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
  • H02G15/02—Cable terminations
• • 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
• • 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
  • H02G15/20—Cable fittings for cables filled with or surrounded by gas or oil
  • H02G15/22—Cable terminations
• • 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
  • H02G15/20—Cable fittings for cables filled with or surrounded by gas or oil
  • H02G15/24—Cable junctions

Definitions

• the present invention relates to a power cable termination arrangement, comprising: an electric conductor; an internal electric insulation attached to and enclosing at least a part of said conductor; an external encapsulation enclosing the conductor and the inner insulation, and; an intermediate electrical insulation medium, provided in a spacing between the external encapsulation and the electric conductor.
• the cable termination arrangement may be part of a so called electrical bushing, by means of which a conductor is led through a wall and connected to any further electrical device. It is within the scope of the invention to regard a bushing as comprising two interconnected cable termination arrangements.
• the invention relates to a gas insulated switchgear and an electric joint arrangement provided with at least one cable termination arrangement according to the invention.
• the inventive arrangement is particularly suitable for high voltage applications, i.e. a voltage above 1 kV, and in particular for extra high voltage applications, i.e. a voltage of even above approximately 200 kV. It is applicable to both DC and AC applications, but in particular to AC applications.
• the above fact does not create any problem, since the cable termination arrangement is relatively short, and heat will be transferred in a radial as well as an axial direction out of the cable termination arrangement.
• the length of the cable termination arrangement needs to be correspondingly increased, and, as a result thereof, the heat transfer through the alternative filling compound will be unsatisfactory in order to maintain a temperature low enough not to deteriorate the internal insulation, i.e. the solid cable insulation that encloses the conductor inside the cable termination arrangement.
• the internal insulation is mainly comprised by a polymer material, and therefore is more sensitive to heat than the other materials of the cable termination arrangement.
• oil is the intermediate insulation medium used in contemporary solutions.
• the present invention should present a cable termination arrangement that promotes the use of a solid or semi-solid intermediate insulation material unable of transferring heat through convection, and therefore providing a lower thermal conductivity than a liquid insulation medium such as oil.
• the object of the invention is achieved by means of the initially defined cable termination arrangement, characterised in that, along a part of the length of the conductor, there is provided a means for increasing the thermal conductivity of the conductor.
• the conductor with the addition of said means, will have an improved ability of conducting heat in an axial direction out of the cable termination arrangement.
• a means for increasing the electrical conductivity of the conductor along said part of the conductor thereby, less heat will be generated by the conductor along said part upon conduction of a given current therethrough. Accordingly, less heat need to be transferred through the intermediate insulation medium than would be the case in the absence of said means.
• the internal insulation does not cover the conductor along said part of the length of the conductor. Accordingly, the conductor, or said means for increasing the thermal conductivity thereof is exposed to the intermediate insulation medium.
• the means for increasing the thermal conductivity of the conductor and the means for increasing the electrical conductivity of the conductor comprises an element of an electrically conducting material, arranged so as to increase the cross-section of the conductor along said part thereof. If the conductor is of tubular shape, the cross section thereof could be increased either by a reduction of the inner radius thereof and/or by an increase of the outer radius thereof by the addition of said electrically conducting material.
• the electrically conducting material will form part of the conductor, thereby contributing to the thermal and electrical conductivity of the latter.
• the means for improving the thermal conductivity and the electrical conductivity of the conductor may, accordingly, be defined as a local increase of the cross section of the conductor, as compared to the cross section of the part thereof that is covered by the internal insulation.
• Alternative solutions to said addition of the element of electrically conducting material may include solutions by which the electrical and/or thermal conductivity of the conductor along said part is increased in any other way, for example by means of a manipulation of the material of the conductor.
• said element comprises a metal.
• said element comprises a sleeve provided on the outer periphery of the conductor.
