Patent Publication Number: US-3876820-A

Title: Pressurized fluid insulation for high voltage cable

Description:
United States Patent 1191 Mashikian 1 Apr. 8, 1975 PRESSURIZED FLUID INSULATION F0 3.544.700 12/1970 Priaroggia 174/21 R x HIGH VOLTAGECABLE 1 3,737,556 6/1973 Cunningham 174/19 [75] Inventor: Matthew S. Mashikian, Huntington Woods, Mich.  
 [731&#39; Assignee: The Detroit Edison Company,  
  Detroit, Mich. 221 Filed: Feb. 1, 1974 [21] Appl. No.: 438,575  
 [52] US. Cl. 174/19; 174/73 R; 339/117 P; 174/21 R [51] Int. Cl. H02q 15/22 [58] FieldofSearch 339/117 R,1l7 P,118 R, 339/136 R, 137, 149 R, 150 R, 150 C, 151 R, 151 C, 200 R, 201, 206 R,210 R, 213 R, 213 T,217 R,217 PS; 174/19,21 R,21 C, 73 R [56] References Cited UNITED STATES PATENTS 3,538,241 11/1970 Rein 174/73 R Primary Examiner-Roy Lake Assistant Examiner-DeWalden W. Jones Attorney, Agent, or Firm-Whittemore, Hulbert &amp; Belknap 57 ABSTRACT- An electrical connection for high votlage insulated cable, either to a cable termination or to a second cable is provided with a hollow tubular sleeve of resilient elastomeric insulating material which surrounds the insulated end portion of one or more cables. The sleeve is surrounded by a rigid shell or casing and contains an insulating fluid under elevated pressure provided to cause the inner surface of the sleeve to engage under elevated pressure in surface-to-surface contact with the exterior surface of the end portion of the insulation provided at the end or ends of the cable or cables.  
 33 Claims, 10 Drawing Figures PATENTEBAFR 81975 SHEET 1 BF 4 I ill I my? FIGS PATENTEBAPR a 1915 SQU 3 OF 4 HEB APR 8 1915 sumuqgd BRIEF SUMMARY OF THE INVENTION In providing a connection to the end of a high voltage insulated conductor, either to a terminal fitting or to the end portion of the conductor of a second cable, a problem has been presented in obtaining a proper surface-to-surface contact between an insulating sleeve provided to surround the end portion of insulating material adjacent the end of the cable or cables, and the outer surface of the insulation adjacent the end of the cable. I  
  Where the insulating material is in the form of a resilient elastomeric filler, it has been difficult to provide adequate compression when the cable expands and contracts as a result of its daily and seasonal load cycle. Another disadvantage of this kind of cable termination (or connection) lies in the difficulty experienced in installing it. The difficulties in employing a fluid (liquid or gas) insulating mate rial with or in place of the elastomeric material, with accompanying problems of sealing against leakage, are obvious.  
  In accordance with the present invention the insulating material is in the form of a sleeve which surrounds the end portion of the cable and is formed of a resilient elastomeric insulating material such for example as butyl or silicone rubber, or polyurethane, and is so shaped as to be hollow, or in other words, to be provided with an annular interior cavity. In use, this sleeve is received in a rigid shell which in accordance with the particular type of connection employed, may either be a metallic shell or it may be a rigid insulator body. The hollow interior of the sleeve is charged with an insulating fluid, either gas or liquid, at an elevated pressure sufficient to provide for inward displacement of the inner wall of the sleeve into a firm continuous surfaceto-surface pressure contact with the outer surface of the end portion of the insulation adjacent the bared end of the conductor of the cable. Silicone or polybutene oil are examples of suitable insulating liquids, and sulfur hexafluoride, nitrogen and freon are examples of suitable insulating gases.  
  In general terms, the invention may be applied to a cable termination in which the bared end of the conductor may be suitably connected to an exterior fitting. Alternatively, the construction may be in the nature of a connection or joint between the ends of two sections of high voltage cable, in which case the ends of the conductors of the cables are bared and electrically connected together by conventional means, after which the connection between the conductors as well as the end portions of the insulation surrounding the conductors adjacent the ends of the cables, is surrounded by the hollow tubular insulating sleeve, the hollow interior chamber of which is charged with insulating fluid under elevated pressure.  
  Generally, an electrical stress reliefelement is provided in contact with one end of the hollow tubular sleeve. For this purpose the end of the hollow tubular sleeve remote from the bared conductor end of the cable is tapered to provide an outer generally conical surface. The stress relief sleeve is formed of a semiconductor such for example as insulating resin containing particles of conducting material such for example as graphite or carbon black particles, and has its inner I surface tapered into conformity with the outward taper provided at the end of the hollow sleeve. The tapered surfaces are brought into contact and may in fact be permanently bonded together by suitable means. There is thus provided a generally conical interface which has the effect of preventing localized electrical stress when the connection is carrying high voltage current.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a simplified embodiment of the present invention applied to a cable termination.  
  FIG. 2 is a longitudinal sectional view of a further embodiment of the present invention.  
  FIG. 3 is an enlarged fragmentary detail of the sleeves.  
