Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
  • H02G15/00—Cable fittings
  • H02G15/08—Cable junctions
  • H02G15/10—Cable junctions protected by boxes, e.g. by distribution, connection or junction boxes
  • H02G15/103—Cable junctions protected by boxes, e.g. by distribution, connection or junction boxes with devices for relieving electrical stress
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
  • H02G15/00—Cable fittings
  • H02G15/02—Cable terminations
  • H02G15/06—Cable terminating boxes, frames or other structures
  • H02G15/064—Cable terminating boxes, frames or other structures with devices for relieving electrical stress
  • H02G15/068—Cable terminating boxes, frames or other structures with devices for relieving electrical stress connected to the cable shield only
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
  • H02G15/00—Cable fittings
  • H02G15/08—Cable junctions
  • H02G15/18—Cable junctions protected by sleeves, e.g. for communication cable
  • H02G15/184—Cable junctions protected by sleeves, e.g. for communication cable with devices for relieving electrical stress

Definitions

• the present invention relates to a cable termination of the kind referred to in the preamble to claim 1.
• the cable termination is designed for high- and medium-voltage cables (power cables) in the voltage range of up to 450 kV which are insulated with a solid insulating material, preferably crosslinked polyethylene (PEX) .
• the cable termination is adapted to be used for connection to electric switching devices and other connection objects with insulation of solid insulating material, licruid or pressure gas, such as, for example, insulators and metal-enclosed switchgear.
• Other fields of use are jointing into a corresponding power cable or to other cables, for example paper-insulated power cables.
• a field-controlling component a so-called stress cone, of insulating elastic material partially surrounded by a conducting external coating.
• the stress cone is intended to control the electric field strength around the cable end such that the field- strength gradient along the cable insulation is maintained sufficiently low to avoid partial discharges and hence the risk of breakdown of the insulating medium surrounding the cable termination.
• the insulating medium consists of air, which provides simple and inexpensive terminations which are easy to handle. At high voltage, however, such devices become bulky.
• a PEX cable is often provided with a liquid-insulated termination in an electrically insulating enclosure of plastic or a ceramic material.
• Such a design entails increased costs of the insulating fluid and its insulating enclosure, as well as costs for expansion volume for the thermal expansion of the insulating fluid.
• a problem with the terminations filled with insulating fluid is also the risk of leakage.
• a problem with the cable termination described above is the sealing. Because of its elasticity, the stress cone has limited possibilities of resisting the stresses exerted by the gas pressure. This has necessitated the introduction of special support members to prevent the stress cone from being deformed or pushed out of the enclosure.
• An additional problem with the known termination is that the introduced support members, which in principle form a stiff tube, may contribute to deformation of the insulation of the cable and of the stress cone when being loaded. This may result in spark discharge, which successively destroys the insulation.
• the object of the present invention is to achieve, in a power cable with solid insulation, a cable termination with small dimensions and which with rational methods can be connected to an electric circuit so as to form a closed current path without the risk of flashover.
• the termination is intended tb eliminate the disadvantages mentioned above and permit a rapid and leakage-free installation without handling oils at the site of the installation.
• the cable termination is to be able to withstand mechanical load and also permit functions, such as tightness and flashover, to be tested in advance.
• the cable termination is intended for direct connection to metal-enclosed swithchgear insulated with SF6 gas but may also be advantageously used, for example, for jointing cables, connection to an electric switching device, or to other electric outdoor components etc.
• the cable termination is designed as a so-called dry cable termination, thus eliminating the handling of oil at the site of the installation as well as excluding the risk of leakage.
• the cable termination compri- ses one female part and one male part which are assembled into an electrically conducting mechanical joint surrounded by a stress cone, formed from insulating rubber, with an externally conducting coating.
• the male part is composed of the cable with a contact member attached to the stripped con- ductor thereof.
• the female part is composed of an insulating body with a contact sleeve which is cast into one end thereof and which is connected to a conductor running coaxially through the insulating body. This conductor is electrically connected to the circuit which is to be connected.
• the insulating body is adapted to be rigidly attached to the circuit, such that the attachment becomes gas-tight and can withstand mechanical forces.
• the contact member fixed to the cable conductor is adapted to be pushed into the sleeve body arranged at the connecting conductor.
• the contact member is fixed to the sleeve body by means of a mechanical joint such that a good contact is obtained and such that the joint also serves as a tensile strain relieving device.
