Abstract:
An exhaust chamber for an arc resistant cabinet directs high temperature, expanding gases away from locations where personnel are likely to be present. The exhaust chamber may have an open top, directing gases outward through the center of the exhaust chamber&#39;s top. Alternatively, the exhaust chamber may be completely enclosed, directing expanding gases through a duct.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to arc resistant cabinets for electrical equipment. More specifically, the invention relates to an exhaust chamber for such a cabinet, adapted to channel high temperature expanding gases away from personnel. 
     2. Description of the Related Art 
     Electrical equipment such as circuit breakers are typically contained within arc electrically grounded resistant cabinets, intended to provide isolation for the components therein, and to protect personnel working around the circuit breaker from electrocution and from hot gases in the event of an electrical arc within the cabinet. Such an electrical arc would cause a sudden pressure increase inside the cabinet and localized overheating. 
     Presently available arc resistant cabinets typically include a frame having a hinged flap assembly. Such flaps are designed to support the weight of personnel working on top of the cabinet, but to open to relieve pressure inside the cabinet when an arc occurs. However, such gases may be deflected off the ceiling and wall of the room wherein the cabinet is located, down on to personnel working near the cabinet. Current and proposed safety standards require that the temperature of such gases be tested by placing highly flammable cotton indicators at a height of 2 meters around the perimeter of the cabinet, and these cotton indicators must not ignite when an internal arc occurs. 
     Accordingly, there is a need for an arc resistant cabinet having a means for directing high temperature, expanding gases exiting the cabinet away from locations where personnel are likely to be present. Additionally, there is a need for an arc resistant cabinet having a means for relieving pressure from high temperature, expanding gases while being easier and less expensive to produce than other arc resistant cabinets. 
     SUMMARY OF THE INVENTION 
     The preferred embodiments of the present invention are exhaust chambers for use with arc resistant cabinets. Such exhaust chambers are particularly useful for arc resistant cabinets containing electrical equipment, such as circuit breakers. 
     The exhaust chamber will preferably be located at the top of the arc resistant cabinet. A typical arc resistant cabinet includes a plurality of hinged flaps on the roof, thereby permitting high pressure, high temperature gases caused by an electrical arc inside the cabinet to exit the cabinet by pushing open these hinged flaps. The exhaust chamber includes a plurality of vertical walls surrounding that portion of the roof having these hinged flaps. One embodiment of the exhaust chamber includes horizontal shelves extending inward from the top of the vertical walls, thereby defining an opening in the center of the exhaust chamber&#39;s top. An alternative embodiment includes a top extending across the entire exhaust channel, thereby completely enclosing the channel. In this second embodiment, a duct is connected to the exhaust chamber, leading away from areas where personnel are likely to be present. This duct could be extended in any direction, for example, vertically, to either side, to the front, or to the rear. 
     During normal operation of the electrical equipment within the cabinet, the hinged roof flaps will remain closed. If an electrical arc occurs, the high temperature, expanding gases apply upward pressure to the hinged flaps, thereby pushing the flaps upward. As the gases enter the exhaust chamber, they will have room to expand, thereby reducing their pressure. The gases will also have additional time to cool before exiting the chamber. If an open top expansion chamber is selected, the expanding gases will be directed by the vertical walls and horizontal shelves towards the center of the expansion chamber, where they will exit through the top of the chamber. If the enclosed expansion chamber is selected, the gases will expand into the chamber, and then continue expanding to enter the duct. Both embodiments will reduce the pressure of the gas, and permit sufficient time for cooling, to ensure the safety of personnel working around the cabinet. 
     It is therefore an aspect of the present invention to provide an expansion chamber for use with arc resistant cabinets. 
     It is another aspect of the present invention to provide an expansion chamber directing high temperature, expanding gases towards an opening in the chamber&#39;s top, thereby providing sufficient time for cooling before these gases reach personnel. 
     It is a further aspect of the present invention to provide an enclosed expansion chamber, for directing high temperature, expanding gases into a duct. 
     These and other aspects of the present invention will become apparent through the following description and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric top view of an arc resistant cabinet having an exhaust chamber of the present invention, illustrating the exhaust flaps on the cabinet in their closed position. 
     FIG. 2 is an isometric top view of an arc resistant cabinet having an exhaust chamber of the present invention, illustrating the exhaust flaps on the cabinet in their open position. 
     FIG. 3 is a cross-sectional side view of an arc resistant cabinet having an exhaust chamber of the present invention. 