  FIG. 4 is an enlarged sectional view illustrating a modification of the structure shown in FIG. 2.  
  FIG. 5 is a longitudinal sectional view of structure in which the invention is applied to a connection between the ends of two high voltage cables.  
 FIG. 6 is a sectional view on the line 66, FIG. 5.  
  FIG. 7 is a fragmentary view illustrating a modification of a stress relief sleeve applied to the construction of FIG. 5.  
  FIG. 8 is a fragmentary sectional viewillustrating a modification of the hollow sleeve and insulation, as illustrated in FIG. 5.  
  FIG. 9 is an enlarged sectional view of one of the valves providing connection to the interior of the hollow sleeve.  
  FIG. 10 is a fragmentary longitudinal sectional view through a construction in which a modified form of the present invention is applied to the connection between two high voltage cables.  
 DETAILED DESCRIPTION The present invention may be applied to different types of electrical connections such for example as the termination of a high voltage cable or the interconnection between the ends of two cable sections. Embodiments of these two different applications of the present invention will be described under separate headings below:  
 CABLE TERMINATION Referring first to FIG. 1 there is illustrated a very simi ple application of the present invention to a cable termination. In this Figure there is illustrated a high voltage electrical cable 10. Cables of this type are ordinarily provided with an external conducting ground shield. To apply a terminal connection to such a cable, the shield of the cable is pencilled as indicated at 12, providing a short tapered section beyond which the conducting shield is removed. The insulation of the cable indicated at 14 is stripped away to bare the end of the conductor as indicated at 16. The end portion of the cable is received in the hollow interior 18 of an insulator body of usual configuration having a metal cap 22 permanently affixed to the outer end of the insulator body. The metal cap includes a tubular portion 24 through which the bared end of the conductor 16 extends. A permanent connection between the bared end of the conductor 16 and the tubular portion 24 of the cap 22 is provided by crimping the tubular portion 24 into tight permanent crimped engagement with the bared end of the conductor 16. Electrical connection is made with the cable conductor by means of a conventional clamp type connector installed around the tubular portion 24.  
  The dimension of the elongated generally cylindrical cavity 18 within the insulator body 20 is proportioned with respect to the dimension of the end portion 14 of the insulation on the cable so as to leave an annular space within the insulator body surrounding the cylindrical insulation on the end portion 14 of the cable.  
  The annular space intermediate the end portion 14 of the cable and the inner surface 18 of the insulator body is filled with an assembly made up of a hollow insulating sleeve 30 having an inner wall 32 and an outer wall 34. The sleeve 30 is closed at its ends&#39;and the hollow interior annular chamber 36 is filled with an insulating fluid, either liquid or gas. If the fluid is a liquid, a silicone oil, polybutene oil, or the like may be employed.  
 If an insulating gas is used, gas such as sulfur hexafluoride, nitrogen, freon and the like may be employed.  
 These fluids must of course be chemically compatible with the material forming the hollow insulating sleeve.  
  Associated with the hollow insulating sleeve 30 is a stress relief sleeve 40. The stress relief sleeve may be formed of a suitable insulating polymer such for example as the same material employed to form the hollow insulating sleeve 30 except that it will contain conducting particles such as graphite or carbon black in an amount to make the material of the sleeve 40 a semiconductor having a resistivity not exceeding 10 ohms X cm.  
  The end of the hollow sleeve 30 remote from the bared end of the conductor 16 is provided with an outer tapered surface 42 and the adjacent end of the stress relief sleeve 40 is provided with an internal tapered generally conical surface 44 which conforms to the surface 42. The interface between the surfaces 42 and 44 is thus a tapered or substantially conical interface which provides stress relief.  
  The stress relief sleeve 40 may also be hollow and provided with an annular interior chamber 46 which may be separately charged with insulating fluid, either liquid or gas, as previously described. The tapered end surfaces 42 and 44 of the sleeve may be impervious or I they may be provided with openings 47 provided for transfer of the insluating fluid between the hollow interior of the sleeves 30 and 40.  
  In the construction as thus far described it is contemplated that the hollow sleeve 30 and the sleeve 40 if it is provided with a hollow interior, are charged with the insulating fluid and permanently sealed when they are fabricated. It will be understood that the material of which the sleeves 30 and 40 are formed is a resilient elastomer such for example as butyl or silicone rubber. As intially charged with the insulating fluid at the factory, the sleeve 30, and the sleeve 40 if it is also hollow, are expanded by the fluid contained therein so as to be oversize with respect to the transverse dimensions of the annular chamber defined between the cylindrical interior surface of the cavity 18 of the insulator body and the exterior cylindrical surface of the insulation provided adjacent the end of the cable 10. Accordingly, after the sleeves have been inserted in the cavity, the insertion of the end portion of the cable 10 as illustrated in FIG. 1 displaces the inner surface of the sleeve or sleeves outwardly and results in a full surface-tosurface contact at a suitably elevated pressure.  