• the stress cone which was previously fitted onto the cable, is passed over the joint so as to surround the joint. At the same time, the externally conducting coating of the stress cone is brought into contact with the externally conducting layer of the cable, thus forming a favourable field distribution.
• Figure 1 shows a cross section of a cable termination according to the invention for connection to a gas- insulated metal-enclosed switchgear unit
• Figure 2 shows a cross section of a gas-insulated insulator for outdoor use and a cable termination according to the invention, connected thereto,
• Figure 3 shows a cross section of a joint between two PEX cables, in which two oppositely located cable terminations according to the invention are used
• Figure 4 shows a cross section of a joint between a PEX cable and a power cable with paper insulation, a cable termination according to the invention being used to connect the PEX cable.
• a connection of a high-voltage cable 1, insulated with a solid insulating material, into a metal-enclosed switchgear unit (not shown) is shown in Figure 1.
• the cable 1 has an inner conductor 2, usually of copper or aluminium, surrounded by a solid insulation 3, preferably of crosslinked polyethylene (PEX) .
• the insulation 3 is surrounded by an outer conducting layer 4, which is extruded on the insulation.
• a metallic shield Surrounding this conducting layer 4 and in electrical contact therewith is a metallic shield (not shown), preferably of copper wires.
• the cable is surrounded by a sheath 5, for example of polyethylene (PE) , which is tight and has good mechanical properties.
• PE polyethylene
• a circular contact plug 6 On the exposed cable conductor 2 there is arranged a circular contact plug 6, which is fixed to the conductor with a screw joint 7, the task of which is to ensure good electrical and mechanical connection between the contact plug 6 and the cable conductor 2.
• An only partially shown attachment flange 10 comprising a hole 11, limited by a circular collar 13 of the attachment flange folded out towards the cable, is gas- ightly attached to a switchgear unit (not shown) .
• a cylindrical insulating body 12 Through the hole 11 is arranged a cylindrical insulating body 12 with a slot 14 for the collar 13 and with a corbelled-out portion 15 which makes contact with the inside of the attachment flange to bring about good sealing.
• the insulating body 12 is homogeneous and preferably consists of epoxy, which is cast to the hole 11 such that no air pockets arise. Through the insulating body there extends coaxially a rod-shaped conductor 16, for example of copper, which, with good tightness, is attached to the insulating body 12.
• the conductor On the inside of the switchgear unit, the conductor is connected to an electric component (not shown) , with which the cable 1 is adapted to form a closed circuit.
• the end of the conductor facing the cable is connected to a contact sleeve 17, the outside 18 of which is cup-shaped with an outer diameter equal to that of the insulating body and gas-tightly cast into the insulating body 12.
• the contact plug 6 is adapted to be inserted into the contact sleeve 17 so as to obtain a coupling with good electrical conductivity.
• a screw joint 8 fixes the contact plug to the contact sleeve, whereby the screw joint is adapted such that the screws 9 are oriented in an axial direction and are accessible for tightening outside the cable insulation 3.
• a stress cone 20 of an elastically insulating material with an outer con ⁇ ducting coating 21 is adapted to surround the joint.
• the stress cone 20 is preferably constructed from partly insu ⁇ lating, partly conducting EPDM rubber.
• That part of the stress cone facing the cable is formed with a cylindrical neck 22, of a conducting material, which surrounds the cable insulation and is electrically connected to the outer con ⁇ ducting layer 4 of the cable.
• the neck changes into a cone-shaped part 23 of insulating rubber, where the conducting coating follows the outer contour.
• the stress cone then changes smoothly into a cylindrical portion 24 which surrounds the joint and part of the insulating body 12.
• the cylindrical part has a thickness which is sufficiently large to bring about a satisfactory insulation around the joint.
• the stress cone then changes into a slightly cone-shaped part 25, converging towards the attach ⁇ ment flange, which surrounds the insulating body 12 and extends so far towards the attachment flange as to overlap the collar 13.
• the stress cone has a coaxial through-hole in two sections with different inner diameters.
• the narrower hole section is intended to tightly surround the cable insulation and has, in non-extended state, an inner diameter smaller than the diameter of the cable insulation.
• the wider hole section is intended to tightly surround the insulating body 12 and has, in a non-expanded state, an inner diameter smaller than the outer diameter of the insulating body.
• a ring 26 of electrically conducting rubber is arranged in the area around the transition from the narrower to the wider section.
• the ring 26 is in electrical connection with the contact sleeve 17 and the contact plug 6 and adapted to smoothly control the electric field so as to avoid field concentrations.
• the ring In a rotationally symmetrical cross section, the ring is exposed on the inside of the stress cone 20 at the transition between the two sections and a certain dis ⁇ tance into the respective section and extends arcuately into the insulating layer of the stress cone.
• the recess also allows the edge of the wider hole section to make contact, with a dimensionable pressure, with the contact sleeve 17 so as to prevent the occurrence of field-disturbing air pockets.
