GB2229555A

GB2229555A - Electric traction system

Info

Publication number: GB2229555A
Application number: GB9005811A
Authority: GB
Inventors: Alan Edward Seddon
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1989-03-17
Filing date: 1990-03-15
Publication date: 1990-09-26
Also published as: GB9005811D0; GB8906182D0

Abstract

In an overhead electric traction system, the tension in a contact wire 1 and catenary 2 of the system is maintained at a predetermined constant value by means of at least one tensioning device 10 comprising a rod 11 in screw threaded engagement in a tube 12. In response to a rise or fall of tension in the contact wire 1 and catenary 2 sensed by a load cell 17, a transducer amplifier 18 will automatically operate a motor 16 to rotate the rod 11 with respect to the tube 12 in the appropriate sense to cause the tube to move lengthwise with respect to the rod and so restore the tension in the contact wire and catenary to the constant value. The tensioning device 10 is especially suitable for fixing to the roof 3 of a tunnel. <IMAGE>

Description

AN IMPROVED OVERHEAD ELECTRIC TRACTION SYSTEM In an overhead electric traction system it is the general practice to divide the system into a plurality of sections and to maintain the or each contact wire and its supporting catenary or catenaries, all for convenience included in the generic term "conductors", in each section of the system under a predetermined constant tension by means of tensioning apparatus located at one or each end of the section. Tensioning apparatus which for many years has been widely used includes balance weights which are indirectly connected to a conductor or conductors by a wire rope or other flexible elongate member passing around a pulley assembly usually mounted on a pole, mast or other upstanding support disposed alongside the route of the system.The balance weights maintain the conductor or conductors under a predetermined 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.

Whilst such tensioning apparatus is wholly satisfactory where the route of an overhead electric traction system of which it forms a part is in the open or passes under bridges or through tunnels of a length that does not-exceed a few times that of a section of the system (a section typically being approximately 1500m in length), where the route of the system runs through a tunnel which is of such a length that the part of the system in the tunnel will be divided along its length into a large number of sections, as for example is the case in the proposed tunnel under the English Channel, and a large number of tensioning apparatus must be disposed at spaced positions along the length of the tunnel, the additional expense that must be incurred in locally modifying the wall of the tunnel at each of a large number positions along the length of the tunnel in order to accommodate the pulley system and balance weights of such tensioning apparatus substantially exceeds any financial advantage that might otherwise be obtained by use of such simple and inexpensive tensioning apparatus.

It is an object of the present invention to provide an improved overhead electric traction system incorporating at least one tensioning device which maintains the tension in a conductor or conductors in at least one section of the system at a predetermined substantially constant value, which tensioning device is especially, but not exclusively, suitable for use in a tunnel through which the route of the system passes.

According to the invention, in the improved overhead electric traction system, the tension in a conductor or conductors in at least one section of the system is maintained at a predetermined substantially constant value by means of at least one tensioning device comprising two substantially rigid elongate members disposed with their longitudinal axes substantially parallel to one another and so inter-engaged the one with the other that one elongate member (the movable member) is constrained to move to a limited extent with respect to the other elongate member (the fixed member) in either sense in a direction substantially parallel to said longitudinal axes, the movable member being directly or indirectly connected to said conductor or conductors of the system and the fixed member being connected to a fixed support positioned along the route of the system; means carried by the device for driving the movable member in either sense in said direction with respect to the fixed member; means carried by the movable member for continuously monitoring the tension in said conductor or conductors; and, operatively inter-connected between said tension-monitoring means and said drive means, means for automatically controlling operation of said drive means, the arrangement being such that, when said tension-monitoring means detects a rise or fall in tension in said conductor or conductors of the system from said predetermined value, said control means will automatically operate said drive means to cause the movable member to move with respect to the fixed member in the appropriate sense to gradually decrease or increase the tension in said conductor or conductors and, when said tension-monitoring means detects that the tension in said conductor or conductors has been restored to said predetermined value, said control means will automatically stop said drive means.

By virtue of the fact that the or each tensioning device of the improved overhead electric traction system includes neither a pulley system nor balance weights, the space required in a tunnel as compared with that required by tensioning apparatus hitherto proposed and used in such a system is so substantially reduced that the tensioning device can be installed in a tunnel with little or no modification to the wall of the tunnel.

