ELECTRIFICATION equipment inside the Severn Tunnel is deteriorating so quickly that trains may have to use diesel mode when running through the 6km structure.
At the moment, the switch from electric to diesel traction on down trains takes place at Bristol Parkway, but it had been hoped to complete electrification to Cardiff later this year.
However. it has emerged that recently-installed earthing straps connected to the overhead conductor rails inside the tunnel are already breaking down. Network Rail had estimated that they would be all right for 25 years.
The first signs of trouble were reported last year.
The problems are due to the highly humid, saline atmosphere inside the tunnel. Pumps remove more than 60 million litres of water a day, which come from the ‘Great Spring’, and there are drainage tunnels under the main tunnel that take water to the pumps at Sudbrook, on the eastern side. Even so, conditions inside the tunnel are always unusually damp, no matter what the weather might be at either portal.
One immediate solution would be to use the diesel engines of the bi-mode Intercity Expresses when passing through the tunnel, but Network Rail has drafted in electrification specialists in a bid to find a longer-term remedy.
The DfT said it was ‘aware of an issue’ and that an investigation is under way to ‘resolve this as quickly as possible’.
In the meantime, Network Rail said it was still on course to be ready for an improved GWR timetable between London and South Wales in December this year.