• the entire cable termination is enclosed by a protective sleeve 30 of metal, which is connected to a ring 31 arranged around the cable and composed of two halves.
• the two halves comprise a connecting collar 32 for fixing the protective sleeve 30 and are adapted to mechanically fix the cable 1 by means of a clamping joint.
• the contact surface 19, which is common to the contact plug 6 and the contact sleeve 17, may be arranged cylindrical or slightly conical.
• Axially oriented spring elements (not shown) or the like may also be introduced into the contact surface 19 to ensure good electrical contact.
• the insulating body is not limited to being cast into an attachment flange but may also be formed in two parts, which are attached to each other from separate sides of the hole in the flange. The insulating body may also be cast or flanged directly to the casing of the switchgear unit.
• FIG. 2 shows a cable termination connected to a gas- insulated insulator 40.
• the insulator comprises an insulator. 41 of porcelain or polymeric material and a socket in the form of a mounting flange 42.
• the insulating body 12 descri- bed above is here extended into the insulator where it is shaped as a field-controlling component 45 of a previously known appearance.
• a layer of a conducting coating 46 surrounds that part of the field-controlling component 45 facing the cable and is electrically connected to an attach- ment flange 43, into which the extended insulating body is attached.
• the conducting coating consists of a collar pressed from the attachment flange.
• the attachment flange 43 is adapted to be gas-tightly fixed to the insulator 40 by means of a joint, in which case a seal, preferably an O-ring 44, makes contact with the mounting flange 42 or the end surface of the insulator 41.
• a seal preferably an O-ring 44
• Coaxially through the extended insulating body runs a rod- shaped conductor 47, which, in its end facing the cable, is connected to a contact sleeve 17 of the above-mentioned kind.
• the other end of the conductor is formed with a jointing device 48 to create a closed current path with the circuit to be closed.
• a contact plug 6, attached to the cable conductor is inserted into the contact sleeve 17, and the insulating body 12 is surrounded by a stress cone 20 of the kind described above.
• Figure 3 shows a joint between two PEX cables arranged with the aid of two cable terminations according to the above, turned towards each other.
• a mirror-symmetrical insulating body 50 common to both cable terminations surrounds a con- ducting jointing member 51, a contact sleeve 17 being connected to each end thereof.
• a contact plug 6 is inserted into each contact sleeve, which contact plug 6 is fixed to the respective cable conductor by means of a joint.
• a stress cone 20 of the type described above, with a inner conducting ring 26 and an outer conduc ⁇ ting coating 21, surrounds the respective joint such that the outer conducting coating of each stress cone is electrically connected to each other.
• a ring 52 of conducting material is cast into the surface of the central part of the insulating body to achieve a satisfactory overlap between the stress cones so that no electric stress concentrations are obtained.
• Figure 4 shows how a joint between a PEX cable and a cable 60 insulated with paper 61 may be achieved by means of the cable termination described above.
• the paper 61 is impregnated with an insulating fluid and wound around a conductor 62 which is electrically connected, by means of a splice joint, to a con ⁇ ducting, rod-shaped connecting piece 63, which in its other end is connected to a contact sleeve 17 of the kind described above.
• a contact plug 6 of the kind described above is inser- ted into the contact sleeve, the conductor of the PEX cable 1 being electrically connected to the contact plug.
• the connec ⁇ ting piece 63 is coaxially cast into an insulating body 64, which is tightly cast to an attachment flange 10 and which is conically extended towards the paper-insulated cable.
• a stress cone 20 of the kind described above is arranged, surrounding the contact sleeve 17 with the inserted contact plug 6, which stress cone makes contact with the insulation of the PEX cable and with the insulating body 64.
• an insulating sleeve body 65 is arranged. This sleeve body 65 is composed of paper which is impregnated with insulating fluid and wound around the joint into the desired thickness.
• the sleeve body thereby surrounds part of the paper insulation 61 of the cable, the conductor 62 and the jointing body 63 and is wound in such a way as to prevent air pockets.
• a container 66 filled with insulating fluid is arranged.
• the casing of the container is made of solid material, for example metal, and at the other end of the container a bushing 67 is arranged for fixing of and sealing against the paper-insulated cable 60.

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• Cable Accessories (AREA)

Applications Claiming Priority (3)

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ID=20399368

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Country Status (4)

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• 1995
  • 1995-09-05 SE SE9503048A patent/SE504919C2/sv not_active IP Right Cessation
• 1996
  • 1996-09-03 WO PCT/SE1996/001087 patent/WO1997009762A1/en not_active Application Discontinuation
  • 1996-09-03 JP JP9511131A patent/JPH11512280A/ja active Pending
  • 1996-09-03 EP EP96930466A patent/EP0848864A1/en not_active Withdrawn

Non-Patent Citations (1)

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