GB2357271A

GB2357271A - Power rail earthing mechanism

Info

Publication number: GB2357271A
Application number: GB9929767A
Authority: GB
Inventors: Geoffrey Robert Brown
Original assignee: Balfour Beatty PLC; BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1999-12-17
Filing date: 1999-12-17
Publication date: 2001-06-20
Anticipated expiration: 2019-12-17
Also published as: GB9929767D0; GB2357271B

Abstract

The mechanism comprises an electrical conductor 12 having contacts e.g. shoes 8, 10 for forming an electrical connection between a power rail 2 and an earth rail e.g. a running rail 4 respectively, characterised in that the contacts are adapted to be literally moved into/out of contact with respect to the power rail and earth rail, and the mechanism further comprises means for mounting the conductor on a rail vehicle.

Description

2357271 POWER RAIL EARTHING MECHANISM This invention relates to a power

rail ea-thing mechanism for an electrified railway, in which power is supplied to rail traffic by me., of an electrified power rail.

Some DC electrified railway systems have conductor rails mounted on the sleepers in addition to the two running rails. Current is collected from a conductor rail ('power rail') by collector shoes on each train. After passing through the electrical equipment on the train, the current is returned either through the axles and wheels to one or both of the running rails, as is the case on the South Zone of Railtrack's railway network in UK, or through conductor shoes to a return conductor rail (the running rails for this purpose and return conductor rails being collectively referred to as 'earth rail' herein). The power rail is normally supported on insulators mounted on the sleeper ends outside the running rails. The return conductor rail, if fitted, is normally mounted on the sleepers between the running rails, as is the case on the London Underground railway system. The tops of the conductor rails are normally higher than the tops of the running rails. Gaps are provided in the is conductor rail at points and crossings, at some train stop or signal positions, at track crossings and at other locations for sectioning purposes. Where there is a gap, ramps are provided to facilitate the smooth passage of the collector and conductor shoes.

The power rail equipment for each running line is kept electrically separate from that of other lines and is also divided into sections by means of switcligear at sub-stations and track paralleling huts. Each section is divided into sub-sections by isolating switches. These switches are either located adjacent to, or mounted directly on, the power rail and are suitably connected by insulated cable. When it is necessary to perform essential routine maintenance operations on or near to the power rail equipment and its connections, the sub section of the power rail system at the stretch of track to be worked on may be isolated by opening the relevant switches, whilst the electricity supply on other sections and sub sections is maintained. Such routine maintenance operations must be scheduled to be carried out in gaps between normal rail trM-ic, and hence these are often carried out during the night. As a result, the normal period that maintenance personnel may take possession of a section of track ('maintenance possession') is only 3.5 to 5 hours in length.

As a failsafe system to protect personnel working on the track, the power rail must be short circuited with the earth rail to prevent any accidental re- energisation by any means.

The conventional means for short circuiting the power rails, as specified in "D.C. Electrified 2 Lines Instructions" produced by Railtrack in UK, is by the use of a short circuiting strap applied between the power rail z the earth rail (a process known as 'strapping out'). A short circuiting strap must ai lied to each sub-section to be worked on. The short circuiting strap comprises a cabic having conductive clamps at either end, which may be manually applied to the power rail and earth rail respectively. Although such short circuiting straps work in a satisfactory manner, application and removal of the straps takes about 20 minutes at the start and end of any maintenance possession. This combined loss of 40 minutes can have a significant impact upon the amount of time allowed to undertake maintenance work. Furthermore, if several sub-sections are to be worked on, the application and removal time must be multiplied by the number of strapping out operations to be performed.

It is an object to reduce the time required to strap out a power rail in a sub-section of electrified track.

According to the invention, there is provided a power rail earthing mechanism comprising an electrical conductor having contacts for forming an electrical connection between a power rail and an earth rail respectively, characterised in that the contacts are adapted to provide mobile electrical connections with respect to the power rail and earth rail, and the mechanism further comprises means for mounting the conductor on a rail vehicle.

By use of contacts adapted to provide mobile electrical connections and means for mounting the conductor on a rail vehicle, the earthing mechanism may be mounted directly on a track maintenance vehicle and earth the power rail as the vehicle advances along the track. In this way, the strapping out operations for each sub-section of track to be worked on using the maintenance vehicle are performed automatically without the need to manually apply short circuiting straps.

