GB2323974A - Insulating electrified railway overhead power-lines - Google Patents

Abstract

An overhead railway power supply line has a power-supply contact wire supported by a catenary wire mounted on a first region of a boom 22 via a support means 102. An insulating means 50 is placed immediately adjacent to where the support means 102 contacts the contact wire and between the support means 102 and a second region of the boom 22. The insulating means 50 may be a shroud means extending around the support means 102, which may be a pulley.

Description

IMPROVEMENTS IN AND RELATING TO ELECTRIFIED RAILWAY OVERHEAD POWER SUPPLY LINES This invention relates to improvements in the design of overhead power supply lines for electrified railway track, and in particular to preventing earthing.

Overhead electrical supply of power to electric trains has been in use for 50 or more years now. One problem which occurs with conventional overhead electrical power supplies for electric trains is that the live power supply can be shorted out by objects providing a short circuit between the live components and the grounded booms or gantries that carry the overhead live wires. Typically a live power supply contact wire is supported from a catenary wire, via droppers, the catenary wire passing over pulley wheels and having counterweights to support the weight of the catenary wire, the live wire, and the droppers. The pulley wheels are supported on overhead booms. The pulley wheels (or other catenary wire support) are insulated from the boom: the pulley wheels.

catenary wire, droppers and power supply contact wire, are all live, and the boom is earthed. Unfortunately, birds (or other conductors) can interpose themselves between the live pulley wheels and their earthed support booms, causing a short circuit, with the live components earthing at the pulley wheel, via the bird.

This can cause several problems. A current can be transmitted to the track which can ruin track signalling arrangements (where the rails of the track are used to transmit small signalling currents). The insulator block joints are designed to insulate signal currents and not the currents which would be generated by the overhead live wires shorting to the track, and can therefore be buried out by large currents induced by shorting.

A further problem can be that the short circuit can burn through one or more strands of the catenary wire, and eventually if there are repeated bird strikes at the same place, bring down the catenary wire and (and hence the power-supply wire). This can cost tens of thousands of pounds to put right, and inconveniences train timetables, and puts the lives of track-workers in danger by having them work on the track more frequently than may be necessary.

Each time that there is a short at a pulley wheel. for example due to a bird or squirrel, it is usual to send a team of four or five men out to patrol a seven-mile stretch of track looking for the reason for the short.

It is not possible to assume that it is safe to run trains following a short.

We need to identify the reason for the problem and be assured that the track/power supply is still safe. The identification of the cause of the short typically comprises looking for burned birds or animals by the side of the track and then looking for blackened pulley wheels nearby, followed by a check of the pulley wheel, catenary wire and power supply wire. All of this takes time and increases the down-time of that section of track.

Up until now the fact that bird strikes at pulley wheels will occur has simply been accepted: it is a fact of life.

We wish to challenge this acceptance.

According to a first aspect of the invention we provide an overhead railway power-supply line comprising a power-supply contact wire supported from a catenary wire, thc catenary wire in turn being supported by support means which is mechanically mounted at a first region of a boom via an insulating member, and in which insulating means is provided between the support means and a different, second, region of the boom immediately adjacent the part of the support means which contacts the power-supply contact wire, thereby eliminating the possibility of a short circuit between said part of said support means and said second region of the boom.

Preferably the insulating means is supported by the part of the support means that it contacts. Preferably the insulating rneans is provided on the straight line extending between the support means and the boom that has the shortest distance between the support means and the boom.

Because pulley wheels that support catenary wires are conventionally mounted on booms offset from the insulation between the mechanical connection to their support struts this perniits there to be a shortest distance straight line to the boom that does not pass through the mounting insulator, and this means that short circuits can be caused by bird strikes when the effective minimum distance between the live components and the earthed components is reduced by the presence of an object. We introduce an additional insulating means at that region.

It may be thought that fencing off the region of the boom adjacent the pulley wheel would be the easiest answer to preventing birds getting in where they are not wanted, but we prefer to provide an appropriate insulating barrier between the pulley wheel (or other catenary wire support) and the boom that mounts the support. Having a fence to keep out birds leaves the fence as a potential conductor, and we believe will be more expensive.

The support means will usually be a pulley wheel.

The insulating means may comprise shroud means adapted, in use, to extend adjacent or around, or substantially surround, the support means. Because a portion of the support means forms part of the shortest path from the live components to the earthed components surrounding the support means in an insulator reduces the risk of shorting between the live and earthed components.

The shroud means may be integrally formed from resilient material and may have one or more flexible regions adapted to be moved/displaced to enable the shroud means to be applied to (or over or around) the pulley wheel/support means. This provides a robust structure which is easy to manufacture and yet inexpensive. They may be a one-piece moulding.