• a sleeve applied to the outer periphery is advantageous from many practical points of view. For example, it is relatively easy to produce and to tailor (length, thickness, conductivity, etc.) for the specific implementation. A sleeve will also be relatively easy to attach to an existing conductor.
• the material of said sleeve has a higher thermal conductivity than that of the material of the intermediate insulation medium. Since the sleeve, in reality, might occupy space that would otherwise have been occupied by the insulation medium, it is advantageous that the material of the sleeve is a better thermal conductor than said intermediate medium.
• the material of said sleeve has a higher thermal conductivity than that of the material of the internal electrical insulation.
• the sleeve might occupy space that would otherwise have been occupied by the internal insulation. Therefore, it is advantageous that the material of the sleeve is a better thermal conductor than the material of the internal electrical insulation.
• the sleeve comprises a material of equal or lower electrical resistivity than that of the conductor itself. Since the conduction of electric current through any rod-shaped or tubular conductor will be concentrated to the outer periphery, it is of advantage to have the material of higher electrical conductivity arranged on the outer periphery, as hereby suggested.
• the sleeve is of tubular shape.
• the cross section thereof is circular.
• regular and rounded shapes are better than irregular or edgy shapes with regard to the electric load that the surrounding insulation will be subjected to.
• the sleeve is exposed to and in direct contact with the intermediate insulation medium.
• the intermediate insulation medium comprises a semi-solid or solid material.
• a semi-solid or solid material such a material, especially a solid one, will be easy to handle, and will not run the risk of leaking out of from the power cable termination arrangement.
• the intermediate insulation material comprises a gas.
• a liquid intermediate insulation medium might be conceived.
• the power cable termination arrangement comprises an electrically conducting shield that surrounds at least a part of the internal insulation along a first part thereof, and a stress relief means provided for the purpose of controlling or lowering the intensity of an electrical field along a second part of the internal insulation.
• the second part of the internal insulation is not provided with the shield. From the point, in the longitudinal direction of the cable, where the shield ends, a very intense and strong electric field will be likely to exist. The task of such a stress relief means is to make the electric field less concentrated along said second part of the insulation.
• the power cable termination arrangement comprises a first end flange connected to earth, in the region of which the conductor is covered by the internal insulation, and a second end flange, through which the conductor passes relieved from said internal insulation, wherein the part of the length of the conductor along which there is provided a means for increasing the thermal conductivity of the conductor extends to the second end flange.
• Fig. 1 is a partly cut side view of a cable termination arrangement according to prior art
• Fig. 2 is a partly cut side view of a cable termination arrangement according to an embodiment of the invention
• Fig. 3 is a schematic representation of joint comprising a cable termination arrangement according to the invention.
• Fig. 4 is a schematic representation of a gas insulated switchgear provided comprising a cable termination according to the invention.
• Fig. 1 shows a cable termination arrangement according to prior art
• fig. 2 shows an embodiment of a cable termination arrangement according to the present invention
• the cable termination arrangement of fig. 2 comprises a conductor 1, an internal electric insulation 2, an external encapsulation 3, and an intermediate electric insulation medium 4. At opposite ends of the external encapsulation 3 there are provided a bottom flange 5 and a top cap 6 respectively.
• the conductor 1 is rod- shaped or tube-shaped. Preferably, it comprises a material of high electric conductivity such as copper or aluminium.
• the conductor 1 forms part of a cable, wherein the internal insulation 2 is a typical cable insulation, made of a solid dielectric material such as a polymer, attached to the outer periphery of the conductor 1.
• the external encapsulation 3 of the embodiment shown in fig. 2 is provided for the purpose of preventing electrical surface flash-over at the outer periphery of the cable termination arrangement, thereby defining an external electric insulation.
• the external encapsulation preferably has a characteristic wave-shape as is well known per se within this technical field, and comprises a suitable material.
• the external encapsulation 3 may comprise an electrically insulating material such as a polymer, for example silicon, or porcelain.
• the length of the external encapsulation 3 in the axial direction of the conductor 1 /cable 7 is adapted to the breakdown strength thereof. Accordingly, the length of the external encapsulation 3 will have to be increased with increasing voltage of the conductor.
• the intermediate electric insulating medium 4 is provided inside the above- mentioned housing and fills the interior spacing thereof.