Preferably, the means for mounting the conductor on a rail vehicle enables movement of the conductor between an operational position, in which the conductor forms an electrical connection between a power rail and an earth rail under the rail vehicle, and a retracted position, in which the conductor does not form an electrical connection between the power rail and the earth rail. In this way, the earthing mechanism may he conveniently applied once the relevant sub-section of track has been isolated and the maintenance work is due to commence, and removed when the maintenance work is finished.

3 Suitably, at least one of the contacts does not make electrical contact with either the power rail or the earth rail when the mechanism is in the retracted position. Thus, the contact(s) may be physically moved out of contact with the power rail andlor earth rail upon movement of the conductor to its retracted position.

Suitably, the contacts comprise conductor shoes. Conductor shoes are widely used on rail vehicles for collecting current from the conductor rails. They provide good sliding electrical connections with the conductor rails, and ensure that the power rail is properly earthed at all times when the mechanism is applied with the conductor in its operational position, whether the rail vehicle is moving or stationary.

According to another aspect of the invention, there is provided a rail vehicle comprising a power rail earthing mechanism as described above. Preferably, the vehicle comprises four power rail earthing mechanisms, two being attached at either side towards the front of the vehicle and two being attached at either side towards the rear of the vehicle.

By the use of four rail earthing mechanisms in this configuration, earthing of the power rail of consecutive sub-sections is assured as the vehicle moves over the gaps from one sub section to the other by virtue of the longitudinal spacing of the mechanisms towards the front and rear of the vehicle. Similarly, as vehicle moves over a section of track where the power rail changes from one side of the track to the other, both power rails will be earthed by virtue of the lateral spacing of the mechanisms on either side of the vehicle.

According to a third aspect of the invention, there is provided a method of earthing a power rail, the method comprising forming an electrical connection between a power rail and an earth rail by means of an electrical conductor having contacts, characterised in that the contacts are adapted to provide mobile electrical connections with respect to the power rail and earth rail, and the conductor is mounted on a rail vehicle.

A power rail earthing mechanism according to the invention will now be described by way of example only with reference to Figures 1 and 2, in which:

Figure 1 is an elevation of the earthing mechanism in an operational position in electrical contact with a power rail and an earth rail; and Figure 2 is an elevation of the earthing mechanism in a retracted position not in electrical contact with the power rail or the earth rail.

Figures 1 and 2 show a rail earthing mechanism according to the invention for use on a railway system in which one of the running rails acts as the earth rail. As shown in the 4 figures, the power rail earthing mechanism comprises a mounting bracket 1 fastened to the front of a bogey of a rail tamping vehicle (not shown) in a substantially vertical plane above and transverse to the power rail 2 and earth rail (running rail) 4 of the track. A shoe beam 3 is mounted parallel to the mounting bracket 1 at a pivot point 5 between the running rails so that it is free to pivot in a substantially vertical plane about the pivot point. A pneumatic actuator 6 is mounted on the mounting bracket with its actuator rod fastened to the shoe beam at a radius from the pivot point 5 such that it acts in a substantially tangential direction to control movement of the shoe beam about the pivot point. Two parallel arcuate support bars 7 extend from the shoe beam and interact with guides (not shown) on the mounting bracket to support and guide the shoe beam through its locus of movement. A stop bolt 9 passes through the end of the shoe beam remote from the pivot point and interacts with a stop plate 11 extending from the mounting bracket when the shoe beam is in its lower most position to form a stop. A locking nut 13 serves to lock the stop bolt 9 in position. A travel lock comprises a retractable bolt 14 mounted in the mounting bracket which, in its retracted position is flush with the face of the mounting bracket to allow the shoe beam to pivot, and in its extended position stands proud of the face of the mounting bracket and fits into a cut out section 16 of the shoe beam when in its raised position to prevent movement into its lowered position. Two conductor shoes 8, 10 are flexibly mounted on the shoe beam 3 via rubber bushings (not shown) at such positions that, with the shoe beam in a lowered position, the conductor shoes contact the upper surfaces of the power rail 2 and earth rail 4 respectively as shown in Figure 1. The conductor shoes 8, 10 are connected electrically to each other by means of a 1251M2 cable 12 attached to their terminals 15, 17.

