Clamps for pulling of cables

Area of the invention

The present invention relates to a clamping device for receiving one or more cables, for pulling said cables through a borehole.

Background of the invention.

High voltage cables are normally held in stretches in the air over a land formation or in ditches in the ground. However, there has been a growing need to lay such cables in boreholes in rock formations or in the ground and soil. How to drill holes for laying cables is known, but the equipment presently available does not allow for pulling cables through long boreholes. For example, it is desirable to be able to pull such cables through boreholes which are several hundred metres long and also several kilometres long.

In order to pull such cables through long boreholes, it is important that the friction between the cable bundle and the interior borehole is low. Furthermore, in many cases it will also be important that the cables are in an ordered cable bundle.

Purpose of the present invention.

Thus it is an aim of the present invention to develop a clamping device that can hold several cables together in a bundle. Often there is also a need to transport other cables in addition to, or other than, high voltage cables by pulling through a borehole, and the clamp should therefore also comprise means for the simultaneous carrying of such cables, such as, for example, a fibre cable. When pulling cables through long boreholes, such as horizontal, inclined, arched and vertical boreholes, friction forces between the cable bundle and the inside surface of the borehole arise. These frictional forces have until now not allowed for the pulling of cables through long boreholes without causing cable damage. Furthermore, it can also be a need to lay the cables in organised bundles such as when single-wire high voltage cables are laid in three-foil arrangement. It is therefore an aim of the invention to provide clamps which, while bundling together a number of cables, also cause reduced friction in the borehole. Thus, it is an aim of the invention that the clamps are either directly or indirectly equipped with friction reducing means.

When pulling cables through long boreholes or through boreholes with a steep incline, forces can be so great in the cables that they can be overloaded if the pulling is directly on the cable. Therefore it is an aim of the invention to provide clamps, which can also directly or indirectly be attached to the cable so that parts of the pulling forces will go through the clamps, i.e. so that in practice one exerts forces at several points along the elongated length of the cable. Preferably, the clamps are evenly distributed along the longitudinal direction of the cable bundle. It is an aim of the invention to provide a clamping system that allows the pulling of cables through long boreholes. The system must therefore;

1 . Include friction reducing means (such as wheels) between clamps and the inner surface of the borehole, for transferring the cables in (and out of) the borehole

2. Avoid damage to the outer sheath of the cable when pulling.

3. Bundling of cable, such as for example in a three-foil arrangement. For example, for single-wire high voltage cables it is important that they are in a three-foil arrangement to reduce power loss.

4. Securing the cable set in case of short circuiting. That the system keeps the cables in position when a short circuit occurs in the cable set.

5. To be able to withdraw the cable set when a faulty system occurs or during renewal/upgrades on the installation.

6. Rails (mechanical reinforcement) can be used if the forces during pulling or during the operational phase become too large for the cables to be exclusively present in the clamps. Wheels can then be mounted on the rails to reduce friction during pulling. Use of rails means the clamps will be anchored to the rail Summary of the Invention

The present invention relates to, in a first aspect, a clamping device for receiving one or more cables, for pulling said cables through a borehole, characterised in that the device comprises a clamping element and an insertion element, where the clamping element extends around said cables for the clamping of said cables, and where the insertion element is arranged radially outside the cables and radially inside the clamping element, and where the insertion element is given a shape adapted to receive the various cables.

In one embodiment, the insertion element has an arched shape adapted to the cables that shall be received in the clamp.

In one embodiment, said insertion element is made of a material that is more flexible or softer than the clamping device.

In one embodiment, the insertion element is made of a material which has a given elasticity so that the clamping forces which are exerted by the constriction of the clamping element cause the insertion element (24) to form an engagement with both the cables and the clamping element.

In one embodiment, there are a number of friction-reducing means provided on the exterior surface of the clamping element. In one embodiment, said friction reducing means are wheels or balls.

In one embodiment, the shaft of said wheels is arranged adjoining to the clamping element so that the wheels extend through or are embedded in the clamping element and/or the insertion element. In one embodiment, the clamping unit comprises a number of attachment points for attachment to a coupling element for connecting a number of clamping devices in the longitudinal direction of the cable. In one embodiment, said coupling element comprises a number of friction-reducing means.

In one embodiment, the clamping device comprises a number of parts which are snap coupled or hinged together.

In one embodiment, the clamping device can be opened and can be closed, and it can be folded into a closed position by a fastening and coupling element.

In one embodiment, the width of the coupling element stretches in the main radially outwards from the longitudinally running axis of the cable bundle, as the coupling element is fastened to the clamps and the cable bundle.

In one embodiment, said friction reducing means comprises a number of wheels, and the centre axis of said wheels is embedded in the coupling elements.

In one embodiment, said fastening and coupling means are adjustable with an adjustment screw, adapted to exert controlled pressure via the insertion element and cables. In one embodiment, said insertion element comprises a number of parts. Description of the figures

Preferred embodiments of the invention will now be described in more detail with reference to the accompanying figures, where:

Figure 1 shows schematically in perspective an arrangement where clamps according to the invention are used to hold together a number of cables. Figure 2 shows schematically in perspective a different arrangement where clamps according to the invention are used to hold together a number of cables. Figure 3 shows schematically in perspective an embodiment of a clamp with friction reducing means.

Figure 4 shows schematically in cross section a cable arrangement with clamps, friction reducing means and coupling means.

Description of preferred embodiments of the invention.

