converter stations are built by the same manufacturer, the two converter stations of the 2,000MW scheme were built by different manufacturers (although both have subsequently become part of the same parent company, Alstom). The Sellindge converter station was built by GEC and the Les Mandarins converter station was built by CGE Alstom. This HVDC-link is long in route, with between the two ends. The undersea section consists of eight long 270kV submarine cables, laid between Folkestone (UK) and Sangatte (France), arranged as two fully independent 1,000MW Bipoles, each operated at a DC voltage of ±270kV. Cables are laid in pairs in four trenches so that the magnetic fields generated by the two conductors are largely cancelled. The landside parts of the link consist of 8cables with lengths of in England, and in France. In common with the 1961 scheme, there is no provision to permit neutral current to flow through the sea. Although each station includes an earth electrode, this is used only to provide a neutral reference, and only one of the two electrodes is connected at a given time so that there can be no current flow between them. The system was built with solid-state semiconductor thyristor valves from the outset. Initially these were air-cooled and used analogue control systems, and in 2011 and 2012 respectively, the thyristor valves of Bipole 1 and Bipole 2 were replaced by modern water-cooled thyristor valves and digital control systems supplied by Alstom. This system remains the world's largest-capacity submarine cable HVDC system. In November 2016, during Storm Angus, a ship dragging an anchor cut four of the eight cable components, reducing capacity by 50%. Repairs were completed by the end of February 2017. The equipment occasionally faults, causing capacity to drop: in a bad year, this might happen several times. To maintain grid frequency and power, the National Grid has a variety of frequency response assets, of which market batteries are the first to respond. In September 2021, a major fire at the Sellindge converter station led to the shutdown of the link. National Grid initially announced that half of the link capacity would be restored within a fortnight, with full capacity being restored in March 2022. The shutdown came at a time of high prices and supply shortage in the UK electricity market, caused by low wind speeds and high prices for natural gas. On 15 October 2021, National Grid