Electricity: conductors and insulators – Conduits – cables or conductors – Combined
Patent
1992-03-02
1994-01-25
Nimmo, Morris H.
Electricity: conductors and insulators
Conduits, cables or conductors
Combined
174 22R, 174 76, 174 88R, 174DIG8, H02G 1508
Patent
active
052817636
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of blocking an electric power cable joint against the ingress of water or other moisture, hereinafter referred to generally as "moisture", and to a moisture-blocked cable joint. The invention is particularly though not exclusively applicable to joints between multi-core cables, that is to say to cables containing at least two cores, and typically cables having either three or four cores, possibly with the addition of an earth core. The joint may be an in-line joint, between two cables, or it may be a branch joint, between two, three or more cables. In the case of a branch joint, the main cable may be unbroken and have a branch cable leading therefrom, or the joint may be between two main cables and a branch cable.
Modern electric power cables are usually made by the multi-extrusion of a plurality of cable components one on top of the other, including layers of polymeric insulation material around the individual conductor(s) thereby to form individual cable core(s), and also, in a multi-conductor cable, around the plurality of cores to form the complete cable. It is possible, for example due to damage to some of the outer components or layers of the cable, for moisture to enter the cable and to travel therealong between successive layers and/or cores. Such moisture in the cable can be particularly disadvantageous in the region of a cable joint where, in a multi-conductor cable for example, the outer, common layers of the cable are removed to expose the individual cores and where the insulation of the individual cores is removed, or at least disturbed, to allow connection between respective cores of two, or more, cables. In this region, the removal and/or disturbance of cable insulation inherently increases the electrical stress in comparison with its value elsewhere along the cable. The re-formed cable joint thus has to ensure that such stress is kept below a value that could cause damage or inhibit proper and safe operation of the jointed cable. The presence of water in this region inherently has the effect of increasing the electrical stress.
It is known from GB-A-2100281 to locate a hydrophobic filing composition around a plurality of connections of a telecommunications cable splice, to contain the filler within a polymeric wrapper and finally to enclose the splice with a recoverable polymeric sleeve. In GB-A-1177915, a non-hygroscopic, non-melting, water-repellant grease is urged by means of a heat-recoverable sleeve around a stranded conductor at a joint or termination of an electrical cable where the conductor emerges from insulation. Thus cable joints are known in which ingress of water from outside the cable is prevented.
It is one object of the present invention to provide an improved electric power cable joint, and a method of producing it, wherein the electrical stress is minimised by preventing substantially any moisture that may be in the cable from entering the joint region. This is acheived by blocking the cable joint against the flow of moisture along the cable, at the region where at least one outer layer, such as the cable jacket, has been removed in order to allow access to the core or to the individual cores for connection purposes.
Thus, in accordance with one aspect of the present invention there is provided a joint between electric power cables in which at least two cable cores are exposed beyond the ends of outer jackets of at least two cables and in which conductors of the two cores are electrically connected to each other, wherein sealing material that is substantially impervious to moisture is located around the cores so as to prevent any moisture reaching the electrical connections of the conductors; wherein blocking material is located within the joint so as to prevent the sealing material from migrating away from the connections into or around the cables; and wherein a protective sleeve encloses the cable connections and the sealing and blocking materials.
In accordance with another aspect of the present invention, there is provided a method o
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Barnwell David E.
Esser Axel
Hey Stephen A.
Hoffman John W.
Midgley John A.
Burkard Herbert G.
Nimmo Morris H.
Raychem GmbH
Zavell A. Stephen
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