UK's Western HVDC Link due back in service week starting March 15: Nat Grid

London — The Western HVDC Link is expected to return to service week commencing March 15, National Grid told S&P Global Platts March 5.

The 2.25 GW subsea cable, which runs from Hunterston in Scotland to Flintshire Bridge in Wales, helps transit Scottish wind to load centers in the south, sidestepping the transmission bottleneck on the Scottish border with England.

The 420-km cable "tripped on Monday 15th February 2021 and is currently unavailable. It is expected to return to service w/c March 15th 2021," a National Grid spokesperson said. No reason for the outage was given.

The asset, owned by National Grid and Scottish Power, has suffered a number of technical problems in the run-up to and since full operation in October 2018.

This prompted energy regulator Ofgem in January 2020 to launch an investigation into delivery and operation of the cable, with an outcome yet to be published.

A consortium of Siemens and Prysmian built the link, the first submarine interconnector to use a DC voltage level of 600 kV.

"Since the link went offline on Feb. 15, GB metered wind output has been sharply constrained, with output up to 2.1 GW lower than National Grid's final forecasts, failing to outturn above 12 GW," S&P Global Platts Analytics said March 3.

Within the Balancing Mechanism, the volume of accepted bids in Scotland reached 430 GWh in February, up from 46 GWh in January when the link was fully available, it said.

Between Jan. 1 and Feb. 15 National Grid reported daily average constraint costs of GBP0.5 million/day. This rose to GBP6.1 million/day from Feb. 16 to Feb. 25, before wind generation dropped.

"Balancing Services Use of System (BSUoS) charges – the cost of balancing the transmission system of which both generators and suppliers are liable – reached an intra-day high of GBP15.3/MWh on Feb. 25, the highest level since Dec. 27, 2020," Platts Analytics said.