GB2212005A - Insulation barriers - Google Patents

Abstract

An insulation barrier is provided for an electrical cable termination in which the cable 2 is connected to a terminal 4 having an insulating bushing 6. The barrier comprises an insulating adaptor bush 9 of elastomeric material. The bush has a substantially cylindrical main body portion and a plurality of flexible internal annular ribs 12 adapted to engage resiliently at lips at their inner peripheries over a range of insulating bushings of different external diameters. A tubular shroud 8 of insulating material has a first end portion 16 of substantially cylindrical form dimensioned to engage sealingly over the bush 9, and an opposite end portion 18 of frustoconical form for sealingly engaging over the cable 2. The shroud also has an intermediate portion of corrugated flexible construction permitting the said end portions 16, 18 to be set at any angle up to 90 DEG to each other. Thus the barrier can be adjusted on-site to suit the layout of the termination. <IMAGE>

Description

Insulation Barriers This invention relates to insulation barriers for electrical terminations and for electrical terminations incorporating the same.

Power cables have for many years been paper insulated, but there is now an increasing use of cables with polymeric insulation and this in turn, has given rise to an increasing demand for insulating protection in unfilled cable end boxes. Such protection is required because the air clearances from phase to phase and from phase to earth within the box are inadequate to prevent fLashover.

Insulation barriers have been devised for this purpose, for example as described in the specification of UK Patent 2171264. The construction described in that specification is satisfactory from the point of view of protection it affords, but the installation requires a substantial number of parts which are matched rather closely to the dimensions and layout of the termination in question.

The present invention, however, provides an insulation barrier for an electrical cable termination in which the cable is connected to a terminal having an insulating bushing, the barrier comprising an insulating adaptor bush of elastomeric material, the bush having a substantially cylindrical main body portion and a plurality of flexible internal annular ribs adapted to engage resiliently at their inner peripheries over a range of insulating bushings of different external diameters, and a tubular shroud of insulating material having a first end portion of substantially cylindrical form dimensioned to engage sealingly over the said bush, an opposite end portion of frustro-conical form and an intermediate portion of corrugated flexible construction permitting the said end portions to be set at any angle up to 900 to each other.

With this arrangement, a barrier consisting of only two components can be adjusted as necessary on siteto suit a termination which may be a right-angled or an in-line connection or any intermediate position. The adaptor bush will accommodate a wide variation in sizes of insulating bushing, be it cylindrical or tapered, and the frustro-conical end portion of the shroud can be trimmed off to adjust the internal diameter to suit the actual cable size to be enclosed.

The invention also includes an electrical termination comprising a cable connected to a terminal having an insulating bushing and comprising an insulation barrier consisting of an adaptor bush and a shroud, the bush engaging sealingly over the insulating bushing and the shroud having a first end portion of generally cylindrical form sealingly engaged over the adaptor bush, an intermediate portion of flexible corrugated construction and an opposite end portion of frustro-conical form, the extreme end of which engages sealingly over the cable.

An embodiment of the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a sectional elevation of a termination in accordance with the invention; Fig. 2 is a side elevation of a shroud; and Fig. 3 is a cross-section of an adaptor bush.

Fig. 1 shows in cross-section and somewhat diagrammatically an insulated cable termination in which a cable lug 1, fitted to the end of a cable 2 is connected to terminal 4 provided with an insulated bushing 6 in known manner to form a right-angle connection.

The termination is protected by an insulation barrier consisting of a flexible shroud 8 and an adaptor bush 9. The shroud and bush are shown to a larger scale in Figs. 2 and 3.

The adaptor bush 9 is made of an insulating, elastomeric material, preferably silicone rubber,- and-is moulded in the form shown in Fig. 3, to have a relatively thick walled cylindrical body 11 and a plurality (in the bush illustrated three) of flexible internal annular ribs 12, each terminating at an axially directed lip 13. As seen in Fig. 1, the adaptor bush engages over the bushing 6, the ribs being deformed and stretched so as to fit tightly against the bushing, but without any substantial increase in the outside diameter of the bush 9. The flexible ribs 12 can adapt themselves in this way to a wide range of sizes of bushing 6.

The shroud 8 is conveniently manufactured by blow-moulding from materials such as thermo-plastic rubber or, for example, a mixture polypropylene and E.P.D.M. (Ethylene-propylene-diene monomer), or may be injection moulded in EPDM.

The medial portion 14 of the shroud is formed with annular corrugations which render the portion relatively flexible about a transverse axis. The corrugations have rounded corners to reduce electrical stresses at these regions in use. One essentially cylindrical portion 16 is preferably provided with annular ribs 17 to serve as guides to facilitate severing the shroud to enable it to be readily adjusted on site to suit the particular installation. At its opposite end, the shroud has a frustro-conical end portion 18 the internal diameter at the extreme end of which is dimensioned to suit the diameter of the smallest cable 2 to be accommodated by the shroud. A series of annular guide ribs 19 is preferably provided to facilitate severing of the portion 18 to suit larger sizes of cable.