Alternatively, but perhaps less preferably. the shroud means may be provided in a number of parts which are held together adjacent or around the support means (e.g. pulley wheel).

Preferably the shroud means has drainage means provided to allow water which may collect within the shroud means to escape.

A boom may, of course, support a plurality of catenary wires, and have a plurality of support means, in which case we would probably provide respective shroud means.

According to a second aspect of the invention we provide a method of reducing earthings of an overhead electrical railway power supply line comprising providing insulating means adjacent the pulley wheel (or other catenary wire support means) that supports a catenary wire.

Preferably, the insulating means is provided on the straight line that is the shortest distance from the catenary wire or its support means and the grounded support boom by which it is supported.

The method preferably comprises substantially entirely surrounding at least the lower regions of the pulley wheel with an insulating cover or shield, and preferably substantially surrounding the whole pulley wheel.

The method may comprise retro-fitting insulating means to existing electrical train power supply lines.

The method may comprise fitting the insulating means adjacent some, but not all, pulley wheels (or other catenary wire support means) of a line. There may be some parts of an electrified railway line which historically just do not suffer from bird strike, or vandal attack (e.g.

remote parts away from cities). It may be wasteful to retro-fit additional insulating means to such parts of a railway line. On the other hand there may be known "hot-spots" for bird strikes, or vandal-induced shorts. and the invention may be used there.

The method may include the step of selecting areas of the railway line that are particularly susceptible to shorting between the catenary/pulley wheel and the boom, and introducing the insulating means there, but not elsewhere on the line.

Preferably the method comprises fitting insulating means to the support means supporting the catenary Wire. This advantageous because it provides an insulating mcmber within the shortest path to earth from the live components.

Preferably the method comprises shrouding the support means with an insulating shroud means. This provides a convenient way fitting the insulator.

The method may comprise entirely, or substantially entirely, surrounding the support means within an insulating material, perhaps the shroud means.

A self supporting shroud means may be used to fit around the support means and support itself on the support means. This provides a convenient way of attaching the shroud means to the support means.

The shroud means may be fitted to the support means without the need for tools. A user may simply be able to manipulate the shroud means so that it can be passed onto the support means. An advantage of this is that the shroud means is quick and inexpensive to fit to the support means.

According to a third aspect of the invention there is provided an insulating member comprising a shroud means adapted, in use, to be fitted to and substantially shroud a supporting structure of overhead railway power-supply fines.

An advantage of such an insulating member is that it can be retrofitted to existing supporting structures to improve them or can be fitted to new supporting structures as they are assembled. Further, the use of such a member provides insulation within the shortest path from the live components of the ovcrhead railway power-supply line to earthed components and therefore reduces the chance of short circuits between these.

Of course, the supporting structure may or may not be live depending upon the position of other insulators.

The shroud means may be a one piece fabrication and may be fabricated from a resilient material (e.g. plastics material). These features provide a convenient way of fabricating the shroud means which result in an inexpensive article.

Further, the shroud means may be adapted, in use, to be slipped over an existing support means. The shroudishield may be clipped to the support means. The user may be able to manipulate the shroud means so that it fits over the support means and then cause or allow the shroud means to adopt a formation holding itself in place shrouding the support means. An advantage of such an operation is that the shroud means are simple to fit.

Should the shroud means be fabricated from a resilient material then the manipulation required to allow the shroud means to fit around, in use, a support means may be deformation of the shroud means. This provides a simple way of allowing the shroud means to be fitted.

The shroud means may define a chamber in which the pulley wheel is received in use.

The shroud means may be provided with a drainage channel allowing water entering the shroud means to escape. It is clearly disadvantageous to have water collecting around the live parts because its presence will cause them to corrode more rapidly, and it is a good conductor .

The drainage channel may feed to an additional housing member covering an opening in the shroud means. This ensures that there is no opening in the shroud means through which shorts can occur.

The housing member may have a sloping. e.g. concave (i.e. curved toward the inside of the housing member) wall ensuring that water cannot collect within the housing member: the slope helps drainage.

Engagement means may be provided to engage, in use, portions of the support means providing a way of securing the shroud means in place.

The engagement means may comprise surfaces defining hollow recesses provided in a body of the shroud means. These recesses may be adapted, in use, to receive portions of the pulley wheel (e.g. the axle) which engage the inner surface defining the recesses, so providing support-engaging portions of the shroud means.

The recesses may be cylindrical. Additionally, or alternatively, the recesses may comprise an elongate channel or groove, for example a wedge-shaped portion.

