GB2376041A

GB2376041A - Mounting ladder on overhead cables

Info

Publication number: GB2376041A
Application number: GB0113075A
Authority: GB
Inventors: Simon Neve
Original assignee: Balfour Beatty PLC
Current assignee: Balfour Beatty PLC
Priority date: 2001-05-30
Filing date: 2001-05-30
Publication date: 2002-12-04
Anticipated expiration: 2021-05-30
Also published as: GB2376041B; GB0113075D0

Abstract

A ladder arrangement is provided for working on overhead cables. A ladder (24) extends between two cable supports (20,22), each cable support enabling the cable support to move along a cable (10,12). An adjuster (34,36,38) enables adjustment of the spacing between the cable supports (20,22). The ladder arrangement can easily be mounted at the location of a pylon, and then moved to the desired location for work on the cables, for example installation of a spacer.

Description

LADDER ARRANGEMENT This invention relates to a ladder arrangement, in particular for working on overhead transmission cables.

There are various maintenance operations which require a linesman to gain access to the cables (each cable carrying a different phase) of an overhead transmission system. As one example, it may be desirable to provide insulating spacers between the different cables, to provide fixed spacing between the cables, and thereby prevent accidental contact between them. This could otherwise arise in the event of different cables sagging by different amounts. This may for example be caused by the build up of snow or ice on the cables.

It is now common procedure to insert these spacers between cables in existing systems which were originally constructed without using spacers. In order to insert the spacers between cables, a so-called"MEWP" (Mobile Elevated Work Platform) has conventionally been used. The platform is driven to the required location to allow the linesman to insert the spacer. The platform must then be driven to the location of the next required spacer.

This approach is time consuming and uses expensive machinery. Furthermore, it may be difficult to provide access for the MEWP to the location of the overhead cables.

According to the invention, there is provided a ladder arrangement comprising a ladder extending between two cable supports, each cable support comprising a mounting arrangement which enables the cable support to move along a cable, and wherein an adjuster is provided to enable adjustment of the spacing between the cable supports.

The invention provides a ladder which can be mounted on two cables by mounting arrangements, for example rollers or a sliding arrangement, so that the ladder can

easily be mounted at the location of a pylon, and then moved to the desired location for installation of a spacer. The spacing between the mounting arrangements is adjustable so that the ladder arrangement can be used to provide the correct spacing between cables to enable easy installation of a spacer of fixed dimensions. This also allows the ladder arrangement to be used for installation of different sized spacers for different overhead transmission systems.

Preferably, one end of the ladder is fixed to one cable support and a portion of the ladder nearer the other end of the ladder is fixed to a first portion of the adjuster, a second portion of the adjuster being fixed to the other cable support. In this way, one coupling between the ladder and the mounting arrangement is through the adjuster, so that a compact and easy to use adjuster design can be achieved. For example, the adjuster may comprises a threaded shaft, rotation of which varies the distance between the first and second portions of the adjuster. A handle is then provided for the linesman to rotate to effect adjustment of the spacing between the cables.

A platform is preferably provided at one end of the ladder. Thus, when installing the spacer, the linesman will stand on the platform for carrying out connection to the lower phase, and will stand on the ladder for carrying out connection to the upper phase.

A control rope assembly is preferably provided for controlling the movement of the ladder arrangement along the cables.

The invention also provides a method of installing a spacer between cables of an overhead cable system, the method comprising: mounting a ladder arrangement between the cables, suspended by the cables, the ladder arrangement being supported on the cables by means of mounting arrangements which enable the ladder arrangement to move along the cables; moving the ladder arrangement along the cables until the desired location of a spacer is reached;

attaching the spacer between the cables.

This method enables a simple portable ladder arrangement to be used to fit spacers between cables. The ladder can be mounted at the pylon locations, avoiding the need for expensive and bulky lifting equipment.

The spacing between the cables may adjusted before attaching the spacer so that the spacing corresponds to the spacer dimensions, the adjustment being carried out by operating an adjuster of the ladder arrangement which enables adjustment of the spacing between the mounting arrangements. The ladder arrangement in this way can be adjusted for different spacings. The adjustment can also be used to allow for differential in sag between two phases.

The ladder is preferably moved along the cables by releasing a control rope connected to the ladder arrangement. This provides controlled descent of the ladder arrangement towards the central sag in the cable span, and allows the ladder to be returned to the pylon for dismounting. Guide rollers may be mounted for the retrieval rope at regular intervals as the ladder arrangement is moved along the cables.

An example of the invention will now be described in detail with reference to the accompanying drawings, in which: Figure I shows the ladder arrangement of the invention being used by a linesman for installing a spacer between cables of an overhead transmission system; Figure 2 is used to explain the order of installation of spacers when four spacers are required between pylons; Figure 3 is used to explain the order of installation of spacers when three spacers are required between pylons; and Figure 4 is used to explain the order of installation of spacers when two spacers are required between pylons.

Figure 1 shows the ladder arrangement of the invention being used by a linesman for installing a spacer between cables of an overhead transmission system. Two cables 10,12 are shown, which may comprise the top and middle phases of a three- phase system. A spacer 14 has been mounted between the cables 10,12. The spacer is mounted around protective clamps 13 (called armour rods) which provide local strengthening and protection of the cables. The spacer design will be well known to those skilled in the art, and typically comprises a ceramic insulator.

The linesman 16 stands on the ladder arrangement 18 for mounting the spacer 14.

The ladder arrangement 18 has two cable supports 20,22 so that the ladder 24 extends between the two cables. The top end of the ladder 18 is provided with one cable support 20, whereas the other cable support 22 is provided towards the bottom end of the ladder 24. The bottom end of the ladder extends beyond the cable support 22 and is provided with a platform 26, so that when the linesman stands on the platform 26, the lower end of the spacer 14 can easily be attached to the lower cable 12. The linesman 16 is connected to one end of a safety line 17, the other end of which may be connected either to the ladder arrangement, for example to the upper cable support 20, or to an earth wire trolley associated with an earth cable.

