GB2431779A

GB2431779A - Replacing an overhead powerline

Info

Publication number: GB2431779A
Application number: GB0518888A
Authority: GB
Inventors: Simon Harry Neve
Original assignee: Balfour Beatty PLC
Current assignee: Balfour Beatty PLC
Priority date: 2005-09-15
Filing date: 2005-09-15
Publication date: 2007-05-02
Anticipated expiration: 2025-09-15
Also published as: GB0518888D0; GB2431779B

Abstract

An apparatus for use in the replacement of a conductor (1, Fig 1) between a pair of towers (A,B, Fig 1) has a support cable (8, Fig 1) and a plurality of support blocks (14, Fig 1) for fixing to the support cable (8, Fig 1) and for use in supporting the conductor to be replaced (1, Fig 1) when tension in the conductor (1, Fig 1) is reduced. The support blocks (14, Fig 1) have first 40 and second 42 members which are hinged together to define a closable chamber 46, with a roller 48 in the chamber 46. The second member 42 comprises a pair of claws 54,56 which are parallel and face opposite directions, a channel 60 being provided between the claws 54,56 for receiving a cable parallel with the claws 54,56, and wherein the support block (14, Fig 1) is rotatable with respect to a cable received in the channel into a gripped orientation in which cable portions (8, Fig 1) are retained beneath the claw ends. This apparatus uses a lightweight support block (14, Fig 1) which is easily lifted to the top of the tower (A,B, Fig 1). Furthermore, the block (14, Fig 1) is attached to the support cable (8, Fig 1) by a simple push and twist operation, pushing the channel 60 between the claws 54,56 over the support cable (8,Fig 1), and then twisting the block (14, Fig 1) to grip the cable (8, Fig 1).

Description

1 2431779

METHOD OF REPLACING CONDUCTOR AND APPARATUS FOR USE IN SUCH A

METHOD

This invention relates to overhead power transmission systems, namely power transmission systems in which electrical conductors are supported along their length by towers, masts or other structures (hereinafter referred to simply as towers).

The invention can, in principle, be employed with systems of any voltage for example from 10 kV to 400 kV. Such systems are normally divided into a number of sections each of which corresponds to a single length of conductor or conductor set. At each end of a section, a tension tower both supports the conductor(s) and applies the correct tension to the lengths of conductor, while between the tension towers one or more suspension towers may be present whose purpose is simply to support the conductors with adequate ground clearance. in such systems, it may be necessary, from time to time, to replace one or more of the electrical conductors, for example because the original conductor has become damaged due to lightning, corrosion or for other reasons.

it is known to achieve this by reducing the tension in the conductor, attaching a running out block at each tower and supporting the conductor by the running out blocks, connecting a new conductor to the old conductor, and pulling the old conductor in along the length of the section so that, once the old conductor has been pulled in, the new conductor extends along the length of the section. The new conductor can then be tensioned correctly (sagged) by applying the correct tension to the conductor at one or each section end, and supported at each tower by the insulators.

While such a procedure may be employed along most of the path of the transmission system, it cannot be employed where the conductor spans buildings, roads or other rights of way or lower voltage overhead lines, without additional safety procedures being adopted.

For a long time, the practice had been to build scaffolding across such areas in order to prevent any interference to traffic, people, or other overhead systems caused by the conductor as the tension is reduced and the conductor height falls below the minimum required ground clearance. However, the cost of erecting scaffolding is extremely high.

GB 2 311 899 discloses a method of replacing an old conductor with a new conductor between a pair of towers, in which a supporting cable is first extended between the towers, and is suspended beneath the conductor to be replaced. When the tension in the conductor is lowered, the supporting cable supports the conductor and limits the sagging of the conductor. An end of the new conductor is then attached to an end of the old conductor, and the old conductor is pulled in. This method does not require the erection of scaffolding in order to provide protection to traffic or other personnel below the span of the conductors, and provides a relative]y simple procedure for replacing a conductor. This method is termed below the "catenary support system".

