Patent Publication Number: US-2023145762-A1

Title: Tamper resistant plug

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority from the U.S. Provisional Application No. 63/278,215, filed on Nov. 11, 2021, the disclosure of which is hereby expressly incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     Field 
     This disclosure relates generally to a tamper resistant plug and, more particularly, to a tamper resistant plug for a hermetically sealed tank associated with medium-voltage switchgear, where the plug includes a polygon shaped interface surface with only rounded edges. 
     Discussion of the Related Art 
     An electrical power distribution network, often referred to as an electrical grid, typically includes a number of power generation plants each having a number of power generators, such as gas turbines, nuclear reactors, coal-fired generators, hydro-electric dams, etc. The power plants provide power at a variety of medium voltages that are then stepped up by transformers to a high voltage AC signal to be connected to high voltage transmission lines that deliver electrical power to a number of substations typically located within a community, where the voltage is stepped down to a medium voltage for distribution. The substations provide the medium voltage power to a number of three-phase feeders including three single-phase feeders that carry the same current, but are 120° apart in phase. A number of three-phase and single phase lateral lines are tapped off of the feeder that provide the medium voltage to various distribution transformers, where the voltage is stepped down to a low voltage and is provided to a number of loads, such as homes, businesses, etc. Some power distribution networks may employ a number of underground single-phase lateral circuits that feed residential and commercial customers. Often times these circuits are configured in a loop and fed from power sources at both ends, where an open circuit location in the loop isolates the two power sources. 
     Power distribution networks of the type referred to above typically include a number of switching devices, breakers, reclosers, current interrupters, etc. that control the flow of power throughout the network. Standalone pad mounted and underground switchgear including electrical disconnect switches, fuses and/or circuit breakers used to control, protect and isolate electrical equipment are often employed to de-energize equipment to allow work to be done and to clear faults. Switchgear often include load-interrupter switches, resettable, vacuum fault interrupters and other equipment that are enclosed in a hermetically sealed and gas-insulated steel tank to provide electrical isolation. The tank is generally filled with a blend of CO 2  and 3M™ Novec™ 4710 insulating gas (CO 2 -Novec) through a fill port, and the fill port is subsequently sealed with a plug, where the plug is designed to be opened with a special tool. However, the plug in existing switchgear tanks can generally be opened with a flat head screwdriver or other commonly available tool. Even though these tanks are hermetically sealed at the factory, they can leak over time, which would lead the owner of the switchgear to remove the plug using these tools and refill the tank, possibly with the wrong insulating gas, such as SF 6 . 
     Hermetically sealed gas-insulated equipment (GIE) can be defined under regulations as being pre-charged with covered insulating gas, sealed at the factory and designed by the manufacturer to not be fillable by the GIE owner or a third-party designee. In order to meet this definition of hermetically sealed GIE, the plug for these tanks needs to be redesigned such that it is not able to be removed by the equipment owner or a third-party designee and filled with insulating gas. 
     SUMMARY 
     The following discussion discloses and describes a tamper resistant plug that has particular application for sealing a fill port in a hermetically sealed and gas-insulated tank associated with medium-voltage switchgear. The plug includes a body portion and a top annular rim defining a central recess and having an internal surface facing the recess, where the internal surface has a polygon shape with only rounded edges. In one embodiment, the polygon shape is a trilobe. 
     Additional features of the disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an isometric view of medium-voltage switchgear including a hermetically sealed and gas insulated tank; 
         FIG.  2    is a cutaway isometric view of the tank in the switchgear shown in  FIG.  1    and illustrating a fill port sealed with a tamper resistant plug; 
         FIG.  3    is a side view of the tamper resistant plug separated from the fill port; 
         FIG.  4    is a top view of the tamper resistant plug separated from the fill port; and 
         FIG.  5    is an isometric view of a specially configured tool operable to be seated in the plug for rotating the plug. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following discussion of the embodiments of the disclosure directed to a tamper resistant plug is merely exemplary in nature, and is in no way intended to limit the disclosure or its applications or uses. For example, the tamper resistant plug has particular application for sealing a fill port of a hermetically sealed and gas-insulated tank in medium-voltage switchgear. However, as will appreciated by those skilled in the art, the plug may have application for sealing other enclosures. 
       FIG.  1    is an isometric view of medium-voltage switchgear  10  mounted on a pad  12  and including an enclosure  14 . The switchgear  10  is intended to represent any suitable switchgear employed in an electrical power distribution network as discussed above, and can include any and all components for a particular application. 
       FIG.  2    is a cutaway isometric view of a hermetically sealed steel tank  20  that can be used in the switchgear  10  shown in  FIG.  1   . Typically, vacuum circuit breakers, disconnect switches and other components and electrical equipment (not shown) associated with the operation of the switchgear  10  would be enclosed in the tank  20  to provide the equipment in a gas-insulated environment. The tank  20  is filled with an insulating gas, such as CO 2 -Novec, through a circular, threaded fill port  22  during manufacture of the switchgear  10 , and the fill port  22  is sealed with a circular, tamper resistant steel plug  24 . 
       FIG.  3    is a side view and  FIG.  4    is a top view of the plug  24  separated from the tank  20 . The plug  24  includes a threaded body portion  28  that attaches to the threaded fill port  22  to allow the plug  24  to be rotated and be inserted and removed from the fill port  22 . The plug  24  also includes an outer top annular rim  30  that defines a recess  32  in the top of the plug  24 . An inner surface  34  of the rim  30  facing the recess  32  has a specially configured shape that prevents off-the-shelf, readily available and/or common tools, such as screw drivers, sockets, pliers, channel locks, etc., from engaging the rim  30  in a manner that allows the tool to rotate the plug  24  and remove it from the fill port  22 . Particularly, the inner surface  34  has a polygonal shape with only rounded edges, i.e., no corners or flat edges, that might otherwise allow the common tool to engage the surface  34 . In one embodiment, the polygonal shape is a trilobe defined by lobe indentations  36 ,  38  and  40 . Therefore, the plug  24  cannot generally be removed from the fill port  22  by an owner of the switchgear  10  after the switchgear  10  has left the factory. In one non-limiting embodiment, the recess  32  has a diameter of about 0.850″. 
       FIG.  5    is an isometric view of a specially designed tool  50  that is operable to engage the inner surface  34  of the rim  30  to rotate the plug  24 . The tool  50  includes a cylindrical portion  52  and a head portion  54 . The head portion  54  includes an outer surface  56  that is the same size and shape as the recess  32 . Thus, when the head portion  54  is inserted into the recess  32 , the outer surface  56  perfectly engages the inner surface  34  such then when the tool  50  is rotated, the plug  24  also rotates. Thus, the plug  24  can initially be inserted in the fill port  22  and can later be removed at the factory if the tank  20  needs to be refilled with gas. 
     The foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.