Overhead Lines For Rail Vehicles

The present invention relates to overhead lines for electric vehicles, and in particular to an overhead line installation and to a device for tensioning overhead lines.

Overhead lines are widely used for transmitting power to electric vehicles of various types including (1) rail vehicles-trains, trams etc; (2) road vehicles such as trolleybuses, mine vehicles etc; and (3) water vehicles including tugs to pull barges and ships in canals. An electrical conductor is suspended above the vehicle's path from a row of upright poles or masts, and the vehicle typically carries a pantograph type mechanism which supports an electrical terminal, urging it upwards against the conductor to form the necessary electrical connection. A conventional suspension arrangement of the type used in existing train installations is schematically illustrated in Figure 1. The mast 2 supports a horizontal bracket arm 4. A vertically extending electrically insulating hanger 6 serves to suspend the electrical line 8 from the bracket arm 4. Lateral stabilisation of the line 8 is provided by means of a horizontal stabilising arm 10 which is beneath the bracket arm 4 and is coupled at one end to a lower part of the hanger 6 and at its other end to the mast 2. As seen in Figure 2, the line is maintained in a shallow "zig-zag" pattern which helps to equalise wear across

the width of the vehicle's electrical terminal, since the point of contact between line and terminal moves back and forth across the terminal. This pattern is created by means of the stabilising arms 10. Each end of the line 4 is led to an anchoring arrangement and tension is applied to the line through an end tensioner in a region 12, which pulls along the length of the line and must maintain tension despite for example changes in line length resulting from changes in its temperature. Where the line is self

supporting, the rise and fall of the line between masts is determined by the tension applied to it, and the necessary tension is large, so that the end tensioners are substantial and expensive. The length of an individual line 8 is limited. Its ends are anchored either to a fixture at ground level or to a mast which is braced to withstand the line tension. Of course in the case of one of the ends this is done through the end tensioner. The ends of adjacent lines overlap, as seen in region 9 of Figure 2, to provide continuity of supply to the vehicle.

This is well established and successful technology but the investment involved in creating a n o verhead 1 ine sy stem i s v ery 1 arge a nd t here a re i mportant c ommercial incentives to economise, to simplify installation and to reduce the parts count.

In a ccordance with a first aspect of the present i nvention there is an overhead line installation for providing electric power to a vehicle, comprising an electrically conductive overhead power supply line ("the line") suspended by means of hangers at intervals along the length of the line, each hanger having an upper fixed part coupled to a supporting structure and a lower free part through which it is coupled to the line, characterised in that the relative positions of the fixed parts of the hangers are such that the fixed parts of the hangers are offset from the line along a direction transverse to the line, the line thereby being laterally stabilised without provision of additional means for restraining transverse motion of the free parts of the hangers.

The hangers are preferably supported through respective masts, the sole coupling between the line and at least some of the masts being made through the hanger. The masts may be simple wooden poles, although in principle metal structures could be

used. An economical embodiment uses a lateral bracket arm projecting from the mast to support the hangers above the rails, but again other constructions are possible. For example some known masts are themselves curved at their upper ends, so allowing the bracket arms to be dispensed with.

It is particularly preferred that some of the hangers are offset to one side of the line and others are offset to the opposite side. Still more particularly, the offsets form an alternating pattern to one side of the line and the other. This pattern is appropriate along straight sections of track, but on curves it can be appropriate instead to place all of the hangers to the outside of the curve.

The offset may alternate from one hanger to the next (i.e. it has a repeat interval equal to two hangers). Alternatively, the offset may alternate from one side of the line to the other with a pattern whose repeat interval is more than two hangers.

In a preferred embodiment, each hanger has two limbs forming an inverted "V" shape. The hangers preferably comprise synthetic rope.

In accordance with a second aspect of the present invention there is a tensioning device for an overhead line for providing electrical power to a rail vehicle, the device comprising means for applying a transverse force to the line.

In a preferred embodiment, the device comprises a suspended mass whose weight is referred to the line to provide the transverse force. The mass may be suspended through a cord connected to the line.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a schematic representation of a conventional mast and suspension arrangement for an overhead line, viewed from one side;

Figure 2 i s a s chematic representation o f a c onventional o verhead 1 ine i nstallation, viewed from above;

Figure 3 a is a schematic representation of a mast and suspension arrangement embodying the present invention, viewed along the length of the line, and Figure 3b represents the same arrangement viewed along a direction perpendicular to the line;

Figure 4 is a more detailed representation of the suspension arrangement of the Figure 3 embodiment, viewed from one side;

Figure 5 is a schematic representation of a first overhead line installation embodying the present invention, viewed from above;

Figure 6 is a schematic representation of a second overhead line installation embodying the present invention, viewed from above;

Figure 7 is a schematic representation of a tensioning arrangement embodying an aspect of the present invention, viewed from one side.