  In order to insure proper contact between the stress relief sleeve 40 and to control the pressure conditions existing in the fluid filled hollow sleeve 30, an adjustable closure 50 is carried at the inner end of the insulator body 20 and is adapted to bear against the outer end of the stress relief sleeve 40. Screws indicated at 52 are provided for attaching the closure 50 to the insulator body 20 and may be adjusted to apply the desired pressure to the sleeves 30 and 40.  
  Referring now to FIG. 2 there is illustrated a second embodiment of the present invention. In this case the end portion of the cable is indicated generally at 56 and is pencilled as indicated at 58 so that the end portion 60 has an outer cylindrical surface formed of insulating material from which the conducting shield indicated at 62 has been removed.  
  The structure illustrated in FIG. 2 is a cable termination and the insulation 60 is stripped from the end of the cable to bare a portion of the conductor as indicated at 64. The end portion of the cable 56 is received in an insulator body 66 including an end closure portion 68 having an aperture through which the bared end 64 of the conductor of the cable extends. Exterior of the insulator body 66 there is provided a connector cap 70 having a tubular portion 72 which is crimped or otherwise suitably secured to the end of the conductor. In assembly the enlarged head of the connector 70 engages an O-ring 73 provided in an annular groove 74 at te end of the insulator body.  
  Surrounding the end portion of the cable is a hollow insulating sleeve indicated generally at 76 having an inner cylindrical wall 78 in full surface-to-surface contact under elevated pressure conditions with the cylindrical surface of the insulation 60 at the end of the cable. The sleeve 76 includes an outer cylindrical wall 80 engaging the inner cylindrical surface 82 of the insulator body 66.  
  The hollow interior 84 of the sleeve 76 is connected to a valve 86 extending through the end wall 88 of the sleeve, the valve including an O-ring seal 90 and a removable cap 92. A second valve 94 is provided which may be identical with the valve 88 and also communicates with the interior annular chamber 84 within the hollow sleeve 76. The two valves are provided so that when the insulating fluid is caused to flow into the annular chamber 84 through one of the valves, the interior chamber may be purged through the other valve.  
  The end of the hollow insulating sleeve 76 remote from the bared end of the conductor 64 is provided with an outer tapered surface 98 which is generally conical in shape but which as illustrated is slightly concave in axial section.  
  Secured to the inner open end of the insulator body 66 is a tubular shell or casing 100 which is longitudinally tapered to have a smaller diameter adjacent its upper end as illustrated in the Figure. At its upper end the shell 100 is provided with a flange 102 which is assembled to flange 104 provided at the lower end of the insulator body 66 by suitable fastening devices such as the screws 106 and the nuts 108. At its outer end the shell 100 is provided with a second flange 110 by means of which it supports an end closure plate 112 through suitable assembly devices such as the screws 114 and the nuts 116.  
  Located within the shell 100 is the stress relief device or sleeve which as shown is hollow and provided with an internal annular chamber or pocket 122. The end of the stress relief sleeve 120 adjacent the hollow insulating sleeve 76 is provided with an internal tapered surface 124 whichi&#39;s conformed to the tapered surface 98 of the hollow sleeve 76. These tapered surfaces are generally conical but as illustrated, are provided with a slight longitudinal outwardly concave/convex curvature, respectively.  
  To interior of the stress relief sleeve 120 is connected to valving means indicated at 94 through which insulating fluid may be introduced into the annular pocket 122. In the event that the pocket 122 is sealed against communication with the pocket 84 provided in the sleeve 80,two such valves will be employed, one for introducing fluid under pressure and the other for purging air from the interior. However, it is also contemplated that the adjacent wall portions of two sleeves at the tapered ends thereof may be provided with passages 128 so that fluid may flow between the hollow interiors of the sleeves. In this case of course it is only necessary to have two valves, one of which communicates with the interior of the sleeve 120 and the other of which communicates with the interior of the sleeve 76.  
  With the parts of the connectorassembled with the end portion of the cable, as illustrated in FIG. 2, the insulating fluid, eitherliquid or gas, may be introduced into the hollow interior or interiors of the sleeves, thus tending to expand the sleeves and to force the inner walls of the sleeves into firm engagement with the outer surfaces of the end portion of the cable. It will be observed that the stress relief sleeve 120 is adapted to engage the portion of the cable provided with the ground shield 62, whereas the hollow insulating sleeve 76 engages only the end portion of the insulation 60 from which the shielding material has been removed by pencilling as indicated at 58.  
  The introduction of fluid under pressure into the hollow interior tube of the sleeve 76 and the sleeve 120 insures full perfect surface-to-surface contact between the interiorsurfaces of the sleeves 76 and 120 throughout the entire end portion of the cable 56.  
  Referring now to FIG. 3, a stress relief device 130 is provided in place of the stress relief sleeve 120. In this embodiment of the invention the end of the sleeve 130 adjacent the end of the cable is provided with an inner tapered surface 132 conforming to the outer tapered surface 98 of the hollow sleeve 76. In this case the stress relief sleeve 130 is formed of a resilient elasto meric material which may be the same as the resilient elastomeric material from which the hollow sleeve 76 is formed except it contains conducting particles such as carbon black or graphite in order to increase its conductivity. The tapered surface 132 of the sleeve 130 may be chemically bonded to the tapered surface 98 of the hollow sleeve 76 along the generally tapered interface. In this embodiment of the invention it will be apparent that when the end closure plate 112 engages the ,outerend of the sleeve 130, the sleeve 130 may be sufficiently elongated so that the closure plate 112 engages the end and forces the sleeve 130 inwardly of the tapered shell 100, thus causing the sleeve 130 to exert an inward pressure on the cable insulation as the closure plate 112 is tightened by means of the screws 114 and nuts 116.  
