Abstract: In one embodiment, a fuse cutout cover has an integral roof portion. The roof portion covers the energized top of a fuse in a first type of cutout. An attachable roof extension covers the energized top of a fuse in a larger second type of cutout, such as a Fault Tamer™ cutout. By adding the roof extension, the same cover may be used with two types of cutouts, and there is not a large gap over the fuse, preventing wildlife from entering the gap. In another embodiment, a second roof is formed over the first roof portion to accommodate different types of cutouts. Electrical insulation between wildlife and the energized cutout is also increased.

Abstract: A power supply device is presented. The power supply device includes a voltage conversion unit. The voltage conversion unit includes a capacitor divider circuit. The capacitor divider circuit includes a plurality of capacitors coupled to each other in series. Further, the voltage conversion unit includes a step-down transformer coupled to at least one of the plurality of capacitors. The power supply device also includes a low pass filter configured to be coupled to at least one high voltage power line and the voltage conversion unit, where the low pass filter is configured to provide filtered power to the voltage conversion unit.

Abstract: A variable diameter termination includes an elastomeric tubular housing having a first portion with a first inner diameter, a second portion with a second inner diameter, and a third portion disposed between the first portion and the second portion and with a transition inner diameter. The elastomeric tubular housing is disposed on a tubular core that includes a first portion with a third outer diameter, a second portion with a fourth outer diameter, and a third portion disposed between the first portion and the second portion and with a transition outer diameter. The first portion of the elastomeric tubular housing is disposed over the first portion of the tubular core, the second portion of the elastomeric tubular housing is disposed over the second portion of the tubular core, and the third portion of the elastomeric tubular housing is disposed over the third portion of the tubular core.

Abstract: An interface breakdown-proof locomotive roof composite insulator. The composite insulator comprises: a support body; and at least five shed groups arranged side by side along the axial direction that are provided around the sidewall of the support body, the at least five shed groups includes: at least four shed groups located on the upper end with each group including a large shed and a small shed; and at least one shed group located on the undermost end with each group including two small sheds. For such a shed structure, it is favorable to tolerate impulse voltage, and it is difficult for the interface to be broken down; the electric field on the interface even does not exceed 3 kV/mm, and even if a gas exists on the interface, it will not break through the interface.

Abstract: Method for replacing a suspension insulator on a tower having a davit arm supporting an attached insulator and a conductor shoe attaching an energized conductor to the insulator lower end including the steps of mounting a non-conductive board to the tower below the davit arm, mounting non-conductive struts between the board and the tower, positioning a movable slider in a track on the board, the slider supporting a jack and a conductor lifting bar attached to the jack, positioning the slider and operating the jack to lift and support the energized components, detaching the shoe from the insulator, moving the energized components to a remote position on the board, detaching and replacing the insulator while it is supported by a helicopter, positioning the slider and operating the jack to lift the shoe into alignment with the insulator and attaching the shoe to the insulator.

Abstract: A high-voltage insulator includes a metal armature, an insulating tube joined to the metal armature, which is adhesively bonded to the metal armature at an end formed as a supporting ring, and an axially symmetrical adhesive-bonding joint disposed around the axis of the insulating tube. An annular grove, which is formed in the metal armature, is disposed around the axis of the insulating tube and receives an end portion of the supporting ring. Sealing surfaces are respectively formed in the groove and in the supporting ring. The sealing surfaces are arranged and formed in such a way that, when the insulating tube and the metal armature are joined, they slide on one another, thereby forming a seal, and the supporting ring acting as a displacement body presses adhesive that has been introduced into the groove before the joining into the adhesive-bonding joint.

Abstract: An insulator usable in high current ion implantation systems includes increased surface due to the configuration of an inner cylinder and an outer cylinder coupled to the inner cylinder at one end. A cylindrical cavity extends between the two cylinders increasing the surface area and making the insulator resistant to being coated by a coating that could produce a leakage path.

Abstract: The present invention relates to a composite insulator comprising: (i) a composite body having at least two connectors and (ii) a housing, wherein the housing includes silicone rubber and the composite body is located inside the housing.

Abstract: A method and arrangement is provided to form a gas-tight joint between an end flange and a tubular rod. The joint is formed via a heat-shrink process to provide an interference fit. The rod is provided with grooves to retain adhesive during the assembly process.

