Abstract:
A method and device prevents injuries when performing maintenance on a circuit breaker including a body portion and one or more outwardly extending bushings having terminals at the ends thereof for connection to power lines. The circuit breaker is first de-energizing. A cover is provided and wrapped around one or more of the circuit breaker bushings in a manner leaving the bushing terminal exposed. The cover is secured and will prevent escape of at least some fragmented materials in the event of a bushing explosion.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional patent application No. 60/020,321 filed on Jan. 10, 2008 and entitled Sub-Station Applied Insulator Containment Device, which is hereby incorporated by reference in its entirety 
     
    
     TECHNICAL FIELD 
       [0002]    This invention is generally related to sub-station personnel protective devices for pressurized bushings. 
       BACKGROUND 
       [0003]    High voltage circuit breakers, such as the one shown in  FIG. 1 , generally include a body portion  2  and outwardly extending bushings  3 . The ends of the bushings  3  include one or more terminals  4  that are coupled to electrical power lines  5 . Within the body portion  2  the circuit breaker mechanism selectively electrically connects or disconnects internal contacts. 
         [0004]    Commonly, the body portion  2  and bushings  3  contain an arc resisting gas under pressure. The gas is used primarily to prevent arcing between internal contacts. Typically, the body portion  2  of the circuit breaker is made of a metallic material and the bushings are made of a non-conducting, non-metallic material. Often times, the bushing is made of porcelain or other brittle non-conducting material. While bushings of this type are corrosion resistant and effective insulators, the use of the brittle material can pose a safety concern to service personnel when performing maintenance. In particular, if the structural integrity of the bushing  3  is compromised, the pressure of the internal gas could cause the bushing  3  to explode. Any service personnel near-by could be seriously injured by the potentially lethal projectiles. Standards relating to safety include ANSI/AIHA Z10-2005, Section 5 paragraph 5.1.1, Hierarachy of controls and OSHAS 18001-2007, Section 4, paragraph 4.3.1, Hazard identification, risk assestment and determining controls. 
         [0005]    Thus, there is a need in the art for a protective device that prevents service person injuries due to exploding bushings. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect of the present invention, a method is provided for preventing injuries when performing maintenance on a circuit breaker including a body portion and one or more outwardly extending bushings having terminals at the ends thereof for connection to power lines. The method includes de-energizing the circuit breaker. A cover is then provided having a top edge, a bottom edge, a first side edge and a second side edge. The cover is wrapped around at least one bushing, wherein at least a portion of the cover overlaps, and the terminal remains at least partially exposed. The cover is radially constrained to prevent unwrapping. If the bushing explodes, releasing fragmented materials, the cover prevents escape of at least some of the fragmented materials. 
         [0007]    According to another aspect of the present invention, a device is provided for preventing injuries when a circuit breaker bushing explodes, projecting fragments outwardly therefrom. The device includes a cover having a top edge, a bottom edge, a first side edge and a second side edge. A plurality of lateral straps are secured to the cover, spaced from each other and oriented parallel to the top edge. Each lateral strap includes at least one fastener for securing one end of the lateral strap to the opposed end of the same lateral strap. The cover, when wrapped around the bushing, contains at least some of the fragments of the exploding bushing. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]      FIG. 1  is an exemplary sub-station high voltage breaker. 
           [0009]      FIG. 2  is an elevated view of the safety device according to the present invention in the unwrapped configuration. 
           [0010]      FIG. 3  is an elevated view of the safety device of  FIG. 2  in the wrapped configuration. 
           [0011]      FIG. 4  is an elevated view of the safety device of  FIG. 2  showing the opposed side of the wrapped configuration. 
           [0012]      FIG. 5  is a perspective view of the safety device of  FIG. 2  partially installed on the bushing of a high voltage circuit breaker. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring now to  FIG. 2 , a safety device is shown and generally indicated by the numeral  10 . Device  10  includes a generally square or rectangular cover  12 . In one or more embodiments, cover  12  is a thin (relative to the length and width) fabric material. In a particularly preferred embodiment, cover  12  may be Kevlar fabric. The Kevlar may be, for example, a three layer 3000 denier with a break strength of 1,800 lb/inch. In any event, once installed, cover  12  must be strong enough to withstanding the force of an exploding insulator and contain the outwardly projecting pieces thereof. 
         [0014]    Device  10  includes a top edge  14  and a bottom edge  16  that are joined by a first side edge  18  and a second side edge  20 . A plurality of laterally extending straps  22   a - f  are secured to cover  12  at spaced intervals. In one embodiment six straps  22  are provided and are spaced ten inches apart. It should be appreciated, however, that the particular number and spacing of lateral straps  22  may vary depending on the size of the bushing being covered. Lateral straps  22  are attached to cover  12  with stitching, though other fastening methods may be used, such as, for example, adhesives. 
         [0015]    Proximate to first side edge  18 , D-rings  24   a - f  are secured to the end of each lateral straps  22   a - f . As will be further understood hereinafter, in the present embodiment, two D-rings  24   a  are provided at lateral strap  22   a . The end of lateral strap  22  opposed from D-ring  24  does not extend all the way to second side edge  20 . In one or more embodiments, the lateral strap  22  extends from first side edge  18  to about ⅗ of the lateral length of cover  12 . Snap hooks  26   b - f  are secured to the end of lateral straps  22   b - f  opposed from D-rings  24 . As will become apparent, when installed over a bushing, snap hooks  26  are adapted to selectively engage and couple to D-rings  24 . In one or more embodiments, all straps of the present invention are two inches thick with a 12,000 lb failure strength. In these or other embodiments, the engaged D-ring  24  and snap hook  26  have a failure strength of 5,000 lbs. The end of lateral strap  22   a  opposite of D-ring  24   a  does not include a snap hook, and includes an extended portion  28  that extends beyond straps  24   b - f , closer to second side edge  20 . 