  Referring now to FIG. 4 there is shown a different embodiment of the invention in which the structure shown in FIG. 4 is substituted for the structure located within the tapered shell 100. In this construction the cable 56 is pencilled as indicated at 58 to expose the insulation 60, leaving the shield 62 in place. In this embodiment of the invention the metallic shell 136 is tapered as shown with the small end of the shell located at the top of the Figure. The shell is provided with ears 138 having tapped openings 140 for the reception of screws adapted to secure the shell 136 to flanges such as those illustrated at 104 provided at the lower end of the insulator body 66. As in the embodiment of the invention illustrated in FIG. 2, the construction includes a stress relief structure comprising a resilient semiconducting sleeve 142 which may be formed of an elastomeric resilient insulating material provided with particles of graphite or carbon black to produce a resistivity not exceeding 10 ohms X cm.  
  The outer surface 144 of the sleeve is tapered and conforms generally to the taper of the shell 136. The inner surface of the sleeve 142 includes a generally conically tapered surface 146 seen at the upper end of the Figure, while the inner surface 148 at the lower end of the sleeve 144 is generally cylindrical. In addition, the length of the sleeve 142 is such that in initial assembly the lower end 150 of the sleeve extends outwardly from the flange 152 provided at the lower end of the shell 136. An end closure plate 154 is provided having a central opening 156 through which the cable 56 extends and the plate is adapted to be attached to the flange 152 by suitable fastening means such for example as the screws 158 and nuts 160. With this arrangement, when the plate 154 is drawn toward the flanges 152 it applies compressive force to the sleeve 144 and, due in part to the tapered shape of the sleeve, produces radially inward pressure of the sleeve against the portions of the high voltage cable 56 therewithin.  
  In this embodiment of the invention there is provided a hollow insulating sleeve 162 which may be formed of the same material as the semi-conducting sleeve 144 except that this hollow sleeve does not include conducting particles and is fully insulating. The hollow sleeve 162 has a tapered outer surface 164 which conforms to the taper of the surface 146 of the sleeve 144 and is adapted to be engaged in full surface-to-surface pressure contact therewith in the assembled connector. The hollow interior of the sleeve 162 thus provides an annular chamber 166 adapted to receive insulating fluid, either liquid or gas, under elevated pressure, so as to insure full surface-to-surface pressure contact between the inner surface of the hollow sleeve 162 and the outer surface of the cable insulation 60. The interior chamber 166 of the hollow sleeve 162 is provided with suitable valve means such as indicated at 168 and 170 so that the insulating fluid may be introduced into the chamber 166 through one of the valves and air initially contained therein purged through the other valve.  
  It will be apparent from a-comparison of FIGS. 2 and 4 that when the structure of FIG. 4 is substituted for the shell 100 shown in FIG. 2, the surface 146 and 164 provide an interface which is of generally conical shape establishing a stress relief construction. In this case, the portion of the cable termination received within the insulator body 66 may be provided with a hollow insulating sleeve substantially similar to that shown in FIG. 2 except that its lower end will conform to the upper end surfaces of the sleeves 142 and 162.  
  The constructions illustrated in FIGs. 2 and 4 may be assembled in the field and after the components are assembled as shown, the annular chambers 84, 122 and 166 will be charged with insulating fluid under substantial pressure adapted to maintain full surface-to-surface pressure contact between the inner surface of the sleeves and the adjacent outer surfaces of the cable through extended use during which the cable may undergo repeated expansion and contraction.  
 CABLE INTERCONNECTION A is illustrated in FIG. 10.  
  Referring first to FIGS. -9 the construction comprises an enlcosure which may be formed of metal and comprises two relatively deep cup-shaped elements .200 provided with flanges 202 which may be interconnected by suitable means such for example as screws 204 and nuts 206. The end or bottom walls of the cups are illustrated at 208 and are apertured as illustrated to receive the ends of high voltage cables 210. The cables include conducting shields 212, pencilled portions 214, and end portions from which the conducting shields have been removed to expose the cable insulation 216.  
 The conductors are bared as indicated at 218. The bared cable conductors are interconnected by any conventional means such for example as compressed conducting sleeves, soldered sleees, welding or the like. A split conductor clamp 220 is provided, details of which are best seen in FIG. 6. Referring to this Figure it will be observed that the clamp comprises two portions 222 and 224 each recessed as indicated at 226 to receive the ends of the bared conductors. The portions 222 and 224 of the clamp are interconnected by suitable means such for example as screws 228 extending through openings 230 in the portion 222 and engaging in threaded openings 232 in the clamp portion 224. Coil compression springs 234 are porvided between the portions 222 and 224 and are compressed as the portions 7 are brought into clamping engagement by the screws Adjacent opposite ends of the cups 200 there are provided sleeves 236 which as shown, are adapted to bottom against the end walls 208 of the cups. The sleeves 236 are formed of resilient elastomeric insulating material such for example as butyl rubber, silicone rubber, or polyurethane, but contain a small quantity of conducting particles such for example as particles of carbon black or graphiteso as to render the sleeves 236 semi-conducting. The radially inner surfaces 240 at the inner ends of sleeves 236 are tapered as illustrated into generally conical configuration modified to provide the longitudinal convex configuration illustrated.  