In use, prior to connection of the cable, the adaptor bush 9 is pushed over the insulating bushing 6, and the shroud 8 is loosely threaded over the cable 2, the frustro-conical end portion 18 having first been trimmed off as necessary to suit the size of the cable 2. The cable lug 1 is connected securely to--the terminal 4 and the shroud is then passed up over the connection, one end being sealingly engaged over the bush 9 and the other, frustro-conical end engaging tightly over the cable 2.

It will be appreciated that, once installed, the ribs 12 in the bush 9 tend to resist disengagement, particularly because all of the ribs are directed in the axial direction in which removal would be effected.

Additionally, the ribs also prevent electrical tracking at test voltage levels.

Assembly is assisted by the application of silicone grease which dries to form bonds between the bush 9 and shroud 8 and between the shroud and the cable.

An insulation barrier of the form described above is inherently adapted for use with a wide variety of cable sizes and with insulation bushings, of different lengths, diameters and forms, e.g. cylindrical or frustro-conical, and of course can be applied to rightangle connections, as illustrated, or to in-line connections. It can be used with cables insulated with paper or with polymeric insulation.

Claims (1)

1. CLAIMS:

   1. An insulation barrier for an electrical cable termination in which the cable is connected to a terminal having an insulating bushing, the barrier comprising an insulating adaptor bush of elastomeric material, the bush having a substantially cylindrical main body portion and a plurality of flexible internal annular ribs adapted to engage resiliently at their inner peripheries over a range of insulating bushings of different external diameters, and a tubular shroud of insulating material having a first end portion of substantially cylindrical form dimensioned to engage sealingly over the said bush, an opposite end portion of frustro-conical form and an intermediate portion of corrugated flexible construction permitting the said end portions to be set at any angle up to 900 to each other.

   2. A barrier according to claim 1, wherein the said flexible ribs of the adaptor bush terminate at their inner peripheries at axially directed lips, the said lips all extending in the same axial direction.

   3. A barrier according to claim 1 or 2, wherein the frustro-conical end portion of the shroud is formed externally with annular guide ribs to facilitate severing of the end portion to suit sizes of cable larger than the smallest internal diameter of extreme end of the said frustro-conical end portion.

   4. An electrical termination comprising a cable connected to a terminal having an insulation barrier consisting of an adaptor bush and a shroud, the bush engaging sealingly over the insulating bushing and the shroud having a first end portion of generally cylindrical form sealingly engaged over the adaptor bush, an intermediate portion of flexible corrugated construction and an opposite end portion of frustro-conical form, the extreme end of which engages sealingly over the cable.

   6. An insulation barrier substantially as herein described with reference to the accompanying drawings.

   7. An electrical termination substantially as herein described with reference to Fig. 1 of the accompanying drawings.

   Amendments to the claims have been filed as follows 1. An insulation barrier for an electrical cable termination in which the cable is connected to a terminal having an insulating bushing, the barrier comprising an insulating adaptor bush of elastomeric material, the bush having a substantially cylindrical main body portion and a plurality of flexible internal annular ribs adapted to engage resiliently at their inner peripheries over a range of insulating bushings of different external diameters, and a tubular shroud of insulating material having a first end portion of substantially cylindrical form dimensioned to engage sealingly over the said bush, an opposite end portion of frustro-conical form and an intermediate portion of corrugated flexible construction permitting the said end portions to be set at any angle up to 900 to each other.

   2. A barrier according to claim 1, wherein the said flexible ribs of the adaptor bush terminate at their inner peripheries at axially directed lips, the said lips all extending in the same axial direction.

   3. A barrier according to claim 1 or 2, wherein the frustro-conical end portion of the shroud is formed externally with annular guide ribs to facilitate severing of the end portion to suit sizes of cable larger than the smallest internal diameter of extreme end of the said frustro-conical end portion.

   4. An electrical termination comprising a cable connected to a terminal having an insulation bushing and an insulation barrier consisting of an adaptor bush and a shroud, the bush engaging sealingly over the insulating bushing and the shroud having first end portion of generally cylindrical form sealingly engaged over the adaptor bush, an intermediate portion of flexible corrugated construction and an opposite end portion of frusto-conical form, the extreme end of which engages sealingly over the cable.

   6. An insulation barrier substantially as herein described with reference to the accompanying drawings.

   7. An electrical termination substantially as herein described with referent to Fig. 1 of the accompanying drawings.