The shrouding means may be fabricated From polypropylene.

Alternatively, or additionally. other insulating materials may be used.

Preferably the shroud means is substantially imperforate. It is of course, undesirable to have openings in an insulating member through which shorts could occur to the earthed structure of the railway powersupply lines.

The shroud means may be generally cylindrical in shape and may have an opening at a top portion allowing, in use, a support means to be received into the shroud means. The opening may be enlargeable during the fitting of the shroud to the pulley wheel (support means).

The radius of the shroud means may be substantially between 75mm and 170mm. Preferably the radius is substantially between 100mm and 150mm. In the most preferred embodiment the radius of the shroud means is substantially 122mm.

The wall thickness of the shroud means may be substantially between lmm and IOmm. Preferably the wall thickness is substantially between 2.5mm and 7.5mm. In the most preferred embodiment the wall thickness of the shroud means is substantially 5mm. Of course, it will be realised that the wall thickness will have to be sufficient to give the desired amount of insulation. Therefore, the use of some insulating materials would require thicker ( or thinner ) walls of the shroud means than would other materials.

The shroud means may comprise a housing having a first wall spaced from a second wall, at least one of the walls having a flexible portion, and the walls defining an opening into a chamber defined between the walls and a connecting portion of the housing. There may be a drainage formation ar the base of the housing. The connecting portion may comprise part of a cylindrical surface. The shroud means may comprise an open-topped cylindrical casing which, in use, clearly overlies the side surfaces of a pulley wheel. One or both of the inside surfaces of the usually vertical side walls of the shroud may have a stopped channel/interior cavity adapted in use to receive a component or member which supports the pulley wheel (and to insulateishield that element - e.g.

element 152). This is illustrated in Figure 11.

According to a fourth aspect of the invention, we provide an overhead electrified power supply pulley wheel with an insulating sleeve fitted over it.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings of which: Figure 1 shows schematically a prior art overhead power supply line of a railway track; Figure 2 shows schematically detail of a pulley wheel support for a catenary wire of the overhead power supply of Figure 1, and a support boom for that pulley wheel: Figure 3 shows a schematic perspective view of a shrouding means according to an aspect of the present invention; Figure 4a-c respectively show a side elevation, an end elevation and a plan view of the shrouding means shown in Figure 3; Figure 5 shows an end elevation of a support member (pulley wheel) which the shrouding means is adapted, in use, to shroud; Figure 6 shows an end elevation of a different embodiment of the shrouding means; Figure 7 shows an end elevation of a support member (pulley wheel) which the shrouding means of Figure 6 in adapted, in use, to shroud; Figure 8 shows a side elevation of the shrouding means of eirher of Figures 3, 4, or 6 showing a water escape path; Figure 9 shows a schematic diagram of the shrouding means in use; Figure 10 shows, in use, a shrouding means fitted to a supporting means (pulley wheel); and Figure 11 shows the inside face of a side wall of a shroud showing a stopped rebate for receiving a support arm of a pulley assembly.

Figure 1 shows a prior art system for supporting a power supply contact wire 12 of an overhead power supply for an electrified railway track. The power supply wire 12 is supported on a catenary wire 14 via droppers 16. The catenary wire 14 (which serves to support the weight of the contact wire 12) passes over pulley wheels (or catenary wire supports), and is attached to counterweights 20 which support the weight of the power supply wire 12, the droppers 16, and the weight of the catenary wire itself. (The counterweights allow the catenary wire 14 to expand/contract). The pulley wheels 18 are mounted on booms 22 and 24 which typically extend across the railway track. The booms 22 and 24 are supported above the track by upright pylons 26. Although in Figure 1 only two spans are shown between a weight 20 and a fixed, anchor.

end 21 there may be up to 1S spans in an actual installation.

[It will therefore be realised that should the catenary burn through due to shorts up to 15 spans of the power supply line 12 will be lost.] Figure 2 shows the boom 22 viewed from the direction in which the railway track extends. The pulley wheel 18 is supported by a support 30 which is suspended from an insulator 32. The insulator 32 is mounted on a metal plate 34 which in turn is supported on the boom 22. Thus the support 30 is "live" at say 25kV, and the boom 22 is earthed. The boom 22 is supported by a support member 26.

When a bird. represented at 36 in Figure 2, sits on the boom adjacent the pulley wheel 18 it can provide an electrical path to the earthed boom and cause arcing from the pulley wheel (or the catenary wire in the vicinity of the pulley wheel) to the bird and then to the boom, providing a short circuit. The bird 36 is usually killed, and the operator of the track is left with the problems previously discussed.

