Keeping electrification on track

Rail electrification was a polarising debate going back as early as the late 19th century. While some rail networks opted for 25kV AC systems using overhead lines, others chose the 750V DC third rail system, also known as the live rail system which uses a semi-continuous rigid conductor placed alongside or between the rails of the track. Both strategies benefit from faster, more reliable electric trains that cause less track wear than diesel trains, but have their own advantages and disadvantages for rail networks.

Primarily, the 750V DC third rail network is limited by its power capability. The number of substations needed to power 750V DC is significantly higher than 25kV AC, as a lower voltage requires more electrical current.

When Peter Dearman of Network Rail suggested that the third-rail network should be converted into 25kV AC overhead lines in June 2011, it was less surprising when the UK government announced its £4.2bn investments in 25kV AC rail electrification schemes only.

As of April 2019, 3,736 miles of British rail network were electrified. That’s 38% of the nation’s tracks. Of this electrified system, only a very small fraction is 750V DC third rail. The electrified network is set to expand further over coming years, as 25kV electrification is extended to currently unelectrified lines including the Midland Main Line and lines in the North of England.

With 25kV AC now the international standard for rail electrification, what does this mean for locomotive builders? How can train manufacturers meet the varying needs of local rail operators, rail infrastructure and environmental transportation demands?

Ultimately, it’s important to remember a standard isn’t a regulation. While locomotive builders will likely experience the most sales of 25 kV AC trains and systems, it doesn’t remove the fact that other electrification systems exist in varying voltages, frequencies and configurations. For example, in some parts of the world, 25kV is doubled to 50kV to obtain greater power and increase the distance between substations, such as the Sishen-Saldanha heavy-haul railway in South Africa.

While some train builder businesses continue to focus on the surplus 25kV AC market, others may niche down on the lesser common electrification systems. Some manufacturers are even creating multi-system locomotives and trains that can operate in more than one voltage. This is already established technology, with some locomotives in Europe capable of using four different voltage standards. Could this level of flexibility become the norm in the future?

Similarly, flexibility is required by the design engineers that are continually developing new rail vehicles in line with rail network developments. Even seemingly low tech parts such as the steering and suspension components can have vastly different design specifications depending on the electric system that the vehicle will be used for.

Take panhard rods and suspension links for example. In a new electric locomotive project, small changes to the design of this part often need to be carried out at short notice, as per adjustments to peripheral parts. This is where supplier relationships are crucial. Rail parts suppliers such as Pailton Engineering can work closely with locomotive builders, to make suspension design changes quickly and keep the project moving.

Small details such as the construction of the rubber panhard joints can make or break the success of the vehicle. Without them, the suspension system is likely to wear more quickly, but not every supplier will give you this design option.

While government investment into rail electrification is certainly welcome, it will be tier two supplier flexibility and capabilities that will ensure locomotive builders can take on the challenge and develop dynamic and long lasting vehicles.