Abstract:
A panel, preferably a ceiling panel, for an arc resistant cabinet defines at least one flap dimensioned and configured to bend outward in response to excessive pressure within the cabinet. The flap is bent into a position wherein it will direct high temperature, expanding gases exiting the cabinet away from areas where personnel are likely to be located. The panel also includes a frame below the flap, thereby permitting the entire panel, including the flap, to support the weight of people working on top of the cabinet.

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 a panel defining a flap adapted to support weight from above, and to open in response to excessive pressure within the cabinet, thereby directing gases away from personnel. 
     2. Description of the Related Art 
     Electrical equipment such as circuit breakers are typically contained within arc resistant cabinets, intended to protect personnel working around the circuit breaker 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 embodiment of the present invention is a pressure release panel for use with arc resistant cabinets. Such pressure relief panels are particularly useful for arc resistant cabinets containing electrical equipment, such as circuit breakers. 
     The pressure relief panel includes at least one flap defined by a plurality of cuts within the panel. Some preferred embodiments include multiple flaps. A support system is secured below each flap, being dimensioned and configured to prevent the flap from bending downward when pressure is applied to the top of the panel. One preferred support system includes a beam extending lengthwise along each cut. 
     A preferred and suggested method of making such a pressure relief panel includes providing a solid panel, cutting the panel at appropriate locations to define at least one flap, with one preferred cutting method being a laser, and securing the support system below the flaps. A preferred material for the panel is steel, with 14-gauge steel being suggested. Preferred methods of securing the support system below the flaps include bolting and welding the support system in place. 
     In use, such pressure relief panels will typically form the roof of an arc resistant cabinet, although they may be used at other locations inside the cabinet. Such cabinets are typically used to contain electrical equipment such as circuit breakers. When an arc occurs within a circuit breaker, the result is high pressure, high temperature expanding gases within the cabinet. Relieving the pressure inside the cabinet requires releasing these gases in a direction wherein the gases are not likely to cause injury to personnel working around the cabinet. 
     During normal operation of the circuit breaker, the flap will remain closed, and the support structure beneath the flap will permit personnel to walk over the panel and flap without causing the flap to collapse. When an electrical arc occurs, the high temperature, expanding gases will apply upward pressure to the pressure relief panels and flaps, causing the flaps to bend outward. The material type and thickness of the pressure relief panel will preferably be selected to ensure that such expanding gases are likely to push the flap into an approximately vertical position. The location of the pressure relief panel on the roof of the arc resistant cabinet, combined with the substantially vertical flaps, direct the expanding gas upward, and away from locations where personnel are likely to be present. The number, size and shape of the flaps can be selected to more specifically direct the flow of expanding gases out of the cabinet so that, by the time the gases reach the ceiling and walls of the room in which the cabinet is located, and are thereby directed back downward, the gases have cooled sufficiently so that they are unlikely to cause serious injury to personnel. 
     It is therefore an aspect of the present invention to provide a pressure relief panel for use with arc resistant cabinets. 
     It is another aspect of the present invention to provide a pressure relief panel capable of supporting the weight of personnel standing on the panel. 
     It is a further aspect of the present invention to provide a pressure relief panel wherein excess pressure underneath the panel will position a flap defined with the panel into an orientation wherein the flap directs expanding gases to locations where personnel are unlikely to be present. 
     It is another aspect of the present invention to provide a pressure relief panel wherein excess pressure below the panel pushes the flaps defined within the panel into a vertical orientation. 
     It is a further aspect of the present invention to provide a support structure beneath the flaps defined within a pressure relief panel for resisting downward movement of the flaps. 
     It is another aspect of the present invention to provide a pressure relief panel for arc resistant cabinets that is simple and inexpensive to manufacture while maintaining or exceeding the effectiveness of other pressure relief systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side cross-sectional view of a circuit breaker and arc resistant cabinet according to the present invention, illustrating gas flow at the moment of arcing. 
     FIG. 2 is a top isometric view of a ceiling panel for an arc resistant cabinet according to the present invention. 
     FIG. 3 is a top view of an alternative embodiment of a ceiling panel for an arc resistant cabinet according to the present invention. 
     FIG. 4 is a top view of another alternative embodiment of a ceiling panel for an arc resistant cabinet according to the present invention. 
     FIG. 5 is a top view of yet another alternative embodiment of a ceiling panel for an arc resistant cabinet according to the present invention. 
     FIG. 6 is a top view of a further embodiment of a ceiling panel for an arc resistant cabinet according to the present invention. 
     FIG. 7 is a top view of an alternative embodiment of a ceiling panel for an arc resistant cabinet according to the present invention. 
     FIG. 8 is a top view of yet another alternative embodiment of a ceiling panel for an arc resistant cabinet according to the present invention. 
     FIG. 9 is a top view of a further embodiment of a ceiling panel for an arc resistant cabinet according to the present invention. 
     FIG. 10 is a top view of a further embodiment of a ceiling panel for an arc resistant cabinet according to the present invention. 
     FIG. 11 is a top isometric view of a ceiling panel and associated lower braces for an arc resistant cabinet according to the present invention. 
     FIG. 12 is a bottom view of a ceiling panel and associated lower braces for an arc resistant cabinet according to the present invention. 
     FIG. 13 is a top isometric view of a ceiling panel for an arc resistant cabinet of the present invention, showing the position of the flaps after an arc has occurred. 
    
    
     Like reference numbers denote like elements throughout the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment of the present invention is a pressure relieving panel. Such a panel is particularly useful for the construction of arc resistant cabinets for electrical equipment, such as those used to contain circuit breakers. 
