GB2220402A

GB2220402A - Improved tensioning apparatus for overhead electric traction systems

Info

Publication number: GB2220402A
Application number: GB8914367A
Authority: GB
Inventors: Farhad Janani; John Doughty
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1988-06-23
Filing date: 1989-06-22
Publication date: 1990-01-10
Anticipated expiration: 2009-06-22
Also published as: GB8914367D0; GB2220402B; GB8814951D0

Abstract

In tensioning apparatus for overhead electric traction systems in which the risk of shock loads on the tensioning apparatus and/or on a conductor of the system arising from breakage of the conductor is reduced, the pulley assembly of the apparatus includes a stop 17 which is pivotably mounted with respect to the mast at a position below a toothed wheel 3 coaxial with the pulley 4 of the assembly and which has a plurality of teeth 18 so shaped and mutually spaced that teeth of the stop can inter-engage sequentially with teeth 15 of the wheel. In the event of breakage of the conductor and rotation of the pulley assembly caused by falling balance weights, the pulley assembly pivots downwardly with respect to the mast so that teeth 18 of the toothed wheel coaxial with the pulley inter-engage sequentially to cause rotation of the pulley to be gradually and smoothly arrested. <IMAGE>

Description

IMPROVED TENSIONING APPARATUS FOR OVERHEAD ELECTRIC TRACTION SYSTEMS In overhead electric traction systems it is the general practice to maintain the or each contact wire and its supporting catenary or catenaries, all hereinafter for convenience included in the generic term "conductors", under constant tension by means of tensioning apparatus located at one or each end of a section of the system. Such tensioning apparatus generally includes balance weights which are indirectly connected to a conductor by a wire rope or other flexible elongate member passing around a pulley assembly. The balance weights maintain the conductors under constant tension regardless of any change in conductor temperature and the degree of tension imparted can be readily adjusted as required by increasing or decreasing the number of balance weights in the tensioning apparatus.

In the event of breakage of one of the conductors to which the tensioning apparatus is connected, the balance weights will fall freely and impart an undesirable tensile load on the unbroken conductor or conductors unless a safety device is incorported in the tensioning apparatus to limit the extent to which the balance weights can fall should breakage of a conductor occur. One safety device that is employed is a brake mechanism which is incorporated in the pulley assembly and which limits rotation of a pulley of the assembly in the event of breakage of a conductor and hence prevents transfer of an undesirable tensile load to the unbroken conductor or conductors.

In a pulley system incorporating this currently used braking mechanism, a pulley of the system is rotatably mounted in a stirrup which is pivotally connected to a pole, mast or other upstanding support about a substantially horizonal axis, a wheel integral and coaxial with the pulley has a multiplicity of teeth spaced around its circumference and a stop is fixedly secured to and protrudes from the pole, mast or other upstanding support at a position below said wheel, the arrangement being such that, in the event of breakage of a conductor, the stirrup will pivot downwardly under the gravitational force imparted by the balance weights and rotation of the pulley caused by falling of the balance weights will be arrested by inter-engagement between the stop and a tooth on the wheel1 thereby preventing further fall of the balance weights and hence an undesirable tensile load on the unbroken conductor or conductors.

Whilst this known form of braking mechanism, in the event of a conductor breakage, successfully prevents excessive fall of the balance weights and hence transfer of an undesirable tensile load to the unbroken conductor or conductors, it has the disadvantage that rotation of the pulley is stopped abruptly by impact contact between the stop and a tooth on the wheel with the result that there is an undesirable shock load on the tensioning apparatus and, in particular, on the pulley assembly which can cause structural damage to the tensioning apparatus and, in some circumstances, to a conductor or conductors of the overhead electric traction system.

It is an object of the present invention to provide improved tensioning apparatus for an overhead electric traction system in which the risk of shock loads on the tensioning apparatus and/or on a conductor or conductors of the system arising from breakage of a conductor is substantially reduced.

According to the invention, the improved tensioning apparatus comprises a pulley assembly including a pulley rotatably mounted in a stirrup which is pivotably connected to a pole, mast or other upstanding support about a substantially horizonal axis, a wheel which is integral with or secured to and coaxial with said pulley and which has a multiplicity of teeth circumferentially spaced around the wheel, and a stop which is pivotably mounted with respect to the pole, mast or other upstanding support about a substantially horizontal axis at a position below the wheel and which has a plurality of teeth so shaped and so mutually spaced that teeth of the stop will inter-engage sequentially with teeth of the wheel, the arrangement being such that, in the event of breakage of a conductor of the overhead electric traction system and rotation of the pulley caused by falling of balance weights indirectly connected to said conductor by a wire rope or other flexible elongate member passing around the pulley assembly, the stirrup will pivot downwardly under the gravitational force imparted by the balance weights, at least one tooth of the stop will initially engage a tooth of the wheel and the stop will be caused to pivot in the same rotational direction as that of the pulley, and sequential inter-engagement between other teeth of the stop and teeth of the wheel will occur so that rotation of the pulley will be gradually and smoothly arrested, thereby preventing further fall of the balance weights and transfer of an undesirable tensile load to the unbroken conductor or conductors of the system.

Preferably, the stop has at least three teeth which lie on an arc having a radius of curvature which substantially corresponds to the radius of curvature of the teeth on the wheel.

Preferably also, the stop is pivotably mounted on a substantially rigid elongate member which is secured to and protrudes substantially horizontally from the pole, mast or other upstanding support.

The teeth on the wheel preferably are uniformly spaced around its circumference.