  Intermediate the semi-conducting sleeves 236 is a hollow insulating sleeve indicated generally at 242. This sleeve is formed of insulating resilient elastomeric material such for example as butyl rubber, silicone rubber, or polyurethane, but differs from the material of the sleeves 236 in that no conducting particles are included so that the material of the sleeve 242 is fully insulating.  
  The ends of the sleeve 242 are provided with tapered outer walls 244 shaped to conform to the tapered surfaces 240 of the semi-conductor sleeve 236, and in assembly the surfaces 240 and 244 are in full surface-tosurface contact and it is contemplated that these surfaces may be chemically bonded together. In any case, the tapered interface provided by the surfaces 240 and 244 between the semi-conducting sleeve 236 and the hollow insulating sleeve 242 constitutes a stress relief device.  
  It will be observed that the semi-conducting sleeves 236 extend into contact with the shields on the cables 210. On the other hand, the hollow insulating sleeve 242 terminates adjacent the pencilled portion 214 and extends longitudinally of both end portions of the cable where the insulation 216 is exposed and across the gap between the ends of the cable insulation where the conductors 218 of the cable are electrically interconnected.  
  The outer surface of the sleeve 242 is provided with a layer 245 of semi-conducting material which may be the same material from which the sleeves 236 are composed.  
  The inner wall of the insulating sleeve 242 is provided at its mid-section with a thin layer 246 of conducting material which when the joint is completed is caused to abut against the clamp 220. The conducting material may be in the form a a resilient elastomer containing sufficient conducting particles to provide the requisite conductivity. This layer is just long enough to extend beyond the edges of the cable insulation 216 in such a way as to eliminate electrical stresses in the void space 248 between the ends of the cable insulation.  
  Valve means indicated generally at 250 and illustrated in detail in FIG. 9 are provided to communicate with the interior annular chamber or pocket 252 provided in the hollow sleeve 242. These valves include valve elements 254 secured by suitable means such for example as threads within the interior of the threaded nipples 256. The nipples 256 have threaded exteriors and adapted to receive sealing caps 258 which are associated with sealing means such for example as O-rings 260 to provide an adequate seal. The valves are provided in pairs so that both may be open while insulating fluid is introduced into the chamber 252 through one of the valved openings and air purged from the interior through the other.  
  Referring now to FIG. 7 there is illustrated a further embodiment of the invention in which the solid resilient elastomeric sleeves 236 are replaced by hollow sleeves 262, each provided with an interior annular cavity 264 provided with valve means indicated generally at 260. The sleeves 262 are formed of semiconducting material as previously described and include tubular portions 268 which interconnect the sleeves 262 at opposite ends of the assembly and which engage or are bonded to the outer walls 270 of the intermediate hollow sleeve 242. The interior annular chamber 252 provided in the hollow sleeve 242 communicates with the chambers 264 in the sleeve portions 262 through suitable passages 272.  
  The advantages of this construction are: (a) there is no electrical stress in this conducting portion; therefore, the existence of the sleeve of a check valve presents no voltagerelated problem; (b) owing to the fluid in the pocket or chamber 264, the conducting portion of the sleeve can be more effectively compressed against the cable insulation 216 and the semiconducting shield 212 and also the pencilled portion 9 214; and (c) by providing a valve in communication with the chambers 264 at opposite ends of the assembly, the purging of air from the pockets or chambers 252 and 264 is facilitated.  
 Referring now to FIG. 8 there is illustrated a variation in the construction of the cable joint. In this case the middle portion of the hollow sleeve, here indicated at 280, is made outwardly convex as illustrated and the semi-conducting layer 282 provided at its inner surface accordingly has the tapered ends 284 to improve the electric voltage gradient in that portion of the joint and to provide better compression against the cable surfaces. In any case, the casing formed by mating cup portions 286 have the walls adjacent the ends thereof curved in conformity to the curvature of the hollow insulating sleeve as indicated at 288.  
  It will be understood that while valves andcheck valves are shown for the purpose of charging the interior ofthe hollow insulating sleeves as well as the hollow sleeves formed of semi-conducting material, with pressurized insulating fluidin the field, it is also con templated thatthese annular chambers may be charged in the factory and the sleeves permanently sealed. In this case of course, the check valves will be omitted and the compression of the sleeves will be achieved by forces developed by drawing the cup-shaped shells 200 together in assembly after the electrical connection is established between the .bared ends of the cables and the sleeve or sleeves have been brought into the relative position illustrated in FIG. 5. 1  
  Referring now to FIG. 10 there is illustrated a joint intended for use with very high voltage power cables. In this case the cables are illustrated at 300 and include outer shields 302, pencilled portions 304, and end portions at which the cable insulation 306 is exposed. The cable insulation is cut back to bare the ends of the cable conductors 308 which are electrically interconnected by conventional means 310. A capacitive device 312, details of which will subsequently be described, is positioned around the gap 314 between the ends of the cable insulation 306 in which the conductors 308 are interconnected.  
