GB2528683B - Support block for use in a method of replacing conductors, apparatus including the block and a method - Google Patents

Description

SUPPORT BLOCK FOR USE IN A METHOD OF REPLACING CONDUCTORS, APPARATUS INCLUDING THE BLOCK AND A METHOD

FIELD OF THE INVENTION

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).

BACKGROUND OF THE INVENTION

The invention relates to apparatus and methods of replacement of conductors which can, in principle, be employed with systems of any voltage for example from 10 kV to 400 kV. The invention relates in particular to systems in which each conductive path between towers is provided by multiple conductors, electrically in parallel. The use of multiple conductors in parallel increases the power carrying capabilities of the overhead system.

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 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 relatively simple procedure for replacing a conductor. This method is termed below the “catenary support system”.

This method works extremely well when a span includes a single conductor. If a span includes multiple conductors, the method can be applied one conductor at a time. However, this means that the time required for the replacement method scales linearly with the number of conductors to be replaced. For example, many systems use four conductors in parallel. It would be desirable to be able to reduce this time by operating on the conductors at the same time.

This issue has been recognised, and one solution which has been employed for four cable systems is to support so-called “quad catenary blocks” from the supporting cable (or supporting cables). These supporting blocks enable single units which are attached to the supporting cable (or cables) to support all four conductors at once, so that the tension in all four can be reduced at the same time. The supporting blocks can then be fed out and reeled in only once. This makes the process much more efficient, but original method still required the conductors to be pulled through one by one. A further complication arises when the number of new conductors is less than the number of old conductors. For example, advances in conductor technology may allow a smaller number of conductors to be used for the same electrical performance. Frequently, existing four conductor spans are being replaced with three conductors, and two conductor spans are being replaced with a single conductor. This means there is no longer a simple one-to-one connection between old conductors and new conductors. GB 2430016 discloses a connector designed specifically for making connections between four old connectors and three new connectors, as well as a new support block design. The connector has two one-two-one couplings and a two-to-one coupling. The support block is in the form of an enclosure split into three areas, so that the cables can be kept separate. The separating aspect of the design allows the blocks to be deployed and retrieved with the conductors in a flat formation. This prevents the conductors twisting around each other and clashing. Twisted conductors will not sit in the running out blocks correctly and could damage new conductor.

The three couplings of the connector are joined together for spans which do not require the catenary support system. However, when the catenary support system is to be used, the connector is split into its three couplings. This enables the different couplings to pass through running out blocks as well as to pass through their respective area of the support block enclosure.

Thus, the new conductors are installed one at a time for spans where the catenary support system is used, which again gives rise to a long installation process.

There is a need for a system which allows all the old cables to be reeled in and the new cables to be deployed together, even when catenary support blocks are used.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a support block for use in a method of replacing a set of overhead electrical conductors between a pair of towers, the support block being for supporting the set of conductors to be replaced when tension in those conductors is reduced, the support block comprising: an enclosure for receiving the set of conductors; and a gate for dividing the enclosure into sections, wherein the gate is movable between a closed position in which the sections are separated and an open position in which the enclosure is not divided into sections, and wherein the gate is biased into the closed position.

This support block enables coupled conductors to pass through as a single unit, including a coupling member, when the gate is open. When the gate is closed, separate compartments are defined.

The gate may divide the enclosure into three sections. For example, a first section can be for receiving an old conductor then a new conductor, a second can be for receiving an old conductor then a new conductor, and a third can be for receiving two old conductors then a new conductor. Thus, the block in this example is designed for a replacing four old conductors with three new conductors. The three new conductors each pass through a respective area of the enclosure.

The gate may have a hinged portion at the top of the enclosure. This can open when the coupling between conductors passes, and then close under gravity and optionally under an additional bias.

The gate may comprise a pair of downwardly extending arms, extending down from the hinged portion. This divides the enclosure into three. The arms may extend directly down (i.e. perpendicular to a top bar of the enclosure) or they may be angled.

Each arm preferably has a roller surface, and the the enclosure periphery has roller surfaces. These allow the smooth passage of cables when they come into contact with the edges of their respective areas. The enclosure may for example be substantially square.

The support block preferably has pair of cable gripping connections at the top of the support block for connecting the support block to a pair of support cables. These support cables are put in place to support the block, and multiple blocks are fixed at desired locations along the support cables.

Another aspect of the invention provides apparatus for use in the replacement of a set of conductors between a pair of towers, the apparatus comprising: a pair of support cables; a plurality of support blocks, each in accordance with the invention, for fixing to the pair of support cables, and for use in supporting the set of conductors to be replaced when tension in those conductors is reduced.

