Abstract:
An improved fuse cutout is provided of the type having a fuse tube assembly that moves to a dropout position upon operation in response to a fault current or other overcurrent. These types of fuse cutouts include the pivotal mounting of the fuse tube assembly with respect to a support hinge with the fuse tube assembly being released for pivotal movement to the dropout position when the fuse cutout has operated. The fuse tube assembly includes a collapsible toggle joint that collapses upon operation of the fuse cutout. The improved fuse cutout includes additional dropout assistance that is provided via a resilient member operating between the components of the collapsible toggle joint to apply a force to assist the collapse of the toggle joint.

Description:
This application is a continuation of application Ser. No. PCT/US03/12449 filed on Apr. 14, 2003 which claims the benefit of U.S. Provisional Application Nos. 60/375,800 filed Apr. 26, 2002 and 60/377,516 filed May 3, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an improved fuse cutout and, more particularly, to an improved fuse cutout that has increased dropout characteristics and operating performance. The improved fuse cutout of the present invention is of the type shown in S&amp;C Electric Co. Descriptive Bulletin 351-30, dated Dec. 7, 1998, entitled “S&amp;C Type XS Fuse Cutouts” and in U.S. Pat. Nos.: 2,553,098; 2,745,923 and 4,414,527. This type of fuse cutout may be used with a fuse link of the type sold by S&amp;C Electric Co. as the Positrol® Fuse Link and as generally shown in U.S. Pat. Nos. 4,317,099. 
   2. Discussion of the Prior Art 
   Fuse cutouts and fuse links utilized therein are well known. A typical fuse cutout includes a hollow insulative fuse tube having conductive ferrules mounted to the opposite ends thereof. One ferrule (often called the “exhaust” ferrule) is located at an exhaust end of the fuse tube and usually includes a trunnion which interfits with a trunnion pocket or hinge of a first contact assembly carried by one end of an insulator. The other ferrule is normally held and latched by a second contact assembly carried by the other end of the insulator so that the fuse tube is normally parallel to, but spaced from, the insulator. The insulator is mountable to the cross-arm of a utility pole or a similar structure. The fuse link is located within the fuse tube with its ends respectively electrically continuous with the ferrules. One point of an electrical circuit is connected to the first contact assembly, while another point of the circuit is connected to the second contact assembly. Often, the insulator and the fuse tube are oriented generally perpendicular to the ground so that the exhaust ferrule and the first contact assembly are located below the other ferrule and the second contact assembly. The fuse tube may include a high burst strength outer portion—for example, a fiber-glass-epoxy composite having an arc-extinguishing material within the inner portions thereof. Normal currents flowing through the electrical circuit flow without affecting the fuse link. Should a fault current or other overcurrent, to which the fuse link is designed to respond, occur in the circuit, the fuse link operates as described in more detail hereinafter. 
   Operation of the fuse link permits the upper ferrule to disengage itself from the upper contact assembly, whereupon the fuse tube rotates downwardly due to coaction of the trunnion and the hinge. If the fuse link operates properly, current in the circuit is interrupted and the rotation of the fuse tube gives a visual indication that the cutout has operated to protect the circuit, e.g. dropout operation to a so-called dropout position. Typical fuse links include a first terminal and a second terminal, between which there is normally connected a fusible element made of pure silver, silver-tin, or the like. Also connected between the terminals may be a strain wire, for a purpose described below. The second terminal is electrically continuous with, and is usually mechanically connected to, a button assembly, which is engagable by a portion of the upper ferrule on the fuse tube. The first terminal is connected to a flexible, stranded length of cable. Surrounding at least a portion of the second terminal, the fusible element, the strain wire (if used), the first terminal, and some portion of the flexible stranded cable is a sheath. The sheath is typically made of a so-called ablative arc-extinguishing material which, when exposed to the heat of a high-voltage arc, ablate to rapidly evolve large quantities of deionizing turbulent and cooling gases. Typically, the sheath is much shorter than the fuse tube and terminates short of the exhaust end of the fuse tube. 
   The free end of the stranded cable exits the fuse tube from the exhaust end thereof and has tension or pulling force maintained thereon by a spring-loaded flipper on the trunnion. The tension or pulling force exerted on the cable by the flipper attempts to pull the cable and the first terminal out of the sheath and out of the fuse tube. The force of the flipper is normally restrained by the strain wire, typical fusible elements not having sufficient mechanical strength to resist this tension or pulling force. 
