Southern electrics: the current thinking
It is 100 years since the first electrification of the rail network in the South East of England. PAUL CLIFTON assesses its future
It is 100 years since what we now call South West Trains and Southern Railway started using an electrified third rail.
Electrification actually started before that - in the late 19th century, when Volk’s Electric Railway in Brighton opened in 1883. Currently about 40% of the rail network is powered by electricity, accounting for 60% of journeys. Of the electrified routes, roughly two-thirds use overhead 25kV AC cables and a third uses 750V DC third rail.
The electrified network is now being expanded, with large parts of the Great Western Main Line to be followed by the trans-Pennine route and the Midland Main Line. The proportion using third rail power will therefore reduce.
The London Underground began using a fourth rail system in 1890, on what is now the Northern Line. Suburban electrification in south London followed some years later.
In 1921 a government committee chose 1,500V DC overhead cables to be the national standard, but this was widely ignored. The Southern Railway opted instead for a 660V DC third rail system, and by 1929 its patchy overhead network in south London had been replaced. The Brighton Main Line was finished in 1933, Portsmouth was reached in 1937, and Maidstone in 1939.
During this period the London and North Eastern Railway chose the Woodhead route between Manchester and Sheffield for its first venture into overhead wires, using 1,500V DC. Work began in 1936 but was not completed until the 1950s. As it was not adopted nationally, the route became isolated, and today only the Tyne and Wear Metro uses 1,500V DC overhead lines.
After nationalisation, British Railways expanded electrification and (from 1956) adopted today’s 25kV AC overhead standard for all projects outside the existing third-rail systems in southern England and two lines on Merseyside.
After that, progress slowed. The South Western Main Line to Southampton and Bournemouth was electrified only in 1967, as the steam age came to an end. It reached Weymouth in 1988, built on the cheap with a limited power supply - the consequences of which are still felt by the train operator today.
Only a handful of lines in the South remain diesel-operated. The line from Basingstoke through Salisbury and the route to Uckfield are perhaps the most glaring omissions.
A key electrification debate centres on third rail versus overhead.
“If you were just looking at the ability to transmit electricity, overhead is definitely best,” says William Powrie, Professor of Geotechnical Engineering and Dean of the Faculty of Engineering and the Environment at the University of Southampton.
“Overhead line wins because you can transmit electricity at 25kV. That is to do with distance from the ground.
“In simple terms, if you have a certain voltage it will spark across to the ground. The higher the voltage, the greater the distance it will jump. So if you tried to put 25kV through the third rail, which is about four inches off the ground, it would just arc straight to ground.
“But the great advantage of 25kV is that you do not lose much power in the transmission. Power = voltage x current. So 25,000 volts does not need much of a current. The energy loss is small.”
So why did a large part of the country go with a third rail system, when the power losses of a low-voltage system were well known?
“I think third rail merely came first. It was simpler. The overhead catenary is quite a difficult thing. It is a flexible structure. It hangs in an arc and you need a pantograph that can accommodate that, in addition to the sway of the roof of the train - lateral movement is more of an issue than it is closer to the ground. So the engineering requirement for an overhead power supply is a lot more sophisticated.
“The third rail is a great big piece of metal. It is held pretty rigid, so you can have a simple and cheap collector shoe mechanism on the train.” So, should third rail be replaced? “There is no future for additional installation of third rail,” says Dave Ward, Network Rail’s South East Route Managing Director until his retirement last year.
“You might be able to argue a case for doing Ashford to Hastings, but that’s it. Third rail is not compliant with the Electricity at Work Act, and ORR [the Office of Rail and Road] put a prohibition on further third rail.”
In 2011, Network Rail’s Head of Electrification Peter Dearman suggested there was an economic case to convert the entire third rail network to overhead lines, stating that
I cannot imagine going to our passengers to explain that we might spend billions of pounds to move the electric power from underneath their trains to on top of them. No sane business would do that.
Tim Shoveller, Managing Director, South West Trains
third rail “has no long term future” ( RAIL 673).
Dearman argued that the network was at the limit of its power capability, with trains restricted to a top speed of 100mph, but more generally achieving only 80mph with a quarter of all power lost in the form of heat.
“There have been many attempts to make the economic case,” counters South West Trains Managing Director Tim Shoveller. “There isn’t one. I cannot imagine going to our passengers to explain that we might spend billions of pounds to move the electric power from underneath their trains to on top of them. No sane business would do that.
“The business case for replacing DC assumes that AC would be faster and reduce journey times, with the time benefits bringing additional revenue.
“But the scope for speed is limited. Take the Portsmouth route: most of it is 70mph or 85mph. We could increase that to 90-100mph in places. Journey time is certainly an issue for us, but for that level of improvement we wouldn’t need overhead cables to achieve it.”
In 2012 the concept was introduced of an ‘Electric Spine’ of overhead cables linking Southampton docks to the Midlands to improve freight capacity.
This would entail converting part of the South West Main Line between Southampton Central and Basingstoke to 25kV AC, and was seen as a pilot scheme to develop a business case for full conversion of the third rail network. The High Level Output Specification slated a start date before 2019.
But the autumn 2015 Wessex Route Study states only: “It is intended to provide 25kV AC overhead line electrification between Basingstoke and the docks at Southampton at some point during CP6” [the five-year financial Control Period ending in March 2024]. The recent Hendy Review does not update this.
And there are enough warnings in the Route Study to suggest that it could be kicked into the long grass.
“A significant cost is involved in converting the present day electric passenger fleet to dual voltage capability, it being assumed that it will not prove possible or practicable to keep in place the third rail DC system,” the report states. “There is very little overall passenger benefit,” it adds.
“The economic case for the Electric Spine is shot through,” is Ward’s view. “The spine is in spasm. It was a well-intended idea.”
