Is third rail electrification back on the agenda?
Old-fashioned 750V DC could be the solution to fill in former Southern Region ‘gaps’ and even extend the South East network to the West Country and expand Merseyrail’s electric operations.
THE Department for Transport has withheld approval for Network Rail’s Traction Decarbonisation Strategy amid continuing concerns about the cost of electrification. Up to now the assumption has been that the overhead system where current is collected at 25kV AC would continue to be the method used to expand network electrification, but details have emerged of a new initiative by NR to evaluate the use of a ground level conductor rail.
The reason for renewed interest in third rail electrification is the need to in-fill two remaining sections of the Southern network: the branch to Uckfield and the gap between Ashford and Ore, both of which are currently worked by DMUs. To allow a project to be developed, NR and the Office of Rail and Road, in its role as the safety regulator, are working with the Rail Safety and Standards Board to create standards for the future.
If an acceptable specification can be established for new third rail projects it is likely to become an economic solution for an expansion of the network that could include installing equipment on the South Western main line to Exeter and local branches, with the further opportunity of extending Merseyrail operations.
SYSTEMS DEBATE
The debate about electrification systems was first faced by the amalgamated Southern Railway which was created in 1923. It inherited two systems, with the London and South Western Railway choosing third rail current collection at 600V DC and the London Brighton and South Coast Railway opting for an overhead system powered at 6600V AC. At that point the South Eastern and Chatham Railway had proposed a system based on what was described as a protected live rail providing 1500V DC.
The railway was poorly regarded in the London suburban area and had been losing traffic as the tramway network expanded and electrification was seen as providing a cleaner environment and generating traffic as a result of a ‘sparks effect’.
This meant that the business case for electrification was based on greater revenue as well as reduced operating costs.
It took until 1926 for the SR to conclude that the future standard system would be third rail 600V DC with a conversion of the existing routes using overhead equipment.
The reasons for the choice of third rail current collection merit our attention now. The basic virtue of the system is the relatively low cost of installation as compared to providing overhead wire, with its catenary and supporting structures. There is no interference with signal sighting and in the event of disturbance caused by events such as a derailment, the conductor rail can easily be replaced.
So far as traction was concerned the DC motor had proved reliable and sturdy and offered good power output at low speeds, thus delivering the acceleration needed for services with a short distance between stops.
On the downside a greater number of substations were required to maintain the voltage and an electrified third rail brought obvious dangers to
trackside staff and trespassers, with a lack of suitability for shunting yards and freight terminals.
At the time of the evaluation the advantages seen for the AC system was that it permitted locomotive haulage and allowed easier track maintenance, but there were concerns about signal sighting and the potential for fatalities caused by locomotive firemen using long tools. Acceleration from station stops was also poor, but the big constraint was low bridges, which at the time were seen as being countered by dead sections of wiring.
Once the standardised system was agreed on by the SR there was an immense rolling programme of work with 293 route miles and 800 track miles completed by 1931 at a cost of £11.8 million (£856 million at 2022 value), which included rolling stock that in many cases was provided by adapting existing vehicles.
RENEWED INTEREST
The renewed interest in third rail electrification is for the same reason identified in 2003, when Connex and Govia, who were franchise bidders for the South Central contract included proposals to electrify Hurst GreenUckfield and Ashford-Ore, with an estimate for the work from Brecknell Willis of £27 million.
This was rejected by the Strategic Rail Authority as it had costed the two schemes at a hugely higher sum of £154 million. As a result, the franchise holder was required to order Class 171 DMUs for the services instead. No satisfactory explanation about cost escalation was produced, but there was a suspicion that the plan was to use overhead electrification as a prelude to a gradual replacement of the third rail network.
The same intentions surfaced in 2012 when NR published its electric spine proposal to link Southampton with the West Coast Main Line using the new East–West Railway. On sections where there was third rail electrification it would be converted. The idea was not well received as the freight operators said that if the money was available, it should be used to electrify from Felixstowe and the passenger operators pointed out that they had no dual voltage rolling stock.