   In the operation of typical cutouts, a fault current or other over-current results, first, in the melting or vaporization of the fusible element, followed by the melting or vaporization of the strain wire. Following such melting or vaporization, a high-voltage arc is established between the first and second terminals within the sheath and the flipper is now free to pull the cable and the first terminal out of the sheath and, ultimately, out of the fuse tube. As the arc forms, the arc-extinguishing materials of the sheath begin to ablate and high quantities of de-ionizing, turbulent and cooling gases are evolved. The movement of the first terminal under the action of the flipper, and the subsequent rapid movement thereof due to the evolved gases acting thereon as on a piston, results in elongation of the arc. The presence of the de-ionizing, turbulent and cooling gas, plus arc elongation, may, depending on the level of the fault current or other over-current, ultimately result in extinction of the arc and interruption of the current at a subsequent current zero. The loss of the tension on the stranded cable permits the trunnion to experience some initial movement relative to the exhaust ferrule which permits the upper ferrule to disengage itself from the upper contact assembly. This initiates a downward rotation of the fuse tube and its upper ferrule to a so-called “dropout” or “dropdown” position. 
   As noted above, arc elongation within the sheath and the action of the evolved gases may extinguish the arc. At very high fault current or over-current levels, however, arc elongation and the sheath may not, by themselves, be sufficient to achieve this end. Simply stated, at very high fault current levels, either the sheath may burst (because of the very high pressure of the evolved gas) or insufficient gas may be evolved therefrom to quench the high current level arc. For these reasons, the fuse tube is made of, or is lined with, ablative arc-extinguishing material. In the event the sheath bursts, the arc-extinguishing material of the fuse tube interacts with the arc, with gas evolved as a result thereof achieving arc extinction. If the sheath does not burst, the arc-extinguishing material of the fuse tube between the end of the sheath and the exhaust end of the fuse tube is nevertheless available for evolving gas, in addition to that evolved from the sheath. The joint action of the two quantities of evolved gas, together with arc elongation, extinguish the arc. 
   When a fuse tube is properly positioned between the upper and lower contact assemblies of the mounting, the contacts of the fuse tube are firmly engaged within the contact assemblies of the mounting. When the fuse link operates, gases evolved within the fuse tube thrust it against the upper contact assembly of the mounting. Ideally, the contact cap should not disengage the concavity until the fusible elements of the fuse link completely melts to release the tension in the cable and until the initial thrust of the fuse tube subsides. Release of this tension and subsiding of fuse tube thrust permits a limited amount of relative movement between the exhaust ferrule and the trunnion about a toggle joint therebetween. This limited movement permits the contact cap to move out of the concavity and the fuse tube to begin movement toward the dropout position due to rotation of the trunnion in the hinge pocket. If the fuse tube moves too far transversely during its thrusting, the contact cap may disengage the concavity too early. Third, transverse movement of the fuse tube can apply a bending movement thereon. This bending movement can fracture the fuse tube near the exhaust ferrule. Corrosion that builds up on various parts and dimensional changes of the fuse tube or fuse link sheath, e.g. due to environmental factors, can exacerbate the proper dropout action. 
   Thus, it is important for achieving proper operation as explained above that dropout operation be readily achieved in spite of any deleterious operating environments or conditions. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is a principal object of the present invention to provide a cutout with improved dropout performance. 
   This and other objects of the present invention are achieved by an improved fuse cutout of the type having a fuse tube assembly that moves to a dropout position upon operation in response to a fault current or other overcurrent. These types of fuse cutouts include the pivotal mounting of the fuse tube assembly with respect to a support hinge with the fuse tube assembly being released for pivotal movement to the dropout position when the fuse cutout has operated. The fuse tube assembly includes a collapsible toggle joint that collapses upon operation of the fuse cutout. The improved fuse cutout includes additional dropout assistance that is provided via a resilient member operating between the components of the collapsible toggle joint to apply a force to assist the collapse of the toggle joint. 