Abstract: A polymer SP insulator comprising an FRP core 1, a sheath 2 having a plurality of sheds 6 provided on outer periphery of FRP core 1, and metal-end-fittings 3, 4 crimped to upper and lower ends of FRP core 1, in which a flat plate 11 for adjusting the overall length dimension after crimping the metal-end-fitting 4 is assembled in the inner bottom of the metal-end-fitting 4, and the overall length dimension is uniformly adjusted by the thickness of the flat plate 11. Further, a stress concentration portion such as cross groove is provided in the outer bottom of the lower Metal-end-fitting 4, and prevents instability by deformation of flange 8 when crimping the Metal-end-fitting 4. In this configuration, in spite of the structure of crimping metal-end-fittings at upper and lower ends of the FRP core, the overall length tolerance, parallelism and eccentricity can be suppressed.

Abstract: A method and arrangement is provided to form a gas-tight joint between an end flange and a tubular rod. The joint is formed via a heat-shrink process to provide an interference fit. The rod is provided with grooves to retain adhesive during the assembly process.

Abstract: A composite insulator containing means for providing early warning of impending failure due to stress corrosion cracking, flashunder, or destruction of the rod by discharge activity conditions is described. A composite insulator comprising a fiberglass rod surrounded by a polymer housing and connected with metal end fittings on either end of the rod is doped with a dye-based chemical dopant. The dopant is located around the vicinity of the outer surface of the fiberglass rod. The dopant is formulated to possess migration and diffusion characteristics, and to be inert in dry conditions and compatible with the insulator components. The dopant is positioned within the insulator such that upon the penetration of moisture through the housing to the rod through a permeation pathway in the outer surface of the insulator, the dopant will become activated and will leach out of the same permeation pathway or diffuse through the housing.

Abstract: The present invention relates to a composite insulator comprising: (i) a composite body having at least two connectors and (ii) a housing, wherein the housing includes silicone rubber and the composite body is located inside the housing.

Abstract: The invention relates to the field of electrical insulators, and in particular to the field of electrical insulators for optical phase conductors (OPPCs). The electrical insulator comprises a dielectric rod (1) having at least one slot (10), a flexible optical fiber cable (2) situated in the slot (10), a dielectric material (8) filling the slot (10) and holding the cable (2) in the slot (10) without stressing it, and a dielectric covering (3) surrounding the rod (1) and presenting outwardly-directed projections (30) in the form of skirts, the entire space situated between the rod (1) and the cable (2) being filled with said dielectric filler and holding material (8).

Abstract: A composite insulator containing means for providing early warning of impending failure due to stress corrosion cracking, flashunder, or destruction of the rod by discharge activity conditions is described. A composite insulator comprising a fiberglass rod surrounded by a polymer housing and fitted with metal end fittings on either end of the rod is doped with a dye-based chemical dopant. The dopant is located around the vicinity of the outer surface of the fiberglass rod. The dopant is formulated to possess migration and diffusion characteristics correlating to those of water, and to be inert in dry conditions and compatible with the insulator components. The dopant is placed within the insulator such that upon the penetration of moisture through the housing to the rod through a permeation pathway in the outer surface of the insulator, the dopant will become activated and will leach out of the same permeation pathway.

Abstract: The present invention relates to a composite insulator comprising: (i) a composite body having at least two connectors and (ii) a housing, wherein the housing includes silicone rubber and the composite body is located inside the housing.

Abstract: An elongate high voltage insulator is formed of a rod or tube of insulating material, with a pair of electrodes spaced apart longitudinally thereof. At least part, and preferably the whole of the outer surface of the insulating material is covered by a layer of material including a particulate filler of varistor powder in a matrix having a switching electrical stress-controlling characteristic that is in electrical contact with each of the electrodes. The insulator core may be made of porcelain, and the stress-controlling material may be zinc oxide.

Abstract: A method of providing a shed (2) for a high-voltage insulator (1) includes providing a substantially tubular substrate (3), providing an extruder (10) having an extruder head (11) defining an extrusion direction (A), using the extruder (10) to extrude the shed (2) and applying the shed (2) on the substrate (3) while rotating the substrate relative to the extruder head (11). The extrusion direction (A) substantially coincides with the longitudinal axis of the substrate (3), and the substrate (3) is fed through the extruder head (11).

Abstract: The present invention relates to a composite insulator comprising: (i) a composite body having at least two connectors, wherein the composite body is coupled to a conductor; and (ii) a housing, wherein the housing is a one-piece housing and the composite body is located inside the housing.