Large birds such as crows can bridge quite large distances between the pulley wheel and boom. The problem is exacerbated when the bird 36 jumps up to fly off: it can get nearer to the pulley wheel to cause pulley wheel/bird/boom arcing even though it is no longer in direct contact with the boom (but the air gap is too small).

Birds are, of course, not the only cause of earthing from the pulley wheel/catenary to the boom. Cats or squirrels can climb on the boom, and more likely childrenlvandals can throw objects at the boomlcatenary, which objects can cause a short if they pass into the critical space between the pulley wheel and the boom (referenced as space 38 in Figure 2). It will be appreciated that the pulley wheel is the closest live component to the boom.

The problem of burning through the catenary wire 14 increases with the age of the catenary wire 14; copper forming the catenary 14 becomes work hardened (perhaps by movement of the wire or motion of the wire over the pulleys). Once work hardened it is more susceptible to burning through.

Once a short occurs between the live components and the earthed structure of the overhead power-supply line a fault condition 'will be reported at a control centre. Presently the fault can only be pinpointed to the electrical section of track, which is presently seven miles in length.

The cause of each fault condition should be ascertained to ensure that the fault was not so serious in nature that work needs to be performed to put the fault right. Presently this means that a party of workers is sent to inspect the seven miles of track to see if they can find such a fault.

Clearly this wastes a lot of time. If the problem of earthing can be reduced the number of man hours lost trying to find faults can be reduced.

A substantially cylindrical shrouding means 50 of relatively large radius compared to height is shown in Figure 3. The shrouding means 50 is fabricated from a resilient plastics material such as polypropylene capable of withstanding 25000V. Further, the material is preferably not biodegrade and is not harmful to the environment.

At a lower portion of the shrouding means 50 there is provided a housing member 52 which is substantially a right angled parallelepiped.

At lower edge portions of opposite end faces of the housing member 52 there are provided openings 54. The lower most face of the housing member 52 is curved inwardly such that water cannot cotlect within.

There is provided an opening at an upper most portion 56 of the shrouding means 50 wherein approximately a quarter of the annular wall of the cylinder has been removed.

At centre portions of each end face of the cylindrical portion of the shrouding means 50 there is provided an engagement means 58. On the face shown in Figure 3 the engagement means comprises a hollow cylindrical protrusions the inside of which opens out into the inside of the shrouding means 50.

In a lower most portion of the annular wall of the shrouding means 50 there is provided an drainage opening 60 which can be seen in the plan view of Figure 4c. This drainage opening 60 allows the inside of the cylindrical portion of the shrouding member 50 to communicate with the inside of the housing member 52.

On the end face of the cylindrical portion of the shrouding member 50 which cannot be seen in Figure 3 there is provided an engagement means 62 comprising a wedge shaped portion. This can be most clearly seen in Figure 4b.

Figure 5 shows schematically the support means 64 which the shrouding means of Figures 3 and 4 is adapted, in use, to shroud. The support means 64 comprises a pulley wheel 66 over which runs the catenary wire. A support frame 68 holding the pulley wheel is shown and at a left most side of the support frame 68 (as viewed in the Figure) a crevice 70 protrudes and on the opposite side of the pulley wheel 66 there is a second protrusion 72.

The resilience of the shrouding member 50 is such that a person can deform the structure so as to allow the opening at the upper most portion 56 to be passed onto the support means 64 (after the supply of electricity energising the support means has been turned off). Figure 3 shows schematically with arrows 59 the direction of the manual outward flexing, using the installer's fingers, of the two lip portions 57 of the shroud away from each other so as to enable the shroud to be passed upwards over and around a pulley wheel. The material from which the shrouding member 50 is fabricated is sufficiently elastic to return substantially to its original shape once it has been placed onto the support means 64. The shrouding means 50 is shown in a fitted position in Figures 9 and 10.

In Figure 9 only the arm 100 supporting the pulley wheel 102 is uncovered by insulation. Because the path from the arm 100 to the earthed boom 22 is much longer than from the bottom most portion of the pulley wheel 102 to the boom 22 there is a reduced chance of a bird, etc.

from causing a short circuit between the arm 100 and the boom 22.

Once in position the engagement means 58. 62 respectively engage the second protrusion 72 and the device 70. It will be noted that the engagement means on each side of the shrouding means 50 are configured to correctly enclose either the device 70 or the second protrusion 72.

The elastic nature of the shrouding means retains it in place.

On existing overhead power-supply lines the structure of the support means can vary and the structure shown in Figure 7 can also be found. It will be noted that in Figure 7 there is no device and a frame 80, adapted to support a pulley wheel 82, simply has a first protrusion 84 on a first face and a second protrusion 86 on a second face.

