GB2182088A - Safely clamp assembly for power cables - Google Patents

Abstract

A fusible clamp assembly, especially to hold a power cable to an insulator, consists of a clamp and preformed rods with helical torsion, said clamp having an inside sleeve held to an outside housing by means of at least one shearing element, the outside housing having holding flanges. The inside sleeve (1) and the outside housing (2) are split units. <IMAGE>

Description

SPECIFICATION Safety clamp assembly, especially to hold a power cable to an insulator This invention relates to a clamp assembly, especially to hold a power cable to an insulator, consisting of a clamp and preformed rods under helical torsion.

US Patent 3,539,139 discloses an assembly for suspension of linear bodies, consisting of a split housing in the interior of which a cable is surrounded by a padding of resilient material around which preformed helically twisted rods are placed. The ends of the rods protrude from the housing so as to better distribute the suspension force along a section of cable.

Although providing good suspension, such an arrangement presents inconveniences in practice due to the inflexibility of the clamp, since in cases of excessive axial load on the cables, by virtue of very strong winds, for example, the cable would break and cut off the power supply, or the assembly would be severed, which would also lead to a later break of the cable. In the case of large highvoltage towers with many cables, even the structure of these towers could be affected.

Other clamping arrangements 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. These patents present devices with the common feature residing in offering means of suspension with elements which break or release the cable in case of excessive axial load.

German Patent 492,259 of 1930 suggests a tight sleeve sliding inside an outside guide when releasing the connection between these in the event of excessive longitudinal tension on the cable. However, since the release between these parts would depend upon the inclination of the upper part of the guide in relation to the sleeve, a sudden axial shock could break the cable before this had been released. On the other hand, a very light but constant load that would not cause any danger of breaking the cable could even then cause the sleeve to be released, once the cable was drawn to the limit necessary for this to occur.

US Patents 3,117,181 and 3,519,727 disclose mechanisms that when submitted to extreme loads would completely release the cables held by these, letting them fall to the ground. Depending upon the height of the towers, however, it could occur that by freeing the clamping mechanism of one of these, the load on nearby towers would increase and cause the release in series of cables attached to several towers.

From this, the assembly proposed in US Patent 4,177,352 came to be developed, which offered a clip held to a loop by means of a shearing pin, the interior of said clip holding the cable. The shearing pin can break with a certain pre-set load, releasing the cable to slide longitudinally in the loop. This arrangement has the inconvenience that both the force of the grip and the force of sustenance of the cable are exercised over the same section of cable which is extremely prejudicial to this by forming a critical region of load.

Finally, US Patent 4,360,177 describes a suspension assembly with a housing open on one of the sides inside which the cable is placed encircled by a resilient element on a bed connected to the housing by a shearing element which breaks in case of an excessive longitudinal load, allowing the cable to move longitudinally inside the housing, thus reducing the load on the cable and preventing this from breaking. Also provided are a series of preformed helically twisted rods similar to those appearing in US Patent 3,539,139 mentioned above.

Although presenting relative efficiency over less sophisticated clamps, the clamp described in US Patent 4,360,177 has a series of disadvantages. One of these concerns the difficulty of mounting the preformed rods in the clamp, since these hold not only the cable but also the bed which is fixed inside the housing.

Added to this are other disadvantages relating to the constructional aspects of the mentioned clamp, since the distance between the flanges or the ends of the housing must be at least equal to the diameter of the cable to be housed, so that this can pass without difficulty between these, besides the manufacturing of such clamps being relatively complex, principally in those cases in which the bed is built integrally with the housing. It is also worth mentioning that, so that there be no compromise of breakage or damage to the suspension towers, the extraction load of the cable should be contained within very narrow limits, otherwise the device may not fulfill its objectives.However, the mounting indicated for Patent 4,360,177, where the helical rods are placed in direct contact with the surface, over which they will slide in case of severage of the pins from the proper rugosity of the surface represented by the rods will offer resistance to this movement, whose magnitude is difficult to define accurately. Besides this, after severance of the shearing elements, it is necessary to change the entire clamp for a new unit, involving removal of the bed from inside the preformed rod assembly.

The present invention provides a clamp assembly, especially to hold a power cable to an insulator, consisting of a clamp and preformed helically twisted rods, said clamp having an inside sleeve fixed to an outside housing by at least one shearing element, the outside housing having holding flanges, the inside sleeve and the outside housing are being split.

