Has third rail had its day?
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.
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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.
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.
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