Abstract:
A busduct joint assembly comprising a stack of electrically insulating separator plates, a respective busbar receiving gap between defined between each pair of separator plates for receiving respective busbar ends of adjacent busduct sections therein to be in electrical contact with at least one connector plate located therein, upper and lower cover plates being located on either side of the stack of separator plates, a fastener extending between the cover plates and through mutually aligned apertures formed therein in order to clamp the separator plates and connector plates between the cover plates, a side cover being provided on at least one side of the separator plates and having at least one heat exchange rib extending into the stack of separator plates, wherein the at least one heat exchange rib extends between adjacent pairs of separator plates, on an opposite side of the separator plates from the associated busbar receiving gap.

Description:
RELATED APPLICATIONS 
     This application claims priority to United Kingdom national application 1418037.6, filed Oct. 13, 2014, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     This invention relates to a joint assembly for a busduct and in particular to a joint assembly for coupling adjacent busduct sections together wherein the joint assembly incorporates a heat sink assembly. 
     BACKGROUND 
     Electrical power distribution busducts typically include an elongate duct containing a plurality of elongate flat electrically conductive busbars, for example three phase busbars, at least one neutral busbar and an earth busbar, separated by electrically insulating material. A busduct system usually includes a plurality of busduct sections coupled together to provide an appropriate length of busduct to connect one piece of electrical apparatus to another in lieu of cables. 
     One of the major considerations in designing a busduct system is the provision of a busduct joints for joining busduct sections together. The design of these joints presents a number of parameters to consider, including space and size limitations; accommodation of varying numbers of busbars within a single joint design; contact resistances within the joints; insulation break-down between busbars within the joints and arcing between the busbars; attachment of the joints to the busducts and maintenance of the organization of joint components during assembly and installation; and, in particular, the effective dissipation of heat from the conductors within the busduct joint. In addition to designing a joint which takes into account the above-listed design parameters, these parameters must be dealt with in a cost effective manner. 
     The effective dissipation of heat from a busduct section and from a busduct joint in particular is essential to achieving the testing parameters of the UL and IEC standards which outline the maximum temperature rise limit of electrically conductive material within the busduct joint. 
     Examples of known busduct joints are found in U.S. Pat. No. 5,068,763; U.S. Pat. No. 4,950,841; U.S. Pat. No. 4,849,581; U.S. Pat. No. 4,842,533; U.S. Pat. No. 4,705,334; U.S. Pat. No. 4,009,920; U.S. Pat. No. 3,786,394; U.S. Pat. No. 3,383,458; U.S. Pat. No. 3,365,537; U.S. Pat. Nos. 3,183,298; and 3,104,276, which are incorporated herein by reference in their entireties. A typical busduct joint including a fastening bolt surrounded by an insulated sleeve, where the fastening bolt extends through and holds together a stack of adjacent pairs of conductive splice plates and insulator plates. Busbars of adjacent busduct sections are inserted between the opposite ends of adjacent pairs of splice plates when the bolt is loosened. The bolt is then tightened to compress the assembly together and provide a tight engagement between the splice plates and corresponding busbars. Then top and bottom covers are installed once the bolt is torqued. Due to manufacturing tolerances the bolt must be quite loose during installation so that sufficient spacing is provided between pairs of splice plates to permit insertion of busbars. A problem with such existing busduct joints is the difficulty in dissipating heat from the tightly stacked splice plates and busbars within the busduct joint. 
     SUMMARY 
     According to a first aspect of the present invention there is provided a joint assembly for a busduct comprising a stack of electrically insulating separator plates arranged in mutually adjacent pairs, each pair of separator plates having at least one electrically conductive connector plate located therebetween, each pair of separator plates defining a respective busbar receiving gap therebetween for receiving respective busbar ends of adjacent busduct sections to be in contact with the at least one connector plate therebetween such that said connector plate provides electrical continuity between respective busbars, upper and lower cover plates being located on either side of the stack of separator plates, the separator plates and connector plates having mutually aligned apertures formed therein, a fastener extending between said cover plates and through said mutually aligned apertures in order to clamp the separator plates and connector plates between the cover plates, a side cover being provided on at least one side of the stack of separator plates extending perpendicular to the separator plates, said side cover having at least one heat exchange rib extending from an inner face of the side cover to extend into the stack of separator plates, wherein said at least one heat exchange rib extends between adjacent pairs of separator plates, on an opposite side of the separator plates from the associated busbar receiving gap. 