   
     DESCRIPTION OF THE DRAWING 
       FIG. 1  is a perspective view of an improved fuse cutout according to the present invention; 
       FIG. 2  is an elevational view of a fuse tube assembly of the cutout of  FIG. 1 ; 
       FIG. 3  is an enlarged, partial view of the fuse tube assembly of  FIG. 2  in an operative position; and 
       FIG. 4  is an enlarged elevational view of a dropout assist member of the cutout of FIGS.  1 - 3 . 
   

   DETAILED DESCRIPTION 
   Referring first to  FIG. 1 , there is shown an improved cutout  12  according to the present invention that includes an insulator  14  and a mounting member  16  extending therefrom. The mounting member  16  permits mounting of the insulator  14  and the fuse cutout  12  to an upright or a crossarm of a utility pole or the like (not shown). Affixed to the upper end of the insulator  14  is an upper contact assembly generally designated  18 . Further, affixed to the lower end of the insulator  14  is a lower contact assembly  20 . The cutout  12  also includes a fuse tube assembly  22  (also shown in  FIG. 2 ) that in the normal, circuit-connected or unoperated condition of the cutout  12  may be maintained in the generally vertical position shown in  FIG. 1 , e.g. cutouts are typically mounted at a slight angle to the vertical. 
   Considering now more specific features of the fuse tube assembly  22 , the fuse tube assembly includes an insulative fuse tube  24  of a well-known type, which may comprise an epoxy-fiber-glass composite outer shell lined with an arc-extinguishing material. Mounted or affixed to the upper end of the fuse tube  24  is an upper ferrule assembly  26 , while at the opposite lower or exhaust end of the fuse tube  24  is a lower or exhaust ferrule assembly  28 . In the position of the fuse tube assembly  22  depicted in  FIG. 1 , the lower ferrule assembly  28  is held by the lower contact assembly  20 , while the upper ferrule assembly  26  is held, and latched against movement, by the upper contact assembly  18 . 
   The upper contact assembly  18  includes a support bar  30  and a recoil arm and contact hood  32  which runs generally parallel to a portion of the support bar  30 . Near the top of the insulator  14 , the bar  30  and the arm  32  are mounted by a fastener or the like at  36  to a portion of a connector assembly  40  that is affixed to the top of the insulator  14 . The connector assembly  40  facilitates the connection to the upper contact assembly  18  to a cable or conductor of a high-voltage circuit. 
   The upper contact assembly  18  also includes a spring contact arm  42  and a backup spring  44  that is positioned between the spring contact arm  42  and the recoil arm and contact hood  32 , e.g. the backup spring  44  is positioned at one end over a convexity  45  extending from the top of the contact arm  42  and at the other end over a convexity (not shown) extending downwardly from the recoil arm and contact hood  32 . The backup spring  44  provides high contact pressure between the contact arm  42  and the top of the fuse tube assembly  24  as will be explained in more detail hereinafter. As is typical in the power industry, the support bar  30  at a downwardly bent portion  35  includes attachment hooks  48  for cooperation with a portable loadbreak tool. 
   The upper ferrule assembly  26  of the fuse tube assembly  24  includes a ferrule  50  affixed to the upper end of the fuse tube  24 . The ferrule  50  typically includes a threaded portion (not shown) onto which is threaded a contact cap  52 . The contact cap  52  is configured so as to fit into and be held when the fuse tube assembly  22  is in the position shown in  FIG. 1 , e.g., by an indentation or concavity (not shown) formed in the spring contact  42  opposite the convexity  45 . The ferrule  50  typically also includes a pull ring  54 . The pull ring  54  may be engaged by a hook stick or the like to move the upper ferrule assembly  26  away from the upper contact assembly  18  while the lower ferrule assembly  28  rotates in the lower contact assembly  20 , as described hereinafter. 
   In view of the nature of high voltage circuits, this opening movement of the fuse tube assembly  22  must be effected while the circuit connected to the cutout  10  is de-energized or else an arc will form between the upper ferrule assembly  26  and the upper contact assembly  18 . The fuse tube assembly  22  may also be opened by initially attaching between the attachment hooks  48  and the pull ring  54  a portable loadbreak tool. Such a portable loadbreak tool permits the fuse tube assembly  22  to be opened with the circuit energized, momentarily having transferred thereto the flow of current in the circuit  10  and interrupting such current internally thereof. 
