Electric cable

Abstract: The invention relates to an electrical cable comprising: an electrically conducting core; a first semi-conducting jacket arranged therearound; an insulating jacket arranged therearound; a second semi-conducting jacket arranged therearound; an electrically conducting earthing jacket arranged therearound; a sealing jacket arranged therearound which is expandable under the influence of water; an electrically conducting outer jacket arranged therearound; and electrical conducting means which place the earthing jacket and the outer jacket locally in mutual contact. Present for this purpose in the cable according to the invention are the electrical conducting means which place the earthing jacket and the outer jacket locally in mutual contact.

Description: The invention relates to an electric cable comprising: an electrically conducting core; a first semi-conducting jacket arranged around said electrically conducting core; an insulating jacket arranged around said first semi-conducting jacket; a second semi-conducting jacket arranged around said insulating jacket; an electrically conducting earthing jacket arranged around said second semi-conducting jacket. Such an electric cable is known from e.g. FR-A-2 385 194. Relative to this prior art reference the electric cable according to the invention is characterized by a sealing jacket arranged around said electrically conducting earthing jacket which sealing jacket expands under the influence of water; an electrically conducting outer jacket arranged around said sealing jacket; and electrical conducting means which place the earthing jacket and the outer jacket locally in mutual contact. The sealing jacket arranged around the electrically conducting earthing jacket serves the purpose of ensuring a tight sealing of the cable structure against the penetration of water. Under critical conditions, e.g. conditions under which the sealing jacket comes in contact with penetrating water the jacket builts up an additional barrier preventing the water from further penetrating into the cable structure due to the fact that the jacket expands under the influence of the penetrated water. The electrically conducting outer jacket which can be further covered by a mechanically protecting and electrically insulating protective jacket can for instance consist of aluminium foil. The outer jacket must assume the same electrical potential as the electrically conducting earthing jacket. The sealing jacket present between the two said jackets and expanding under the influence of water has in this respect more or less conducting properties. In conditions where short-circuiting occurs, a comparatively high voltage difference can occur between the earthing jacket and the outer jacket whereby breakdown can result. This can result in local charring or other degeneration of the expandable sealing jacket. It is desirable to improve the contact between the earthing jacket and the outer jacket, particularly in case of short-circuit, and nevertheless retain a physical separation between the earthing jacket and the outer jacket. The expandable sealing jacket has to be retained to ensure the longitudinal water-tightness of the electrical cable in certain conditions. Present for this purpose in the cable according to the invention are the electrical conducting means which place the earthing jacket and the outer jacket locally in mutual contact. These conducting means can be embodied in diverse ways, in particular as electrically conducting spacer elements between the earthing jacket and the outer jacket. A very simple embodiment is that in which the conducting means comprise a conducting wire extending through the sealing jacket. From a production technology viewpoint the most simple and best controllable embodiment is that wherein the wire is wound helically. In order to ensure a good contact with a more or less homogeneous distribution of the contact locations, a specific embodiment has the feature that the earthing jacket comprises at least one helically wound conductor and that the pitch of the conducting wire differs from the pitch of the at least one conductor of the earthing jacket. A preferred embodiment of this type has the special feature that the earthing jacket comprises a number of mutually adjacent helically wound conducting wires and that the pitch thereof is opposed to the pitch of the said conducting wire. This ensures in all conditions that the said conducting wire which must bring about the contact between the earthing jacket and the outer jacket can never be pressed inward and assume a position between the helically wound conducting wires of the earthing jacket. Very simple is the embodiment wherein the sealing jacket is arranged by extrusion. The conducting wire, in particular a copper wire, lies prior to the extrusion process against the outer surface of the earthing jacket. When the cable finished thus far is fed through the correspondingly dimensioned extrusion head the surface of the wire located radially the furthest outward remains at least locally exposed. When a strip of aluminium foil is then laid in lengthwise direction against the cable and closed with adhesive round the cable with a longitudinal seam with overlapping edge zones, a local contact between the earthing jacket and the outer jacket can be ensured due to the light pressure which is used in one movement for arranging the aluminium foil immediately after the extrusion process. After the extrusion treatment which takes place at increased temperature, the relevant material such as medium density polyethylene (MDPE) or high density polyethylene (HDPE) cools, whereby a certain shrinkage occurs which results in a desired increased contact pressure. As stated, the cable can be finished by arranging a protective jacket round the electrically conducting outer jacket. The invention will now be elucidated with reference to the annexed drawing which shows a partly broken away perspective view of a cable according to the invention. The cable according to the invention comprises an electrically conducting core 1, a first semi-conducting jacket 2 arranged therearound, an insulating jacket 3 arranged therearound, a second semi-conducting jacket 4 arranged therearound, an electrically conducting earthing jacket 5, 6 arranged therearound, a sealing jacket 8 arranged therearound which expands under the influence of water, an electrically conducting outer jacket 9 arranged therearound and a copper wire 7 which is embedded in the sealing jacket 8 and which with its inner surface makes contact with the earthing jacket 5, 6 and with its outer surface makes contact with the electrically conducting outer jacket 9 consisting of aluminium foil. The earthing jacket comprises a number of mutually adjacent, helically wound wires 10 together forming a cylindrical jacket and, arranged therearound, a strip 6 of copper foil wound with opposing pitch. It is noted that if desired this strip 6 of copper foil can be omitted. The copper wire 7 has a pitch opposed to that of the wires 10. The sealing jacket 8 expandable under the influence of water is arranged on the cable by extrusion during the production stage in which the cable still consists of the electrically conducting core 1 and the jackets 2, 3, 4, 5, 6 and the conducting wire 7.

Claims: Electric cable comprising: an electrically conducting core (1); a first semi-conducting jacket (2) arranged around said electrically conducting core (1); an insulating jacket (3) arranged around said first semi-conducting jacket (2); a second semi-conducting jacket (4) arranged around said insulating jacket (3); an electrically conducting earthing jacket (5, 6) arranged around said second semi-conducting jacket (4); characterized by a sealing jacket (8) arranged around said electrically conducting earthing jacket (5,6) which sealing jacket expands under the influence of water; an electrically conducting outer jacket (9) arranged around said sealing jacket (8); and electrical conducting means (7) which place the earthing jacket (5, 6) and the outer jacket (9) locally in mutual contact. Cable as claimed in claim 1, characterized in that the conducting means comprise a conducting wire (7) extending through the sealing jacket (8). Cable as claimed in claim 2, characterized in that the wire (7) is wound helically. Cable as claimed in claim 3, characterized in that the earthing jacket (5, 6) comprises at least one helically wound conductor (5, 6) and that the pitch of the conducting wire (7) differs from the pitch of the at least one conductor (6) of the earthing jacket (5, 6). Cable as claimed in claim 3, characterized in that the earthing jacket comprises a number of mutually adjacent helically wound conducting wires and that the pitch thereof is opposed to the pitch of the said conducting wire. Cable as claimed in claim 2, characterized in that the sealing jacket (8) is arranged by extrusion.

Inventors: ACHTERBOSCH WILLIBRORDUS FRANC, VAN DEVENTER GIJSBRECHT COENRA, ACHTERBOSCH, WILLIBRORDUS FRANCISCUS JOZEF, VAN DEVENTER, GIJSBRECHT COENRAAD
Applicants: TWENTSCHE KABELFAB BV, B.V. TWENTSCHE KABELFABRIEK
Application year: 1993
Main classification: H01B9
IPC codes: H01B9