  A combination of insulating sleeve and stress relief assembly 313 is provided and is inserted within the tapered ends of the capacitive device 312 as illustrated. Theentire assembly is housed in two rigidmetallic sleeves or cup-shaped members 316 attached to each other through flanges 318 and suitable clamping means such as screws 320 and nuts 322.  
  The assembly 313 is provided with an annular pocket 324 formed between insulating walls 326 and 328 formed of an elastomeric resilient fully insulating material. The outer ends of the pocket 324 are bounded by curved surfaces 330, which are surfaces-of revolution defining convexly curved walls having a stress relief function. The outer ends of the assembly 313 are provided by annular portions 332 formed of a resilient el&#39;astomeric essentially insulating material, which however is provided with conducting particles to render the end portions semi-conducting as previously described. It will be understood that the portions 332 may be formed of the sameresilientelastomeric material as the walls 326 and 328 which define the longitudinally tapered annular chamber 324, except that the walls 326 and 328 do not include the conducting particles and hence are fully insulating.  
  If desired, the end portions 332 may be provided with internal annular pockets substantially as suggested in FIG. 7.  
  The pocket 324 provided in the assembly 313 is connected to two valve means indicated generally at 334 and 336 through which insulating fluid may be introduced and the air within the pocket 324 suitably purged.  
  The capacitive device 312 comprises a specially shaped tubular body having at opposite ends inwardly tapered recesses 340 for the reception of the inner tapered ends of the assembly 313 and interconnected by a cylindrical through opening 342 which receives the means interconnecting the ends of the cable conductors. The device is essentially comprised of two sets of cylindrical conducting rings 344 aligned on the same axis and embedded in an insulating mass 346 of a suitable material such for example as electrical grade epoxy. The diameters of the rings 344 are increased gradually from the center of the device toward its ends. The innermost cylindrical wall 348 is designed to be in good electrical conducting contact with the connecting clamp illustrated at 310 in FIG. 10. The outer surface of the device is conducting and may comprise a cylindrical metal shell 350. The rings 344 and the innermost cylindrical wall 348 may conveniently be formed of cylindrical metal rings or tubes.  
  This device will operate to distribute the voltage uniformly along the slanting surfaces of the conical end recesses 340.  
  With the construction illustrated in FIG. 10 it may be noted that the insulating structure within each end of the housing completely fills the space defined by the outer and end walls of the cup portions 316, the outer surfaces of the cables within the housing, and the inclined tapered surfaces 340 of the recesses at the ends of the voltage distributor 312. The inner and outer walls of the insulating sleeve which define the inner and outer limits of the chambers 324, are formed of insulating material. The chambers 324 are further defined by the curved annular end walls 330&#39;forming a part of the sleeve portion 332. The sleeve portion 332 is also formed of resilient elastomeric material but it is rendered semi-conductive by the presence of conducting particles therein. Accordingly, the curved surface 330 constitutes a stress relief cone or device.  
  Where the annular sleeve 332 is itself provided with an elongated internal chamber such as illustrated at 264 in FIG. 7, the entire structure made up of the sleeves 332 and the chamber walls 326 and 328 is expansible to insure that the sleeves completely fill the aforesaid spaces, expelling all air therefrom, and maintaining full surface-to-surface pressure contact between the radial inner surface of the sleeve assembly and the outer surface of the cable throughout the period of service including repeated expansions and contractions of the cable in use.  
  The voltage distributor specifically illustrated in FIG. 10 is constituted by a multiplicity of capacitive devices arranged in series in which each adjacent ring 344 axially overlaps the adjacent rings and is separated therefrom by dielectric material. With this arrangement it will be observed that the inner tube 342 is at the voltage of the conductor and the outer tube 350 is at ground potential, assuming that the housing 314 and the cable shield 300 are at ground potential. Accordingly, the entire applied voltage is divided between the series capacitances as is well understood so that the voltage drop along the inclined conical surface 340 has a uniform gradient.  
  From the foregoing it will be observed that the common feature present in all embodiments of the invention is the provision of one or more hollow sleeves formed of insulating or semi-conductive material and provided with elongated annular chambers for the reception of insulating fluid at elevated pressure effective to produceessentially radial inward and outward expansion of the sleeves into full surface-to-surface contact with outer restraining surfaces and the radially outer exposed surfaces of the portions of the cable or cables within the sleeves. An additional feature is the division of the sleeve structure into two separate components one of which is fully insulating and the other of which is formed of semi-conducting material, the two portions having tapered or generally conical interfaces forming stress relief cones. The two portions of the sleeves may be provided with separate and separately chargeable annular recesses or they may be interconnected by passages providing for flow of insulating fluid therebetween.  
