GB2265501A

GB2265501A - Protective devices for cable terminations.

Info

Publication number: GB2265501A
Application number: GB9306276A
Authority: GB
Inventors: Nicholas Grenville Roy Bowden
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1992-03-27
Filing date: 1993-03-26
Publication date: 1993-09-29
Anticipated expiration: 2013-03-26
Also published as: GB2265501B; GB9306276D0; GB9206759D0

Abstract

A protective device for a cable termination of the kind in which a lug (1) secured to the end of a cable (2) is connected to a bushing insulator (2) is made of electrically insulating material and comprises a generally tubular body member (6) having a forward pant (7) shaped to engage and grip the insulator and a rear part (8) having two like openings. A tapered generally tubular shroud member (15) is shaped and dimensioned for engagement at will at either the first (12) or the second (13) opening, to accommodate "in-line" or "elbow" terminations respectively, and a closure member (14) is shaped and dimensioned for engagement at whichever of these openings is not occupied by the shroud member. The front and rear parts of the body member may be separable (by cutting) and the proximal end of the rear part may fit the opening of an identical body member to accommodate a termination with two (or by repetition more than two) cable ends (Figure 3). <IMAGE>

Description

Protective Devices for Cable Terminations This invention relates to protective devices for electric cable terminations of the kind in which a lug secured to the end of a cable is connected to a bushing insulator, for example by a screw-threaded connection.

Such terminations are widely used in the electricity distribution system at voltages up to about 36kV, and in many cases the connection is protected by a device (sometimes called an insulating "boot") which encloses the live metallic parts of the termination to provide additional insulation and so allow closer spacing than air flash-over distances would otherwise permit and/or to eliminate any substantial risk of accidental contact and/or reduce exposure to atmospheric contaminants.

Such terminations are normally made with the cable located in one of two distinct positions: in an "in-line" termination it approaches the insulator along its axis, and in the more frequent "elbow" termination it approaches perpendicular to the axis. In both cases, the flexibility of the cable and/or the possibility of offset at the connection between the lug and the insulator may give rise to some departure from the nominal angles of 1800 and 900 respectively, but angles between 110 and 1600 are not frequently encountered.

Current protective devices are made of resilient flexible materials and are formed with corrugated sections extensive enough to allow bending through more than 900. We have recognised that this is undesirable because it makes the protective device more flexible than it needs to be in the finished termination, and so less secure from accidental displacement, and because certain parts of the protective device may be subject to appreciable tension when used in an elbow termination and so become susceptible to cracking after a few years' ageing.

The protective device in accordance with the invention is made of electrically insulating material and comprises a generally tubular body member having a forward part shaped to engage and grip a bushing insulator and a rear part (intended to enclose the connection between the bushing insulator and the cable lug) having two like openings, the first opening being in the distal end of the rear part and the second opening being in the side of the rear part; a tapered generally tubular shroud member shaped and dimensioned for engagement at will at either the first or the second said opening; and a closure member shaped and dimensioned for engagement at whichever of said openings is not occupied by said shroud member.

Preferably at least one of the body member and the the shroud member is flexible enough to allow realistic departures from the nominal angles of 1800 and 900 and/or from the nominal dimensions for which the device is designed. A corrugation or a few corrugations may be used to make the body member axially compressible, in particular to accomodate variations in the dimensions of the insulator. Either or both of the body member and the shroud member may be stiffened where they engage, for example by a ring insert of relatively hard insulating material; the closure member may be relatively rigid.

Preferably the shroud member and the closure member fit inside respective openings, but the part of the body member containing the respective opening could fit inside the corresponding other member if preferred.

In a development of the invention, the forward and rear parts of the body member are separable one from the other, preferably by cutting, and the proximal end of the rear part is so shaped and dimensioned that it can be engaged in the opening at the distal end of another identical body member; this allows two or more standard protective devices to be used (discarding the front part of one or more of them) to enclose a termination in which two or more cables are connected to the same insulator.

The front part of the body member may also be designed so that by cutting or otherwise removing a portion of it, or not doing so, the body member may be engaged with different sizes or designs of bushing insulator.

The invention will be further described, by way of example, with reference to the accompanying drawings in which: Figure 1 is is a cross-section through an elbow termination incorporating a protective device in accordance with the invention; Figure 2 is a cross-section through a body member for a protective device in accordance with the invention; Figure 3 is a cross-section showing one whole body member assembled with the rear part of another body member; and Figures 4 and 5 show assemblies in which different cut body members are used in applying the protective device to a different design of insulator.

