First electric trains operate through Severn Tunnel

The first electric service trains began running through the Severn Tunnel on June 5, following an extensive and challenging electrification programme for the four-mile-long estuarine bore.

Following a six-week blockade in 2016, 1,400 supporting structures were drilled into the roof to support rigid contact beams for the overhead line equipment.

However, approaching energisation, electrolytic corrosion was discovered between the copper contact wire and aluminium beams in the tunnel. The corrosion was caused by the dissimilar metals.

An aluminium contact wire system which prevents electrolytic corrosion was subsequently developed, tested and adopted in a year, and replaced the earlier copper installation. Although it is less resilient to wear than copper, Network Rail told RAIL that it does not expect this to be a major problem.

Meanwhile, soot on the insulators caused by diesel trains running through the tunnel was tackled in late 2019. This delayed energisation of the tunnel to after that of the route to Cardiff, but with fewer diesel trains now running through the tunnel, Network Rail is to undertake month-by-month condition monitoring of the tunnel to check for corrosion and emissions pollution. It expects to have to run cleaning cycles every two years or so, although this will be subject to the findings of the condition monitoring.

At energisation, NR Managing Director for Wales and

Western Mark Langman said: “Electrification has reduced journey times between South Wales and London by as much as 15 minutes and provided an additional 15,000 weekday seats compared with a year ago, with the possibility of further increasing the number of services and seats from South Wales in the future.

“It has been a hugely complex task to electrify the tunnel, but I’m thrilled that the final piece of the puzzle is now complete.”

Rail Minister Chris Heaton-Harris praised the ten-year project, while the Welsh Government’s Minister for Economy, Transport and North Wales Ken Skates added: “The completion of the electrification works in the Severn Tunnel is welcome news in terms of improving journey times between capitals and delivering towards our decarbonisation agenda.

“I hope that the completion of this work can be taken as a strong signal of intent from Network Rail and the UK Government that there is more investment to come to improve journey times and capacity across South Wales in the future, including electrification westwards beyond Cardiff.”