The arrangement illustrated in Figures 3 and 4 has an upright mast 14 formed as a simple wooden pole whose lower end is buried in the ground to a depth in the region of 2 metres. The mast serves to support a bracket arm 16 which in the present embodiment i s a s teel t ube w hose i nner e nd i s c oupled t o t he m ast b y means o f a junction plate 18 secured to the mast 14 by through-going bolts 20 and having a laterally projecting collar 22 which receives the bracket arm's inner end. This coupling is not required to withstand loading on the bracket arm in cantilever fashion, such loading instead being borne by a diagonal stay 24 led from an eye bolt 26 near the outer end of the bracket arm 16 to a loop 26 around the mast 14, the loop being above the coupling 18,20,22. In the present example the stay is formed of stainless steel rope. The resulting structure is robust but simple and economical to make.

The power supply line itself is indicated at 28 and is a metal member having a substantial cross section commensurate with the large current it carries. The line has a cross section (which is conventional and is not illustrated herein) which is circular but for a pair of recesses to be gripped from above by "ear clamps", leaving the underside of t he 1 ine, w hich m akes c ontact w ith t he v ehicle-mounted t erminal, u ninterrupted. These aspects are well known and need not be described further herein.

The line 28 is suspended from the bracket arm 16 by means of a hanger 30. In principle this could take a number of different forms. In the present embodiment it is formed as a flexible strop. The hanger serves to electrically isolate the line and to this end is formed from insulating material. The material used in the present embodiment is a synthetic rope. A suitable rope is manufactured by Linear Composites Ltd under

the registered trade mark Parafil. In the illustrated embodiment the hanger comprises two limbs which, viewed in a direction across the line 28, form an inverted "V" shape. At its mid-point the hanger is passed over the bracket arm 16 and its location along the arm is fixed by a location ring 32. The upper part 34 of the hanger, through which it is itself suspended from the bracket arm, will be referred to as its "fixed part".

Note from Figures 3a and 4 that, viewed in a direction along the length of the line 28, the hanger is inclined to the vertical. That is, the fixed part of the hanger is horizontally offset from the line 28. To appreciate why, consider Figure 5, which shows part of an overhead line installation, comprising multiple masts 14 alongside railway or tram tracks 36, supporting the line 28 above the tracks. Note that the fixed parts 34 of the hangers 30 do not lie on a straight path or a fair curve following the line of the tracks. Instead they are offset from such a notional fair path in an alternating pattern, first to one side of the path and then to the other. The line 28 is caused to adopt a corresponding wave or zig-zag path. The line 28 of course tends to straighten itself, in order to take the shortest possible route, but this tendency is resisted by a horizontal force applied to the line 28 by the hangers 30: the tension in the hangers has a horizontal component because of their inclination to the vertical. The fixed parts 34 of the hangers thus lie outside the path adopted by the line 28, as seen in the drawing.

The offsetting of the hangers from the fair path (and from the line itself) serves to laterally stabilise the line 28 - that is, to reduce its tendency to move from side-to-side in pendulum fashion under the influence of wind etc. As a result no other means for lateral stabilisation need be, or is, provided. Specifically, the stabilising arm 10 of the

prior art suspension arrangement (Figure 1) is dispensed with. As noted above, in such prior art arrangements the line would typically be caused to adopt a "zig-zag" path, but this is not because the hangers are inclined. The path is instead defined by the effect of the stabilising arms 10.

Note that where the tracks 36 - and hence the fair path to which the line approximates - is curved, the offset of the hangers need not follow an alternating pattern. The necessary inclination of the hangers can be achieved by offsetting several successive hangers to the outside of the curve.

Figure 5 shows a pattern in which the hangers 30 are offset to opposite sides of the line on successive masts 14, but other alternating patterns, with a longer "wavelength", may instead be used. Figure 6 shows an example with a wavelength equal to eight times the separation between neighbouring masts. The inclination of the line 28 to the notional fair path 38 is thereby reduced, and the significance of this will be explained shortly.

As noted above, a large tension must be applied to the line 28 to prevent it from sagging excessively between masts. Figure 7 shows a suspension arrangement which is similar to that of Figures 3 and 4 but differs in that it additionally comprises a tensioning arrangement in which the tensioning force is applied not along the length of the line, but transversely to it. A mass 38 is suspended alongside the mast 14 from a cord 40 which is led up the mast, through an eyelet 42, to a pulley 44 carried on a bracket mounted upon the mast 14 at approximately the same height as the line 28. Having p assed o ver t he pulley, t he c ord i s 1 ed t o a p ositioning b racket 46 t brough

which it is coupled to the line 28. Hence a transverse force equal to the weight 38 is applied to the line 28. The tension required in the line to withstand this lateral force is of course very much greater than the weight of the mass 38. The relationship between the line tension and the transverse force on the line depends on the sine of the angle by which the line is caused to deviate from its fair path. Now the significance of the long wavelength pattern seen in Figure 6 should be apparent. It serves to reduce this angle, and hence to increase the line tension. In practice a mass of as little as 50 to 100 kilograms is found to be sufficient (although it must be clearly understood that the invention is not limited to any particular mass). Ends of the line 28 are of course anchored in some way, e.g. by being led to fixtures at ground level.