Siemens has been awarded an order for a high-voltage direct current (HVDC) transmission system to connect the British and Belgian national grids via subsea cable. Siemens will be responsible for the turnkey installation of both converter stations using HVDC Plus technology with a transmission voltage of ±400kV DC. The customer is Nemo Link, a joined venture between the British grid operator National Grid and Belgian Transmission System Operator Elia Group, who together have founded this joint project. After its completion, Nemo Link will provide 1,000 mw of capacity, enough to power 500,000 households. The link will run 140 km between Richborough on the Kent coast and Zeebrugge near the city of Brugge with a combination of subsea and underground cables. Commercial operation of the link is scheduled for 2019. The contract also includes a service and maintenance agreement for a period of five years.
Using subsea cables Nemo Link will connect two high-voltage alternating current (HVAC) electricity systems separated by the North Sea. The utilization of HVDC avoids the need to synchronize the two interconnected AC networks. Both converter stations will be using HVDC Plus voltage-sourced converters in a modular multilevel converter arrangement (VSC-MMC) that convert AC to DC and DC back to AC on the other side of the link. In contrast to line-commutated converter technology, the HVDC Plus system works with power transistors that can be also switched off (IGBT), enabling the commutation processes in the power converter to run independently of the grid voltage. The very fast control and protective intervention capabilities of the power converters provides a high level of stability in the transmission system, which primarily serves to reduce grid faults and disturbances in the three-phase AC network. This significantly increases supply reliability for utility companies and power customers.
Siemens HVDC Plus technology allows efficient transportation of electrical power over large distances and in particular for subsea applications with losses of around two percent excluding cable losses. It is also highly controllable and brings operational benefits to both transmission systems. The Nemo Link interconnector will allow power to flow in both directions and will be the third electricity connection between UK and Europe. The 1,000-MW-interconnector BritNed between UK and the Netherlands was also developed by Siemens and went into operation in 2011.
Interconnectors play a crucial role in the European Union’s strategy to achieve a competitive and integrated European energy market. By allowing the UK and Belgium to trade power, the Nemo Link interconnector will increase security and diversify both countries’ electricity supply. To meet international and domestic renewable and climate change targets, the UK and Belgium will generate more power from renewable sources, including offshore wind. By its nature, wind power generation is intermittent and interconnectors provide an effective way to manage these fluctuations in supply and demand.