     A pressure relief panel of the present invention is best understood through and explanation of a conventional medium voltage circuit breaker. Referring to FIG. 1, a switchgear assembly  10  is illustrated. The switchgear  10  includes cabinet  12 , having a front compartment  60 , middle compartment  62 , and rear compartment  64 . Front compartment  60  contains a circuit breaker  14 . The back  16  of the circuit breaker  14  includes means for electrical connection with a circuit, which are preferably at least one pair of quick disconnects  18 , with each quick disconnect  18  terminating with a plurality of contact fingers  20 . The cabinet&#39;s rear wall  22  includes means for connecting to the means for electrical connection of the circuit breaker to a circuit, which preferably include a pair of channels  24 , with each channel  24  containing a primary contact or stab  26 . Quick disconnects  18  and contact fingers  20  are dimensioned and configured so that, when the quick disconnects  18  are inserted into the channels  24 , the contact fingers  20  are electrically connected to the primary contact or stab  26 . A typical medium voltage circuit breaker will include a combination of three pairs of quick disconnects  18  and three corresponding pairs of channels  24 . The bottom  28  of circuit breaker  14  may include a plurality of rollers  30 , dimensioned and configured to permit the circuit breaker to move along the rails  32 , extending from the cabinet&#39;s rear  22  to the cabinet&#39;s front  34 . The levering in assembly typically used to move the circuit breaker from its rearward position wherein the quick disconnect  18  engage the stabs  26 , and its forward position wherein the quick disconnect  18  and stabs  26  are disconnected, is well known and therefore not shown. The middle compartment  62  typically contains the supply buses  66 , and the rear compartment  64  typically contains the cable connections  68 . 
     If arcing should occur inside the switchgear, 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  12  to avoid extensive internal damage but in a manner not likely to injure personnel working around the switchgear  10 . 
     Referring to FIG. 2, a pressure relief panel  36  is illustrated. The pressure relief panel  36  includes at least one integral flap  38 , defined by a plurality of slots  40  and covering an opening  58  defined within the panel  36 . The flaps  38  are dimensioned and configured to bend outwards in response to pressure from below the pressure relief panel  36 . The slots are thin enough to maintain the integrity of the cabinet, and prevent objects such as tools, fingers, etc. from entering the cabinet. A preferred width of the slots  40  is less than {fraction (1/64)} inch. 
     The number and configuration of flaps  38 , and the material and thickness of the pressure relief panel  36 , are selected to maximize the probability that an expected pressure level inside the cabinet  12  will push the flaps  38  into an orientation wherein the flaps  38  may best direct pressurized, heated gases exiting the cabinet  12  away from personnel working around the cabinet  12 . One preferred material includes steel, such as 14-gauge steel. Referring to FIGS. 3-10, several alternative embodiments of the pressure relief panel  36  are illustrated. All embodiments of the pressure relief panel  36  are referred to simply by the number  36 , whereas specific embodiments of the pressure relief panel  36 , and elements therein are referred to by the reference number followed by a letter. Embodiments  36   a - 36   h  thereby include flaps  38   a - 36   h,  defined by slots  48   a - 48   h.  The illustrated embodiments include some examples of the numerous ways that the number and configuration of flaps  38  within the pressure relief panel  36  may be selected to best direct the exiting gases away from personnel. 
     Referring to FIGS. 11 and 12, the means for resisting downward movement of the flap  38  are illustrated. These means include the support structure  42 , having a plurality of support beams  44  secured to the panel  36 , under the flaps  38 , although other configurations are possible. Preferred configuration of the support structure  42  includes at least one end beam  46  extending between a pair of side beams  48 , with the end beam  46  and side beams  48  directly underneath and substantially parallel to the slots  40  defining the flap  38 . Such a configuration has the additional advantage of preventing foreign objects from entering the cabinet  12  by blocking the slots  40 . Preferred methods of securing the support beams  44  to the panel  36  include bolting the support beams to the panel, and welding the support beams  44  to the panel  36 . 
     Referring to FIGS. 1 and 13 the operation of a pressure relief panel  36  in conjunction with an arc resistant cabinet  12  is illustrated. The pressure relief panels  36  will typically be installed in the ceiling  50  of the arc resistant cabinet  12 . During installation of the pressure relief panels  36 , and during normal use of the circuit breaker  14 , the flaps  38  will be in their original, closed position of FIG.  3 . The support structure  42  will permit personnel to safely walk across the flaps  38  without the flaps  38  bending inward, preventing personnel from falling into the cabinet  12 . 
     In the event of an electrical arc  52 , which is most likely to occur in the front compartment  60  pressure relief panels  36  will operate in conjunction with internal pressure relief panels  54  and ventilation flaps  56  (FIG. 2) to direct the resulting high temperature, expanding gases away from locations where personnel are likely to be present. The internal pressure relief panels  54  are weakened, thereby permitting them to fail before other components within the cabinet  12  fail. The expanding gases push the ventilation flap  56  closed, ensuring that none of the expanding gases exit through the front  34  of the cabinet  12 , where personnel are likely to be located. At the same time, the expanding gases push the internal pressure relief panel  54   a  open, permitting the expanding gases to move through the opening previously covered by the panel  54   a.  The expanding gases is next directed upward, pushing the panel  54   b  open, finally reaching the ceiling  50  of the cabinet  12 . The expanding gas then pushes the flap  38  from the position of FIG. 2 to the position of FIG.  13 . As the expanding gas exits the cabinet  12  through the opening  58 , previously covered by the flaps  38 , the flaps  38  are pushed into a vertical orientation, wherein the flaps  38  continue to direct the expanding gas upward after it has left the cabinet  12 . This additional upward travel of the expanding gas provides additional time for the gas to cool before it reaches area 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.