High voltage direct current cable termination apparatus

#The present invention relates to a direct current cable termination apparatus for terminating a high voltage direct current cable, HVDC, cable. The apparatus may comprise a current-carrying device comprising a terminal portion of the direct current cable, the cable at least comprising an electrical conductor, a circumferential electrically insulating layer located outside of the electrical conductor, and a circumferential conductive shield located outside of the insulating layer and the electrical conductor. The apparatus may comprise a housing comprising a tubular outer shell with an inner periphery, the outer shell defining a longitudinal axis and being formed by an electrically insulating and polymer-containing material, and the current-carrying device is adapted to extend in the axial direction of the outer shell. Along at least a part of the axial extension of the current-carrying device the outer shell may extend axially with a space between its inner periphery and the current-carrying device, and the housing is adapted to separate the space from an atmosphere outside the outer shell. Further, the present invention relates to an electric installation comprising an apparatus of the above-mentioned kind.

#Today, the level of the rated voltage of high voltage direct current, HVDC, applications is increased in the technical field of HVDC. With this development, improved HVDC cable terminations, which can withstand higher voltage levels, are required.

#A HVDC cable is used for power supply in power distribution networks and power transmission networks. Generally, the HVDC cable comprises at least an inner or central live electrical conductor, e.g. made of copper or aluminium, an electrically insulating layer which circumferentially surrounds the electrical conductor, and a conductive shield, also called outer semicon, which circumferentially surrounds the insulating layer and the electrical conductor, the conductive shield being held on ground potential. Additional layers may be present, e.g. a so called inner semicon, which is a conductive layer circumferentially surrounding the electrical conductor and located inside of the insulating layer, and e.g. an outer cable jacket circumferentially surrounding the conductive shield.

#The present invention will now be described, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, in which:

#FIG. 1 is a schematic side view showing a longitudinal section of a first embodiment of the direct current cable termination apparatus according to the present invention;

#FIG. 2 is a schematic side view showing a longitudinal section of a second embodiment of the direct current cable termination apparatus according to the present invention; and

#FIGS. 1-3 schematically shows three embodiments of the direct current cable termination apparatus according to the present invention, for terminating a HVDC cable for high voltage (e.g. 10 kV and above, especially 50 kV and above). With reference to FIGS. 1-3, each of the three embodiments of the apparatus comprises a current-carrying device 102, or a voltage-carrying device, comprising a terminal portion 104 of the HVDC cable, the cable at least comprising a central electrical conductor 106, generally made of a suitable metal, e.g. copper or aluminium, a circumferential electrically insulating layer 108 which circumferentially surrounds and is located out-side of the electrical conductor 106, and a circumferential conductive shield 110, or layer/screen, also called outer semicon, which circumferentially surrounds and is located outside of the insulating layer 108 and the electrical conductor 106. The circumferential conductive shield 110 may be made of an electrically conducting polymer. The structure of a HVDC cable and its parts, which may comprise further layers, is well known to the skilled person and thus not discussed in more detail herein. The HVDC cable may e.g. comprise a so called inner semicon, which is a layer/screen circumferentially surrounding the electrical conductor and being located inside of the insulating layer. The inner semicon may be made of an electrically conducting polymer.

#Further, the apparatus comprises a housing 111 comprising a tubular outer shell 112 with an inner periphery 114. The outer shell 112 defines a longitudinal axis x-x and is formed by an electrically insulating and polymer-containing material, e.g. a composite. The apparatus is substantially rotation symmetric around the axis x-x. The outer periphery of the outer shell 112 is provided with sheds 116, or lips/wings, for example made of silicone. The current-carrying device 102 is adapted to extend in the axial direction of the outer shell 112. Along at least a part of the axial extension of the current-carrying device 102 the outer shell 112 extends axially with a space 118 between its inner periphery 114 and the outer periphery of current-carrying device 102. The housing 111 is adapted to separate the space 118 from an atmosphere outside 120 the outer shell 112. A tubular partition 122, which is positioned around the current-carrying device 102, separates the space 118 into a first chamber 124 and a second chamber 126. The partition 122 may be made of an electrically insulating and polymer-containing material, for example glass fibre reinforced epoxy. The first chamber 124 is filled with an electrically insulating first fluid 125 in the form of an electrically insulating gas, e.g. SF6, CO2 or N2, or a mixture thereof. The conductive shield 110 terminates inside the second chamber 126. The conductive shield 110 is terminated and forms a termination 109 in the form of a circumferential edge (also called semicon edge). An electric field control member 128, e.g. in the form of a stress cone as previously disclosed, is located within the second chamber 126 in the proximity of the termination of the conductive shield. The electric field control member 128 may comprise a rubber, polymeric or elastomeric body 129 stretched, or pushed, over the current-carrying device 102, more precisely the terminal portion 104 of the HVDC cable. The elastomeric body 129 may be mushroom-shaped. However, other materials and shapes of the elastomeric body 129 are possible. Other types of electric field control members known to the skilled person may also be used. The apparatus may also include a plurality of electric field control members, i.e. two or several electric field control members. The electric field control member could also be in the form of a linear or non-linear resistive field grading material layer, e.g. in the form of a sleeve made of a non-linear resistive material. Further, the electric field control member 128 may comprise a semiconducting, or conductive, layer 130, e.g. made of metal or a polymer material, which in conventional ways may be provided on the lower inner curved periphery of the elastomeric body 129. Alternatively, the semiconducting, or conductive, layer 130 may be embedded in the body 129 of the electric field control member 128. The semiconducting, or conductive, layer 130 may be formed and composed in various ways known to the skilled person. The conductive layer 130 may be called deflector. Advantageously, the conductive shield 110 terminates adjacent to the lower part of the electric field control member 128, below, or prior to, the triple point which is formed by the insulating material of the electric field control member 128, the insulating material of the electrically insulating layer 108, and the material of the semiconducting layer 130. The second chamber 126 is filled with an electrically insulating second fluid 127 in the form of an electrically insulating gel or an electrically insulating oil, or a mixture thereof.

#The outer shell 112 has a first end portion 132 adjacent to the first chamber 124 and also adjacent to the high voltage side, where the apparatus is connected to e.g. an overhead line or bus bar etc. The outer shell 112 has a second end portion 134 adjacent to the second chamber 126. The housing 111 may comprise a first flange 138, e.g. made of a metal, at the second end portion 134 of the outer shell 112, and a second flange 152, e.g. made of a metal, at the first end portion 132 of the outer shell 112. The HVDC cable enters the outer shell 112 via the second end portion 134 and via a first opening 136 defined by the first flange 138. Along at least a part of the axial extension of the partition 122 the outer shell 112 extends axially with a gap 140 between its inner periphery 114 and the outer periphery of the partition 122. A first part 142 of the terminal portion 104 of the cable has the circumferential conductive shield 110, whereas a remainder part 144 of the terminal portion 104 of the cable has the conductive shield 110 removed, such that the insulating layer 108 is exposed. The first part 142 may be called semicon end and the remainder part 144 may be called stripped cable. The first part 142, with the conductive shield 110 present, is situated within the second chamber 126 and outside the first chamber 124.