The improved brake mechanism as hereinbefore described is especially, but not exclusively, suitable for use in tensioning apparatus incorporating a pulley assembly with a 3:1 ratio, which apparatus is widely used to control tension variations in the conductors of overhead electric traction systems.

The improved tensioning apparatus has the important advantage that risk of damage to the apparatus and/or to a conductor or conductors of an overhead electric traction system arising from breakage of a conductor is substantially reduced and hence, the costs that would otherwise be incurred in maintenance and/or re-assembly of the apparatus and/or system are also greatly reduced. Moreover, the braking mechanism of the improved tensioning apparatus can be repeatedly used when conductors break because risk of damage to the mechanism when it gradually and smoothly arrests rotation of the pulley is substantially reduced.

The invention is further illustrated by a description, by way of example, of tensioning apparatus which is suitable for use in an overhead electric traction system and which incorporates a preferred braking mechanism, with reference to the accompanying drawings, in which: Figure 1 is a side view of the tensioning apparatus and preferred braking mechanism; Figure 2 is a side view of the toothed wheel and stop of the preferred braking mechanism of the tensioning apparatus, drawn on an enlarged scale, and Figure 3 is a side view of the stop of the preferred braking mechanism drawn on a greatly enlarged scale.

Referring to the drawings, the tensioning apparatus is of a known form and comprises a pulley assembly including a pulley 3 rotatably mounted in a stirrup 2 which is pivotably connected to a mast 1 about a horizontal axis. Secured to and coaxial with the pulley 3 is a smaller pulley 4 around which is wound a wire rope 5 indirectly connected via a flexible electric insulator 6 to a stirrup 7 in which is pivotably freely rotated a pulley 8. The adjacent ends of the contact wire W and catenary C of the overhead electric traction system are connected to the ends of a length of wire rope 9 which passes around the freely rotatable pulley 8. A length of wire rope 11 is secured to and is wound around the pulley 3 and balance weights 12 are connected to the wire rope 11 and are suspended alongside the mast 1. The balance weights 12 maintain the contact wire W and catenary C under constant tension regardless of any change in temperature of the contact wire and the degree of tension imparted can be readily adjusted as required by increasing or decreasing the number of balance weights in the tensioning apparatus.

To prevent the balance weights from falling freely and imparting an undesirable tensile load on an unbroken conductor or conductors of the system in the event of breakage of the contact wire W or catenary C, the tensioning apparatus incorporates the preferred braking mechanism comprising a wheel 14 which is integral and coaxial with the pulley 3 and which has a multiplicity of teeth 15 circumferentially spaced around the wheel and a stop 17 which is pivotably mounted on a rigid elongate member 16 secured to and protruding horizontally from the mast 1 and which has three teeth 18 so shaped and so mutually spaced that teeth of the stop will inter-engage sequentially with teeth of the wheel.

In the event of breakage of the contact wire W or catenary C of the overhead electric traction system and rotation of the pulley 3 caused by falling of the balance weights 12, the stirrup 2 will pivot downwardly under the gravitational force imparted by the balance weights, one tooth 18 of the stop 17 will initially engage a tooth of the wheel 14 and the stop will be caused to pivot in the same rotational direction as that of the pulley, and sequential inter-engagement between other teeth 18 of the stop and teeth 15 of the wheel will occur so that rotation of the pulley 3 will be gradually and smoothly arrested, thereby preventing further fall of the balance weights 12 and transfer of an undesirable tensile load to an unbroken conductor or conductors of the system.

Claims

CLAIMS:

1. Tensioning apparatus for an overhead electric traction system comprising a pulley assembly including a pulley rotatably mounted in a stirrup which is pivotably connected to a pole, mast or other upstanding support about a substantially horizontal axis, a wheel which is integral or secured to and coaxial with said pulley and which has a multiplicity of teeth circumferentially spaced around the wheel, and a stop which is pivotably mounted with respect to the pole, mast or other upstanding support about a substantially horizontal axis at a position below the wheel and which has a plurality of teeth so shaped and so mutually spaced that teeth of the stop will inter-engage sequentially with teeth of the wheel, the arrangement being such that, in the event of breakage of a conductor of the overhead electric traction system and rotation of the pulley caused by falling of balance weights indirectly connected to said conductor by a wire rope or other flexible elongate member passing around the pulley assembly, the stirrup will pivot downwardly under the gravitational force imparted by the balance weights, at least one tooth of the stop will initially engage a tooth of the wheel and the stop will be caused to pivot in the same rotational direction as that of the pulley, and sequential inter-engagement between other teeth of the stop and teeth of the wheel will occur so that rotation of the pulley will be gradually and smoothly arrested, thereby preventing further fall of the balance weights and transfer of an undesirable tensile load to the unbroken conductor or conductors of the system.

2. Tensioning apparatus as claimed in Claim 1, wherein the stop has at least three teeth which lie on an arc having a radius of curvature which substantially corresponds to the radius of curvature of the teeth on the wheel.

3. Tensioning apparatus as claimed in Claim 1 or 2, wherein the stop is pivotably mounted on a substantially rigid elongate member which is secured to and protrudes substantially horizontally from the pole, mast or other upstanding support.

4. Tensioning apparatus as claimed in any one of the preceding Claims, wherein the teeth on the wheel are uniformly spaced around its circumference.

5. Tensioning apparatus as claimed in any one of the preceding Claims, wherein the pulley assembly has a 3:1 ratio.

6. Tensioning apparatus for an overhead electric traction system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.