Each cable support has a roller arrangement 28 to enable the cable support to roll along the cable. In the example shown, the upper cable support 20 has two pairs of rollers, to maintain the ladder 24 perpendicular to the cable 10, whereas the lower cable support has only one pair of rollers. The two cable supports 20,22 thereby enable the complete ladder assembly to roll along the span between pylons.

The ladder arrangement is mounted on the cables at the location of a pylon. A control rope 30 is connected to the upper cable support 20 and is used to control the release of the ladder arrangement from the pylon, and to enable the ladder arrangement to be pulled back to the pylon. A rope may also be connected to the lower end of the ladder arrangement (not shown) so that an operator on the ground can ensure the ladder remains upright as the ladder arrangement is moved.

As the ladder arrangement is rolled away from the pylon, guide blocks 32 may be mounted at fixed intervals (for example every 20m) to provide free movement of the control rope 30.

The ladder arrangement is provided with an adjuster 34 to enable adjustment of the spacing between the cable supports 20,22. The adjuster extends between the lower cable support 22 and a mounting portion 36 at which the adjuster 34 is connected to the ladder 24. In this way, the coupling between the ladder 24 and the lower support 22 is through the adjuster 34. The adjuster comprises a threaded shaft 38, rotation of which varies the distance between the rollers 28 of the cable support 22 and the mounting portion 36. A handle 40 is provided for the linesman to rotate to effect adjustment.

The adjuster enables the ladder to be used to provide the correct spacing between cables to enable easy installation of the spacer of the required dimensions. This also allows the ladder arrangement to be used for installation of different sized spacers for different overhead transmission systems.

Figure 2 is used to explain the order of installation of spacers when four spacers are required between pylons 50. The ladder arrangement is mounted between the top pair of cables so that it is suspended by the cables. The ladder is mounted at the location of a pylon 50, avoiding the need for lifting equipment. Instead, the ladder arrangement can be lifted using ropes and pulleys, for example using the so-called "endless rope method"with secure attachment to the pylon.

The specific mounting method for the ladder arrangement will be different depending on the type of pylon. For example, a different procedure will be adopted at a line tower than at an angle tower.

After the ladder arrangement has been mounted, it is rolled along the cables into the sag of the cables until the desired location of a spacer is reached. This is under the

control of the control wire 30. The guide blocks 32 are mounted as the ladder arrangement is rolled along the span.

The spacer is then attached between the cables. This involves fitting the preformed armour rods and then attaching the two ends of the spacer. As the ladder arrangement can not roll past a spacer, the spacers are attached in the order A to D in Figure 2, with spacers A and B being mounted from pylon 50a and spacers C and D being mounted from pylon 50b. The control rope assembly is used to retrieve the ladder arrangement, and the guide blocks are removed during this operation.

During fitting of the spacer, the adjuster is used to set the spacing to correspond to the spacer dimensions, and the adjustment can also be used to allow for differential in sag between two phases, which again may require different spacer sizes.

Figures 3 and 4 show the order in which spacers may be mounted when 3 and 2 spacers are required in a span. Again the spacers are mounted in alphabetical order.

Various modifications will be apparent to those skilled in the art. For example, although roller arrangements have been described, the attachment to the cables may be through a sliding connection. Essentially, the invention provides a ladder arrangement which can be mounted at the location of a pylon and which can then be guided to the desired spacer location, and sets the spacing between cables to the desired level.

Claims

1. A ladder arrangement comprising a ladder extending between two cable supports, each cable support comprising a mounting arrangement which enables the cable support to move along a cable, and wherein an adjuster is provided to enable adjustment of the spacing between the cable supports.

2. A ladder arrangement as claimed in claim 1, wherein one end of the ladder is fixed to one cable support and a portion of the ladder nearer the other end of the ladder is fixed to a first portion of the adjuster, a second portion of the adjuster being fixed to the other cable support.

3. A ladder arrangement as claimed in claim 2, wherein the adjuster comprises a threaded shaft, rotation of which varies the distance between the first and second portions of the adjuster.

4. A ladder arrangement as claimed in any preceding claim, wherein each mounting arrangement comprises a roller arrangement.

5. A ladder arrangement as claimed in claim 4, wherein each roller arrangement comprises at least two rollers for mounting on opposite sides of a cable.

6. A ladder arrangement as claimed in any preceding claim, further comprising a platform at one end of the ladder.

7. A ladder arrangement as claimed in any preceding claim, further comprising a control rope assembly for controlling the movement of the ladder arrangement along the cables.

8. A method of installing a spacer between cables of an overhead cable system, the method comprising:

mounting a ladder arrangement between the cables, suspended by the cables, the ladder arrangement being supported on the cables by means of mounting arrangements which enable the ladder arrangement to move along the cables; moving the ladder arrangement along the cables until the desired location of a spacer is reached; attaching the spacer between the cables.

9. A method as claimed in claim 8, wherein the ladder arrangement is mounted at the location of a pylon.

10. A method as claimed in claim 8 or 9, wherein the spacing between the cables is adjusted before attaching the spacer so that the spacing corresponds to the spacer dimensions, the adjustment being carried out by operating an adjuster of the ladder arrangement which enables adjustment of the spacing between the roller arrangements.

11. A method as claimed in any one of claims 8 to 10, wherein the ladder is rolled along the cables by releasing a control rope connected to the ladder arrangement.

12. A method as claimed in claim 11, wherein guide rollers are mounted for the control rope at regular intervals as the ladder arrangement is rolled along the cables.