Abstract: The method of manufacturing a composite insulator constituted by a rod surrounded by an insulating coating and provided at its two ends with two metal end fittings respectively consists in the following steps: fixing two respective metal interfaces to the two ends of the rod, the metal end fittings of the insulator subsequently being fixed to the interfaces; and putting the coating into place around the rod and around the metal interfaces while leaving an end portion of each metal interface uncovered by the coating so as to enable the metal end fittings to be fixed thereto subsequently.

Abstract: A method of providing a shed (2) for a high-voltage insulator (1) comprises the steps of providing a substantially tubular substrate (3), providing an extruder (10) having an extruder head (11) defining an extrusion direction (A), using the extruder (10) to extrude the shed (2) and applying the shed (2) on the substrate (3) while rotating the substrate relative to the extruder head (11). According to the invention, the extrusion direction (A) substantially coincides with the longitudinal axis of the substrate (3), and the substrate (3) is fed through the extruder head (11).

Abstract: An assembly is provided having a core and a housing. The housing has an internal passageway extending from a first housing end to a second housing end for receiving the core. A coating of an uncured moisture activated material is disposed between the housing and the core. The coating cures upon reacting with moisture penetrating the housing to reseal the housing at a point of moisture penetration. The material cross-links in the presence of the moisture, thereby bonding with the moisture to prevent the moisture from contacting the core. The cured material is a rubber-like substance that adheres to the housing and to the core, thereby resealing the housing at the point of moisture penetration.

Abstract: A composite insulator is provided. At least one metal end fitting is provided having a sleeve portion which defines a bore with a first diameter, d1. An insulator subassembly is then formed. The insulator subassembly includes a rod of electrically insulating plastic material and an insulator sheath covering at least a portion of the outer surface of the rod. An end portion of the sheath has a deformable circumferential ridge formed on the outer surface thereof. This circumferential ridge has a second diameter, d2, which is greater than the first diameter, d1. The insulator subassembly is then inserted into the bore of the metal end fitting with a spacer member interposed between the metal end fitting and at least the circumferential ridge. The spacer member serves to deform the ridge to define a temporary vent for allowing air within the bore to escape.

Abstract: In a method of producing a composite insulator having a core member, end fitting members fixed to both end portions of the core member, and an overcoat member including a sheath portion formed on an outer surface of the core member and shed members, the overcoat member and the end fitting member are connected by curing. Moreover, a clamping operation is performed or a packing member is used for preventing a flow of an overcoat forming material into a seal portion. In this manner, it is possible to improve a seal performance of a connection boundary between the end fitting member and the overcoat member.

Abstract: Methods of manufacturing and assembling a composite insulator are provided. At least one metal end fitting is provided having a sleeve portion which defines a bore with a first diameter, d1. An insulator subassembly is then formed. The insulator subassembly includes a rod of electrically insulating plastic material and an insulator sheath covering at least a portion of the outer surface of the rod. An end portion of the sheath has a deformable circumferential ridge formed on the outer surface thereof. This circumferential ridge has a second diameter, d2, which is greater than the first diameter, d1. The insulator subassembly is then inserted into the bore of the metal end fitting with a spacer member interposed between the metal end fitting and at least the circumferential ridge. The spacer member serves to deform the ridge to define a temporary vent for allowing air within the bore to escape.

Abstract: A high voltage insulator for use with optical fibers includes an insulative support rod with at least one optical fiber wrapped about the support rod. The optical fiber and support rod are covered by an outer elastomeric skirted insulative sleeve which squeezes the optical fibers against the support rod. A dielectric sealant, such as a silicone gel, is dispersed along the optical fiber to fill any voids which occur adjacent the optical fiber, thereby providing a void-free bond between the interior surfaces of the insulator. The elastomeric outer sleeve provides a resilient barrier against the ingress of moisture. In a preferred embodiment, an inner layer of elastomeric material is provided between the support rod and the optical fiber to provide additional cushioning of the fiber and to reduce the size of voids which may occur adjacent the fiber.

Abstract: An improved hollow core composite bushing for use in, for example, a dead tank circuit breaker, is smaller and lighter and offers other advantages over previous designs. The hollow core bushing includes therein a fiber reinforced plastic (FRP) elongated tube that operates to increase the dielectric constant between a conductor and a transition shield. By placing the transition shield external to the hollow core bushing and providing the FRP tube between the conductor and transition shield, the dielectric constant between the shield and conductor is increased thus allowing the inner diameter of the shield and outer diameter of the bushing to be decreased. In addition, the transition shield may be an integral part of the flange that is mounted to the bushing current transformer support column or interrupter enclosure of the dead tank circuit breaker thus further reducing the diameter and overall size of the bushing. Further, the transition shield may be an integral part of the FRP tube.