In operation, a tamping vehicle is fitted with four power rail earthing mechanisms as described, one on either side of each bogie for contacting a power rail 2 and earth rail 4 on the respective side of the track. The tamping vehicle is brought into position on a sub-section of track for maintenance purposes with the shoe beams 3 held in their raised or retracted positions by the travel lock 14 as shown in Figure 2, the shoes being clear of the power rail 2 and earth rail 4. The power rail system is then isolated by means of appropriate isolating switches. Once properly isolated, air is supplied to the pneumatic actuators 6 to hold the shoe beams 3 in their retracted positions while the travel locks are manually released. Once the travel locks have been manually released, the shoe beams 3 are lowered by means of the pneumatic actuators 6 until the conductor shoes 8, 10 on one side of the bogies rest on the power rail 2 and earth rail 4 respectively with a force that is adequate to establish and retain a good electrical connection between the two rails but which enables the shoe to negotiate track imperfections with minimum damage and wear to shoes when the vehicle is moving.

On the other side of the bogies, the shoe beams 3 are lowered until the stop bolts 9 abut against the stop plates 11 with the conductor shoes 8, 10 hanging a little lower than the top surfaces of the power rails and earth rails supporting their respective counterparts on the other side of the bogie.

It is now safe for maintenance personnel to work in the vicinity of the power rail 2 without any danger of accidental re-energisation. The tamping vehicle may proceed along the track at speeds of up to 1 Omph while the maintenance work is carried out, and the conductor shoes 8, 10 will remain in electrical contact with the power rail 2 and earth rail 4 to ensure that the power rail is earthed at all times. As the vehicle passes over gaps in the power rail, the rail shall remain earthed by virtue of the earthing mechanism attached to the same side of the other bogie. Likewise, when the power rail changes from one side of the track to the other, both power rails will be earthed as the vehicle passes over the area of change by virtue of the mechanism on one side of the front bogie and that on the other side of the rear bogie.

Where there are gaps, the shoe beam stops 9 prevent the shoes from dropping below the level of the ramps at the power rail ends, such that the conductor shoes can pass smoothly from one power rail to the next. Upon completion of the maintenance operation, the earthing mechanisms are raised simultaneously to the retracted position by means of the pneumatic actuators 6, the travel locks 14 are reapplied and the vehicle can travel to another work site or return to its depot.

In the event of accidental re-energisation of the power rail while the earthing mechanism is deployed, for example due to the vehicle driving out of the isolated section, or due to another vehicle bridging across from an adjacent live section to the 'isolated' section, each power rail earthing mechanism is capable of carrying up to 90kA for 130ms. This is significantly greater than the maximum expected current of 65kA, and will provide sufficient time for the track circuit breakers to trip. In such event, it is likely that the earthing mechanism will be damaged by the load placed upon it, and the device will need to be withdrawn from service until such time as it can be confirmed to be fully functioning again.

Detailed checks are required at regular intervals to ensure its proper functioning.

6 The invention is described herein with reference to Figures 1 and 2 by way of example only. It will be clear that the invention extends to further modifications not described.

7

Claims

1. Power rail earthing mechanism comprising an electrical conductor having contacts for forming an electrical connection between a power rail and an earth rail respectively, characterised in that the contacts are adapted to provide mobile electrical connections with respect to the power rail and earth rail, and the mechanism further comprises means for mounting the conductor on a rail vehicle.

2. Power rail earthing mechanism according to claim 1, wherein the means for mounting the conductor on a rail vehicle enables movement of the conductor between an operational position, in which the conductor forms an electrical connection between a power rail and an earth rail under the rail vehicle, and a retracted position, in which the conductor does not form an electrical connection between the power rail and the earth rail.

3. Power rail earthing mechanism according to claim 2, wherein at least one of the contacts does not make electrical contact with either the power rail or the earth rail when the mechanism is in the retracted position.

4. Power rail earthing mechanism according to claim 3, wherein the contacts comprise conductor shoes.

5. A rail vehicle comprising a power rail earthing mechanism according to any preceding claim.

6. A rail vehicle according to claim 5, comprising four power rail earthing mechanisms, two being attached at either side of. vehicle towards its front and two being attached at either side of the vehicle towards its rear.

7. Method of earthing a power rail, the method comprising forming an electrical connection between a power rail and an earth rail by means of an electrical conductor having contacts, characterised in that the contacts are adapted to provide mobile 8 electrical connections with respect to the power rail and earth rail, and the conductor is mounted on a rail vehicle.

8. A rail mounting system substantially as described herein with reference to the description and Figures 1 and 2.