I’ve been travelling up and down the East Coast Main Line (ECML) quite a lot recently, and generally been delayed every time.
As I am now currently at Kings Cross awaiting my train at 2000 which is going to be late I predict since the inbound service isn’t due to arrive until 1953.5 I thought I’d have a ramble on spaghetti – no not the Italian carbohydrate, but the overhead line that has been causing a lot of the recent problems.
When BR electrified the ECML in 1989/90, ready for the arrival of the Intercity 225 sets in 1991, they were skint so did it on the cheap.
How they did it on the cheap is fairly well documented- they strung the posts that hold the wires up to the maximum distance possible because over 400 miles you save an awful lot of posts. But actually it didn’t end there. They also chose to use head span wiring rather than portal wiring. What this means that instead of, as on the majority of the west coast where each post is an “n” with the wires dangling from the cross bar, on the east coast a wire is strung between two vertical posts (the head span) and the contact wires are strung from that.
This means the foundations for the posts can be smaller as the mass and aerodynamic resistance is reduced, which again over 400 miles all adds up.
The downside of this has become more and more prevelent in recent years as more and more trains run on the railway – dewirements.
A dewirement is when the pantograph and the contact wire lose contact. In most cases this is where the pantograph of the train lifts over the top of the contact wire and then drags it off the posts resulting in spaghetti all over the railway.
With portal wiring, a dewirement generally only affects the track the recalcerent train is on as the wires on the other lines are all attached to the portal individually.
With head span wiring, all the string is attached to each other, so if you dewire on one line, the chances are the whole lot comes down and the east coast grinds to a halt while you sort it all out.
But don’t despair, Network Rail have been investigating a solution and currently have a trial at Potter’s Bar. The natural thinking would be to replace the head spans with portals but a) the current posts aren’t strong enough to have the cross bar out in, and b) the foundations aren’t strong enough to replace the whole post assembly with a portal one.
Added to this is a desire to run the east coast at 140mph which requires a thicker (and therefore heavier) contact wire.
The solution devised is to install a lightweight aluminium portal crossbar to the existing posts. The claim is that the ensemble, even with 140mph contact wire, is no heavier than the current head span wiring.
A picture of the portal trial is here showing a class 325 passing underneath it.
Having said all this, today’s late running wasn’t caused by a dewirements at Retford like most recent delays, but by a trespasser. I don’t know why people go on the track; it’s not a playground. All it caused was a lot of angst for a lot of people. The 1900 ish service to Peterborough doesn’t normally have this many people rushing to get on it.