Track circuits

Track circuits

12/09/2020

It’s been a couple of weeks since the last post! There has been lots of tea drinking, drawing diagrams on the back of scrap paper and talking about everything apart from what we are working on! But things have progressed well. As what is now normal, all work has been carried out following the ever changing government guidelines on social distancing. Plus all disruptive work has only been carried out when the line has been blocked and no trains have been running. You will see and understand as you read on.

So the first job to be explained is the removal of the two location cases that was intended to be used in the original plan. But like any other job that I have been involved with, we / the drawing office changed there minds! Georgie and her machine was called for and made quick work of lifting the two location cases out and taking them back to the storage area. While the machine was working Georgie also trimmed the embankment back at the side of the line on route to the outer home.To achieve a straighter line for the signal wire run! The straighter the signal wire is, the lighter the pull on the leaver. The lighter the pull, the happier the signaller is!

The next job that has been done that we are looking at. Is digging more holes and filling them in again! This is the new and not moving again location case base at the section starter. This is a smaller location case but still with plenty of room in it for what is to be housed. Since this picture was taken, the cables have been run into the bottom of the base ready to be connected up once the location case it’s self is on. This will be explained in the next picture.

This is the two location cases at Spey lodge. These are part of the assets that we gained with the Highland mainline resiganling project at Aviemore. Curtesy of Network Rail. In the pictures you can see that one has now been stripped out, ready to be rewired and placed on it’s base at the section starter. The second one that Stephen is working on. Will be going out to the outer home. The equipment that is to be housed in these locations is; Feed units for the track circuits. As well as relays, points detection circuits and signal lightning circuits. Which moves us on to the track circuits.

This is a simple drawing of what we are bringing into use. The first of the track circuits is feed from the section starter through the points and to the outer home. We are implementing the use of a medium voltage DC track circuit. Then from the outer home and 380yd beyond, we are putting in a diode type track circuit. If you would like more information about these types of track circuits, then nip over to the IRSE website (Institution of Railway Signal Engineers). https://pdf4pro.com/cdn/train-detection-dc-track-circuits-irse-4fd1b6.pdf
Hear you will find some interesting information and standards that we must maintain. There is one thing that we are currently short of, for this part of the project. This is the IRJ‘s (insulated rail joint). They go on in the same way as fishplate joints do between the rails. The only difference there is between the two is IRJ’s have a plastic skin to them so one rail dose not touch the other, Keeping the track circuits independent from each other and prevent one track circuit from influencing the other. This is also the reason why the positive rail on one track is staggered to the other. Insuring, if the joint brakes down the the track circuits fail safe. The railway currently has four IRJ’s in stock of the correct type. But unfortunately another five needs to be purchased, at a cost of about £250 a set. If you would like to help with the cost of them. Then your generosity will be much appreciated.

This is the remote end of the diode track circuit. Around 380yd north of the outer home. The track tails have been attached to the rails, they just need clipped to the sleeper. IRJ’s are ready for the p-way to install. The short circuit has been attached to the rails beyond the track circuit. This is hear so if the IRJ’s bracket down, then the track circuit dose not feed out beyond where it is required. Maintaining if the IRJ fail then the track circuit fails safe! The disconnection box that houses the diode still needs mounting and tails attached, that is all that is left to do hear.

This is what the bonding looks like for the track circuits. Two solid wires over each joint from the section starter, to the remote end of the diode track circuit. Two nights work after the trains have finished for the day. Has been spent drilling and bonding up. This job had to be done after the train had finished, as it is not permitted and certainly not safe to have a drilling machine on the rail with a chance of a train approaching.

Hear is a wee clip showing the railway’s own drilling machine working! Drilling two holes at a time. This took some time and only 4 drill bits to drill over 232 individual holes. Thanks to Davie Dow who gave the machine a service before we started.

So this is how the outer home is looking now! Old location cases have gone, embankment has been trimmed back, for the signal wire. New “correct” location case base has been dug in. Power cable and 19 core, needs a bit of cable management but is ready to connect up, once the location case is dropped on top of the base. Track circuit tail cables are attached to the rails and ready to connect into the location. The tail cables just need clipped down to the sleeper. One  IRJ is on site, but unfortunately need to wait until we can purchase some more IRJ’s to complete.