GB2214359A - Releasable clamping of overhead cables - Google Patents

Description

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SPECIFICATION OF THE PATENT OF INVENTION FOR "SUPPORT ASSEMBLY FOR RELEASABLE CLAMPING OF OVERHEAD CABLES OR LINE"

The present invention refers to a support assembly for releasable clamping of overhead cables or lines.

US Patent 3.539.139 discloses a support assembly for linear bodies consisting of a split body within which is placed a cable encircled by a cushion of resilient material around which are placed helically twisted preformed rods whose ends project from the body so as better to distribute the supporting force along a section of the cable.

Although a good support is provided, this arrangement has certain disadvantages in practice due to the rigidity of the clamp since, in the case of excessive axial loads resulting from rupture of the cable, the support assembly, together with the network, resists the dynamic stresses and tranfers the elevated load to the structure (pylon) which causes deformation or even rupture of the latter.

In an attempt, at least partially, to solve such problem, various devices have been proposed such as those described in German Patent 492.259 and US Patents 3.117.181, 3.519.727, 4.177.352 and 4.360.177. Such documents discose devices having in common the provision of supporting means having elements which break or liberate the cable should excessive axial loads develop.

f k_ US Patents 3.117.181 and 3.519..727 disclose mechanisms which, when subjected to extreme loads, completely release the cables supported thereby and allow them to fall to the ground. Depending on the height of the pylons, however, the releasing of t6 clamping mechanisms of one of them increases the load on the neighbouring pylons which might provoke liberation at various pylons, In a chain reaction.

As a result the assembly of US Patent 4.177.352 was proposed which provides a clamp fixed to a loop by ipeans of a shear pin, the cable being held in the interior of the clamp. The shear pin breaks at a predetermined load so as to liberate the cable which is able to slide longitudinally in the loop. In this case there is a disadvantagethat the cable tightening force-and supporting force are applied to the same region of the cable which is extremely prejudicial, forming a-critical load region.

- US Patent 4.360.177 describes a support group with a housing open on one side and in which a cable is arranged encircled by a resilient element on a cradle connected to the housing by means of a seal element which breaks in the case of excessive longitudinal load which then permits the cable to slide longitundinally within the housing, thus eleviating the load on the cable and avoiding its rupture. It as.o discloses a series of helically twisted preformed rods similar to the disclosure of above-mentioned US Patent 3.539.139.

Although it is relatively efficient when compared with less sophisticated clamps, the clamp of US Patent 4.360.177 has a series of disadvantages. One of these is related to the difficulty in mounting the preformed rods In the clamp since they not 3 z T_.

only encircle the cable, but also the cradle which is fixed within the housing. In addition, there are further disadvantagec with respect to the structural nature of said clamp since the differences between the flanges or ends of the housing must be at least equal to the diameter of the cable to be received therein so that the cable may pass without difficulty there,between. Moreover the manufacture of such clamps is relatively complex, principally in those versions in which the cradle is integral of the housing. It should also be mentioned that,, in order to avoid breakage or damage of the pylons or support towers, the cable extraction load should be within narrow limits since otherwise the device'may not serve it purpose. However, the assembly indicated in USPatent 4.360.177 where the helicall rods are placed in direct contact with the surface on which they will slide if the pins shear, the roughness of the surface of the rods will produce a sliding resistence whose magnitude is difficult to define with any precision. Apart from this, after rupture of the shear elements, the whole clamp has to be exchanged for a new one which makes it necessary to remove the cradle from within the preformed rod arrangements.

German Paten.t 492.259 teaches a shoe which is rigidly clamped to the cable to be supported and is slidably arranged within a support ring attached, for example, to an insulator of a high voltage power. Between the ring and the tower, there is a connecting element pivotally coupled to the ring, such element having a locking tongue which co-operates with a recess In the shoe and prevents the shoe from shifting out of position once placed within the ring.

Release of the shoe will occur only when there is an axial load in excess of a given limit and the connecting element inclined sufficiently for the locking tongue to escape and no longer prevent shift of the shoe. In this manner the shoe Is extracted from the support ring and moves together with the cable In the direction of the applied loads avoiding possible dam4ge to the structure of the tower or even to the cable which then-slides freely within the ring.

once the shoe has left the rings however. this known arrangement has a disadvantage that, should the axial load on the cable be reversed, the shoe may be pulled once more into the ring at which time it Is probable that there will be a shock between abutting faces of the shoe and the ring since the fit therebetween is fairly close and there will be no means of guaranteeing that the shoe may then return centralized into the ring. Depending on the magnitude of this shock, there may be a danger of the tower being damaged. or even of the cable breaking.

The possibility of the direction of the axial load being reversed after the shoe leaving the ring is not so remote since, In high winds, the cables may swing at random and may thus be submitted to sudden stresses in both directions.

The purpose of the present invention is to develop the assembly known from German Patent 492.259 In such a way that both Its disadvantages and those of other known arrangements be eliminated.

The Invention relatesi thereforeg to a support assembly for freely clamping overhead lines or cables, comprising a clautping element pivotally connected to an outer housing within which a sliding shoe may be introduced, the shoe being suitable for receiving therein,, and in fixed relation a line or cable to be supported and the clamp element having a protuberance or recess which co-operates with a recess or protuberance, respect- Y- -P 1. ( ively, integral with the shoe so as to prevent axial movement of the shoe within a predetermined rnge of angles of the clamping element. with respect to the housing, the shoe being permitted to become free'of the clamping element when said range of ahles is exceeded.

