High-voltage cables were installed in the disused Victorian railway tunnels in the 1960s, bringing new electricity supplies to the Manchester area from power stations east of the Pennines.
The decision to put cables in the tunnels rather than building new overhead power lines across the moors was made after representations to a public inquiry by the Peak Park Planning Board. The tunnels were bought by National Grid's predecessor organisation, the Central Electricity Generating Board (CEGB), and are now owned by National Grid.
The Woodhead Tunnel cables form part of the 400,000-volt transmission system, which runs between National Grid's substations at Thorpe Marsh, near Doncaster and Stalybridge, east of Manchester.
These cables are now nearing the end of their operational life and need to be replaced to ensure continued safe and secure electricity supplies to Greater Manchester.
It is not possible to install new electricity cables alongside the existing cables in the Victorian tunnels for two reasons.
Firstly, to ensure continued safe and secure electricity supplies for Greater Manchester, the existing cables need to remain in service while new cables are installed. Because of the confined space, there is not enough room to carry out major engineering works to install new cables in the tunnels alongside the existing "live" 400,000-volt cables.
Secondly, despite a great deal of maintenance work over the years, the condition of the Victorian tunnels has continued to deteriorate and they would require considerable civil engineering works at substantial additional cost to be made safe for long-term use for any purpose.
Therefore the replacement cable circuits have been installed in the third, more modern, Woodhead Tunnel, which dates from 1953. This tunnel was closed in 1982 and was bought by National Grid in the early 1990s with this purpose in mind.
This project forms part of National Grid's ongoing national investment programme and represents a significant investment in the region's power network.