Adhesive bonding and miscellaneous chemical manufacture – Methods – Making electrical conductors of indefinite length
Patent
1987-12-30
1989-05-09
Dawson, Robert A.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Making electrical conductors of indefinite length
156 52, 156 86, 174 36, 174 73R, 174 85, 174DIG8, 428 3691, 428913, H01B 1306
Patent
active
048286346
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a method of re-establishing mutually insulated semi-conducting layers around respective ones of a pair of spliced electric cables in connection with insulating the spliced cables.
A known shield for a high-voltage cable comprises an electrically conducting part disposed around an electrically semi-conducting part which serves to ensure as even a distribution of the electric field as possible, while the electrically conducting part carries the capacitive currents and fault currents. In connection with so-called crossbond cable systems where the shield conductors are crossbonded to reduce shield currents, it is necessary to puncture the shield of each cable at suitable intervals, preferably in connection with splicing of the cable.
Shield puncture, as mentioned above, can very easily result in field concentrations which may cause breakdown, and it is therefore very important to avoid such field concentrations. For example the EP No. B1 88450 discloses a procedure for re-establishing the insulation of the cable and the semi-conducting layers of the cable, so that the semi-conducting layers are mutually insulated. However, the risk of electrical breakdown in this and related methods has been undesirably great even though the rather laborious splicing operation has been performed with very great care.
The object of the invention is to provide a method of re-establishing the semi-conducting layers, as explained above, and where the risk of electric breakdown in the re-established area is reduced.
This object is achieved in that the semi-conducting layers of one cable are terminated with the stable cable insulation as a base. Then, the cable joint and the semi-conductor termination may be surrounded in a manner known per se by a cross-linkable material and be subjected to such heat and pressure conditions that the insulation of the cable joint and the mutual insulation between the semi-conducting layers are crossbonded and at the same time cause bonding between the incorporated components.
The invention is based on the finding that the breakdown phenomena are caused by the fact that the re-established semi-conducting layers differ noticeably from an ideal geometrical shape, when the layers have been established on top of a layer of an insulation material which becomes partly liquid in a subsequent heat treatment. It is common--see e.g. the above-mentioned EP patent specification--to re-establish the insulation of the cable around the splice by winding vulcanizable polyethylene tape, which can be crossbonded in the heat treatment, around the splice. When the area where the semi-conducting shields are mutually insulated is placed outside the splice area portion which comprises a thick layer of polyethylene tape, a very stable base is obtained precisely for the critical part of the re-established, semi-conducting layers. This method can even be performed in a single operation and without strict tolerance requirements as to the execution of the job.
The method of the invention might be carried out by winding semi-conducting tape around the insulation, or by pulling back the semi-conducting layer, but, preferably, the method is carried out using a sleeve, which provides a very great stability in shape, since at least one of the semi-conducting layers is terminated by means of a relatively rigid, semi-conducting sleeve, whose inside diameter is only slightly greater than the outside diameter of the cable insulation. It may occur in practice that quite a few layers of vulcanizable tape are wound around the cable insulation, and precisely because of the axial extent and rigidity of the sleeve, the softening of the tape during the heat treatment has in practice no influence on a well-defined positioning of the sleeve. After re-establishment, the semi-conducting layer of the other cable end extends over the insulation establishment area and past the outer rim of the sleeve, so that the rigidity of the rim also contributes to the positioning of the latter semi-conducting layer, even though there may b
REFERENCES:
patent: 3127291 (1964-03-01), Betz
patent: 4164620 (1979-08-01), Hervig
patent: 4234755 (1980-11-01), Simons
patent: 4479031 (1984-10-01), Ishise
Akieselskabet Nordiske Kabel - og Traadfabriker
Dawson Robert A.
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