6.6 C
Friday, June 14, 2024

Has third rail had its day?

Listen to this article

This fascinating question was posed and debated at the Institution of Mechanical Engineers’ headquarters during a recent seminar organised by the Railway Engineers’ Forum (REF). The REF, a grouping of the railway interests of the engineering and associated professional bodies, aims to hold a joint technical seminar once a year. With the emphasis on growing electrification and the possible spread of 25kV into traditional third rail electrified areas, this was felt to be a subject ripe for debate. One can argue that putting wires up is easy while managing the changeover is not. In principle, many trains are dual system or can easily be made so and economics will drive the change which will commence with the recently-announced freight spine.

An electric spine

Following the usual opening remarks, first off the line as keynote speaker was Peter Dearman, head of energy for Network Rail and the man leading the charge towards full network electrification. Peter openly stated that he wanted the UK to be like Switzerland with an all-electric railway!

The outline of the day was set by the fact that Network Rail is to develop an ‘Electric Spine’, with high-voltage overhead-contact system electrification, between Southampton and the Midlands. This highlights the need to upgrade the power system between Southampton and Basingstoke, a section of railway which is currently electrified at 750 volts DC third rail.

AC or DC?

A study of history reveals two great protagonists – Nikola Tesla and Thomas Edison: Tesla for AC and Edison for DC. In the United Kingdom, the Edison corner won the day as the country has a large proportion of the world’s DC electrified railway.

However, the situation in regard to energy costs has changed hugely since those early days, as have attitudes towards safety. Would anybody really countenance laying down metal bars, electrified at 750 volt DC, all over the transport infrastructure nowadays?

Development costs of DC systems are also high. Peter Dearman pointed out that the fairly recent spend on power supply reinforcement in the South only enabled the railway to stand still in traction capability terms.

There is massive technological development in AC systems already, and this advance is transferrable to renewal in DC areas as well as new development in non-electrified regions. A particular example is in the application of IEC 61850 dealing with rationalised feeding architecture.

Overhead electrification at Crystal Palace [online]DC economics

The seminar was intended to fully debate the subject and was not confined to purely engineering and technical presenters. Peter Dearman was therefore followed by Michael Woods who is head of operations and management research at the Rail Safety and Standards Board (RSSB).

RSSB had enabled a research project, T950, investigating the economics of the third rail DC system compared to other electrification systems. This research, carried out on behalf of the Future Electrification Group (a sub-group of V/TE SIC – the Vehicle/Train Energy System Interface Committee), has considered the long-term options for modification to or replacement of the 750V DC third rail electrified system.

Michael has had considerable experience in managing a third rail DC railway and also has a useful eye for history. He came up with a very relevant quote from Silvanus P Thompson FRS, president of the Institution of Electrical Engineers in 1904, who said ‘live rails … will soon be a thing of the past’.

Following that historical interlude, Michael then moved on to set the agenda for the rest of the day by presenting a list of the potential benefits of changing to a 25kV OLE system which could include:
» Reduction in the capital cost of renewal;
» Reduction in energy consumption and carbon footprint on a ‘like for like’ basis;
» Reduced sensitivity to ice and snow;
» Reduced track maintenance and renewal costs; » Increased system performance enabling reduced journey time, reduced fleet size and increased route capacity;
» Increased line speed above 100mph in some specific cases;
» Reduction in risk of electrocution of lineside workers and trespassers;
» Reduced distribution charges and costs of electrical control;
» Energy and operational cost savings from the electric operation of freight and cross-country passenger services.

Nevertheless, the potential shortcomings of 25kV overhead electrification schemes were not ignored. Events during the week before the seminar had reminded delegates what can happen when things go wrong with major disruption on the East Coast main line at St Neots and the Midland main line at Radlett. (See A ‘bad wire day’ in this issue on page 32.)

An operator’s view

The wider range of the day was then emphasised by Tim Shoveller, managing director of the South West Trains/Network Rail Alliance. Tim put the point from the business angle and was at pains to point out that he would “concentrate on the revenue line.” His early point was “If we don’t get the electricity to the train, the train does not run.”

Tim is well-aware of the shortcomings of the existing system and expressed his concerns regarding traction cable lugs degrading and coming adrift together with other symptoms of a railway seriously overloaded in the traction sense. However, Tim had promised he would surprise the assembled multitude and he did so by reminding us that his railway was full (standing customers inbound from Winchester on occasions) and that his preference would be to put up the wires to Southampton by way of Andover, the Laverstock loop and Romsey!

And now – technology!

Having discussed the business and operating angles, the seminar moved on to the technological one. Next up was Shamil Velji, energy engineer at the RSSB. Project T950 was again visited, and it is worth quoting part of the output from that report as this helped to shape further debate on the day:

“The conclusion of this research is that replacement of the 750V DC system with 25kV AC appears to be both feasible and economically desirable. The economic case is likely to improve as energy costs increase over time. The affordability of the change has yet to be determined,

but an opportunity exists to start the replacement process within the next industry control period so that the advantage can be taken of
the relatively large quantity of DC equipment becoming life expired at that time. To make such a change is a very significant decision to be taken by industry and government (as funder), and would require a large amount of further work to develop a whole industry business and implementation plan to take account of the impact on train operators and the industry’s customers.”

