GB2189949A

GB2189949A - Insulation for terminating screened power cable

Info

Publication number: GB2189949A
Application number: GB08710001A
Authority: GB
Inventors: John Cooper; Michael John Sleeman
Original assignee: Bowthorpe Hellerman Ltd
Current assignee: Bowthorpe Hellerman Ltd
Priority date: 1986-04-30
Filing date: 1987-04-28
Publication date: 1987-11-04
Also published as: GB8610543D0; KR870010645A; GB8710001D0; AU7216387A

Abstract

In terminating a three-core screened power cable PC, each core of the cable is fitted with an insulating tube 16 by heat-recovery over an exposed end length of its screen 12 and is also fitted with an anti-tracking tube 18 by heat- recovery over an exposed end length of its insulation 10. The screen 12 is maintained for a substantial distance along each core thereby avoiding core-to-core electrical stresses and also the required length of anti- tracking tube is minimised. A stress control tube (14) may cover the end of the screen (12) and the insulation (10) near the end of the screen. <IMAGE>

Description

SPECIFICATION Terminating screened power cables This invention relates to a method of terminating screened power cables, particularly cables with elastomeric or plastomeric insulation (e.g.

cross-linked polyethylene).

Conventionally when terminating a 3-core screened power cable, the screen is removed from each core over an end portion commencing close to the point from which the outer sheath of the cable itself has been stripped. A short stress control tube is then fitted to each core, overlapping the end of the remaining screen and the adjacent exposed core insulation. Then a long anti-tracking tube is fitted by heat-recovery over the end portion of each core from which the screen has been removed, overlapping the stress control tube.

Several conical rain sheds are then fitted to each core, over the anti-tracking tube and at spaced intervals.

In accordance with this invention, there is provided a method of terminating a multicored screened power cable, in which method each core of the cable is fitted with an insulating tube by heat-recovery over an exposed end length of its screen, and is fitted with an anti-tracking tube by heat-recovery over an exposed end length of its insulation.

In this method, the screens are maintained for a greater distance along each core. This avoids core-to-core electrical stresses which are found in the conventional terminations where the unscreened cores are in close proximity. Also the cores may now be crossed over, if polarity changes are required, without giving rise to excessive electrical stresses.

Moreover, the length of each anti-tracking tube is considerably less and this leads to a significant cost saving. Finally, the method in accordance with this invention enables all measurements to be taken from the top or outer end of the termination during installation: this permits greater flexibility and leaves less margin for error.

Also in accordance with this invention, there is provided a kit for use in terminating a multicored screened power cable, said kit comprising a plurality of recoverable insulating tubes, one for each core of the cable and each for fitting over an exposed end length of its screen, and a plurality of anti-tracking tubes, one for each core of the cable and each for fitting over an exposed end length of its insulation.

An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawing, the single figure of which is a diagrammatic view of a cable termination formed in accordance with the invention.

Referring to the drawing, there is shown a termination of a 3-core, 1. 1 Kv electric power cable PC. Each core has in this example an elastomeric or plastomeric insulation 10 (e.g.

cross linked polyethylene) and a screen 12 (e.g. of copper tape). The outer sheath and any other outer layers of the cable PC are stripped back to a predetermined point OS in forming the termination, and the screen 12 of each core is stripped back to a point S, a significant distance closer to the end of the cable so that a substantial end length of the screen 12 is left exposed and also a substantial end length of the insulation 10 is left exposed.

A stress control tube 14 is fitted to each core, overlapping the screen 12 and insulation 10 at the extreme end of the length of exposed screen. A heat-shrinkable insulating tube 16 is slid along and then recovered about each core, so as to cover the exposed length of screen 12 and the stress control tube. Then a heat-shrinkable anti-tracking tube 18 is slid along and recovered about each core, so as to cover the length of exposed core insulation 10 and overlap the extreme end of the recovered insulating tube 16. Conical rain sheds 20 are fitted to each core, over the anti-tracking tube at spaced intervals, as in the conventional termination. The tube 18 comprises a material of a composition which is such as to resist electrical tracking (i.e.

electrical leakage currents flowing over its surface): one conventional practice has been to incorporate aluminium trihydrate as an additive to achieve this property. The rain sheds serve to increase the path length along the tube.

It will be appreciated however that, in contrast with the conventional termination, the screens are maintained for a greater distance along each core, thus avoiding core-to-core electrical stress (and even permitting the cores to be crossed over if desired), and also reducing the required lengths of the expensive antitracking tube: thus the tubes 16 do not need to be of anti-tracking material because the un deriying surfaces are all at earth potential.

Moreover, as previously mentioned, all measurements can be taken from the top of the termination during installation and this can provide considerable advantage.

Whilst the invention has been described as applied to a cable having elastomeric or plastomeric insulation for each core, it may be applied to any form of three-cored screened power cable. If for example the method is applied to a cable wherein the insulation of each core comprises lapped paper insulation impregnated with oil, a tube which is impervious to oil would be applied over the exposed insulating tube 16 and anti-tracking tube 18.

Conveniently, a kit may be provided for use in terminating a screened power cable by the method described above, which kit would comprise three insulating tubes 16, three antitracking tubes 18 and three stress control tubes 14.

Claims

1. A method of terminating a multi-cored screened power cable, in which method each core of the cable is fitted with an insulating tube by heat recovery over an exposed end length of its screen, and is fitted with an antitracking tube by heat-recovery over an exposed end length of its insulation.

2. A method as claimed in Claim 1, in which method a stress control tube is fitted to each core to overlap the screen and insulation of that core at the extreme end of the exposed length of screen.

3. A method as claimed in Claim 2, in which method the insulating tube is applied to each core as to cover the stress control tube.

4. A method as claimed in any preceding claim, in which method the anti-tracking tube is applied to each core so as to overlap the extreme end of the insulating tube.

5. A method of terminating a multi-cored screened power cable, the method being as claimed in Claim 1 and substantially as herein described with reference to the accompanying drawings.

6. A kit for use in terminating a multicored screened power cable, said kit comprising a plurality of recoverable insulating tubes, one for each core of the cable and each for fitting over an exposed end length of its screen, and a plurality of anti-tracking tubes, one for each core of the cable and each for fitting over an exposed end length of its insulation.

7. A kit as claimed in Claim 6, further comprising a plurality of stress control tubes, one for each core of the cable and each for fitting so as to overlap the screen and insulation of that core at the extreme end of the exposed length of screen.

8. A kit for use in terminating a multicored screened power cable, said kit being substantially as herein described with reference to the accompanying drawing.