Supporting blocks, termed "catenary blocks" are used initially to suspend the supporting cable from the conductor, and then after the tension is reduced, to support the loosened conductor from the supporting cable. These blocks may be spaced at Sm intervals. One problem with this system is that the supporting cable must be strong enough to support the weight of all of the blocks and the conductor.

The catenary blocks are conventionally metal components, having two compartments which are hinged open. One is for receiving the supporting cable and the other is for receiving the old conductor (which is connected to a new conductor). In addition, the fitting of the catenary blocks takes place at the top of a tower (because they cannot pass through running-out blocks) and their weight and design makes this a difficult operation.

According to the invention, there is provided apparatus for use in the replacement of a conductor between a pair of towers, the apparatus comprising: a support cable; and a plurality of support blocks for fixing to the support cable, and for use in supporting the conductor to be replaced when tension in the conductor is reduced, wherein the support blocks each comprise first and second plastics body members which are hinged together to define a closable chamber, with a roller received in the chamber, and wherein the second plastics body member comprises a pair of claws which are parallel and face opposite directions, a channel being provided between the claws for receiving a cable parallel with the claws, and wherein the support block is rotatable with respect to a cable received in the channel into a gripped orientation in which cable portions are retained beneath the claw ends.

This apparatus uses a lightweight support block which is therefore easily lifted to the top of the tower and also reduces the required load carrying capability of the support cable. Furthermore, the block is attached to the support cable by a simple push and twist operation, pushing the channel between the claws over the support cable, and then twisting the block to grip the cable.

Once in place, the conductor can then be inserted into the chamber. This provides a secure attachment of the block to the support cable, because the conductor and the support cable are very resistant to loealised twisting. The conductor and the support cable are in parallel, and this prevents rotation of the support block to become released from the support cable.

The support block is preferably rotatable by 90 degrees with respect to a cable received in the channel.

At least one of the claws may comprise a sprung locking mechanism for retaining a cable in the gripped orientation after the relative rotation. Also, the first and second plastics body members are preferably lockable with the chamber closed by a spring loaded catch.

The first and second plastics body members may be fonried of Nylon, for example Nylon 6.

The support cable may comprise a Kevlar cable core (for example formed of Ararnid (Trade Mark) having a plastics (polyurethane) coating. This provides a light weight support cable design, which in turn enables the tug power to be reduced.

The support cable may comprise a plurality of collars spaced along the length of the cable for locating the support blocks. The collars may be formed of a plastics material and can be overmoulded over the support cable.

For example, a single collar can be provided for the location of each support block, and wherein the claws grip the support cable around the collar in the gripped orientation.

The invention also provides a method of replacing an old conductor with a new conductors in a span between towers, comprising: putting into place a supporting cable, attaching support blocks to the supporting cable, and connecting the support blocks to the old conductor, thereby suspending the Supporting cable from the old conductor; releasing the tension in the old conductor, thereby suspending the old conductor from the Supporting cable using the support blocks; connecting a new conductor to an end of the old conductor; pulling out the old conductor and thereby pulling in the new conductor, with the old and new conductors suspended from the support cable using the support blocks, wherein attaching support blocks to the supporting cable comprises fitting a clawed end of the support blocks to the supporting cable using a push and twist operation.

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a span of an overhead power transmission system as a supporting cable is being passed out along the old conductor using a known method; Figure 2 is a schematic view of the span once the supporting cable has been installed; Figure 3 is a schematic view of the span as the new conductor is being pulled in; Figure 4 shows support block of the invention for use in the system and method of Figures 1 to 3; and Figure 5 shows a support cable of the invention for use in the system and method of Figures 1 to 3.

The known method of replacing an overhead conductor will first be described with reference to Figures 1 to 3. Further details can be found in GB 2 311 899.