Shoveller agrees: “The case is certainly
dead in the short term. I utterly reject the notion of leaving a diesel route to Salisbury while electrifying an already-electric line to Southampton. It would be a nonsense. Only an engineering company would think of doing that… you get the inference!
“I would absolutely electrify to Salisbury. That would be AC overhead from Worting Junction, because that is the national standard and we are not likely to see new DC third rail. It’s no problem to have a dual-voltage train for that.
“If an Electric Spine is going to happen, great. But I would like to see that money spent via Andover and Salisbury to provide two electric routes to Southampton. That would be much better value for money.”
The element of putting power back must also be considered.
“The impact of regenerative braking is now also a significant factor,” says Powrie. “If you have regen braking on high voltage AC, you can put power back into the wire fairly easily. And from there it can go to the national grid.
“Power put back into the DC third rail at a low voltage cannot go back into the national grid. If you put energy back into the third rail through regen braking, it can only be used by another train in the same section of track. Otherwise it is just lost.
“The surprise to me was when the railway started to claim the overhead line was more resilient to bad weather, because I have always associated it with the risk of high winds and the effects of ice.
“But three years ago, when we had a bad winter, SWT put on a diesel service on my local line between Southampton and Portsmouth. The modern trains have such a lightweight collector shoe that it tends to lose contact, shutting the trains down.
“I would have thought the risk was pretty even. Third rail is more susceptible to the increase in flooding which happens with climate change; catenary is more susceptible to high winds. They’re about equally susceptible to ice.
“One reason we can have chaos now is unforecast heavy ice overnight. If ice is predicted, they put out the de-icing trains to make sure everything is OK by morning. They don’t go out as a matter of routine, because of the cost. In terms of climate change resilience, it’s a close thing.”
The electrification programme is “too
I find it very difficult to believe that you could make an economic case for converting to third rail now. The price would be prohibitive. William Powrie,
Professor of Geotechnical Engineering and Dean of the Faculty of Engineering and the Environment at the University of Southampton
expensive”, he says, shifting the balance.
Powrie thinks that although overhead wires are inherently better, the economic case for replacing third rail is diminishing as a result of the latest programme of electrification.
He points out that when Network Rail’s Dearman argued there was a case for replacement in 2011, the cost of the Great Western electrification was put at about a sixth of the latest estimates.
“I find it very difficult to believe that you could make an economic case for converting to third rail now. The price would be prohibitive,” he says.
“Network Rail is arguing that one justification for the cost increase is that the equipment is much better. Actually, it isn’t. It is all quite agricultural. It is structurally inefficient, and that makes it more expensive.
“If they try to get themselves out of jail using that argument, then any future electrification scheme simply becomes unaffordable, however you try to justify it.
“That really is a worry for people who support the railway. It is not helpful when Network Rail engineers defend the cost of the current scheme. We have to get costs down before the next project.”
Powrie suggests that NR has been let down badly by the supply chain. Its new high output “factory” train, specially built to speed up wiring the Great Western, was designed to drive tubular steel piles to a depth of 5.5 metres.
On previous electrification jobs, a depth of three to five metres was seen as adequate. But the industry has since come up with a revised overhead gantry system that requires much greater pile depths. So rather than 5.5 metres being a maximum depth, it turns out to be a minimum.
Says Powrie: “Part of the problem is that the Furrer + Frey overhead line equipment they are using on the Great Western is a lot heavier and chunkier than before. That means the wind loads are greater. The ice loads are also greater, and you have to design for them. It pushes up the engineering requirements out of all proportion.
“With the new method they have piled a factor of safety on top of a factor of safety, caution on top of caution.
“Network Rail I think now understands it has to redesign the masts. Furrer + Frey Series One equipment uses a lot of steel - it could come down by 40%. That would reduce the weight, and reduce the wind, snow and ice load.”
Powrie explains that a column bolts on top of the steel pile. The boom that stretches across the railway tracks can slide up and down that column. It is then clamped into place, which allows for a margin of error in erecting it at
The industry cannot even begin to consider the replacement of third rail for another ten to 15 years. What we’ve seen on the Great Western in effect will extend the longevity of third rail. Dave Ward, former South East Route Managing Director, Network Rail
not quite the right height. “That adjustability is like having a folding bike,” he says. “If you have a bike which folds in places it doesn’t need to, it is going to be heavier than a bike which does not fold. The adjustability comes from sliding and bolted joints instead of simple welded joints. It is structurally less efficient and therefore needs more steel to achieve the same result. It is therefore heavier and more expensive.
“Foundations have to become bigger to take the extra weight. They take longer. The high output train hasn’t been able to deliver what is now wanted. The whole thing has become a bit of a disaster, really. But they are too far advanced now - they have to push on.”
Ward, formerly in charge of Network Rail’s South East routes, takes a similar view: “The industry cannot even begin to consider the replacement of third rail for another ten to 15 years. What we’ve seen on the Great Western in effect will extend the longevity of third rail. It’s not economically viable or physically deliverable until a modular overhead system becomes available, one that can be installed quickly and without disruption.
“It would be very difficult to install even then. Stand at the end of the platform at either Waterloo or London Bridge and look at the tracks. Now imagine how difficult it would be to install a system of wires above all that. Almost impossible.
“I’d say on a list of priorities for the Southern Region it comes about 15th. There are far more important things to do. South of the river the railway is all about capacity, not speed. And third rail can deliver capacity.
“One day someone will have to grasp the nettle. But the change would take years and cost billions of pounds. For what gain? It won’t produce more than a marginal change in capacity, and there are many other changes which would produce much greater capacity.”
Nowhere in the world is pursuing third rail as an alternative for main line services. Everyone starting from scratch would choose 25kV overhead wires. But third rail power is likely to be with us for a long time yet.