  The constructions may be arranged such that the internal annular chambers are permanently charged with insulating fluid under pressure at the factory and the pressure conditions maintained and controlled by the application of external pressure to portions of the sleeve or sleeves by containing structure therefor.  
  Where reference is made to elevated pressure, it is intended to require a pressure sufficiently above ambient or atmospheric pressure to produce the required surface contact conditions described herein.  
 . In all cases where the stress relief cone or device such as seen at&#39;40 in FIG. 1 or 120 in FIG. 2 is shown as a separate member from sleeves 30 or 76, etc., it will be understood that in all cases these may be united to form in effect a single element. What I claim as my invention 1. A stress relief connection designed for application to insulated high voltage electrical cable comprising a hollow tubular sleeve adapted to surround the insulation adjacent the bared end of an insulated high voltage electrical conductor and formed of resilient elastomeric electrically insulating material having at the end thereof remote from the bared conductor an inwardly tapered exterior surface, a generally tubular stress relief sleeveformed of a material which is at least semiconductive having an outwardly tapered interior end surface in surface-to-surface contact with the tapered exterior surface of said hollow sleeve, a rigid support housing surrounding said hollow sleeve, the interior of said hollow sleeve being an elongated annular chamber adapted to be charged with a pressurized insulating fluid to expand the inner wall of said hollow sleeve radially inwardly to establish intimate contact between the inner surface of said hollow sleeve and the outer surface of the insulation surrounding the conductor adjacent its bared end.  
  2. A connection as defined in claim 1 in which said hollow sleeve is provided with inlet and outlet valves to provide for purging the hollow interior of the sleeve and to fill the hollow sleeve with fluid under pressure.  
  3. A connection as defined in claim 1 in which said tubular stress relief sleeve is formed of resilient elastomeric material and is also hollow to have an elongated annular chamber to receive insulating fluid under pressure.  
  4. A connection as defined in claim 3 in which passages are provided connecting the hollow interior of said hollow tubular sleeve and the hollow interior of said stress relief sleeve.  
  5. A connection as defined in claim 1 in which said hollow tubular sleeve is filled with insulating fluid and permanently sealed.  
  6. A connection as defined in claim 5 in which said connection comprises an enclosing wall movably associated with said housing, and means for moving said wall relative to said housing to apply pressure to said hollow tubular sleeve.  
 7. A connection as defined in claim 1 in which said &#39;fluid is an insulating liquid.  
  8. A connection as defined in claim 1 in which said fluid is an insulating gas.  
  9. A connection as defined in claim 1 in which said connection is a cable termination, and in which said housing comprises a hollow insulator body, comprising connector means exposed at the end of said body adapted to be electrically connected to the bared end of the conductor.  
  10. A connection as defined in claim 1 in which said connection is for connecting the ends of two insulated high voltage cables, comprising means within said hollow tubular sleeve adapted to electrically connect the bared ends of the conductors, and in which the opposite ends of said hollow tubular sleeve are both tapered as aforesaid, and stress relief sleeves as aforesaid are provided at both ends of said hollow insulated sleeve.  
  11. An electrical connection comprising in combination a high voltage cable having a conductor surrounded by insulation, the conductor having an end exposed and extending beyond the end portion of the insulation, a rigid housing surrounding the end portion of the insulation, a hollow tubular resilient elastomeric sleeve having an elongated annular chamber therein interposed between the end portion of the insulation and the housing, said sleeve having at the end thereof remote from the bared conductor a tapered exterior surface, a generally tubular stress relief sleeve formed of a semi-conductive material having at an end thereof a tapered interior surface in surfac-to-surface contact with the tapered exterior surface at said hollow tubular sleeve, an insulating fluid in the chamber in said sleeve under an elevated pressure sufficient to expand the chamber defined by the hollow interior of said sleeve to force the inner wall thereof into firm surface-tosurface contact with said insulation.  
  12. A connection as defined in claim 11 in which said hollow sleeve is provided with inlet and outlet valves to provide for purging the hollow interior of the sleeve and to fill the hollow sleeve with fluid under pressure.  
  13. A connection as defined in claim 11 in which said tubular stress relief sleeve is also hollow and has an annular chamber to receive insulating fluid under pressure.  
  14. A connection as defined in claim 13 in which passages are provided connecting the chamber in said hollow tubular sleeve and the chamber in said stress relief sleeve.  
  15. A connection as defined in claim 11 in which said hollow tubular sleeve is filled with insulating fluid and permanently sealed.  
 16. A connection as defined in claim 15in which said connection comprises an enclosing wall movably associated with said housing, and means formoving said wall relative to said housing to apply pressure to said hollow tubular sleeve.  
  17. A connection as defined inclaim 11 in which said connection is a cable termination, and in which said housing is in the form of a hollow insulator body, comprising connector means exposed at the end of said body adapted to beelectrically connected to the bared end of the conductor.  
  18. A connection as defined in claim 11 in which said connection is for connecting the ends of two insulated high voltage cables, comprising means within&#39;said hollow tubular sleeve adapted to electrically connect the bared ends of the conductors, and in which the opposite ends of said hollow tubular sleeve are both tapered as aforesaid, and stress relief sleeves as aforesaid are provided at both ends of said hollow insulated sleeve.  