As shown in Figure 1, a section of conductor I includes a span that extends between two towers A and B and which passes over a right of way (not shown) that requires protection from any restringing operation. After securing insulator units 2, fixing line ladders 4 and installing running-out blocks 6 at the tower, a supporting cable 8 is fed out from a rope drum 10 located in the region of Tower A. The supporting cable 8 is passed through the running-out block 6 and along the span of the old conductor 1. A tug unit 12 is located on the old conductor at tower A, and the supporting cable 8 is attached to it. The supporting cable 8 is provided with a number of catenary-blocks 14 attached thereto at intervals of about 5 to 25 metres along its length according to a pre-prepared schedule. Thcse are hooked onto the conductor 1 as soon as the supporting cable passes through the running-out block 6. As the tug unit 12 travels along the conductor span between the towers, the supporting cable 8 is paid out from the drum 10, and additional catenary-blocks 14 are hooked onto the conductor.

When the tug unit 12 has arrived at tower B, the supporting cable 8 is unhooked from the tug unit 12 and attached to the end of the insulator unit 2 by means of a temporary sheathed rope catch-off device, and the tug unit is removed by means of a lifting rig. As shown in Figure 2, the supporting cable 8 is then passed through an Ansel-Jones block 20, is passed down to ground, and is anchored to the ground by means of an anchor sledge 22 via a tirfor 24. The Ansel-J ones block 20 is held out from the insulator unit by means of a sling attached to the tower so that the block is separated from the conductor both laterally and vertically by at least 0.5 metres in order to allow the catenary-blocks to rotate. The anchor sledge is positioned in line with the conductor 1 and at a position located from tower B by a distance of at least twice the height of the tower. At tower A, the supporting cable 8 is also anchored to the ground by means of another ground anchor sledge 25. The supporting cable 8 is then tensioned by means of the tirfor 24 so that it becomes self-supporting, and the catenary-blocks 14 rotate by part of a revolution.

Once the section has been prepared for re-stringing, including attaching one end of a new conductor 26 to the end of the old conductor 1 by means ofjoint 28 at one end of the section, the tension in the conductor 1 is reduced, thereby allowing the conductor to sag between the other towers in the section. Between towers A and B, the conductor 1 is supported by the supporting cable 8 and the catenary-blocks 14, causing the catenary-blocks to rotate further until they have rotated by 180 degrees, as shown in Figure 3. The old conductor I is then hauled in at the other end of the section causing the new conductor 26 to travel along the length of the section, and to pass through the catenary blocks 14 between towers A and B. When the new conductor 26 has reached the tension tower at the beginning of the section, the old conductor is removed and the new conductor is terminated in accordance with conventional procedure. The new conductor is then hung on the insulator units of the towers, and is tensioned until the correct tension has been achieved.

During this operation, the catenary-blocks 14 will rotate back part of a revolution as the new conductor 26 becomes self-supporting.

When the new conductor 26 has been correctly tensioned, the tension in the supporting cable may be reduced, thereby causing the catenary-blocks 14 to rotate back under their weight and the weight of the rope 8 until the rope 8 hangs underneath the new conductor. A brake unit is then placed on the conductor 26 and attached to the end of the supporting cable 8. The rope 8 is winched back onto the rope drum 10 while the brake unit ensures that the correct tension is applied to the rope 8 during this operation. Finally, when the rope 8 has been hauled in, the brake unit and the other items of installation equipment such as the running out blocks 6 and the ladders are removed, and the tension in the new conductor is checked and adjusted if necessary using the nomal method.

This invention concerns the design of the support blocks, namely the so-called "catenary blocks" 14.

Figure 4 shows an example of support block 14 of the invention, with four views, two of which are cross sections.

The support block 14 is for fixing to a support cable and for supporting the conductor to be replaced when tension in the conductor is reduced, as described above.

The support block comprises first 40 and second 42 plastics body members which are hinged at hinge 44, to define a closable chamber 46. A roller 48 is received in the chamber supported on an axle 50. The axle 50 and roller 48 are fixed to the body member 40 and open with it, thereby revealing the area 46b, which is for receiving the old conductor. The area 46a is not accessed in use.

A spring loaded release mechanism 52 is used to open the chamber 46. The second plastics body member 42 has a pair of claws 54,5 6 which are parallel and face opposite directions. Each claw defines a slot (the slot 56a can be seen most clearly in the Figure).