Moreover, by virtue of the mode of its operation, the tensioning device of the improved system is especially suitable for mounting on the roof of a tunnel immediately above the route of the system.

The or each tensioning device of the improved system also has the important unique advantage that it will automatically and accurately compensate for any gradual change in tension in a conductor or conductors of the system, such as might be caused by current heating of the conductor or conductors or by an increase or decrease in ambient temperature.

Inter-engagement between the movable and fixed elongate members of the or each said tensioning device may be by means of a rack and pinion arrangement but with a view to providing for close control of the longitudinal movement of the movable member with respect to the fixed member, preferably the movable and fixed elongate members are in screw threaded inter-engagement the one with the other, and the means carried by the movable member connecting the device to the conductor or conductors of the system includes a coupling device by means of which the movable member is so coupled to the conductor or conductors that the movable member can be rotatably driven about its longitudinal axis without imparting any twist in the conductor or conductors or the means carried by the fixed member connecting the device to the fixed support includes a coupling device by means of which the fixed member is so coupled to the fixed support that the fixed member can be rotatably driven about its longitudinal axis without imparting any twist in the conductor or conductors.

The fixed member of the or each tensioning device may comprise a nut in screw threaded engagement with the movable member and a tubular housing in which the nut is so mounted that it is free to rotate with respect to the housing but is restrained against movement with respect to the housing in a direction substantially parallel to the longitudinal axes of the elongate members. In this case, preferably the means for driving the movable member of the or each tensioning device in either sense in said longitudinal direction with respect to the fixed member is carried by or constitutes a component part of the tubular housing of the fixed member.

Preferably, the means for driving the movable member of the or each tensioning device in either sense in said longitudinal direction with respect to the fixed member is a reversible electric motor and, in this case, the means carried by the movable member for automatically controlling operation of the drive motor preferably comprises a load cell operatively inter-connected to the drive motor via a transducer amplifier.

The or each tensioning device may be powered by the overhead electric traction system but preferably each tensioning device will be powered from a source independent of the system. Preferably, also, the or each tensioning device of the system may include an auxiliary battery for use in the event of a failure of the mains power supply to the device.

The or each tensioning device of the improved system may include an audible and/or visual alarm arranged to operate when the tension in the conductor or conductors of the system rises or falls to an undesirable level.

The improved overhead electric traction system may be a railway system or it may be a tramway or trolleybus system.

The invention is further illustrated by a description, by way of example, of a preferred overhead electric traction system for railways with reference to the accompanying drawing which shows a diagrammatic side view of one preferred tensioning device of the system.

Referring to the drawing, the tension in a contact wire 1 and a supporting catenary 2 of a section of an overhead electric traction system extending through a tunnel is maintained at a predetermined substantially constant value by means of a tensioning device 10 disposed adjacent the roof of the tunnel.

The tensioning device 10 comprises a rigid rod 11 which, over a major part of its length, is externally screw threaded and is in screw threaded engagement in an internally screw threaded rigid sleeve 12. At the end of the rod 11 remote from the sleeve 12, the rod is connected to a bracket 4 dependant from the roof 3 of the tunnel by a coupling device 14. At the end of the sleeve 12 remote from the rod 11, the sleeve is indirectly connected to the contact wire 1 and catenary 2 via a rigid bar 6 which is connected to a fitting 15 at the end of the sleeve by a flexible tie 5. The rigid bar 6 serves to distribute the tension imparted by the tensioning device 10 between the contact wire 1 and catenary 2.The coupling device 14 so couples the rod 11 to the bracket 4 that the rod can be screwed into or out of the sleeve 12, thereby causing the sleeve to move with respect to the rod in a direction parallel to their longitudinal axes and in either sense, without imparting any twist in the contact wire 1 and catenary 2.

The tensioning device 10 carries a reversible electric motor 16 which is powered from a source independent of the overhead electric traction system and which is coupled to the rod 11 to drive the rod rotatably about its longitudinal axis in either rotational direction to cause the sleeve 12 to move with respect to the rod in either sense in a direction parallel to their longitudinal axes. Adjacent the fitting 15, the sleeve 12 carries a load cell 17 which is operatively inter-connected to the drive motor 16 via a transducer amplifier 18 and which continuously monitors the tension in the flexible tie 5 and hence in the contact wire 1 and catenary 2.