Abstract: A polymer insulator having a core member, an insulation overcoat member arranged on an outer surface of the core member, and a securing metal fitting fixed to an end portion of the core member in such a manner that the end portion is contacted with the insulation overcoat member is disclosed. The disclosed polymer insulator further includes a seal portion arranged at a boundary between the insulation overcoat member and the securing metal fitting, which is made of a sealing agent in which 80-250 parts by weight of ATH (Alumina trihydrate, Al.sub.2 O.sub.3.3H.sub.2 O) is included with respect to 100 parts by weight of a polymer component. Therefore, the polymer insulator according to the invention has an improved tracking-erosion resistance performance.

Abstract: Polymer Insulator which is characterized by a rode having on its outer surface an umbrella-like housing or insulator layer and having end portions which are formed so as to freely expand with at least one splitting groove; a fixture having a mounting hole in which the end portion of the rod is inserted and which has an inner surface tapering inwards against which the outer surface of said rod abuts in its expanded state; and a wedge fixed in said mounting hole, the wedge being inserted into a splitting groove formed in the end portion of the rod when the end portion of said rod is mounted into said mounting hole of said fixture, the top end of the wedge having an engaging portion which is held in the splitting groove thereby to cause the whole wedge to engage in the splitting grove.

Abstract: A composite insulator includes an insulating rod, end fittings crimped to opposite end portions of said insulating rod, and an elastic insulating material molded around the outer periphery of the insulating rod, wherein each of the end fittings has a flange around the outer periphery of an end fitting body on an axially external side thereof, and the elastic insulating material is molded around the outer periphery of the insulating rod and those of the end fitting bodies such that the elastic material extends up to and between the flanges. A process for the production of such a composite insulator is also disclosed.

Abstract: An electric high-voltage insulator made from plastic comprises at least one glass fiber rod (1), at least one shield covering (2) made from silicone rubber which surrounds the glass fiber rod (1) and has concentric bulges (3) arranged along the longitudinal axis and bent in the shape of sheds in such a way that they form a convex top side and a concave or flat underside, as well as metal fittings (5) on both insulator ends. In this case, the bulges bent in the shape of sheds have at least one groove (4) on the underside preferably with a minimum depth of 1 mm.

Abstract: A load insulator having an elongated, load bearing, electrically insulating body extending between and coupled to opposite metal lugs, for coupling the load insulator in a loaded line, has an electrically insulating cover formed on the outside of the body and extending over and completely covering each of the pair of metal lugs at the opposite ends of the body. The insulating cover, which is of integral, one-piece construction, and may be made of polyurethane, is formed within a mold during construction of the load insulator by leaving a void within the mold around the opposite metal lugs and the body before introducing plastic into the mold, to form the insulating cover. Covering each of the opposite metal lugs as well as the body with the insulating cover forces high voltage-produced currents through the inside of the load insulator by preventing current creep around and flashing over the outside of the insulator body.

Abstract: An insulator in the form of suspension insulator or pin type insulator has an elongated load sustaining body with a plurality of weathersheds extending radially relative to the longitudinal axis of the body on the outer surface of the body. The body and weathersheds are unitarily formed as one piece of rigid dielectric plastic polymer which are molded together. Clevis and eye coupling means are provided on the ends of the body to facilitate connection to support structures and high voltage lines.

Abstract: A method of manufacturing insulators with excellent high-voltage performance having a core member, a sheath arranged on an outer surface of the core member and a shed arranged on an outer surface of the sheath is disclosed. In a first aspect of the invention, a method includes the steps of arranging the sheath made of non-cured polymer materials on an outer surface of the core member, arranging a plurality of the sheds made of cured polymer materials on an outer surface of the sheath, and curing the sheath to connect the sheath to the sheds. In a second aspect of the invention, a method includes the steps of arranging the sheath made of cured polymer materials on an outer surface of the core member, arranging a plurality sheds made of cured polymer materials on an outer surface of the sheath, and connecting the sheath to the sheds by using adhesives.