     In a preferred embodiment a pair of side covers may be provided, located on opposite sides of the stack of separator plates, each side cover having at least one heat exchange rib extending from an inner face of the side cover to extend into the stack of separator plates, wherein said at least one heat exchange rib extends between adjacent separator plates, on an opposite side of said separator plates from the associated busbar receiving gap. 
     Preferably the or each side cover is provided with a plurality of substantially parallel heat exchange ribs arranged to extend between respective pairs of separator plates on a side of the separator plates opposite said connector plates. 
     The or each side cover may be provided with cooling fins on an outer surface thereof for increasing the surface area of the side cover to enhance heat transfer therefrom. 
     The or each side cover may be formed from an electrically conductive material. In a preferred embodiment the or each side cover is formed from aluminium, although it is envisaged that the side covers may be formed from other materials, preferably materials having good thermal conductivity. 
     The or each side cover may include lateral side flanges extending inwardly from upper and lower edges of the or each side cover to increase the surface area of the side covers, further enhancing heat transfer from the joint assembly. 
     A pair of connector plates may be located between each pair of separator plates such that an end of a busbar can be received between each pair of connector plates. 
     The connector plates may be formed from copper or aluminium or an other suitable electrically conductive material. 
     In one embodiment, spacers may be located between each pair of separator plates to maintain a gap between each pair of spacer plates to enable the busbars of adjacent busduct sections to be inserted therebetween. Preferably the spacers are formed from an electrically insulating material. Each spacer may be provided with a central aperture through which said fastener extends. Each separator plate may include a recessed channel formed therein dimensioned to receive a respective spacer therein to locate the spacers in position between respective opposing pairs of separator plates, wherein the spacers engage the recessed channels of the each respective pair of separator plates. Preferably said recessed channel is formed in a raised wall located around the fastener on a side of each separator plate adjacent to the associated at least one connector plate. 
     The or each side cover may be formed by an extrusion process. 
     According to a further aspect of the present invention there is provided a busduct assembly comprising first and second busduct sections, each busduct section comprising a plurality of busbars located within a busduct housing wherein said busbars extending beyond said housing at either end thereof, and a joint assembly in accordance with the first embodiment of the invention, wherein respective busbars of the first busduct are electrically coupled to corresponding busbars of the second busduct via the joint assembly. 
     Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       A busduct joint assembly in accordance with an embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a busduct joint assembly in accordance with an embodiment of the present invention interconnecting two busduct sections; 
         FIG. 2  is a perspective view of the busduct joint assembly of  FIG. 1  with the housing of the busduct sections removed for clarity; 
         FIG. 3  is a side view of the assembly of  FIG. 2 ; 
         FIG. 4  is a plan view of the assembly of  FIG. 2 ; 
         FIG. 5  is an end perspective view of the assembly of  FIG. 2 ; 
         FIG. 6  is an end view of the assembly of  FIG. 2 ; 
         FIG. 7  is a longitudinal sectional view through the assembly of  FIG. 1 ; 
         FIG. 8  is a perspective view of a separator plate of the apparatus of  FIG. 1 ; and 
         FIG. 9  is a detailed perspective view of a spacer of the apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     With reference to  FIG. 1 , a busduct joint assembly  10  in accordance with the present invention is shown joining first and second busduct sections  2 , 4  in end to end relationship. Each busduct section  2 , 4  includes a plurality of electrically conductive busbars  6  enclosed in a rigid duct or housing. The duct of each busduct section has been omitted from  FIGS. 2 to 5  to better show the detail of the busduct joint assembly. The busduct housing may be formed from extruded aluminium sections. Alternatively the housing may be formed from steel or a rigid thermally conductive plastic material, preferably formed by extrusion. 
     As shown in  FIG. 1 , the outer side plates  12  of each busduct housing include upper and lower flanges  14 , 16  disposed at the upper and lower edges of the side plates  12 , extending substantially parallel to the busbars  6 . These flanges  14 , 16  provide strength, a structure from which the busduct may be supported and also provide additional surface area for dispersing heat from the busducts. 