 19. An insulated connection between two high voltage cables having end portions in which bared conduc- I tor ends project beyond the ends of insulation surrounding the conductors to define a gap between the end of said insulation, connector means in the gap electrically interconnecting the bared conductor ends, a capacitive voltage distributor comprising an elongated tubular body formed of a dielectric material having elongated tapered recesses extending into opposite ends and having a central portion provided with a through opening in which are located the bared conductor ends and the connector means, an inner conducting tube in said opening in contact with said connector means, an outer elongated conducting tube covering the outer surface of the voltage distributor, a series of short circumferentially spaced, axially staggered conducting rings extending along and around each of the tapered recesses, said rings overlapping adjacent rings and spaced radially of each other, the rings being entirely embedded in said dielectric body and having the spaces between adjacent rings being filled with the dielectric material of said body.  
  20. A connection as defined in claim 19 which comprises in addition an outer housing formed of conducting material in contact with said outer tube.  
  21. A connection as defined in claim 20 in which said cables have conducting shields extending into the housing, and means electrically connecting said shields to said housing.  
  22. A connection as defined in claim 21 in which the means connecting the shields and housing comprise semi-conducting resilient sleeves in the ends of said housing in surface contact with said shields.  
  23. A connection as defined in claim 22 in whichsaid semi-conducting sleeves have annular pockets formed therein, and insulating fluid in said pockets at elevated pressure to expand the sleeves in full surface-to-surface contact under pressure with the inner surface of the housing and with the outer surface of the cable within said housing.  
  24. A connection as defined in claim 20 which comprises in addition elongated hollow sleeves formed of resilient elastomeric insulating material and having an annular chamber therein extending substantially the full length thereof, the radially outer walls of the axially inner ends of said sleeves being tapered in conformity with the taper of the recesses in the ends of said voltage distributor and received therein in surface-to-surface contact, the interior of said chambers being charged with insulating fluid under pressure effective to press rounding the conductors to define a gap between the end of said insulation, connector means in the gap electrically interconnecting the bared conductor ends, a capacitive voltage distributor comprising an elongated tubular body formed of a dielectric having elongated tapered recesses extending into opposite ends and having a central portion provided with a through opening in which are located the bared conductor ends and the connector means, a generally tubular conducting housing having apertured end walls through which the end portions of said cables extend, the space in each end of said housing defined by the tapered wall of the recess in said voltage distributor, the outer surface of the cable, the end wall of the housing, and the radially outer wall of the housing being filled by a hollow expansible sleeve portion formed of resilient elastomeric material having an elongated annular chamber therein extending subtantially for the full length of the portion of cable insulation exposed therein, said chamber being filled with insulating fluid at elevated pressure to insure full surface-to-surface pressure contact between the inner and outer surfaces of said sleeve portion and the cable insulation and the inner surface of said housing respectively.  
  27. A connection as defined in claim 26 comprising in .addition a second sleeve portion extending axially outwardly from the outer end of each first mentioned sleeve portion, said second sleeve portions forming the axially outer ends of the annular chambers in said first mentioned sleeves and being formed of semiconducting material and shaped to form axially tapered stress relief surfaces, the inner and outer walls of said first mentioned sleeve portions being non-conducting.  
  28. A connection as defined in claim 27 in which both of said second sleeve portions are also hollow and provided with annular chambers adapted to receive insulating fluid at elevated pressure to expand said second sleeve portions into full surface-to-surface contact with the outer surface of said cables and the inner surfaces of said housing.  
  29. A high voltage electric connection comprising an elongated generally cylindrical housing having a side wall and an end wall provided with an opening through which extends the end portion of an insulated high voltage cable, said cable having the end of its conductor bared at a point remote from said end wall and having its insulation intact for a substantial length of said cable within said housing, said housing and the insulation of said cable defining therebetween an elongated annular space, an elongated sleeve formed essentially of resilient, elastomeric insulating material occupying said space, said sleeve having an elongated annular chamber therein between radially inner and outer walls, and  
 insulating fluid filling said chamber under elevated pressure sufficient to maintain the inner and outer walls of said sleeve in firm surface-to-surface pressure contact respectively with the radially outer surface of the insulation of the end portion of said conductor received in said housing and theinner surface of the side wall of said housing.  
  30. An elongated insulating and stress relief sleeve construction for use in a high voltage cable connection, said construction comprising a first elongated sleeve section formed of resilient elastomeric insulating material provided with an elongated annular chamber therein for the reception of insulating fluid at elevated pressure, an end section operatively connected to one end of said intermediate section formed of at least semi-conducting material, said first and end sections having a tapered generally conical interface providing electrical stress relief.  
  31. A construction as defined in claim 30 which comprises in addition a second end section conforming to the definition of the first end section in claim 30 and operatively connected to the other end of said first section.  
  32. A construction as defined in claim 31in which said end section is formed of resilient elastomeric semiconducting material.  
  33. A construction as defined in claim 32 in which said end section is provided with an elongated annular chamber therein for the reception of insulating fluid at elevated pressure.