The apparatus may further comprise a connector block, having a set of four connectors at one side, symmetrical about a centre of the block, and a set of three connectors on the other side, symmetrical about a centre of the block.

The connector can thus be pulled by rolling the old conductors simultaneously around a drive drum, and it balances the tension applied to the three new conductors.

For example, the connector block may comprise five connectors extending between on opposite sides of the connector block. There are two at the outer edges of the block and two nearer the middle, symmetric about on in the centre. A plurality of intermediate spacing blocks may also be provided for fixing to the pair of support cables, between the support blocks. These ensure that in the event of a cable failure, a maximum height of the failed cable above the ground can still be maintained.

The intermediate spacing blocks may comprise a frame and a top roller which form a closed loop which can be opened and closed around the set of conductors, wherein the intermediate spacing block comprises a cable gripping connection at each end of the top roller for coupling to a respective one of the pair of support cables.

The roller allows the spacing block to be deployed without hanging below the conductors, so that maximum clearance can be maintained.

Another aspect of the invention provides a method of replacing a first set of old conductors with a second set of new conductors in a span between towers, wherein the method comprises: suspending a plurality of support blocks from a supporting cable or cables, each block comprising an enclosure for receiving the old set of conductors and the new set of conductors coupled together end to end by a connector block, and a gate for dividing the enclosure into sections; pulling out the first set of old conductors coupled to the second set of new conductors through the blocks at the same time, with the gate in an open position; and biasing the gate into the closed position after the coupling has passed through..

This method allows old conductors to be replaced with new conductors as one simultaneous operation, even when using a catenary support system.

The gate may start in the open position, and be triggered to close when the connector block passes through. However, preferably when the connector block passes through a block it causes the gate to move from an initial closed gate position to the open position to allow all the conductors and the connector block to pass through the enclosure. The gate then closes after the connector block has passed through.

BRIEF DESCRIPTION OF THE DRAWINGS

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 a system and method in accordance with the invention;

Figure 5 shows the support block and intermediate spacer in more detail; and

Figure 6 shows multiple spans having four old conductors replaced with three new conductors, and shows a coupling used in the process

DETAILED DESCRIPTION

The invention provides a catenary support block having an enclosure for receiving a set of conductors and a gate for dividing the enclosure into sections, wherein the gate is movable between a closed position in which the sections are separated and an open position in which the enclosure is not divided into sections, and wherein the gate is biased into the closed position. The gate allows coupled conductors to pass but also enables the conductors to be allocated individual spaces.

Before describing the invention, 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 and GB 2 430 016.

As shown in Figure 1, a section of conductor 1 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. These 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-Jones 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 of joint 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 1 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 normal method.

This known method works well for the replacement of single conductors. A known modification to the method described with reference to Figures 1 to 3 (for example as shown in GB 2 430 016) enables the replacement of four conductors in a more efficient manner than by replacement of each individual conductor in turn.

Two support cables can be used (in the form of ropes) to support closed shape catenary blocks which surround the conductors. The support cables are pulled out by a tug unit in sequence. The two support cables can be supported at one end as a single pilot rope. The catenary blocks for example comprise an essentially square enclosure, one side of which hinges open so that the block can be shut around the existing set of four conductors. The four inner faces are provided with rollers to facilitate the passing of the conductors through the blocks.

The blocks are again attached to the support cables at the top of the tower. However, the connections between the old conductors and the new conductors are made at ground level, and these connections pass through the running out block.

The connection between each old conductor and each new conductor can be by means of a swivel coupler connected to a stocking over the terminated ends of the old and new conductors. These swivel couplers can pass through the running out blocks.

In one design, the set of four conductors are arranged in a regular square, and therefore match the shape of the blocks. Similarly, the running out block has rollers arranged in the same configuration. A problem with this replacement technique is that, for the replacement of four old conductors with four new conductors, each conductor must be pulled in turn because separate connections are required, to enable the connections to pass through the running out block and the catenary blocks. A further improvement is to provide separate compartments for the different conductors to enable them to be arranged in a flat configuration. The separate compartments can be used to prevent tangling of conductors.

Any couplings between conductors have to pass not only over the running out blocks but also through the enclosure compartments. This makes it difficult to couple multiple conductors so that they can be reeled in by a single drum with the same load applied to each conductor.

The invention provides a modified catenary support block which enables the conductors to be arranged in a flat configuration.

