Work to install a customised electrified roof track has started in the Severn Tunnel as part of the electrification of the south Wales mainline.
The Swiss-made device is so advanced Network Rail has set up its own engineering course to train contractors how to install it.
The work will eventually lead to a complete closure of the tunnel in September for six weeks.
Diversions will go via Gloucester.
The component, called the Overhead Conductor Rail System, has been customised in Switzerland and this version of the system has not been installed on a British public track before.
Anthea Dolman-Gair, senior programme manager for Network Rail, said: "A system similar to this has been used on the continent for a while, but this is the first time it's been adapted to be part of the new overhead electric system we are fitting into this country.
"Several years of engineering design and development have been put into this system. We use high-grade stainless steel that's typically used in the maritime industry so it doesn't corrode."
Installation and maintenance of the system requires a qualification not previously taught in Britain.
Network Rail engineers have set up a section of the new rail system in a workshop in Coleg Y Cymoedd in Nantgarw, Rhondda Cynon Taff, to train local contractors.
Some are former miners, and instructors say they have a natural aptitude for this kind of engineering.
Judith Evans, principal of Coleg Y Cymoedd, said the institution could expand off the back of the electrification programme.
"We've got four campuses across Rhondda Cynon Taff and Caerphilly. This particular facility in Nantgarw is easily accessible from the M4.
"I've already started having discussions within the college about whether or not in the next year or two we might even consider expanding. If the growth continues at the speed it is, I can see us having to put on an extension in the future."
The component is designed to have very little maintenance once installed, saving money.
The tunnel will be completely closed for six weeks in September to finish the work. Trains will be diverted around the tunnel via Gloucester.
Source: bbc.co.uk/news