Guest writers: Graeme Brindle and Nathan Sealy
Much has been discussed recently about the state of electrification in the UK, and how it is being delivered at a much higher cost than on the continent.
The article in Rail Engineer titled ‘Getting electrification right’ (issue 164, June 2018) demonstrated the all or nothing method the UK Government has taken in its approach to electrification and the resulting move towards diesel-powered, bi-mode vehicles; an unsustainable option in the pursuit of reducing the nation’s carbon footprint.
North of the border, Transport Scotland has taken a somewhat different approach, and one which seems to have been more successful. Over 25 per cent of the Scottish network is now electrified, and a steady programme of electrification seems to have had results.
In Wales, the Welsh Government took over the franchising of the railway and appointed KeolisAmey to operate and develop the Wales and Borders rail service and South Wales Metro, working in partnership with Transport for Wales, on a 15-year contract from 2018 until 2033.
This lengthy contract term has encouraged both Transport for Wales and KeolisAmey to take a long-term view, which they have already done with the announcement of new rolling stock purchases and a new approach to electrification that taps into hybrid technology already in use in road vehicles.
Balancing the budget
The key challenge of electrification schemes to date has been the ever-rising cost and time to complete the works. Overspend, programme delays and scope reduction of schemes are all reoccurring themes across the board on electrification programmes, largely due to the complexity and extent of the work needed to fully electrify a whole line.
A significant proportion of the cost of any electrification scheme is made up of the track and civils works needed to provide the necessary safety clearances. All overhead line equipment (OLE) has minimum distances to be applied to keep the public safe, such as at any public standing surface (station platforms) and at level crossings.
In addition, many historic bridges and other structures over the railway, built over 100 years ago to much smaller gauge clearances, require considerable alteration work to accommodate the overhead catenary.
These factors mean that a great deal of investment is needed, either to lower the track or raise bridges, to allow for compliant clearances prior to the electrification works. This costly work must be avoided to make electrification a more cost-effective solution.
A different approach to rolling stock
Bi-mode trains are being introduced on several of the UK routes to overcome the limitations of the reduced electrification scope. These trains operate on electric power when under wires but switch to diesel where overhead power is not available.
It’s a simple solution. However, trains must therefore carry pantographs and transformers as well as heavy diesel engines and fuel tanks, all of which need to be carried throughout the journey.
Hybrid technology, now firmly established within the domestic car market, seamlessly blends power from the combustion engine with power from an on-board battery pack. Energy is recovered and stored in the battery through regenerative braking, dramatically improving fuel economy. The latest ‘plug-in hybrid’ cars (PHEV) use the battery pack as the primary power source, with the combustion engine providing an increase in the mileage range and a back-up in the event of an empty battery.
KeolisAmey has come up with a solution for the new Central Metro in Wales that will make use of this state of the art yet well-established hybrid technology in its new train fleets; both tri-mode and metro vehicles.
This change from the existing diesel multiple units (DMUs) on the network to hybrids will lead to a profound reduction in carbon footprint and the on-board batteries will significantly reduce the cost of electrification.
On the Core Valley Lines (CVL), which is everything north of Cardiff Central, tri-mode vehicles will be used from Rhymney and Coryton to Grangetown, powered by OLE and battery only. The addition of the diesel engine adds flexibility to the vehicles to continue on to Penarth, Barry and Bridgend, and elsewhere on the network if future needs demand. (See map, page 38).
Queen Street to Rhymney will operate on OLE and battery power, including an unwired section between Caerphilly and Lisvane & Thornhill, where battery-only operation will be used to avoid costly waterproofing works in Caerphilly tunnel.
Metro vehicles from the three remaining valley heads (Treherbert, Aberdare and Merthyr Tydfil) through to Cardiff Bay will be OLE/battery hybrids only, with no diesel engine. These trains will run wire-free to the new station at the bottom of the Cardiff Bay branch, which will lay the foundations for future ‘on street’ extensions into the city centre.
Permanently earthed sections for cost efficiency
This proposal for the electrification of the Valleys will significantly reduce the number of track and civils interventions. Why? Because the use of permanently earthed sections (PES) will allow the OLE clearances at structures to be significantly reduced, removing the need for many alterations.
These permanently earthed sections of OLE, similar to extended neutral sections, are not a new solution and are already used on conventional electrical schemes for some low structures where track or civils works are not feasible. However, their use is usually only possible in locations where a train has sufficient momentum to ‘coast’ through a non-electrified section – a risk assessment is needed to make sure that a conventional electric train will never stop and become stranded in this area.
The hybrid capability of both new train types means that they can accommodate the use of a PES wherever electrical clearances cannot be achieved, including in station areas. The new rolling stock will switch to battery power through these sections, with the pantograph remaining raised, and switch back to overhead power when live OLE is detected.
The widespread use of PES for the South Wales Metro transformation will avoid up to 55 track or civils interventions across the Valleys. Complex station canopy alterations and the provision of protective screening are also avoided, with track lowering expected to be needed at just 17 sites and only one bridge needing to be lifted.
The cost savings from the use of battery power and PES to overcome areas that are difficult to electrify are evident and, unlike diesel, achieve the zero-carbon operation that is expected of a modern rail network.
This approach to electrification by the Transport for Wales Rail Services, operated by KeolisAmey, may well pave the way for similar methods to be adopted for other networks in the future and, with battery technology ever improving, it is clear that the rail industry must not be left behind.
Graeme Brindle is technical director and Nathan Sealy is regional engineering director, both with Amey Consulting.
This article first appeared in Issue 177 of Rail Engineer, Aug/Sep 2019.