     Fixing blocks  18  may be provided on an outer face of the duct housing side plates  14 , 16  at each end of each busduct section  2 , 4  to facilitate connection of the busduct sections  2 , 4  to the joint assembly  10 , as will be described in more detail below, and to seal the busduct joint assembly  10 , as well as to act an earth path between the busduct joint assembly  10  and the busduct sections  2 , 4  and to enable heat transfer between therebetween and finally to add structural strength to the ends of the busduct sections  2 , 4 . Earth plates  20  extend from each end of the busduct sections  2 , 4  above and below the busbars  6  to provide an earth return path during short circuit events by electrically connecting two busduct sections together through the busduct joint assembly  10 . 
     Various combinations of busbars  6  may be provided in each busduct section  2 , 4 . For example each busduct section  2 , 4  may include three phase busbars, a ground busbar, and one or more neutral busbars. Each busbar  6  may comprise an elongate strip of electrically conductive material, such as copper or aluminium, having a substantially rectangular cross-section which may have rounded corners. For typical applications, the busbars may be configured to carry between 225 and 6600 amperes of current at potentials ranging from 100 to 1000 volts. 
     The busduct sections  2 , 4  and the busduct joint assembly  10  must conduct sufficient heat from the conductive components of the assembly to the external surfaces of the assembly, and hence into the atmosphere, at such currents and potentials to avoid the creation of hot spots exceeding the maximum operating temperatures of the insulation material and/or exceeding the limits of temperature rise set out of IEC 61439 and UL857. 
     The busduct joint assembly  10  comprises a sandwich construction comprising pairs of electrically insulating separator plates  22  having located therebetween pairs of electrically conductive connector plates  24  for electrically coupling the respective busbars  6  of the first and second busduct sections  2 , 4  to one another when the respective busbars  6  are located therebetween, on either side of the joint assembly  10 . A pair of opposing connector plates  24  and cooperating separator plates  22  are provided for each busbar of the busduct sections  2 , 4 . Each of the pairs of opposing connector plates  24  defines a respective space therebetween, open at opposite ends of the busduct joint assembly  10 , for receiving respective busbars  6  of the first and second busduct sections  2 , 4  to electrically couple said busbars  6 . 
     Upper and lower cover plates  26 , 28  are provided to be located on either side of the stack of separator plates  22  and connector plates  24 , the cover plates  26 , 28  having integrally formed fins provided an outer face thereof such that the cover plates  26 , 28  act as heat sinks. The cover plates  26 , 28  are preferably formed from an electrically conductive material having good thermal conductivity, such as aluminium, and may be formed by an extrusion or moulding process. 
     The separator plates  22 , connector plates  24  and upper and lower cover plates  26 , 28  each include a central opening for accepting a bolt  32  therethrough, whereby the bolt  32  can pass through the assembly of plates, such that, when tightened, the bolt  32  clamps the assembly of plates together, compressing each opposing pair of connector plates  24  against the respective busbars  6  of the busduct sections  2 , 4 . 
     The separator plates  22  are fabricated from a thermally conductive and electrically insulating material, such as BMC (Bulk Moulding Compound) or Polyester, having good electrical insulation properties and high thermal conductivity. The connector plates  24  are fabricated from an electrically conductive material, such as copper or aluminium. 
     Moulded spacers  34 , preferably formed from an electrically insulating material, such as plastic, may be located between each pair of separator plates  22  around the bolt openings to maintain spacing between the spacer plates  22  to enable the busbars of adjacent busduct sections to be inserted between the respective connector plate  24  located therebetween. 
     As best shown in  FIG. 8 , each separator plate  22  may include a raised central wall  36  surrounding the central bolt receiving aperture on the side of the spacer plate facing the adjacent pair of connector plates  24 , said raised central wall  36  having a central recessed channel  38  formed therein and extending around the central bolt receiving aperture, the recessed channel  38  being dimensioned to receive a respective spacer  34  therein to locate each spacer  34  in position between respective opposing pairs of separator plates  22 . Respective spacers  34  are located between each pair of separator plates  22 , located within the recessed channels  38  formed in the raised central walls  36  thereof, such that the spacers  34  surround the bolt openings therein, such spacers  34  interlocking with the recessed channels  38  of the separator plates  33 , such that the spacers  34  maintain a gap between the respective opposing pairs of connector plates  22 . The spacers  34  may also serve to electrically insulate the connector plates  24  from the bolt  32 . 