The ends of the two slots comprise a circular opening (the opening 56b can be seen most clearly in the Figure), and these are aligned on a common axis 58.

A chanjiel 60 is defined between the claws for receiving a cable parallel with the claws 54,56, aligned in the direction of arrow 62. Once the cable is received in the base of the channel 60, by a pushing operation, the support cable and the support block are rotated relative to each other by 90 degrees into a gripped orientation. In practice, this involves rotation of the support block 14, as the support cable is partially tensioned as shown in Figure 1. This provides a simple way of applying the support blocks to the support cable.

In the gripped position, cable portions are retained beneath the claw ends, and the orientation of the support cable is as shown by arrow 64.

This provides a lightweight support block which is therefore easily lifted to the top of the tower and also reduces the required load carrying capability of the support cable.

The block is attached to the support cable by a simple push and twist operation, pushing the channel between the claws over the support cable, and then twisting the block to grip the cable.

This also provides a secure attachment of the block to the support cable, because the conductor and the support cable are very resistant to localised bending. The conductor and the support cable are in parallel, and this prevents rotation of the support block to become released from the support cable.

Once the support block is in place, the old conductor to be replaced can be inserted into the chamber 46b, by opening the enclosure and closing it around the conductor.

During this time, the support block is suspended from the support cable, and this is therefore not a heavy operation.

During the pulling out of the support cable, the orientation of the support block is as shown in Figure 4, with the conductor above the support cable. However during the subsequent conductor replacement (as shown in Figure 3), the support blocks are in the opposite orientation, with the conductor running over the roller 48, and beneath the support cable.

The rotation of the support blocks between these two positions need to take place in the same angular direction, to avoid twisting of the support cable and the conductor. The conductor is free running in the space 46b, and the support block may be designed not to grip the support cable tightly to prevent any local twisting forces. However, the support block is also not in a balanced orientation with respect to the axis 64 when vertical.

Instead, rotation about the axis 64 is biased by the weight of the release mechanism 52 to one rotational direction only, and this can ensure that the support blocks all rotate the same way between the orientation of Figures 1 and 3.

As mentioned above, the fact that the conductor and the support cable are parallel provides retention of the support block on the support cable. In addition, at least one of the claws may comprise a sprung locking mechanism for retaining a cable in the gripped orientation after the relative rotation. A release handle enables the support cable to be subsequently released from the opening 56b. This mechanism is shown schematically as 66, and in one view only of Figure.4 The spring loaded release mechanism 52 of the main bodies is shown in most detail in section B-B. As shown, the mechanism 52 comprises a push switch 70 which pushes a locking pin arrangement 72 out of locking engagement between the two bodies 40,42. The main part of the mechanism 52 is an integral part of the body 40, and which houses the locking pin arrangement 72.

The first and second plastics body members 40,42 can be formed of Nylon, for example Nylon 6 or Nylon 66.

The weight of the equipment can also be reduced by forming the support cable as a non-metal component.

As shown in Figure 5, in one example, the support cable comprises a Keviar cable core 80, for example formed of Aramid (Trade Mark) and having a diameter of 13mm. A plastics, polyurethane coating 82 has a thickness of 1.5mm. This provides a light weight support cable design, which in turn enables the tug power to be reduced.

The support cable has plurality of collars 84 spaced along the length of the cable for locating the support blocks. The collars 84 are formed of a plastics material and are overmoulded over the support cable, and form a heat bond with the coating 82.

A single collar 84 can be provided for the location of each support block 14. The collar can have a larger diameter than the opening on each side face of the claws (one of these openings is shown as 56b in Figure 4). Thus, the collar 84 can be retained between the claws. The collar does not need to be as narrow as the width of channel 60 if the claws 54,5 6 are not uniform. The claws can have outer parts shaped to grip the support cable and inner parts which are shaped to grip or surround the collar 84.

The invention is applicable to the replacement of phase conductors or ground wires in a system.

