Patent Publication Number: US-6657842-B2

Title: Disconnector assembly for an arrestor

Description:
BACKGROUND OF THE INVENTION 
     Lighting or surge arrestors are typically connected to power lines to carry electrical surge currents to ground, thereby preventing damage to lines and equipment connected to the arrestors. Arrestors offer high resistance to normal voltage across power lines, but offer very low resistance to surge currents produced by sudden high voltage conditions caused by, for example, lighting strikes, switching surge currents or temporary overvoltages. After the surge, the voltage drops and the arrestor normally returns to a high resistance state. However, upon arrestor malfunction or failure, the high resistance state is not resumed, and the arrestor continues to provide an electrical path from the power line to ground. Ultimately, the line will fail due to a short circuit condition or breakdown of the distribution transformers, and the arrestor will require replacement. 
     To avoid line failure, disconnector assemblies are commonly used in conjunction with arrestors to separate a malfunctioning arrestor from the circuit and to provide a visual indication of arrestor failure. Conventional disconnector assemblies have an explosive charge to destroy the circuit path and physically separate the electrical terminals. Examples of such disconnector assemblies are disclosed in U.S. Pat. No. 5,952,910 to Krause and U.S. Pat. Nos. 5,057,810 and 5,113,167 to Raudabaugh, as well as U.S. Pat. No. 5,434,550 to Putt and U.S. Pat. No. 4,471,402 to Cunningham, the subject matter of each of which are hereby incorporated by reference. 
     However, conventional disconnector assemblies have components loaded within the bracket cavity. Adhesive is used to secure the ground terminal within the bracket. Often, the ground terminals become misaligned before the adhesive cures, thereby rendering the disconnector assembly unfit for use. 
     Additionally, the adhesive may flow into the internal cavity housing the isolator assembly, thereby contaminating the isolator assembly by interfering with the electrical contacts and rendering the disconnector assembly unfit for use. A gasket may be positioned between the ground terminal and the isolator assembly to prevent contamination of the isolator assembly by the adhesive. However, the gasket does not eliminate flow of the adhesive into the bracket cavity. 
     Furthermore, contamination may adhere to the adhesive, thereby forming an electrical track or path across the adhesive. Such an electrical track lowers the insulation resistance of the arrestor, which renders the arrestor unfit for use as an insulator. 
     Production of such unfit disconnector assemblies is costly, as well as time consuming. Manufacturing disconnector assemblies requiring extra parts to protect the isolator assembly increases inventory in addition to increasing costs and manufacturing times. 
     A need exists for an improved disconnector assembly for an arrestor that overcomes the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a primary objective of the present invention to provide a disconnector assembly for an arrestor having a ground terminal partially disposed in a bore in a cap to reduce the possibility of the ground terminal becoming misaligned during manufacture of the disconnector assembly. 
     A further objective of the present invention is to provide a disconnector assembly for an arrestor that requires less adhesive for securing the cap to the bracket, thereby reducing both the likelihood of contaminating the isolator assembly and manufacturing costs. 
     A still further objective of the present invention is to provide a disconnector assembly for an arrestor that having a cap that encapsulates the adhesive, thereby eliminating electrical tracking due to contamination build-up on the adhesive. 
     The foregoing objects are basically attained by providing an assembly for an arrestor. The assembly has a bracket that has a base and a wall. The wall extends substantially perpendicularly from the base and defines a cavity. An isolator assembly is disposed within the cavity. A cap is connected to the wall remote from the base to close the cavity. A bore extends into the cap from a surface thereof remote from the cavity. A stud is partially disposed in the bore. An adhesive between the cap and the wall secures the cap to the wall. 
     The stud is partially disposed in the bore in the cap, thereby eliminating misalignment of the stud. Less adhesive is required to secure the cap to the bracket, thereby reducing the likelihood of contaminating the isolator assembly with the adhesive and eliminating the need for a gasket between the cap and the isolator assembly. Since the adhesive is encapsulated by the cap, contamination is not able to form an electrical path across the adhesive, thereby preventing the occurrence of electrical tracking. 
     Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings that form a part of the original disclosure: 
     FIG. 1 is a side elevational view in cross section of a disconnector assembly according to the present invention; 
     FIG. 2 is a side elevational view of the disconnector assembly of FIG. 1 connected to an arrestor in partial cross section; 
     FIG. 3 is a perspective view of the cap of the disconnector assembly of FIG. 1; and 
     FIG. 4 is a side elevational view of the cap of FIG. 3; and 
     FIG. 5 is a top plan view of the cap of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIGS. 1-5, the present invention relates to a disconnector assembly  11  for connecting and then isolating and disconnecting an arrestor  13  between a power line  15  and ground  17 . The disconnector assembly  11  has a bracket  21  that has a base  23  and a wall  25 . The wall  25  extends substantially perpendicularly from the base  23  and defines a cavity  27 . An isolator assembly  29  is disposed within the cavity  27 . A cap  31  is connected to the wall  25  remote from the base  23  to close the cavity  27 . A bore  33  extends into the cap  31  from a surface  35  thereof remote from the cavity  27 . A stud  41  is partially disposed in the bore  33 . An adhesive  51  between the cap  31  and the wall  25  secures the cap to the wall. 
     Referring initially to FIGS. 1 and 2, a disconnector assembly  11 , according to the present invention, comprises a first, upper electrical terminal  12  electrically connected to arrestor  13 , and a second, lower electrical terminal, or stud,  41  electrically connected to ground  17 . Arrestor  13  is electrically connected to power line  15 , which is representative of a power system. Terminals  12  and  41  are mechanically and electrically coupled to each other. 
     Arrestor  13  is conventional, and thus, is not described in detail. The arrestor may be formed according to U.S. Pat. No. 4,656,555 to Raudabaugh, the subject matter of which is hereby incorporated by reference. 
     Terminals  12  and  41  are mechanically connected to one another by a bracket  21 . Bracket  21  may be formed of any suitably strong insulating material, such as a non-conductive plastic. Preferably, the bracket is made of a glass filled polyester material. As noted above, the bracket  21  has a base  23  and a wall  25  extending substantially perpendicularly from base  23 , with wall  25  defining an internal cavity  27  extending between surface  22  of base  23  and surface  28  of wall  25 . The upper end of cavity  27  is connected to bracket surface  26  by cylindrical upper bore  30 . The lower end of cavity  27  is connected to surface  28  of wall  25  by a stepped lower chamber  32 . The transverse diameter of lower chamber  32  is greater than the transverse diameter of internal cavity  27 . 
     Between cavity  27  and lower chamber  32 , the bracket has a radially extending lower annular shoulder  34 . An upper shoulder  36  extends radially at the interface of cavity  27  and upper bore  30 . 
     Upper electrical terminal  12  is of conventional construction, and has a head portion  38  located within cavity  27  and abutting upper shoulder  36 . An externally threaded shank portion  40  of terminal  12  extends from the head portion through upper bore  30 , such that the shank portion is at least partially exposed exteriorly of bracket  21  for coupling to arrestor  13 . In this manner, head portion surface  42  engages upper shoulder  36 , while head portion surface  44  is exposed in cavity  27 . 
     An isolator assembly  29  is disposed in cavity  27 . The isolator assembly may include a resistor  58 , a cartridge  60 , a spring  46  and a spacer. The spring  46  abuts surface  44  of terminal head portion  38 . Spring  46  provides a biasing force to maintain electrical or physical contact of the isolator assembly components within cavity  27 , and facilitates electrically connecting upper terminal  12  to lower terminal (stud)  41 . 
     Solid cylindrical resistor  58  is mounted in cavity  27  and extends between spring  46  and upper surface of cap  31 , thereby providing a resistive electrical connection between the upper and lower terminals  12  and  41  through conductive cap  31 . 