     As best shown in  FIG. 9 , the spacers may also include laterally projecting portions  40  extending from opposite outer sides thereof to extend between a respective pair of connector plates  24 , such that said portions  40  serve to maintain a gap between each pair of connector plates  24 . Such portions  40  also may act as stops for preventing over-insertion of the busbars  6  into the busduct joint assembly. In the embodiment shown in the drawings, the spacers  34  are each defined by a square shaped peripheral wall having a central opening. 
     Each separator plate  22  may be formed with a raised wall portion  42  surrounding the central opening on the side of the spacer plate  22  opposite the associated connector plates  24 . Such raised walls portions  42  serve to maintain a fixed minimum spacing between adjacent separator plates  22  on the opposite side of the separator plates  22  to the connector plates  24  to enable heat transfer ribs  52  of side cover plates  50  of the joint assembly  10  to be inserted between the separator plates  22 , as will be described in more detail below. 
     Each of the busduct joint separator plates  22  may be provided with tapered edges to facilitate the insertion of busbar ends and the heat transfer ribs  52  of the side covers  50  into the busduct joint assembly  10 . 
     The bolt  32  is configured to force the separator plates  22  into contact with the connector plates  24  and the connector plates  22  into contact with the busbars  6  of the busduct sections  2 , 4  so that electrical circuit integrity can be maintained. The bolt  32  also forces contact between the separator plates  22  and heat transfer ribs  52  of outer covers  50  of the busduct joint assembly  10 , as will be described below in more detail. 
     Bellville spring washers  44  may be located between the head  46  of the bolt  32  and or its cooperating nut  48  and the respective joint cover plate  26 , 28 . The head  46  of the bolt  32  may be received within a shaped recess in the respective joint cover plate  26 , 28  to prevent rotation of the bolt  32 . 
     Busduct joint side covers  50  are provided to be located on either side of the busduct joint assembly  10 . The joint side covers  50  may be fabricated from sections of extruded aluminium and may be cut from the sections on an as-needed basis. The busduct joint side covers  50  are designed to assist with the dissipation of heat from the busduct joint assembly  10 . The outer faces of the side covers  50  are provided with integrally formed cooling fins  54 . Inner faces of the side covers are provided with a plurality of laterally extending heat transfer ribs  52 , adapted to be inserted between adjacent separator plates  22  on an opposite side of the separator plates  22  from the connector plates  24  to facilitate thermal conduction between the busbars  6 , connector plates  24  and the joint side covers  50  via the electrically insulating separator plates  22 . Thus the side covers  50  are thermally coupled to the busbars  6  and connector plates  24  of the joint assembly  10  while remaining electrically insulated from them, via the intervening electrically insulating separator plates  22 . 
     Lateral side flanges  56  extend inwardly from the upper and lower edges of each side cover  50  to further increase the surface area of the side covers, further enhancing heat transfer from the joint assembly. 
     The side covers  50  may be secured to the joint assembly  10  via suitable fasteners inserted into the fixing blocks  18  of the duct housing of each busduct section  2 , 4  at either end of the joint assembly  10 . 
     The upper and lower cover plates  26 , 28  and the side covers  50  effectively disipate heat from all sides of the joint assembly, greatly enhancing heat transfer from the joint assembly. The formation of the cover plates  26 , 28  and side covers  50  from aluminium extrusions, having cooling fins integrally formed on the outer surfaces thereof, maximises conduction and heat dissipation from the assembly. The heat transfer ribs  52  integrally formed on the inners faces of the side covers  50  extending between the separator plates  22  effectively extract heat from within the stack of separator plates  22 , connector plates  24  and busbars  6  and conduct such heat to the cooling fins  54  of the side covers  50 . By locating the heat transfer ribs  52  of the side covers  50  between adjacent pairs of separator plates  22 , on an opposite side of the separator plates  22  from the connector plates  24  and busbars  6 , any risk of short circuits or arcing between the busbars  6 /connector plates  24  and the side covers  50  is avoided. 
     The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention. Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.