When the load cell 17 detects a rise or fall in tension in the flexible tie 5 from the aforesaid predetermined value, a signal is sent to the transducer amplifier 18 which automatically causes the reversible motor 16 to drive the rod 11 rotatably about its axis in such a sense as to cause the sleeve 12 to move with respect and parallel to the rod in the appropriate sense to gradually decrease or increase the tension in the flexible tie and hence in the contact wire 1 and catenary 2. When the load cell 17 detects that the tension in the flexible tie 5 has been restored to the desired predetermined constant value, a signal is sent to the transducer amplifier 18 which automatically stops the reversible motor 16.

The tensioning device 10 will automatically and accurately compensate for any gradual change in tension in the flexible tie 5, and hence in the contact wire 1 and catenary 2, such as might be caused by current heating of the contact wire or catenary or by an increase or decrease in ambient temperature.

Claims

CLAIMS:

1. An overhead electric traction system wherein the tension in a conductor or conductors in at least one section of the system is maintained at a predetermined substantially constant value by means of at least one tensioning device comprising two substantially rigid elongate members disposed with their longitudinal axes substantially parallel to one another and so inter-engaged the one with the other that one elongate member (the movable member) is constrained to move to a limited extent with respect to the other elongate member (the fixed member) in either sense in a direction substantially parallel to said longitudinal axes, the movable member being directly or indirectly connected to said conductor or conductors of the system and the fixed member being connected to a fixed support positioned along the route of the system; means carried by the device for driving the movable member in either sense in said direction with respect to the fixed member; means carried by the movable member for continuously monitoring the tension in said conductor or conductors; and, operatively inter-connected between said tension-monitoring means and said drive means, means for automatically controlling operation of said drive means, the arrangement being such that, when said tension-monitoring means detects a rise or fall in tension in said conductor or conductors of the system from said predetermined value, said control means will automatically operate said drive means to cause the movable member to move with respect to the fixed member in the appropriate sense to gradually decrease or increase the tension in said conductor or conductors and, when said tension-monitoring means detects that the tension in said conductor or conductors has been restored to said predetermined value, said control means will automatically stop said drive means.

2. An overhead electric traction system as claimed in Claim 1, wherein the movable and fixed elongate members of the or each said tensioning device are in screw threaded inter-engagement the one with the other and wherein the means carried by the movable member of said tensioning device connecting the device to said conductor or conductors includes a coupling device by means of which the movable member is so coupled to the conductor or conductors that the movable member can be rotatably driven about its longitudinal axis without imparting any twist in the conductor or conductors or the means carried by the fixed member of said tensioning device connecting the device to said fixed support includes a coupling device by means of which the fixed member is so coupled to the fixed support that the fixed member can be rotatably driven about its longitudinal axis without imparting any twist in the conductor or conductors.

3. An overhead electric traction system as claimed in Claim 2, wherein the fixed member of the or each said tensioning device comprises a nut in screw threaded engagement with the movable member and a tubular housing in which the nut is so mounted that it is free to rotate with respect to the housing but is restrained against movement with respect to the housing in a direction substantially parallel to the longitudinal axes of the elongate members.

4. An overhead electric traction system as claimed in Claim 3, wherein the means for driving the movable member of the or each said tensioning device in either sense in said longitudinal direction with respect to the fixed member is carried by or constitutes a component part of the tubular housing of the fixed member.

5. An overhead electric traction system as claimed in any one of Claims 2 to 4, wherein the means for driving the movable member of the or each said tensioning device in either sense in said longitudinal direction with respect to the fixed member is a reversible electric motor.

6. An overhead electric traction system as claimed in Claim 5, wherein the means carried by the movable member of the or each said tensioning device for automatically controlling operation of the drive motor comprises a load cell operatively inter-connected to the drive motor via a transducer amplifier.

7. An overhead electric traction system as claimed in any one of the preceding Claims, wherein the drive means of the or each said tensioning device is powered by a source independent of the system.

8. An overhead electric traction system as claimed in any one of the preceding Claims, wherein the or each said tensioning device includes an auxiliary battery for use in the event of a failure of the power source to the device.

9. An overhead electric traction system as claimed in any one of the preceding Claims, wherein the or each said tensioning device includes an audible and/or visual alarm arranged to operate when the tension in said conductor or conductors rises or falls to an undesirable level.

10. An overhead electric traction system substantially as hereinbefore described with reference to and as shown in the accompanying drawing.