• the intermediate electric insulation 4 is located in a spacing between the cable 7 and the external encapsulation 3. It acts as an electric insulator and a heat transferring medium, transferring heat from the conductor 1 out through said housing in a radial as well as an axial direction. Thereby, it will have a decisive effect upon the temperature of the internal insulation 2, which preferably comprises a polymer material.
• the intermediate electric insulation medium 4 comprises oil, but in the preferred embodiment the intermediate electric insulation 4 comprises a solid or semi- so lid filling compound.
• An electrical shield 8 is provided around the conductor 1 along a first part of the internal electric insulation 2.
• the shield 8 is connected to earth.
• the power cable termination arrangement of the invention comprises a field-control body 9.
• the field control body 9 comprises a so called stress cone, made of a conducting material and preferably connected to earth at one end thereof.
• the internal electrical insulation 2 ends.
• a tubular outer sleeve 10 on the outer periphery of the conductor 1.
• the sleeve 10 comprises a metal presenting an electric conductivity equal to or higher than that of the material of the conductor 1 to which it is attached. There is full, large surface contact between said sleeve 10 and the conductor 1.
• the sleeve 10 occupy a space that would otherwise have been occupied by the internal electrical insulation, as in prior art (see fig. 2), or by the intermediate electrical insulation medium 4.
• the conductor 1, as now defined by a combination of the original conductor 1 and the sleeve 10 presents a lower resistivity than if there would have been no sleeve 10.
• the sleeve 10 also comprises a material that has a higher thermal conductivity than that of the intermediate electrical insulation 4, thereby contributing to an improved transfer of heat in a longitudinal direction towards the top cap 6 and out from the cable termination arrangement.
• the sleeve 10 extends continuously from the point where the internal electrical insulation 2 ends and up to the end of the arrangement as defined by the top cap 6. It is conceivable, and might even be preferred to let sleeve continue beyond the top cap 6 in order to further improve the ability of conducting heat out of from the housing and from the insulation parts.
• Fig. 1 shows an example of prior art. As can be seen prior art differs from the invention in the sense that there is no region along which there is provided any means for increasing the thermal conductivity and electrical conductivity of the conductor.
• the internal electrical insulation 11 extends all the way from one end of the arrangement to the other, i.e. from bottom flange to top cap.
• Fig. 3 is a schematic representation of a preferred application of the invention showing a joint arrangement in which two meeting cables are interconnected by means of two opposing power cable termination arrangements at least one, preferably both, of which is arranged in accordance with the invention.
• the external encapsulation, here indicated with 14 might be of a different kind than the one shown in the embodiment of fig. 2. but that the principle of the arrangement of the components in the cable termination may be in line with the invention in its general form or as specifically described with regard to fig. 2.
• the intermediate insulation medium 15 may be of any suitable type and state (solid, fluid or gaseous).
• the design of cable joints are well known to the person skilled in the art, and there will no problem for such a person of carrying out the invention as implemented on such a joint.
• the joint of fig. 3 comprises means for controlling the electric field, here formed by opposite stress cones 16, 17 that are shown very schematically.
• the cooling element of the invention is indicated with 18.
• the conductor is indicated with 19.
• Fig. 4 is a schematic representation of a gas insulated switchgear 20, which, according to a preferred application of the invention, comprises a power cable termination arrangement according to the invention.
• the intermediate insulating medium 21 comprises gas.
• the cable termination arrangement of the switchgear 20 comprises a cable 22 entering the arrangement, a means 23 for controlling the electric field, here formed by a stress cone, a conductor 24 of the cable 22, an external encapsulation 25 and a means 26 for improving the thermal conductivity of the conductor 24, said means 26 being formed by a tubular element attached to the outer periphery of the conductor 24.
• the design of gas insulated switchgears is well known to the person skilled in the art, and though the switchgear of fig. 4 is shown very schematically, the implementation of the invention onto such a switchgear will not cause said person any problem.

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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Cited By (5)

Citations (5)

• 2007
  • 2007-03-30 SE SE0700817A patent/SE531888C2/sv not_active IP Right Cessation
• 2008
  • 2008-03-31 WO PCT/EP2008/053800 patent/WO2008119782A1/en active Application Filing

Patent Citations (5)

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