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New electrification system pioneered in Severn Tunnel

Costain inspecting Severn tunnel

A new system for the electrification of the railway track through the Severn Tunnel is being installed by the ABC Electrification joint venture.

The 7km-long, 130-year-old tunnel is currently undergoing work to install the infrastructure needed to allow electrified trains to run on the line.

The joint venture, which comprises contractors Alstom, Babcock and Costain, said that instead of traditional overhead wires, the system going into the tunnel – and several others on the Great Western route between London Paddington and Cardiff – consists of an aluminium rail, held to the tunnel roof by drop tubes and registration arms, with the contact wire that carries the power supply fed into a slot in the base of the rail.

It said that the system was used widely in Europe but had not been previously used in the UK on ballasted track up to speeds of 125mph.

The rigid overhead conductor rail system (Rocs) has been developed by Swiss company Furrer+Frey and has several advantages over the usual overhead wire system, said Costain project manager John Skentelbery.

“It’s a more robust system than overhead wires, with reduced maintenance,” he said. “It also gives improved contact with the pantograph – the device on the locomotive’s roof that conducts the power supply down to the locomotive’s motor.

“Additionally, Rocs is much more compact than the traditional wired system. It can be used in tunnels where headroom is constrained. Wired solutions need quite a bit of headroom; with the conductor rail system, we can minimise the amount of work needed on the track to give us the necessary clearance.”

Skentelbery added that in some tunnels the track level had to be lowered to install electrification equipment; however, with this system that process could be eliminated.

Some particular problems facing the ABC Electrification team are the environmental factors in the Severn Tunnel, including saline water from the Severn Estuary that is located above it and soot deposition from the freight trains carrying coal that pass through it. As a result, the joint venture said that the metalwork holding the Rocs to the tunnel structure would be made of very high grade stainless steel with a lifespan of around 60 years.

It said that this is also the first time – apart from on a test track – that Rocs would be used above ballasted track. Previously, it was used in conjunction with slab track, where the tracks are concreted into the base of a tunnel.

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