In the termination shown in figure 1, a lug 1 is secured on the end of a cable 2 and connected to a hushing insulator 3 (for example to make a connection through the metal casing of a distribution transformer) by a screwed connection 4. The lug 1, connection 4 and metalwork 5 at the end of the insulator are at conductor potential, and require additional insulation and protection from contact. This is achieved by a protective device in accordance with the invention. It comprises a rubber body member 6 consisting of a forward part 7 and a rear part 8. The demarcation between the two parts of the body member is slightly arbitrary, but may be taken as occuring at the line 9.The forward part 7 is formed with a series of flexible skirts 10 which engage resiliently with the body of the insulator 3 and with a couple of corrugations 11 which accomodate variations in length along the axis of the insulator and may contribute to a small angular flexibility as well.

The rear part 8 which encloses the connection 4 has a first opening 12 in its distal end (upper as drawn) and a second opening 13 in its side. When fitted as an elbow termination as shown, the first opening 12 is closed (blanked off) by a closure member 14 of relatively rigid insulating material and the second opening 13 receives a shroud member 15; when fitted as an in-line termination, the shroud member and closure member would be interchanged. The shroud member 15 is made of the same rubber composition as the body member but is stiffened where it enters the opening 13 by a relatively rigid insulating ring 16. It is generally tubular and tapers towards its distal end to fit closely around the cable 2 (the end may be cut off if necessary to accomodate a cable of larger diameter than the end can be stretched over). The shroud member 15 is provided with a single corrugation 17, primarily to allow small departures from 900 in the angle between the axes of the cable 2 and of the insulator 3.

Figure 2 shows the body member 6 of the protective device of figure 1 on a larger scale and in an undistorted (as-moulded) condition. For comparison, it also shows at 20 and 21 respectively the outlines of the maximum and minimum sizes of insulator for which the body member is designed. This figure also shows more clearly the grooves 22, 22 used in this example at the openings 12 and 13 to provide for a secure interlocking engagement with the shroud member or the closure member -as the case may be.

The body member shown in Figure 2 can be cut at the position indicated by the dotted line 24 to expose a formation 25 at the proximal end of the rear part comprising an external annular rib 26 and an internal annular groove 27. The formation 25 is of such shape and dimensions that when so exposed the rib 26 can be fitted into the groove 22 at the opening 12 in another identical body member 28, as seen in Figure 3, to provide for a double elbow termination in which two cables entering along the lines 29 and 30 are connected to the same insulator. Preferably a ring of relatively rigid insulating material is inserted in the groove 26 to strengthen the interlocking engagement. A third cable, or any required number of cables, can be accomodated by repeating this procedure.

As seen in Figure 4, the body member can also be cut at the same position to adapt the protective device for use with an insulator 31 for which it is not primarily designed, (say one of the smaller "ANSI" bushing insulators) using a suitable adaptor 32.

Another possibility is to cut the body member at the lower (as drawn) level indicated by the dotted line 33 in Figure 2, retaining the corrugations 6; as shown in Figure 5, a different design of adaptor 34 may then engage one of the corrugations, leaving the other to fulfil its original function of providing tolerance on the length of the termination.

Claims

A protective device for a cable termination made of electrically insulating material and comprising a generally tubular body member having a forward part shaped to engage and grip a bushing insulator and a rear part having two like openings, the first opening being in the distal end of the rear part and the second opening being in the side of the rear part; a tapered generally tubular shroud member shaped and dimensioned for engagement at will at either the first or the second said opening; and a closure member shaped and dimensioned for engagement at whichever of said openings is not occupied by said shroud member.
2 A device as claimed in Claim 1 in which at least one of the body member and the shroud member is flexible enough only to allow for small departures from nominal angles of 1800 and 900 and/or from nominal dimensions.
3 A device as claimed in claim 1 or claim 2 in which at least one of the body member and the shroud member is made axially compressible by at least one corrugation.
4 A device as claimed in any one of claims 1-3 in which at least one of the body member and the shroud member is stiffened where they engage.
5 A device as claimed in Claim 4 in which at least one of the said members is stiffened by a ring insert.
6 A device as claimed in any one of claims 1-5 in which the shroud member and the closure member fit inside their respective openings in the body member.
7 A device as claimed in any one of claims 1-6 in which the forward and rear parts of the said body member are separable one from the other and the rear part is so shaped and dimensioned that it can be engaged in the opening at the end of another identical body member.
8 A device as claimed in claim 7 in which the said parts are separable by cutting.
9 A device as claimed in any one of claims 1-8 in which the front part of the body member is designed so that by cutting or otherwise removing a portion of it, or not doing so, the body member may be engaged with different sizes or designs of bushing insulator.
10 A protective device for a cable termination substantially as described with reference to and as shown in any one figure of the drawings.
11 A cable termination protected by the device claimed in any one of claims 1-10.