     FIG. 4 is a cross-sectional side view of an arc resistant cabinet having an alternative embodiment of an exhaust chamber according to the present invention. 
     Like reference numbers denote like elements throughout the drawings. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are exhaust chambers. Such exhaust chambers are particularly useful for arc resistant cabinets for electrical equipment, such as those used to contain circuit breakers. 
     An exhaust chamber of the present invention is best understood through an explanation of a conventional arc resistant cabinet, typically used for a medium voltage circuit breaker. Referring to the figures, an arc resistant cabinet  10  is illustrated. The arc resistant cabinet  10  includes a front compartment  12 , a middle compartment  14 , and a rear compartment  16 . Referring to FIGS. 3-4, the front compartment  12  contains at least one circuit breaker  18 . It is well known that the circuit breaker  18  will typically include at least one pair of quick disconnects  20 , mating with at least one pair of corresponding stabs  22 , located within the front compartment rear wall  24 . A levering in assembly  26  permits moving the circuit breaker  18  forward and rearward to connect the quick disconnects  20  and stabs  22  when operation of the circuit breaker is desired, and disconnects the quick disconnects  20  and stabs  22  when servicing the circuit breaker  18  is desired. The middle compartment  14  typically contains the supply buses  28 . The rear compartment  16  typically contains the cable connections  30 . 
     The top  44  of the arc resistant cabinet  10  includes a plurality of flaps  46 , dimensioned and configured to cover the openings  48  in the top  44  during normal operation of the circuit breakers  18 , and to be pushed open by excessive pressure within the cabinet  10 . A typical flap  46  will be hingedly secured to a frame surrounding the openings  48  (not shown and well known). The frame will prevent the flap  46  from collapsing if someone walking on top of the cabinet  10  should step on the flap  46 , but permit the flap to be pushed open by pressure from inside the cabinet  10 . The cabinet  10  also includes internal pressure relief panels  62  and ventilation flap  64 . The internal pressure relief panels  62  are weakened, thereby permitting them to fail before other components within the cabinet  10  fail. 
     If arcing should occur inside the cabinet  10 , the result is a sudden pressure increase and overheating. Materials exposed to the arc may produce hot gases or particles, which must be discharged to the outside of the cabinet  10  to avoid extensive internal damage, but in a manner not likely to injure personnel working around the cabinet  10 . 
     Referring to FIGS. 1-3, an exhaust chamber  32  is illustrated. The exhaust chamber  32  includes a plurality of sides  34 ,  36 ,  38 ,  40 , and a top  42 . The sides  34 ,  36 ,  38 , and  40  are fixed to the top  44  of the cabinet  10 . The exhaust chamber  32  defines a chamber  50 , within the sides  34 ,  36 ,  38 ,  40 , and under the top  42 . The chamber  50  contains the flaps  46 . An opening  52 , defined within the exhaust chamber  32 , is in communication with the chamber  50 , so that the chamber and opening are dimensioned and configured to permit high temperature, high pressure gases to expand and cool, and direct the gases in a safe direction. 
     Alternatively, as illustrated in FIG. 4, the exhaust chamber  32  may include a top  54 , having an opening  56 , dimensioned and configured to adjoin a duct  58 . Although the illustrated example of a duct  58  adjoins the top  54 , the duct may alternatively adjoin any of the sides  34 , 36 , 38 , 40 . 
     During normal operation of the circuit breakers  18 , the flaps  46  will be in their closed position, illustrated in FIG.  1 . In the event of an electrical arc  60 , which is most likely to occur in the front compartment  12 , the flaps  46  will operate in conjunction with internal pressure relief panels  62  and ventilation flap  64  to direct the resulting high temperature, expanding gases away from locations where personnel are likely to be present. The expanding gases push the ventilation flap  64  closed, ensuring that none of the expanding gases exit through the front  66  of the cabinet  10 , where personnel are likely to be located. At the same time, the expanding gases push the internal pressure relief panels  62  open, permitting the expanding gases to reach the top  44  of the cabinet  10 . The expanding gases then push the flaps  46  open, illustrated in FIGS. 2-4. As the expanding gas exits the cabinet  10 , it enters the exhaust chamber  32 , wherein it continues to expand. Depending on the embodiments of the exhaust chamber  32  selected, the expanding gases then exit through the opening  52 , or the duct  56 . This additional upward travel of the expanding gas as it passes through the exhaust chamber  32  provides additional time for the gas to cool before reaching areas where personnel are likely to be present, thereby minimizing the potential for serious injuries. 
     While a specific embodiment of the invention has been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.