The object of the invention is achieved in an extremely simple manner by making the shoe in the form of a split sleeve.

The split sleeve is simply applied over the line or cable without any additional holding element, its compression around the cable which ensures that the cable is maintained therewithin being provided by the outer housing which duly encircles the sleeve. As a result, when the shoe is withdrawn from the interior of the housing, the two halves of the sleeve which constitute the shoe, fall to the ground. In this manner, should the axial load which withdrewthe shoe be reversed, there will be no obstacle preventing the cable from sliding freely through the housing, as in the case of German Patent 492.259 whose shoe was fixed to the cable even after withdrawal from the housing.

The operation, as well as other details of the invention, will be understood from the following description.made with reference to one embodiment which is shown in the drawings. The figures show:

Figure 1 A side view, partially in section, of one embodiment of the invention; Figure 2 A front view, partially in section, of the assembly of Figure 1; and Figures 3a and 3c Schematic showings of three phases of operation of the assembly.

- 6 Or _. k, Figure 1 shows that the support assembly is basically formed by a support element 1 pivotally fixed to a housing 2 which receives shoe 3 in its interior, the inventive assembly differing here from that known in the art in that shoe 3 is in the form of a split cylindrical sleeve.

Support element 1 is the part to be fixed by means of a link, for example, to an insulator 8 (Figure 3a) or other component of the network, acting as a rocker arm, or even other elements for attaching the earth line so as suitably to support the-assembly. Element 1 is placed between two flanges 4 of housing 2, a pin. 5, bolt or the like passing through openings 4a in the flanges and through element 1 so that the latter is freely pivotal with respect to housing 2.

A protuberance 7 from the support element 1 provides locking of shoe 3 within the housing in the position shown in f igure 1.

Advantageously, housing 2 is a split cylindrical housing whose inner diameter is only slightly greater than the outer diameter of shoe.3.-The fact that housing 2 is split greatly facilitates mounting of the assembly, final fixing being able to be carried out by means of a U-shaped part which encircles housing 2 at its central region and is fixed to flanges 4 by the same pin 5 which serves as a pivot pin. Hou.sing 2 is.also provided with an opening 9 through which blocking protuberances 7 of element 1 passes.

Shoe 3 in the form of a split cylindrical sleeve is provided internally with a narrow region 3a with a view better to secure the cable in its interior.

Just a's in the above-mentioned US Patent 3.539.139, that part of the cable which is encircled by the support assembly :7 receives an elastic cushion or the like and, around this latter, an assembly of preformed helical twisted rods so as better to distribute the support forces which actuate over that part of the cable.

The central region of the shoe 3 shown in Figure 1 Is formg4 with a recess or groove which is completely around Its periphery. This recess 6, however, may also be formed only in the upper part of shoe 3 which, on the other hand, would make it necessary when mounting the assembly to ensure the correct position of recess 6.

In Figure 3a the assembly of the invention is fixed to an overhead insulator 8 in the raised position of the cable in which the support element 1 prevents axial shifting of shoe 3.

on appearance of a load in the direction of arrow S shown in Figure 3b, housing 2 Is pulled together with the cable and support element 1 inclines gradually. on reaching an inclination of about 40 0 with respect to the verticle, shoe 3 becomes unlocked and begins to be withdrawn from the interior of housing 2.

Figure j shows the moment when, after total withdrawal of shoe 3, its two halves fall. Thus should the direction of the load applied to the cable be reversed, there will be no danger of the cable being suddenly locked due to collision of the shoe with the housing, as happened in the known assembly of German Patent 492.259, the preformed rods and the cushion which still surround the cable being loosely supported therearound and not preventing relative movement should the rods collide with the housing in a situation such as that mentioned above.

Thus, apart from being safer than the assemblies of the art, the assembly of the present invention is also more easily I manufactured and avoids damage of the various components and to the cable.

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C L A 1 D1 S 1. - Support assembly for the releasable clamping of overhead lines or cables, a clamping element (1) pivotally Joined! to an outer housing (2) within which a slidable shoe (3) Is Introduced, said shoe (3) being suitable to receive therein and in fixed relation a cable or line to be supported by the assembly and said clamping element (1) having a protuberance (7) or recess which co-operates with a recess (6) or protuberance, respectively, integral with the shoe, so as to prevent axial movement of the shoe within a predetermined range of angles of the clamping element with respect to the housing, uncoupling of the shoe with respect to the clamping element being permitted when said range of angles is exceeded, characterized in that the shoe (3) is a split sleeve.

2. - Support assembly according to claim 1 characterized in that the split sleeve which constitutes said shoe (3) has a cylindrical sleeve with a norrowed region (3a) therein, the housing (2) having, at least internally, a cylindrical shape adapted to the outer shape of said shoe (3).

3. - Support assembly according to claim 2 characterized in that said housing (2) Is also cylindrical and split, a U-shaped part encircling the housing (2) for supporting It.

4. - Support assembly according to claim 1 characterized In that said shoe (3) is provided, in its outer central region. with a recess (6) around it periphery.

Published 1989 at The Patent O:Mee, State House,66,"71 High Rolborn, London WC1R4TP. Further coplesmaybe obtained from The Patent OMoe. SmjecBrancn, St llaa77 011!, O;VineLon. Zent M5.7,M). PTinted by Mj)ltiplex techniques ltd, St Mary Cray, Hent, Con. 1/87