The undoubted advantages of electrification were quickly confirmed with the power output of a Class 92 electric locomotive being around twice that of a diesel Class 66. The T950 report initially reviewed two example routes (Basingstoke to Bournemouth/Weymouth and East Croydon to Brighton) with a high level examination of the entire network. A major feeding diagram for the Brighton line configured in a 50kV autotransformer system was fascinating.

The debate then looked at possible economies – for a similar duty, the energy consumption on an AC system is around 15% less than for a DC system.

Input on infrastructure

Railways are a system, so an important part of the agenda for the day was to examine the effect of electrification on various aspects of the railway’s infrastructure. This was reviewed first of all by David Weedon, principal signal engineer for the Thameslink programme. His role is to lead signal engineering activities across the programme as the ‘Technical Authority’ for signalling; and thus he is well placed to appreciate the interaction between electrification and signalling and telecommunications. The S&T function has developed alongside electrification for many years but one task that remains is to develop suitable standards in connection with autotransformer systems.

Generally, the interface with electrification is less of a problem with the more recent signalling technology and moving AC electrification systems into an existing DC electrification area is seen as a preferable option. However, David reminded us that dual AC / DC system areas are much more challenging. Robust, relevant standards should be introduced as soon as possible in order to avoid having to demonstrate interfaces and compliances every time a technological item comes along.

Bill Free then entered the ring to give the civil engineer’s view. Bill is head of business development for Carillion Rail. The impact Image2 [online]of overhead electrification is, of course, significantly different to that of the DC system, but the provision of improved clearances has been part of the civil engineering structural workload in recent years. Appropriately Bill has been closely involved with clearances for freight movement on the very route we are looking at as a case study, including the major works in Southampton tunnel. He emphasised the need, and the ability, to undertake structural works with the minimum of interference to day-to- day rail movements.

Other examples included gauge enhancement works on the North London Line and the way in which partnering and early contractor involvement, with everybody working with aligned goals and no ‘man marking’, could improve performance. Bill’s emphasis was also on the encouragement of innovation and clear remits with less preferential engineering – all vital lessons for the industry.

Don’t forget the trains!

No analysis of the subject of the day would be complete without the rolling stock angle and Euan Smith, head of fleet at Angel Trains, was asked to lay out the facts that relate to the issues of traction conversion.

In summary, the rolling stock provider needs to take on board operational fleet requirements and flexibility when making a valid efficiency comparison between modes. The pros and cons of new build and the complexity of modification have to be considered, along with the vital question of the timing of the change. The proposals being discussed affect only a small percentage of the route on which Angel Trains’ Siemens units are used and questions were raised about maintenance requirements and the effect that any modifications would have on availability. Euan pointed out that on the class 440 there was a low level of preparedness for conversion to AC while class 450 was likely to involve less work.

Back to electrification

Last but not least, we moved back to the electrification function with a thought provoking presentation from Graeme Brindle, technical director for electrical and systems engineering at Amey Consulting. Graeme revisited the subject of electrical clearances but also drew attention to the practicalities of the availability of grid connections and power supplies. He also introduced the quaint term ‘vagabond currents’, currents which leave the surface of conductors where they are positive with respect to their surroundings and carry metal with them. They travel via unintentional routes creating conductor heating and electromagnetic interference.

The question of availability of 400kV and 275kV grid lines in the south of the UK needs to be tackled but his core message was that the track is not earthed in DC systems whereas, in AC systems, it must be earthed. These circumstances do not sit happily together. Electrolytic corrosion is likely to appear – the effect is a function of current density and time and an interim situation could be analysed and risk assessed to allow proper management of the phenomenon.

Lineside installation earthing is an issue that is transient during changeover but needs to be carefully assessed for impact. Most lineside installations and structures, such as stations, signalling power distribution and switch heating, will require traction bonding. Supply authorities will also raise concerns about use of their earthing terminal and this could be dealt with by combined earthing, earthing to traction or an isolating transformer interface. However transformers are costly and take up space.

And that brought the session to a close. As well as practical angles and some technical challenges, the day included some illuminating insights into railway history; both blind alleys and opportunities missed. The conference had achieved its aim of promoting robust debate during the question and answer sessions which, allied with much good-natured questioning of figures and data, had produced some very useful inputs and opinions. Both the Railway Engineers’ Forum and delegates agreed that the seminar had contributed to the debate on the future of railway electrification in the UK. It will be interesting to see plans develop further over the coming years.


Please enter your comment!
Please enter your name here

Latest Rail News

Track replacement work will ensure Manchester tram journeys remain safe, reliable, and accessible

 No trams will run between Piccadilly and Piccadilly Gardens between 22 June and 9 July due to essential track...

More like this...