Figure 1 shows schematically in perspective an arrangement 10 for holding together a number of elongated cables. It is often required to bundle together three such cables 12, 14, 16, but the clamp 20 can be adapted to any number of cables. The clamp 20 can also be adapted to be attached to one cable only. However, the examples below show bundling of three cables 12, 14, 16. In essence, the clamp 20 is comprised of two main elements, namely a clamping element 22 and an insertion element 24. The clamping element 22 extends around the cables which are to be bundled together. The insertion element 24 will ensure proper positioning of the cables in the clamp 20, and recesses are provided in the insertion element 24 for receiving the cables 12,14,16. When constricting the clamping element 22, pressure on the cables 12, 14, 16 is exerted through the insertion element 24.

The clamping element 22 is constructed so that it can be opened and closed.

Preferably, the clamping element 22 comprises two parts, a first part 22a and a second part 22b, which are hinged together (not shown in any detail in figures 1 and 2). In a closed position, as shown in figures 1 and 2, the two parts 22a, 22b are brought together by a fastening and clamping device 26. In the figure, conventional screws 26a are shown, but these may also be a fastening and clamping device 26 which allows adjustment of the distance between the parts 22a and 22b. The clamping element 22 is normally made of a relatively firm and rigid material, such as for example steel. Different variants of steel tape can be used. The clamping element 22 can also be composed of several parts, such as three or four or more, which are coupled together with the help of a snap-on fastener or a hinge. The clamping element 22 can also be constructed by one part only (for example, a steel tape) and is then sufficiently flexible so that it can be partially opened and closed (fastened and clamped).

The insertion element 24 is designed to receive parts of the cavity between the clamping element 24 and the cables, such as the three cables 12, 14 and 16 as shown in figure 1 . It is not necessary that the entire cavity is filled. The insertion element 24 will, as the clamping element 22 is secured and clamped, transfer some of the clamping forces to the cables 12,14,16 so that these are held in the correct position in the clamp 20, both in relation to the longitudinal length of the cables and how the cables are positioned radially in the clamp 20 itself .

The insertion element 24 will normally be made of a more flexible material than the clamping element 22. Different materials can be used, but tests have shown that materials such as plastic or silicone rubber are suitable. As the insertion element 24 is somewhat more flexible than the clamping element 22, then forces from the clamping are transferred evenly and gently to the cables so that they are not damaged when the clamp 20 provides a strong engagement with the cables

12,14,16.

In some variants of the clamp 20, it is sufficient that the clamp 20 positions and holds the cables 12,14,16 together, and the actual pulling of the cables 12,14,16 through the borehole is accomplished by pulling on the actual cable or cable bundle. A number of clamps 20 distributed evenly spaced along the cable length will ensure that the cable does not touch the inner walls of the borehole when pulling. In other variants of the pulling through the boreholes, one will in addition to or exclusively, transmit the pulling forces to the cables indirectly via the clamps 20, i.e. one does not pull the cable 12,14,16 itself, or only parts of the pulling forces are applied to the cable, 12,14, 16 directly. A number of clamps 20 will ensure that one gets many engagements with the cable in the longitudinal direction, and the load on the cable 12,14,16 will not be as large. In these variants it is important to ensure a strong and adequate fastening and clamping of the clamp 20 to the cables 12, 14, 16 and this is ensured by a cooperation between the clamping element 22 and the insertion element 24. The solution, according to the invention, results in great flexibility as the clamping element 22 can be made in a limited number of sizes, while one can easily make the insertion elements 24 in many more shapes and sizes. Thus one can use a clamping element 22 of a given size in several different cable dimensions 12, 14, 16 in that one adjusts the shape and size of the insertion element 24 to the relevant clamping element 22 and cables 12,14,16.

Figure 1 shows a solution where friction reducing means 28 is provided directly on the clamp 20. Figure 3 shows the clamp 20 of figure 1 in more detail. In the perspective outline two main elements are shown; namely, the clamping element 22 and the insertion element 24. The clamping element 22 is preferably provided with lugs so that they can be clamped together with a clamping device 26. Furthermore, one can see the clamping device 26 and a number of friction-reducing means 28.

Figure 2 shows an alternative embodiment of a number of clamps 20 which encloses a number of cables 12, 14,16. The insertion element 24 holds the cables in place, and the clamping element 22 clamps together the insertion element 24 against the cables.

Figure 4 shows a cross section of clamp 20 as shown in the assembly in figure 2. One can see how the cables 12,14,16 are held in place and clamped together by the insertion element 24. The clamping element 22, which extends along the entire perimeter of the insertion element 24, is shown only in part in the figure to illustrate that when, clamping together, it partially presses down in the more flexible and softer insertion element 24 so that an evenly distributed pressure is exerted against the cables 12,14,16. The embodiment of the invention that is shown in figures 2 and 4 shows that the friction reducing means 28 is not arranged on the clamp 20, but is arranged on the coupling elements 30 which extend along the longitudinal direction of the cables 12,14,16, and which connects the various clamps 20 together. To connect clamps 20 together by means of coupling elements 30 (for example, rails 30) is important for embodiments where it is desirable to distribute the pulling forces (by pulling the cable through a borehole) evenly along the cable. Coupling elements 30 with friction reducing means 28 can, of course, be used if one wants to pull directly on the cable or cable bundle. It is preferred to use more than one coupling element 30, and an arrangement with two, three or fire longitudinal coupling elements, is often

advantageous.

The insertion element 22 consists preferably of only one part, but can also be constructed of several parts. For example, one can use multiple parts, to obtain a better fitting for cables of a smaller circumference, i.e. one has a first member to accommodate a limited number of sizes/shapes of the clamping element 24, and then one has further insertion elements inside for adaption if the cables are thin. Furthermore, the insertion element 24 can be comprised of several sectors in the axial direction. By pulling and positioning a number of cables in a borehole in a rock formation, it is also often required to lead other cables other than the power cables through the borehole. This may be for communication or to monitor the advancement and the shape of the borehole. In the insertion element 22 there are recesses adapted to accommodate such additional equipment, such as, for example, one or more fibre optic cables 32.