Figure 4 shows a span in which the modified support blocks 42 are being deployed. The support blocks are supported by a pair of cables 40 in known manner.

Each support block 42 defines an enclosure for receiving the set of conductors. A gate 63 is provided for dividing the enclosure into sections, wherein the gate is movable between a closed position in which the sections are separated and an open position in which the enclosure is not divided into sections. The gate is biased into the closed position.

Figure 4 shows one support block with an open gate and one with a closed gate.

The example of Figure 4 has four old conductors 60 (to the left) and three new conductors 62 (to the right). A coupling 64 in the form of a connector block couples the old conductors to the new conductors.

In the closed configuration, there are three areas formed, a central area and two lateral areas. As shown in Figure 4, one old conductor passes through each lateral area and two pass through the central area. After the coupling 64 has passed through the block, there will be one new conductor in each area.

The gate enables the coupling 64 to pass through the enclosure. Furthermore, the coupling 64 is designed to be able to pass around the running out block 46. This is made possible by using a flat configuration, so that the coupling passes over the top of the rollers of the running out block. In this way, the conductors can all be pulled over the running out block as well as through the support blocks in parallel, both for spans using the catenary blocks and spans that do not need support. This increases the efficiency in the spans requiring support, and thereby improves the efficiency of the overall replacement programme.

Figure 4 also shows a new design of intermediate spacing block 80.

The support block with an open gate, the support block with a closed gate and intermediate spacing block are shown in more detail in Figure 5.

As shown most clearly for the open gate support block, the gate has a hinged portion 66 at the top of the enclosure. The gate 63 comprises a pair of downwardly extending arms 68, extending down from the hinged portion. In the example shown, each arm has a hinge connection 66, but of course the arms may have a cross link at top and a single hinge connection.

Each arm 68 has a roller surface, and the the enclosure periphery (top, bottom and two sides) has roller surfaces. The enclosure as defined without the gate is substantially square in the example shown, although this is just by way of example.

The support blocks have a pair of pigtail connections 70 at the top for connecting the support block to a pair of support cables. Other cable gripping arrangements may of course be used instead.

Figure 5 also shows the intermediate spacing block 80 for fixing to the pair of support cables 40, between the support blocks. The intermediate spacing block comprises a frame 82 (which may be rigid or flexible, such as a wire, rod or chain) and a top roller 84 which form a closed loop which can be opened and closed around the set of conductors. The intermediate spacing block comprises a cable gripping connection 86 at each end of the top roller for coupling to a respective one of the pair of support cables. This can also be a pigtail connection or any other cable gripping arrangement. The roller 84 allows the spacing block to be deployed without hanging below the conductors, so that maximum clearance can be maintained.

Figure 6 shows the process of replacing four old conductors with three new conductors for three spans. It also shows the coupling 64 in more detail.

The coupling 64 is in the form of a connector block, having a set of five connectors extending from one side to the other and a connecting bar over the top.

To make a connection between different numbers of conductors, different connectors are used on the opposite sides. For example, Figure 6 shows four of the connectors being used at one side, symmetrical about a centre of the block, and three of the connectors being used on the other side, also symmetrical about a centre of the block. There are three central one-to-one connectors 80 and two one-to-one edge connectors 82 at the outside edges. One central connector is in the middle and two offset connectors are symmetrically disposed to the sides of the central connector.

For the connection of four old conductors to three new conductors, the four old conductors are coupled to one side of the connector block, at the two edge connectors and the two offset connectors. The three new conductors are coupled to the other side of the connector block, at the two edge connectors and the central connector. In this way, the conductors are balanced on each side of the connector block.

There are thus five connectors in total, coupled together by a bar over the top, so that the five connectors can run over the top of a suitably spaced set of five pulley wheels.

In this example, three connectors are coupled to the new conductors on one side so that two connectors on this side are blank. Four connectors are coupled to the old conductors on the other side so that the central connector on this other side is blank. The three central connectors thus each provide termination to a respective conductor, whereas the edge connectors each provide a one-to-one coupling.

Although each side has five attachment points, all combinations from n conductors on one side (n<=5) to m conductors on the other side (m<=5) are possible, commonly desired connections being 4-3, 4-2, 3-2 and 2-1.

The connectors 80,82 are able to pass over the running out block 46 which has five pulley wheels for this purpose. Thus, the coupling 64 is able to pass over the running block 46 and also pass through the enclosure of the support block when the gate is open.

In Figure 6, one span 90 requires the catenary support (passing over a railway line) and the other two spans 92 do not.