Abstract: A reinforced electrical insulator has a load sustaining mechanical core with a pair of attachment members located at its longitudinal ends. One of the attachment members extends longitudinally into the mechanical core to provide reinforcement to the mechanical core. The mechanical core member is constructed of a rigid, dielectric material with a first end section, a second end section, and a center section. A plurality of weathersheds extending outwardly from the center section of core member in a substantially radial direction relative to the longitudinal axis. The first and second end sections having maximum widths which are larger than the maximum width of the center section. The attachment members have inner portions embedded within the end sections of the core and outer portions extending outwardly from the end sections of the core.

Abstract: A device providing an insulating support for an electrical conductor includes a body having a through bore with an upper, cylindrical portion and a lower, threaded portion. A hook extends integrally from the upper end of the body over the upper end of the cylindrical bore. A piston in the cylindrical bore has an upper end for mating engagement with the hook to define a fully enclosed passageway surrounding the conductor upon movement of the piston from an initial position, wherein the conductor may be moved laterally to a position between the hook and the upper end of the piston, to a terminal position wherein the conductor is fully surrounded by surface portions of the hook and piston. A threaded insert is engaged in the threaded portion of the body axial bore. A passageway through the insert has a one-way valve for injection of silicone gel into the cylindrical portion of the body bore to move the piston from its initial to its terminal position.

Abstract: An electrical insulator includes a pair of endpieces fixed respectively to opposite ends of a cylindrical support. Extruded elastomer insulation material forms annular fins about the support. Each end of the support is inserted into a tubular housing provided in each endpiece. The fins cover a transition surface of tapering shape elastomer rings joining the outside surface of an endpiece to an outside surface of the support. A tapering ring of extruded elastomer material of triangular cross-section backs up against a shoulder of a respective endpiece at the opening to the housing into which the end of the support is inserted. The transition surface is defined by the exterior of the tapering ring.

Abstract: A plastic composite insulator (1) including a shank (2) and at least one shield and caps (19), in which the shank comprises a fiber-reinforced plastic core (3) and, around this core, a jacket (5) of a shielding sheath (4) and in which the shielding sheath is formed by the jacket and at least one shield (6) running spirally around the shank, wherein the shielding sheath is formed in one part and without joints.

Abstract: A composite insulator includes an insulating rod, an elastic insulating material molded around the insulating rod and having a plurality of shed portions, and end fittings fixedly fitted around opposite ends of the insulating rod. The end fittings cover the respective end portions of the elastic material. End faces of the end fittings abut respective shed portions of the elastic insulating material.

Abstract: A composite insulator with a silicone rubber sheath coating the insulator rod between metal fittings. Adjacent the line fitting, at least, a series of weathersheds are mounted on the rod and fastened to the sheath with their hubs in abutting relationship and with one hub abutting the line fitting. Another series of sheds are spaced from each other and from the series of weathersheds having their hubs in abutting relationship.

Abstract: A composite electrical insulator suitable for high tension open air use wherein the insulator has an interior structural rod of an electrically insulating material and an outer coating formed of a thermoplastic material and having a plurality of radially extending sheds formed integrally therewith, the outer coating terminating adjacent the ends of the interior rod, the coating having at least two radially extending abutting surfaces formed to abut against mating abutting surfaces formed on an end fitting. The insulator provides good mechanical properties while being light weight and meeting all electrical requirements.

Abstract: A method of manufacturing insulators with an excellent high-voltage performance having a core member, a sheath arranged on outer surface of the core member and a shed arranged on an outer surface of the sheath is disclosed. In a first aspect of the invention, a method includes the steps of arranging the sheath made of non-cured polymer materials on an outer surface of the core member, arranging a plurality of the sheds made of cured polymer materials on an outer surface of the sheath, and curing the sheath to connect the sheath to the sheds. In a second aspect of the invention, a method includes the steps of arranging the sheath made of cured polymer materials on an outer surface of the core member, arranging a plurality sheds made of cured polymer materials on an outer surface of the sheath, and connecting the sheath to the sheds by using adhesives.

Abstract: Apparatus for manufacturing a composite insulator including an FRP core rod which is integrally provided with a sheath and a plurality of sheds formed of an electrically insulating polymeric material. The core rod has a longitudinal end portion provided with a seat for a metal fitting, which is integral with the sheath. To manufacture such a composite insulator, the core rod is placed in a mold cavity of a mold assembly, with a seat forming member detachably fitted to the end portion of the core rod and arranged between a pair of mold halves. An inner space is formed between a seat forming member and the core rod, which is in communication with the mold cavity. An electrically insulating polymeric material is introduced into the mold cavity to form the sheath and sheds, while admitting the polymeric material into the space between the seat forming member and the core rod so as to form a seat for the metal fitting, which is essentially free from burrs.

