  158 . When the fusible link  132  vaporizes, an arc will occur that creates pressure within the vessel  190 . The pressure will push the cover  155  ( FIGS. 2 and 4 ) off the slot  153 . Thus, the vessel  190  may be sealed or at least be capable of building pressure sufficient to separate the cover  155  from the slot  153 . When the cover  155  is removed, the slot  153  serves as an arc diverter that provides access to the ground plane  160 . Accordingly, an arc fault that melts the fusible link will be diverted to the ground plane  160  as shown in  FIG. 4 . 
       FIG. 4  illustrates the self-pressurized arc diverter  150   a  in operation. An arc fault has occurred on the phase associated with the arc diverter  150   a  and the fusible link  132  ( FIG. 3 ) has vaporized, creating pressure which pushed the cover  155  (not shown) off the slot  153   a . Because no fault has occurred on the phase associated with the self-pressurized arc diverter  150   b , the cover  155   b  still covers the slot  153   b  in the insulator tube  152   b . Since the cover on the self-pressurized arc diverter  150   a  has been removed, the slot  153   a  provides access to the ground plane  160 . The arc, shown schematically as arrows exiting the slot, travels through the slot to the preferred arc path which includes the ground plane  160 , the ground bracket  163 , and the enclosure ground  165 . 
     The arc is drawn to the most proximate path to ground, which is presented by the preferred arc path made accessible by the self-pressurized arc diverter  150   a . The preferred arc path is distantly located from the load components that are often accessed by personnel. Further, because the ground plane  160  is oriented at a 90 degree angle to the secondary bus  125 , magnetic forces induced by the current will tend to shorten the arc, reducing the pressure caused by the arc and the expulsion of hot gases from the enclosure. 
       FIG. 5  shows another example embodiment of a self-pressurized arc diverter  250  installed in an auxiliary compartment  212  of an electrical enclosure. The self-pressurized arc diverter  250  shown in  FIG. 5  is installed on a central primary bus  220   b . The central primary bus  220   b  supports an arc diverter plate  292  that routes an arc to adjacent phases as can be seen best in  FIGS. 7 and 8 . The other primary buses  220   a ,  220   c  may or may not have an arc diverter plate  292 . 
     The primary bus  220   b  includes a fusible link  232  enclosed by a vessel  290  comprised of an insulator tube  252 , a seal  254 , and an interior seal  258  that is part of an insulator tube mounting flange  256 . The interior seal  258  includes holes  259  that serve as an arc diverter. Plugs  280  are inserted into the holes  259  and seal the holes.  FIG. 6  illustrates the function of the self-pressurized arc diverter  250  when the fusible link  232  vaporizes and creates an arc. The plugs  280  ( FIG. 5 ) have been ejected from the holes  259  by the pressure caused by the arc. The plasma jet of the arc exits the holes as shown by the arrow and strikes the arc diverter plate  292 . 
       FIG. 7  is a view of the main compartment  212  illustrating the primary buses  220   a ,  220   b ,  220   c  and self-pressurized arc diverters. The center primary bus  220   b  includes the arc plate  292  that directs the arc to a preferred arc path which is an adjacent primary bus. A fault has occurred on primary bus  220   b  and the plugs  280  have been ejected by pressure caused by the arc. Thus the arc is diverted into the main compartment where it will short phase-to-phase, transferring the uncontrolled arc away from the auxiliary compartment. In alternate embodiments, more than one primary conductor may include an arc plate  292 . 
       FIG. 8  is a view of the main compartment  212  illustrating the primary buses  220   a ,  220   b ,  220   c  and self-pressurized arc diverters. The self-pressurized arc diverters in  FIG. 8  employ an alternate position for holes  259 ′ and corresponding plugs  280 . A fault has occurred on primary bus  220   b  and the plugs  280  have been ejected by pressure caused by the arc. The arc is thus diverted into the main compartment where it will short phase-to-phase, transferring the uncontrolled arc away from the auxiliary compartment. 
     While example systems, methods, and so on have been illustrated by describing examples, and while the examples have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the systems, methods, and so on described herein. Therefore, the invention is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Thus, this application is intended to embrace alterations, modifications, and variations that fall within the scope of the appended claims. 
     To the extent that the term “includes” or “including” is employed in the detailed description or the claims, it is intended to be inclusive in a manner similar to the term “comprising” as that term is interpreted when employed as a transitional word in a claim.