It is advantageous to have the mounting so that the cable is wrapped in the normal manner by a resilient body, such resilient body, however, is enveloped directly by preformed helically twisted rods. The split inside sleeve, acting as a bed, can easily be installed on the preformed rods and the also split outside housing can be connected to the inside sleeve by shearing pins, with the two halves of the housing held together by a clip.

Contrary to the arrangement in US Patent 4,360,177, in the preferred embodiment of the invention the contact surfaces where sliding occurs are smooth and therefore the shearing load will effectively determine the load at which to release the cable.

Besides offering the advantages of similar arrangements already known, the assembly according to the preferred embodiment of this invention is capable of very simple and economical production, since the halves of the split components can be identical, and can provide excellent conditions for suspension of the cables. In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows an exploded perspective view of an embodiment of the present invention; Figure 2 shows a side view of the assembly attached to an insulator, and Figures 2a to 2c show the sequence of operation of the arrangement shown in Fig. 2 when subjected to an excessive axial load.

From Fig. 1 it is possible to identify the different components of an embodiment of a releasable assembly. A resilient element 7 wraps around a cable (not represented) and around this element 7 are arranged central regions 6a of the preformed rods 6, which ends are woven or braided around the cable in order to better distribute the suspension forces along a section of the cable, as mentioned above. A split sleeve having sleeve parts 1 has in a center region 1a of each part, a projection which adjusts to or is shaped to the shape of the median area of the rods, where a reduction of the outside diameter already exists. In this same median section 1a a hole is provided for receiving a shearing element or pin 3 mounted on the interior of an outside housing part 2.The element 7 is easily mounted by moving the resilient element 7 over a section of cable, the preformed rods 6 are installed and, with the inside sleeve 1 already inserted in the respective outside housing part 2, the two parts 2 are placed over middle section 6a of rods 6 and fastened by using "U"-clamp 5 around the outside of the parts 2. The assembly can then be fastened, for instance, to an insulator 8 (Fig. 2) by using a nut and bolt set, which the bolt inserted in the holes made in the ends of clip 5 and in the flanges 2a of outside housing parts 2.

Figs. 2a to 2c permit a better visualization of what occurs when the cable is subjected to an excessive axial load, for example, of 600 kgf in the direction of arrow 5. Such a load severs shearing elements 3, which join the outside housing parts 2 to the inside sleeve parts 1. By virture of that shearing, all components inside of assembled housing parts 2 are pulled therefrom, with the two halves of the inside sleeve 1 separating from the assembly and falling to the ground. In this manner cable 9 can move freely inside the outside housing.

Note that after the assembly has been removed, even if the preformed rods 6 suffer a small radial expansion from the resilient element 7, and even if an inversion occurs in the direction of the load applied to the cable there will be no problem if the rods were again pulled toward the inside of housing 2, since with the inside sleeve 1 removed, a greater gap exists between rods 6 and housing parts 2.

The assembly is obviously substituted very simply by changing housing 2 whose shearing elements were broken and, in case both halves of sleeve 1 are not immediately located, these can also be changed for new ones.

An advantageous modification consists in placing the shearing pins in the inside sleeve and the corresponding holes in the outside housing, since in the event of overload on the cable, only the inside sleeve needs to be substituted, besides the fact of the inside surface of the housing being smoother and so eliminating the possibility that, in the form illustrated, a fragment of the shearing pin that has been held to the housing can damage the cable.

Claims (6)

1. A clamp assembly, especially to hold a power cable to an insulator, consisting of a clamp and preformed helically twisted rods, said clamp having an inside sleeve fixed to an outside housing by at least one shearing element, the outside housing having holding flanges, the inside sleeve and the outside housing are being split.

2. An assembly in accordance with claim 1, wherein each part of the outside housing is equipped with a shearing element in form of a pin cooperating with a hole in each part of the inside sleeve.

3. An assembly in accordance with claim 1 or 2, and comprising a "U''-clamp arranged to maintain the two halves of the outside housing together.

4. An assembly in accordance with claim 2 or 3, wherein the preformed rods do not present torsion qn the central region to be encircled by the clamp.

5. An assembly in accordance with any one of the preceding claims, wherein the preformed rods are covered in the mounted state by the inside sleeve.

6. A clamp assembly substantially as herein before described with reference to the accompanying drawings.