   The lower contact assembly  20  includes a support member  56  attached to a mount  58  by a fastener or the like at  60 . The support member  56  carries a connector  62 , such as a parallel groove connector, to facilitate connection of the lower contact assembly  20  to another cable or conductor of the high-voltage circuit in which the fuse cutout  12  is to be used. The support member  56  provides a hinge function via trunnion pockets  64 . The trunnion pockets are designed to cooperate with and hold outwardly extending portions  66  of a trunnion  68  (also shown in  FIG. 3 ) carried by the fuse tube  24 . Specifically, a lower ferrule  72  affixed to the fuse tube  24  pivotally mounts the trunnion  68  at a toggle joint  70 . Thus, the trunnion  68  functions as a toggle member and defines a double pivot mounting for the fuse tube  24 , the first pivot being defined at the toggle joint  70  and the second pivot being defined by the extending portions  66  of the trunnion  68  within the trunnion pockets  64  of the hinge support member  56 . 
   As hereinafter described, the trunnion  68  and the ferrule  72  are normally rigidly held in the relative position depicted in FIG.  1 . In this normal relative position of the trunnion  68  and the ferrule  72 , the contact cap  52  is engaged by the spring contact  42  to maintain the fuse tube assembly  22  in the position depicted in FIG.  1 . Also, as described in more detail below, when a fuse link (not shown) within the fuse tube  24  operates, the trunnion  68  and the ferrule  72  are no longer rigidly held, and the ferrule  72  may rotate downwardly relative to the trunnion  68  about the toggle joint  70 . This movement of the ferrule  72  permits the contact cap  52  to disengage the spring contact  42 , following which the entire fuse tube assembly  22  rotates about the lower contact assembly  20  via rotation of the extending portions  66  in the trunnion pockets  64 . Considering additional structural features, rotatably mounted to the trunnion  68  is a flipper  74 . A spring  75  mounted between the trunnion  68  and the flipper  74  biases the flipper  74  away from the lower or exhaust end of the fuse tube  24 . The trunnion  68  includes shoulders  76  or other similar features. The support member  56  also includes features, such as shoulders  78 , normally spaced from the shoulders  76  when the extending portions  66  of the trunnion  68  are seated in their respective trunnion pockets  64 . The normal spacing between the shoulders  76  and  78  is sufficient to permit appropriate movement of the fuse tube  24  with respect to the lower contact assembly  20  during operation as explained hereinafter. 
   In use, a fuse link is first installed into the fuse tube assembly  22 . Suffice it here to say that the contact cap  52  is removed and the fuse link is inserted into the interior of the fuse tube  24  from the upper end thereof. A portion of the fuse link abuts a shoulder (not shown) at the top of the ferrule  50 , following which the contact cap  52  is threaded back onto the ferrule  50 . Reference may be made to S&amp;C Electric Co. Instruction Sheet  351 - 500  and the aforementioned patents for additional information and details. A flexible stranded cable  80  forming a part of the fuse link exits an exhaust opening at  81  in the lower or exhaust end of the fuse tube  24 . The flipper  74  is manually rotated against the action of the spring  75  to position it adjacent the exhaust opening at  81  following which the cable  80  is laid into a channel at  82  in the flipper  74 . Following this, the cable  80  is wrapped around a flanged bolt  84  (shown in  FIGS. 2-4 ) that is threaded into the trunnion  68  via a threaded portion  85 . Following tightening of the flanged bolt  84  to hold the cable  80 , the flipper  74  is maintained against the bias of the spring  75  in the position shown in  FIG. 1 , whereat there is a constant tension force applied to the cable  80  and the remainder of the fuse link within the fuse tube  24 . It is this connection of the cable  80  to the trunnion  68  by the flanged bolt  84  and the action of the spring  75  on the flipper  74  that normally holds the trunnion casting  68  and the ferrule  72  in the position depicted in  FIG. 1  relative to the toggle joint  70 . 