     Cartridge  60  with an explosive charge is mounted in cavity  27  adjacent resistor  58 . Cartridge  60  is elongated along a cartridge axis which is substantially perpendicular to the longitudinal axis of terminals  12  and  41  and of bracket cavity  27 . The configuration of cartridge  60  is generally cylindrical with one end being tapered. The lateral exterior of cartridge  60  may be substantially covered or surrounded by a gap spacer to prevent movement of the cartridge within cavity  27 . Alternatively, cartridge  60  may be held loosely within cavity  27 . However, allowing such movement may cause the assembly to rattle, which may be considered to be undesirable in certain environments. 
     As shown in FIGS. 3-5, cap  31  is connected to the wall  25  remote from the base  23  to close the cavity  27 . Preferably, cap  31  has a substantially annular shape. Cap  31  has a surface  37  for connecting to wall  25  of bracket  21 . Surface  37  has a groove  39  for receiving distal surface  28  of wall  25 . Preferably, a press fit is created between cap  31  and wall  25 . Preferably, groove  39  is substantially circular. Bore  33  extends into cap  31  from surface  35  that is remote from cavity  27 . Bore  33  extends only partially through cap  31 , as shown in FIG.  1 . Cap  31  is made of any conductive material, such as plastic or metal. Preferably, cap  31  is die cast. 
     Lower terminal  41  is a conventional stud. Lower terminal, or stud,  41  has a shank portion  50  received by bore  33  in cap  31 , such that the stud is only partially disposed in the bore. Stud  41  is maintained in position in bore  33  by any suitable method, including, but not limited to, threading, welding, forming and crimping. 
     An adhesive  51  between the cap  31  and the wall  25  secures cap  31  to wall  25 . Preferably, adhesive  51  is disposed in groove  39  of cap  31 , and on distal surface  28  of wall  25 , inner surface  53  of wall  25 , and radially inwardly extending lower shoulder  34 . The adhesive secures cap  31  to wall  25  of bracket  21 , in addition to the press fit. Any suitable adhesive may be used, but preferably the adhesive is a thick epoxy that has a fast curing time in air to avoid contaminating the isolator assembly during the manufacturing process. Since adhesive  51  is completely encapsulated by cap  31  and bracket  21 , erosion and contamination of the adhesive is prevented, thereby preventing loosening of the cap over time and eliminating adhesive tracking problems. 
     Assembly and Disassembly 
     A fully assembled disconnector assembly  11  is shown in FIGS. 1 and 2. Upper electrical terminal  12  is inserted through bore  30  to connect bracket  21  to an arrestor  13 . The isolator assembly  29  is then simply dropped into cavity  27  over terminal  12 . Cavity  27  is then sealed by securing cap  31  to wall  25  of bracket  21  with adhesive  51 . Disconnector assembly  11  is then completed by partially disposing stud  41  in bore  33  of cap  31 . 
     During normal non-fault operation of the arrestor, little or no current passes through isolator assembly  29  due to the high resistance of the arrestor. When subjected to lighting or surge currents, the arrestor experiences high pulse currents which travel through arrestor  13  and isolator assembly  29 . Within the isolator assembly, the current will arc over between spring  46  and conductive portion of the gap spacer for connection to terminal  41  and to ground  17 . 
     When the arrestor is properly functioning, the gaps spark over for high current, short duration pulses which last less than 100 milliseconds for lightening and less than several milliseconds for switching currents. For such short sparkovers, insufficient energy is generated to activate or denote the cartridge. However, if the lightening arrestor fails to withstand the voltages, the arcs are generated over a sufficiently extended period to activate the unprimed cartridge, causing explosion that separates the terminals mechanically from one another. The force of the exploded charge forces at least one of the terminals, usually lower terminal  41 , from the housing. This action electrically disconnects arrestor  13  from the system, and provides a visual indication of the need for arrestor replacement. 
     While an advantageous embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined in the appended claims.