Patent Publication Number: US-3878321-A

Title: High voltage electric insulator termination constructions

Description:
[22] Filed:  
 United States Pat-ent [191 Ely [ HIGH VOLTAGE ELECTRIC INSULATOR TERMINATION CONSTRUCTIONS [75] Inventor: Richard Anthony Ely, Redmarley,  
 England [73] Assignee: Transmission Development Limited,  
 Gloucester, England Jan. 28, 1974 [21] Appl. No.: 437,028  
 [30] Foreign Application Iriori ty Data [58] Field of Search.. 174/73 R, 127, 140 R, 140 C, 174/140 11,140 S, 140 CR, 141 R, 141 C, l42,l44,176,l77,178,l79, 180,181,186,  
 [56] References Cited UNlTED STATES PATENTS Hawley 174/140 S [4 1 Apr. 15, 1975 3,318,995 5/1967 Buckley et a1. 174/142 3,328,515 6/1967 Vose 174/140 S FOREIGN PATENTS OR APPLICATIONS 1,665,427 l/l970 Germany 174/140 R Primary Examiner-Laramie E. Askin Attorney, Agent, or Firm-Young &amp; Thompson [57] ABSTRACT An end-fitting electrode for a high voltage insulator has a nose spigot and outside this spigot is positioned an electrically conductive nose ring which is flexibly and electrically connected with the spigot so that mechanical stresses in the insulation material of the insulator are kept low in the region of the nose ring outer surface which is where the electrical interface occurs. The nose ring may be a rigid conductive material which is interconnected with the nose spigot by a flexible sealing material. An electrically conductive screen may be embedded in the insulating material surrounding the nose ring and nose spigot combination to provide for electrical stress relief.  
 10 Claims, 2 Drawing Figures HIGH VOLTAGE ELECTRIC INSULATOR TERMINATION CONSTRUCTIONS parts ofcrossarms or other structural members for supporting overhead line conductors a pole or tower and can themselves be used for directly supporting such conductors, i.e., without the use of the pin insulators or insulator strings normally used.  
  Other conductors that can be directly or indirectly supported by such insulators are. for example. bus-bars and the overhead contact wires of railway electrification systems wherein the insulators may, for example, be used as steady arms. The insulators may also form insulated bushings or insulator posts.  
  The end terminations of conventional insulators of this type are formed in various ways. In one construction the insulator body is provided with one or more high strength rigid core members formed, for example, from resin-bonded fibrous material. To the ends of the core(s) are attached end-fitting electrodes, leaving annular spaces between the core(s) and the end-fitting. The resinous insulating material is then cast or moulded about the core(s) and fills the space between the core(s) and the end-fitting. The open end of the end-fitting is provided with a curved surface, forming a nose spigot, and the resin is moulded around the nose spigot so that good surface contact or adhesion is achieved between the insulating resin and the nose spigot. the curved surface of which forms the electrical interface between the electrode and the insulating resin.  
  It is important. in such constructions, to keepthe mechanical stresses within the insulating resin body as low as possible, particularly in the region of the nose spigot of the end-fitting, since rupture of the insulation could be detrimental to the insulation properties of the insulator.  
  It is an object of this invention to provide a termination construction for such insulators which has good resistance to mechanical stress.  
  Accordingly, this invention provides a termination construction for high voltage electric insulators comprising an end-fitting electrode having a nose spigot provided with an electrically conductive nose ring which is flexibly and electrically connected with the nose spigot onto which the insulating material for the insulator may be bonded, and which will provide the electrical interface.  
  The flexible interconnection between the nose spigot and nose ring allows relative movement there-between so as to alleviate the mechanical stresses which may occur in the insulating material forming an insulator provided with the termination constructions of this invention.  
  In one preferred embodiment. the nose ring is constructed from metal or other rigid conductive material, such as a metal-powder filled resin. In this embodiment it is preferred that the inner surface of the nose ring and the outer surface of the nose spigot are bonded together by a flexible sealing material to provide the flexible connection. The sealing material can be a solid or foamed elastomer, e.g., rubber or a silicone rubber LII foam. In one arrangement the sealing material is so formed that a part thereof which will be subjected substantially only to shear stresses is a solid material and the remainder of the sealing material is a closed-cell foam-type material. The sealing material may be bonded to the nose spigot and nose ring by an adhesive bonding rubber curable at room temperature or at elevated temperatures.  
  Preferably, where a nosering formed from a rigid conductive material is used, the nose spigot and nose ring are electrically interconnected by a metal strip, such as a stranded wire in a protective sheath, so as to eliminate leakage current from the sealing material. Alternatively, or ideally additionally, and electrically conductive screen is electrically interconnected with the nose spigot and nose ring and is provided as a screen over the electrical interfaces of the nose spigot and the outer surface of the nose ring. This screen may be a metal gauze stress shield.  
  The invention also extends to complete high voltage insulators comprising a body of insulating material such as an epoxy resin or any other insulating polymeric material. with the termination construction of the invention bonded to the end thereof. The electrical interface between the end-fitting electrode and the insulation material will occur in the region of the outer face of the nose ring.  
  The invention may be performed in various ways, and preferred embodiments thereof will now be described by way of example only, with reference to the accompanying drawings,in which:  
  FIG. 1 is a partly vertically sectional side elevation showing the end of an insulator provided with one preferred arrangement ofa termination construction in accordance with the invention, incorporating a metal nose ring. and separate elastomeric seals;  
  FIG. 2 is a side view of a complete insulator incorporating an assembly as shown in FIG 1.  