   Following operation of a fuse link within the fuse tube  24 , the flipper  74  is able to move the cable  80  downwardly within the fuse tube  24 . The release of the tension force applied to the cable  80  by the flipper  74  permits relative movement of the ferrule  72  and the trunnion  68  about the toggle joint  70  to permit separation of the contact cap  52  from the spring contact  42 . The relative movement of the ferrule  72  and the trunnion  68  occurs after tension in the cable  80  is released and after an initial upward thrust of the fuse tube  24  subsides. As more fully explained in the aforementioned patents, when a fusible element (not shown) of the fuse link within the fuse tube  24  melts, there follows the rapid evolution of arc-extinguishing gas within the fuse tube  24 . This evolved gas exits the exhaust opening at  81  of the fuse tube  24  at a very rapid rate, thrusting the fuse tube  24  upwardly. 
   When the fuse link operates, the tension on the cable  80  is released at the same time the fuse tube  24  thrusts up. While the relative movement of the trunnion  68  with respect to the ferrule  72  and about the toggle joint  70  does not immediately occur simultaneously with the rapid gas exhaust, it is able to occur shortly thereafter in response to the release of tension in the cable  80 . This relative movement permits the contact cap  52  to disengage from the contact arm  42  and the fuse tube assembly  22  to rotate to a “dropout” position via rotation of the extensions  66  of the trunnion  68  in the trunnion pockets  64 . All of the above is “timed” so that rotation of the fuse tube assembly  22  is initiated as or after the fuse link has interrupted current in the circuit. 
   There is a tendency for frictional resistance caused by corrosion, contamination or sleet such that the trunnion  68  may not be able to pivot about the hinge support member  56 . If that should occur, the fuse tube  24  would remain in place and not dropout, thus not providing the desirable and necessary air gap to prevent leakage over the fuse tube  24 . To this end, an anvil surface  86  is provided on the lower surface of the trunnion  68  that is engaged by the upper edges  88  of the spaced sidewalls  90  of the flipper  74 . Thus, the impact of the flipper  74  as well as the action of the spring  75  act to assist in pivoting the trunnion  68  about the toggle joint  70 . In some circumstances it may be desirable and/or necessary to further improve the dropout performance, especially where 1. the fuse link or fuse tube components might experience dimensional changes due to environmental factors and/or 2. where the cutout mounting and fuse tube assembly are from different manufacturers which may not be ideally suited to work with each other, i.e. the interfacing, cooperating components are not identical to those for which they were designed. 
   In accordance with important aspects of the present invention, additional dropout assistance is provided via a spring  92  carried about the shaft of the bolt  84 , e.g. the shaft of the bolt  84  having a narrowed portion  94  beyond the wider, threaded shaft portion  96 . Ina specific embodiment, the narrowed portion  94  includes a threaded portion  98  for affixing the spring  92  to the bolt  84 . The spring  92  is compressed when the bolt  84  is threaded into the trunnion  68  and tightened to hold the cable  80 . The spring  92  is compressed against an extending tab  100  of the ferrule  72  of the lower ferrule assembly  28 . Accordingly, when the fuse operates and the cable  80  is released, the spring  92  acts to directly rotate the trunnion  68  about the toggle joint  70  to assist in the dropout action of the fuse tube assembly  22 . It should be noted that this assist action is more positive than that of the pivoting of the trunnion  68  due to its being released and also over a wider range and time than that of the release of the flipper  74 . 
   Accordingly, the bolt  84  with the spring  92  as an overall assembly  104  performs a dropout assistance function and also functions to retain or clamp the cable  80  to maintain the fuse tube assembly within the upper and lower contact assemblies  18  and  20 . It should also be noted that since every fuse cutout of the type  12  utilizes a bolt such as  84  to clamp the cable  80 , the dropout assistance assembly  104  is capable of easy retrofit in the field merely by substituting the dropout assistance assembly  104  for the conventional bolt for clamping the cable  80 . Further, the desired additional dropout assistance is variable in specific embodiments via the selection of the resilient characteristics of the spring  92 . It will also be clear to those skilled in the art that the leading surface of the spring  92  and/or the extending tab  100  of the ferrule  72  of the lower ferrule assembly  28  should be prepared and/or finished so as to provide unfettered rotation of the spring  92  when tightening the bolt  84  during installation of the fuse link as well as reliable disengagement thereof during operation of the fuse cutout  12 . 
   While there have been illustrated and described various embodiments of the present invention, it will be apparent that various changes and modifications will occur to those skilled in the art. Accordingly, it is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the present invention.