         [0016]    Device  10  includes a longitudinally extending strap  30  that extends upwardly from bottom edge  16  and traverses each laterally extending strap  22 . The top end of longitudinally extending strap  30  extends beyond top edge  14 . Two D-rings  32  are secured to the top end of longitudinal strap  30  and two D-rings  33  are secured to the bottom end of longitudinal strap  30 . Longitudinally extending strap  30  is parallel to, and laterally offset from first side edge  18 . In one or more embodiments, longitudinally extending strap  30  is offset from first side edge  18  by about ⅙ the total lateral width of cover  12 . 
         [0017]    A second longitudinally extending strap  34  also runs parallel to first side edge  18  and is offset therefrom. In one or more embodiments, second longitudinally extending strap  34  is offset by about ½ the total lateral width of cover  12 . Second longitudinally extending strap  34  is secured to cover  12  from a point proximate to bottom edge  16  to a point approximately half way between bottom edge  16  and top edge  14 . In one embodiment, second longitudinal strap  34  is secured to lateral straps  22   d - f  and to the portions of cover  12  therebetween. A top portion  36  of second lontigudinally extending strap  34  is not secured to either cover  12  or lateral strap  22 . Likewise, a bottom portion  38  of second longitudinally extending strap  34  is not secured to either cover  12  or lateral strap  22 , and extends beyond bottom edge  16 . As seen in  FIG. 2 , bottom portion  38  is substantially longer than top portion  36 . 
         [0018]    Device  10  includes a third longitudinally extending strap  40  positioned proximate to top edge  14 . In one embodiment, third longitudinally extending strap  40  extends from top edge  14  to lateral strap  22   a . A D-ring  42  is secured to the top end of third longitudinally extending strap  40 , proximate to top edge  14 . Device  10  includes a fourth longitudinally extending strap  44  positioned proximate to bottom edge  14 . In one embodiment, fourth longitudinally extending strap  44  extends from a point between lateral strap  22   e  and terminates on lateral strap  22   f . A D-ring  46  is secured to the bottom end of fourth longitudinally extending strap  44 , proximate to bottom edge  16 . 
         [0019]    Finally, device  10  includes a top strap  48  that extends laterally proximate to top edge  14  and second side edge  20 . A top snap-hook  50  is secured to top strap  48  and extends laterally beyond second side edge  20 . A bottom strap  52  extends laterally proximate to bottom edge  16  and second side edge  20 . A bottom snap-hook  54  is secured to bottom strap  52  and extends laterally beyond second side edge  20 . 
         [0020]    Protective device  10  is used to protect service personnel in the following exemplary manner. If the circuit breaker is active and resides in a sub-station, the circuit breaker must first be de-energized. All switches must be opened and grounded properly. Next, maintenance personnel may use a man-lift, scaffolding or other approved method to reach a desired installation height. Next, the protective device  10  is installed around the bushing  3  according to the method described hereinafter. The maintenance personnel may then perform mechanical testing of the circuit breaker in accordance with maintenance procedures of the manufacturer. Once testing and maintenance is completed, the protective device is then removed and the breaker may be re-energized. 
         [0021]    Protective device  10  may be installed according to the following method. Device  10  is positioned near the bushing  3  with top edge  14  located proximate to terminal  4  and bottom edge positioned proximate to body portion  2 . Beginning with second side edge  20 , the cover  12  is wrapped around the bushing  3  so that the cover  12  overlaps a substantial portion of unstrapped area  56  between snap-hooks  26  and second side edge  20 . In conjunction therewith the various fasteners are connected according to the following method. D-ring  42  is attached to top snap hook  50 . Next, D-rings  24   a  receives extended portion  28  so that strap  24   a  may be cinched tightly around bushing  3  in an adjustable manner. Next, snap-hooks  26   b - f  are secured to b-rings  24   b - f  respectively. Next bottom snap-hook  54  is secured to D-ring  46 . D-rings  32  then receive top portion  36  in an adjustable, cinching manner. Finally, bottom portion  38  is wrapped around body portion  2  and is received in D-rings  33  in an adjustable, cinching manner. 
         [0022]    In this manner, lateral straps  22  provide the radial support in the event of an explosion, to prevent the unwrapping of cover  12 . First longitudinal strap  30  loops over the top of the bushing and second longitudinal strap extends around body portion  2  to ensure proper longitudinal positioning of the cover  12 . The resulting device surrounds substantially the entire bushing, wherein only the terminals  4  extend above device  10 . Because device  10  is wrapped around the bushing  3 , high tension wires  5  may remain connected to contact  4  during installation and removal of device  10 . Thus, in addition to the above exemplary use, device  10  of the present invention may be used for circuit breaker transportation, installation, commissioning, storage and maintenance. 
         [0023]    The present invention protects maintenance personnel from potentially hazardous flying debris. The device  10  will not prevent a explosion, but will limit or contain a bushing explosion in a manner that allows the controlled escape of high pressure and porcelain fragments to escape at the top and bottom of the device  10 . Further, device  10  may be installed on presently installed breakers without the need to disconnect, for example, the high voltage line  5  from terminals  4 . 
         [0024]    It is to be understood that the description of the foregoing exemplary embodiment(s) is (are) intended to be only illustrative, rather than exhaustive, of the present invention. Those of ordinary skill will be able to make certain additions, deletions, and/or modifications to the embodiment(s) of the disclosed subject matter without departing from the spirit of the invention or its scope, as defined by the appended claims.