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Contractors World UK Ireland Vol 6 No 2


NewElectrification System

Pioneered In Severn Tunnel

An innovative system for the electrification of the railway

track through the Severn Tunnel is being installed by the

ABC Electrification joint venture that includes Costain.

Instead of traditional overhead wires, the system

going into the 7km-long, 130-year-old tunnel (and several

others on the Great Western route between London

Paddington and Cardiff) will consist of an aluminium rail,

held to the tunnel roof by drop tubes & registration

arms, with the contact wire that carries the power supply

fed into a slot in the base of the rail.

The system is used widely in Europe but not previ-

ously in the UK on ballasted track up to speeds of

125mph. Made by Swiss company Furrer+Frey, the Rigid

Overhead Conductor Rail System (ROCS) 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 pan-

tograph – the device on the locomotive’s roof that con-

ducts the power supply down to the locomotive’s


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.”

In some tunnels the track level has to be lowered to

install electrification equipment:

“Remember that these are Victorian tunnels that

were never designed for electrification. We’re

trying to minimise the amount of intervention

needed on the track.”

Some particular problems facing the ABC

Electrification team, which also includes Alstom and

Babcock, are the environmental factors in the Severn

Tunnel including saline water from the Severn Estuary

above it and soot deposition from the freight trains

carrying coal that pass through it. For that reason, the

metalwork holding the ROCS to the tunnel structure will

be made of very high grade stainless steel with a lifespan

of around 60 years.

It is also the first time – apart from on a test track

– that ROCS has been used above ballasted track.

Previously, it was used in conjunction with slab track,

where the tracks are concreted into the base of a


The whole system is being put through a product

acceptance process with Network Rail.