Western HVDC Link

Laying a cable down the Irish Sea in 2016, the installation crew found the almost intact wreck of UB-85, a German submarine from the First World War. It was one of the more unusual events in the building of the Western HVDC Link, a 422 km cable that runs west of the Isle of Man from Hunterston in North Ayrshire to Flintshire Bridge, near Connah’s Quay in north Wales.

The link was built to carry renewable power from Scotland southward, by sea, alongside the land routes across the border. How transmission limits force generators to be turned down is explained in the grid congestion guide. National Grid and SP Energy Networks own it jointly.

It set a technical first: the first subsea cable to run at 600 kV. It carries 2,250 MW, with transmission losses of under 3%, and 385 km of its length is underwater. The Wikipedia article on the link gives the cost as £1.2 billion. Siemens built the converter stations and Prysmian the cable.

The build did not go smoothly. Construction began in 2013 against an Ofgem deadline of 31 March 2017. Problems in cable manufacture caused a delay of about a year. The link started at a reduced 900 MW on 7 December 2017, reached full capacity on 16 October 2018, and was formally handed over on 22 November 2019. In November 2021 the two owners agreed with Ofgem to pay a penalty of £158 million over the late delivery, £15 million of it as consumer redress.

The early years were also marked by faults. Wikipedia lists outages from 19 February to 22 March 2019, an undersea cable fault on 6 April 2019, another outage on 10 January 2020, and a month out of service from 15 February to 13 March 2021.

The link now has company. Eastern Green Link 1 and Eastern Green Link 2 will do the same job down the North Sea coast, each at 2,000 MW. Both follow the pattern the Western link set: a DC cable offshore, parallel to a congested land corridor.