In some cases, the supporting cable or cables may be pulled out along the old conductor, and pulled back in again, by means of a rope extending to the ground. In some cases, however, this may not be appropriate, for example where the span crosses a busy road, in which case the support rope will be pulled out by means of a tug unit, as shown above. The tug units comprise a petrol motor that is located in a housing and powers one or more drive wheels that are arranged to sit on the conductor. The unit includes a braking mechanism and a control device, so that it can be made to travel along the conductor under its own power in order to pull a rope or other device along the conductor.

The supporting cable is preferably insulating since this enables the method to be conducted single circuit live, that is to say, where the towers support a pair of three phase circuits, one of the circuits may be on load while the other circuit is being repaired. Also, the use of an insulating rope enables the method to be used where the conductors span another overhead system, e.g. an 11, 33 or 66 kV system, without the need for an outage on the other system. However, this is not essential, and the support blocks of the invention could also be used with conducting support cables.

Various other modifications will be apparent to those skilled in the art.

Claims

Claims: I. Apparatus for use in the replacement of a conductor between

a pair of towers, the apparatus comprising: a support cable; and a plurality of support blocks for fixing to the support cable, and for use in supporting the conductor to be replaced when tension in the conductor is reduced, wherein the support blocks each comprise first and second plastics body members which are hinged together to define a closable chamber, with a roller received in the chamber, and wherein the second plastics body member comprises a pair of claws which are parallel and face opposite directions, a channel being provided between the claws for receiving a cable parallel with the claws, and wherein the support block is rotatable with respect to a cable received in the channel into a gripped orientation in which cable portions are retained beneath the claw ends.

2. Apparatus as claimed in claim 1, wherein the support block is rotatable by degrees with respect to a cable received in the channel.

3. Apparatus as claimed in claim 1 or 2, wherein at least one of the claws comprises a sprung locking mechanism for retaining a rotated cable in the gripped orientation.

4. Apparatus as claimed in any preceding claim, wherein the claws extend from an end face of the support block.

5. Apparatus as claimed in any preceding claim, wherein the first and second plastics body members are lockable with the chamber closed by a spring loaded catch.

6. Apparatus as claimed in any preceding claim, wherein the first and second plastics body members are formed of Nylon.

7. Apparatus as claimed in claim 6, wherein the first and second plastics body members are formed of Nylon 6.

8. Apparatus as claimed in any preceding claim, wherein the support cable comprises a Kevlar cable core having a plastics coating.

9. Apparatus as claimed in claim 8, wherein the core has a diameter of 10- 20mm, and the coating has a thickness of 1-5mm and is formed of polyurethane.

10. Apparatus as claimed in claim 8 or 9, wherein the support cable comprises a plurality of collars spaced along the length of the cable for locating the support blocks.

11. Apparatus as claimed in claim 10, wherein the collars are formed of a plastics material and are overnioulded over the support cable.

12. Apparatus as claimed in claim 10 or 11, wherein a single collar is provided for the location of each support block, and wherein the claws grip the support cable around the collar in the gripped orientation of the cable.

13. A method of replacing an old conductor with a new conductors in a span between towers, comprising: putting into place a supporting cable, attaching support blocks to the supporting cable, and connecting the support blocks to the old conductor, thereby suspending the supporting cable from the old conductor; releasing the tension in the old conductor, thereby suspending the old conductor from the supporting cable using the support blocks; connecting a new conductor to an end of the old conductor; pulling out the old conductor and thereby pulling in the new conductor, with the old and new conductors suspended from the support cable using the support blocks, wherein attaching support blocks to the supporting cable comprises fitting a clawed end of the support blocks to the supporting cable using a push and twist operation.

14. A support device for use in the replacement of a conductor between a pair of towers, for fixing to a support cable, and for use in supporting the conductor to be replaced when tension in the conductor is reduced, wherein the support device comprises first and second plastics body members which are hinged together to define a closable chamber, with a roller received in the chamber, arid wherein the second plastics body member comprises a pair of claws which are parallel and face opposite directions, a channel being provided between the claws for receiving a cable parallel with the claws, and wherein the support block is rotatable with respect to a cable received in the channel into a gripped orientation in which cable portions are retained beneath the claw ends.