The old conductors are pulled in by a motorized drum 94 which pulls all the cables simultaneously. The four old conductors are wound onto respective collection drums 96.

The new conductors are fed from respective delivery drums 98 and brought together at drum 99.

Drums 99 and 94 can be of the same design. Drum 94 functions as a pulling machine, for example with a pulling force of 50kN per conductor, 200kN total. Drum 99 functions as a tensioning machine, which causes resistance in the conductor to maintain ground clearance during pulling operations.

The invention also provides a method of replacing a first set of old conductors with a second set of new conductors in a span between towers. A plurality of the support blocks described above are suspended from the supporting cables. The first set of old conductors are pulled out when coupled to the second set of new conductors. The coupling, in the form of a connector block, passes through the blocks at the same time, with the gates in an open position, and the gates are then closed position after the connector block has passed through.

The example above has gates which start from an initial closed gate position and only open when the connector block passes through. However, they may be mounted in a latched open position so that the connector block does not need to open the gate. The connector block can then have a trigger mechanism to release the gate latch so that the gate closes after the connector block has passed through.

When the gate is closed, it defines three sections, a first for receiving an old conductor then a new conductor, a second for receiving an old conductor then a new conductor, and a third for receiving two old conductors then one new conductor.

The example above shows how blocks which enclose a set of conductors can be for the replacement of four old conductors with three new conductors. Other combinations can be used. More generally, the gate allows all the conductors to pass through, but when closed it can define any desired number of compartments to the enclosure.

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 or cables employed in the methods above may be electrically conducting, for example formed from steel, or may be electrically insulating, for example formed from a water-blocked stranded structure. 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.

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

Claims (14)

1. A support block for use in a method of replacing a set of overhead electrical conductors between a pair of towers, the support block being for supporting the set of conductors to be replaced when tension in those conductors is reduced, the support block comprising: an enclosure for receiving the set of conductors; and a gate for dividing the enclosure into sections, wherein the gate is movable between a closed position in which the sections are separated and an open position in which the enclosure is not divided into sections, and wherein the gate is biased into the closed position.

2. A support block as claimed in claim 1, wherein the gate divides the enclosure into three sections.

3. A support block as claimed in claim 1 or 2, wherein the gate has a hinged portion at the top of the enclosure.

4. A support block as claimed in claim 3, wherein the gate comprises a pair of downwardly extending arms, extending down from the hinged portion.

5. A support block as claimed in claim 4, wherein each arm has a roller surface, and the the enclosure periphery has roller surfaces.

6. A support block as claimed in any preceding claim, wherein the enclosure is substantially square.

7. A support block as claimed in any preceding claim, comprising a pair of cable gripping connections at the top of the support block for connecting the support block to a pair of support cables.

8. Apparatus for use in the replacement of a set of conductors between a pair of towers, the apparatus comprising: a pair of support cables; a plurality of support blocks, each as claimed in any preceding claim, for fixing to the pair of support cables, and for use in supporting the set of conductors to be replaced when tension in those conductors is reduced.

9. Apparatus as claimed in claim 8, further comprising a connector block, having a set of five connectors, arranged symmetrically about a central connector.

10. Apparatus as claimed in claim 8 or 9, further comprising a plurality of intermediate spacing blocks for fixing to the pair of support cables, between the support blocks.

11. Apparatus as claimed in claim 10, wherein the intermediate spacing blocks comprise a frame and a top roller which form a closed loop which can be opened and closed around the set of conductors, wherein the intermediate spacing block comprises a cable gripping connection at each end of the top roller for coupling to a respective one of the pair of support cables.

12. A method of replacing a first set of old conductors with a second set of new conductors in a span between towers, wherein the method comprises: suspending a plurality of support blocks from a supporting cable or cables, each block comprising an enclosure for receiving the old set of conductors and the new set of conductors coupled together end to end by a connector block, and a gate for dividing the enclosure into sections; pulling out the first set of old conductors coupled to the second set of new conductors through the blocks at the same time, with the gate in an open position; and biasing the gate into the closed position after the connector block has passed through.

13. A method as claimed in claim 12, wherein when the connector block passes through a block it causes the gate to move from an initial closed gate position to the open position to allow all the conductors and the connector block to pass through the enclosure.

14. A method as claimed in claim 12 or 13, wherein the gate is for dividing the enclosure into three sections, a first for receiving an old conductor then a new conductor, a second for receiving an old conductor then a new conductor, and a third for receiving two old conductors then one new conductor.