SVR Telecomms - Line Plant Page

svrtel.org.uk

Introduction

As indicated in the introduction, there are two main classes of line plant used. These are:

1. Underground cabling
2. Overhead lines on poles

Underground Cabling

Trenching in S & T cables between Bewdley and Kidderminster
(Awaiting new picture)

Cables are generally our preferred type of line plant, because they are electrically better in performance, and require less maintenance. The cables, once buried, only require attention if damaged.

Because the cables are generally laid alongside the track, in the "cess", damage occasionally occurs due to Permanent Way work. The Permanent Way department are responsible for maintenance of the railway track itself, and in the course of their work use excavators to remove old ballast, dig out drains, etc. Generally, we can find these faults without too much problem, because their location is pretty much guaranteed to be where the P Way last worked!

Occasionally, a fault shows up for no apparent reason. These are usually caused by damage that took place when the cable was buried, and gradual ingress of water into the cable makes circuits fail years later. Locating this type of fault can be frustrating. Electrical measurement techniques will allow the general area of the fault to be found, but the final solution involves digging out a length of the cable until the damage is spotted.

Cables are installed in four basic ways.

1. In station areas, which experience the most P Way work, and which may require extra cables from time to time, concrete troughing is used. This has the advantage that the route of the cabling is visible, and so the P Way workers can avoid damaging the cables, secondly, by lifting the trough lids, new cables can be added relatively easily.
2. Where only one or two small cables are needed, and the terrain is suitable, our mole plough is used. This comprises a frame with a vertical hollow blade sticking downwards. In use, a hole is dug to allow the blade to drop into the ground, and the whole affair is dragged by main force through the ground. A suitable railway locomotive supplies the brute force! As a consequence, this method cannot be used at the same time trains are running, the SVR being single track. As the mole plough progresses, cable is fed down through the blade, and is introduced into the ground. The slot cut by the plough is so narrow that it virtually closes over the cable, and no spade work is required afterwards.
3. If the cables are too large for mole ploughing, then resort has to be made to our trenching machine. This is a petrol powered machine which winches itself along a steel wire, whilst an endless chain digs out a slot 3" (75mm) wide behind it. Cable is fed into the slot behind the trencher (as the slot may collapse with the vibration of passing trains), then the loose dirt is shovelled back into the trench.
4. The fourth method involves spades and back-breaking work, and we don't like to talk about it!

Overhead Lines

Pole route work
(Awaitng new picture)

Overhead wires are the historical way of running circuits beside railways (or anywhere else for that matter). When the SVR took over the line, this was what had been used, and furthermore, parts of the pole route had been renewed not long before the line closed, so were in good shape. Many of the poles were still standing, or lying down on the bank where they had been jacked out of the ground, and it was a relatively easy matter to restore communication by renovating the old pole routes. As a result, most of the northern end of the line was equipped in this way.

Later, as the railway expanded south towards Bewdley, a change to cable was made, in the light of experience. Much of the pole route that was at the north end of the line has subsequently been replaced by cable, however, there is a length at Bridgnorth which has been deliberately maintained in working order for preservation. Some other lengths, at Hampton Loade and Highley stations, have been retained for visual effect, but are not however in use.

This sign adorns a telegraph pole at Bridgnorth. Broken insulators used to be a big problem with open-wire lines!

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Copyright © Chris Wright 2000			Last updated: 24th June 2000
Page URL http://cgwright.demon.co.uk/sv-line.htm			Email me mail@svrtel.org.uk