  Referring firstly to FIG. 1, there is shown a galvanised cast iron or aluminium end-fitting electrode 1 into which has been embedded, by casting or moulding, a body 2 of insulating resin. The resin body 2 is formed about a central tensile core 16, formed, for example from resin bonded glass fibre. Also embedded in the resin body 2, below the first shed 3 thereof, is a nose ring 4 formed from a similar metal (or other rigid conductive material, such as a resin filled with metal powder), and spaced from the nose spigot 5 of the end fitting l by a body of flexible material 6 providing a weatherproof seal and possibly also having electrical ifl sulating properties. Rivetted to the nose ring 4 and nose spigot 5, so that they are electrically interconnected, is a tinned copper stranded wire 7 protected by an elastomeric sheath, such as a silicone sheath. The  
 &#39; sheath prevents the resin from impregnating the stranded wire 7, thereby protecting the wire from possible mechanical overstressing resulting from thermal changes or mechanical loading of the insulator.  
  The curved surface 4A of the nose ring provides the electrical interface between the end-fitting electrode 1 and the insulating resin body 2. The wire 7 accommodates leakage currents, and eliminates electrical leakage across the seal 6 which could result in seal degradation. If required, a copper or brass gauze or mesh stress shield 8 may be provided to minimise any problems of internal discharge. This stress shield 8 is rivetted by rivets 9 to the nose ring 4 (and preferably also to the endfitting electrode 1) and is embedded in the resin body 2. The shield 8 now provides the electrical front so that there is no electrical stress in the areas behind it and voids will not cause discharge problems. The particular shape of the nose ring 4 shown in the drawing substantially protectsthe nose spigot area and the. insulating body 6 so that the gauze shield 8 may not be necessary.  
  The nose ring 4 is suitably contoured to give good electrical stress distribution the relatively large external diameter of the nose ring facilitates natural cleaning and provides a relatively large surface to transmit leakage current to the surface of the resin.  
  The flexible insulating body 6 is illustrated as having a solid rubber section 6A and a silicone rubber foam section 68. The resin body 2 is bonded to the cylindrical surface 2A of the core and also to the nose ring, the surface 4A of which may be regarded as a planar surface which is mutually perpendicular to the cylindrical core surface 2A. When the resin body 2 contracts. during cooling. the mutually perpendicular surfaces 2A of a foam-like material. If desired, the whole of the insulating body 6 could be formed from a closed-cell foam-like material the essential characteristic is that the body 6 should have sufficient flexibility whilst offering minimal mechanical resistance. Ideally. the material will also be suitable for long term outdoor exposure.  
  The termination construction shown in FIG. 1 is particularly suited for use in crossarm (or cantilever) insulators where the mechanical stresses in the insulating resinbody are produced not only by shrinkage due to cooling. but also by bending forces applied to the insulator body which will vary around the circumference of the .body. The flexible connection between the endfitting electrode and the insulator body allows the combination of tensile and compressive stresses in the insulation body to be alleviated, thus significantly reducing the possibilities of rupturing of the insulation. These constructionsrcan equally be used as terminations for tension. suspension or post insulators.  
  The complete insulation assembly is indicated in FIG 2. An end-fitting electrode 1 is secured to both ends of thetensile core 16 by pins 17 and the nose spigot of each electrode is provided with a nose ring assembly 18 (diagramatically illustrated). integrally cast about the core 16 and within the electrode I is the resinous insulating body 2 formed with the sheds 3 as indicated. if desired. a stress flange 19 may be provided on each electrode 1 for protection of the nose ring assemblies 18 from damage should flashover occur.  
 I claim: I  
  1.. A termination construction for high voltage electric insulators comprising a hollow end-fitting electrode providing an open end for receipt of a tensile core and having a nose spigot at said open end forming an outer surface. an electrically conductive nose ring formed from a rigid conductive material, the nose ring having an inner surface which faces said outer surface of the nose spigot. a flexible sealing material bonding said inner and outer surfaces together, means electrically interconnecting the nose ring with the nose spigot, and a surface of the nose ring, remote from the nose spigot, providing an area onto which the insulating material for the insulator may be bonded, and which will provide the electrical interface.  
  2. A construction according to claim 1 wherein the nose ring is formed from metal.  
 3. A construction according to claim I wherein the nose ring is formed from a resin filled with metal powder.  
  4. A construction according to claim 1, wherein the sealing material is an elastomer, selected from the group consisting of solid rubber, foamed natural rubber and a silicone rubber foam.  
  5. A construction according to claim 1, wherein the sealing material is formed in two parts each comprising elastomer. wherein the one part, which will. during use in an insulator, be subjected substantially only to shear stresses is a solid material and the other part of the sealing material is a closed-cell foam-type material.  
  6. A construction according to claim 1, wherein an adhesive bonding rubber curable at at least room temperature bonds the sealing material to the nose spigot and to the nose ring.  
  7. A construction according to claim 1, wherein a metal strip electrically interconnects the nose spigot and nose ring.  
  8. A construction according to claim 7 wherein the metal strip is a stranded wire in a protective sheath.  
 9. A construction according to claim 1, wherein an &#39;electrically conductive screen is electrically interconnected with the nose spigot and nose ring and is provided as a screen over the electrical interfaces. of the nose spigot and the outer surface of the nose ring.  
 10. A construction according to claim 9, wherein the screen is a metal gauze stress shield.