Abstract: A composite insulator having a core member and a housing member integrally arranged around the core member, the housing member being constructed by a trunk portion and a shed portion, has a creepable distance extending means arranged on a lower plane of the shed portion. Moreover, a segment used for producing the composite insulator has a pair of segment molds detachably connected at a partition plane having a through-hole at its center portion through which the core member is arranged, an upper plane forming portion arranged at its one end surface for defining an upper plane of the shed portion, and a lower plane forming portion arranged at its other end surface for defining a lower plane of the shed portion; and a partition for forming the creepage distance extending means arranged at the lower plane forming portion.

Abstract: A composite electrical insulator includes a metal fitting (3, 4) fixedly secured to a fiber-reinforced plastic rod (1) at one end thereof. The rod has a stress-relieved zone (8) situated opposite to the metal fitting (3, 4), and formed by a heat treatment of the rod (1) after an end portion of the rod (1) has been inserted into a bore (5) in the metal fitting (3, 4) and the metal fitting (3, 4) fixedly secured to the rod (1). The heat treatment of the rod (1) is performed at a temperature which is not lower than a heat transition temperature of a matrix resin of the fiber-reinforced plastic material.

Abstract: A composite electrical insulator (1) includes a plastic rod (2), e.g., an FRP rod, which is covered by a sheath which includes a resilient and electrically insulating material. A metal fitting (4, 5) on each side of the insulator (1) has a radially inwardly deformable sleeve portion formed with a bore in which the end portion of the plastic rod (2) is covered by the sheath (3). The end portion of the sheath (3) has an outer surface opposite to the metal fitting (4, 5), which is provided with at least one circumferential ridge (7a, 7b).

Abstract: A composite insulator includes a FRP core rod and a sheath which is formed by integrally molding an insulating polymeric material to cover the core rod over substantially the entire length thereof. The sheath is composed of a plurality of molded portions which are aligned with each other in the axial direction of the core rod. Adjacent molded portions of the sheath are arranged relative to each other so that a gap is left between the opposite ends of the molded portions. The gap is filled by a joint insulating material which is integrally united to the polymeric material of the adjacent molded portions.

Abstract: A metal fitting for a composite electrical insulator (1) including a plastic rod (2), e.g., an FRP rod. The metal fitting (4) includes a radially inwardly deformable sleeve portion having a bore (5) into which an end portion of the rod (1) can be inserted for fixedly securing the metal fitting (4) to the rod (1). The bore (5) in the metal fitting (4) has an inner surface which is formed with fine protrusions (7). These protrusions (7) provide a satisfactory resistivity to the tensile force applied to the insulator (1), to thereby effectively prevent withdrawal of the rod (2) from the metal fitting (4) when it is in use.

Abstract: A process for producing, by compression molding, an insulator having a core and a housing consisting of a sheath portion and at least one shade portion around the sheath portion, including the steps of: (A) preliminarily forming a rubbery layer around an outer periphery of the core to obtain a preliminarily molded body by extrusion molding, (B) placing the preliminarily molded body between at least two mold units of a mold; (C) forming a compressed molding by compression molding said preliminarily molded body in a given shape inside a cavity defined by the at least two mold units; and (D) curing the resulting molding. An apparatus is also disclosed for producing such an insulator by compression molding, which apparatus includes (A) a preliminary molding unit, (B) a molding unit form forming a compressed molding from the preliminarily molded body in a given shape by using a mold, and (C) a heater for curing the rubber in the rubber layer.

Abstract: An electrical insulator comprising a cylindrical core (2) of an insulating refractory material, such as porcelain, onto a portion of the curved surface of which a sleeve (8) of insulating polymeric material is fitted. Metal end-caps (4), for electrically connecting the insulator, are fitted to the ends of the porcelain core such that there is an exposed portion (10) of the curved surface of the core between the sleeve and each end-cap. Thus, any damaging electrical activity which takes place at the metal end-caps is directed primarily onto the surface of the porcelain core (2), and not onto the surface of the electrically vulnerable polymeric sleeve (8), which serves to protect mechanically the relatively brittle porcelain core. Optionally, the polymeric sleeve (8) may have a convoluted or a shedded outer surface (12) to increase the leakage path length of the insulator, or to prevent the formation of a continuous moisture path, or both.