The skilled person will realise that this requires a change to the engagement means 62 of the embodiment shown in Figure 4. Figure 6 shows a shrouding means 90 in which identical engagement means 92, 94, comprising hollow cylindrical protrusions, are provided at a centre portion of each end face of the cylindrical portion of the shrouding means.

Apart from the different shapes of the engagement means the shrouding means of Figure 4 and 6 are identical.

It will be appreciated that because there is an opening at an upper most portion 56 of the shrouding means 50 that rain water can freely enter the shrouding means 50. To prevent this water from accumulating and corroding the support means, and forming a conducting film, a drainage channel is provided. The drainage channel comprises the drainage opening 60 and the two openings at either end faces of the housing member 52. The path of the water is schematically shown in Figure 8.

The skilled person will appreciate that having an uncovered drainage opening in a lower most portion of the shrouding means would negate the insulating properties of the shrouding means. Therefore, the housing member 52 is provided to ensure that there is no short circuit path from the live components held, in use, within the shrouding means to the earthed components below. The apertures 54 and 60 are offset and it is not possible accidentally to bridge them.

Figure 10 shows a shrouding means 148 fitted around a pulley wheel 150. A supporting frame 152 supports the pulley wheel 150 and engagement means 154. 156 engage protrusions of the supporting france 152 thus retaining, in use, the shrouding means 148 in place.

The edge portion 158 of the opening at an upper most portion of the shrouding means is shown in broken line. It can be seen from the Figure that the top of the pulley wheel 150 extends above the edge portion 158 of the opening and thus a catenary wire 160 supported by the pulley wheel 150 is not obstructed by the shrouding means 148. The skilled person will appreciate that because the pulley wheel supports the catenary wire 160 the catenary wire will always pass over the top of the pulley wheel 150. The skilled person will also appreciate that the pulley wheel is fabricated from metal (and is therefore live) so that it gives adequate wear and is not worn away by the catenary wire.

Claims (18)

1. An overhead railway power-supply line comprising a power-supply contact wire supported from a catenary wire, the catenary wire in turn being supported by a support means which is mechanically mounted at a first region of a boom via an insulating member, and in which insulating means is provided between the support means and a different, second, region of the boom immediately adjacent the part of the support means which contacts the power-supply contact wire, thereby eliminating the possibility of a short-circuit between said part of said support means and said second region of the boom.

2. A power-supply line according to Claim 1, in which the insulating means is supported by the part of the support means that it contacts.

3. A power-supply line according to Claim 1 or 2, in which the insulating means is provided on the straight line, extending between the support means and the boom, which has the shortest distance between the support means and the boom.

4. A power-supply line according to Claim 1, 2 or 3, in which the support means consists essentially of a pulley wheel.

5. A power-supply line according to any one of Claims 1 to 4, in which the insulating means comprises a shroud means adapted, in use, to extend adjacent or around, or to substantially surround, the support means.

6. A power-supply line according to Claim 5, in which the shroud means is integrally formed from a resilient material.

7. A power-supply line according to Claim 6, in which the shroud means has one or more flexible regions adapted to be moved or displaced to enable the shroud means to be applied to, over or around the support means.

8. A power-supply line according to Claim 6 or 7, in which the shroud means comprises a one-piece moulding.

9. A power-supply line according to Claim 6 or 7, in which the shroud means is provided in a number of parts adapted to be held together adjacent or around the support means.

10. A power-supply line according to any one of Claims 5 to 9, in which the shroud means is provided with drainage means, whereby water collecting within the shroud means can escape.

11. A insulating member adapted, in use, to be fitted to a power-supply line according to any one of Claims 1 to 10.

12. An insulating member according to Claim 11, said insulating member comprising a shroud means according to any one of Claims 5 to 10.

13. An insulating member for use in connection with an overhead railway power-supply line, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. A method of reducing earthings of an overhead railway power-supply line according to any one of Claims 1 to 10, said method comprising providing insulating means adjacent the means supporting the catenary wire.

15. A method according to Claim 14, in which the insulating means is provided on the straight line which is the shortest distance between the catenary wire or support means and the grounded support boom.

16. A method according to Claim 14 or 15, which comprises substantially surrounding at least part of tie support means with an insulating cover or shield.

17. A method according to Claim 16, which comprises substantially surrounding the whole of the support means with an insulating cover or shield.

18. A method according to any one of Claims 14 to 17, in which the support means consists essentially of a pulley wheel and the insulating cover or shield comprises a shroud means according to any one of Claims 5 to 10.