New Fenno-Skan 2 HVDC pole with an upgrade of the existing Fenno-Skan 1 pole

SUMMARY Fenno-Skan 2 is an extension of the existing Fenno-Skan 1 scheme commissioned in 1989. FennoSkan 2 is 800 megawatt and 500 kilovolt HVDC interconnector between Finland and Sweden. The total length of the transmission link is approximately 300 kilometres, of which the actual submarine cable will account for some 200 kilometres. Fenno-Skan 2 increases the electricity transmission capacity between Finland and Sweden by approximately 40 per cent, integrating the Nordic electricity market even more closely together. In practice, the inter-connector will reduce temporary differences in the price of electricity between the various countries within the electricity market. The Fenno-Skan 2 scheme also reduces losses in the Nordic transmission grids and improves power system security. The project consists of several subprojects: converter stations at Rauma and Finnbole, including upgrade and retrofit at Dannebo, greenfield HVDC overhead line Dannebo-Finnbole, subsea cable across the Gulf of Bothnia, upgrade of the existing HVDC overhead line Rihtniemi-Rauma and finally the upgrade of the sea electrode. The practical implications of brown field installation and interfaces are elaborated such as semidistributed location of the converter stations and new neutral circuit arrangements. One pole of the 20 years old HVDC overhead line Rihtniemi - Rauma was upgraded from 400 kVdc level to 500 kVdc. Different studies were conducted and conclusions are discussed. AC filter interactions between the poles as well as electrode line unbalance supervision are briefly covered. The 20 years old electrode replacement with new titanium mesh and applied design parameters are discussed. Finally, the power market implications during the transmission testing and mitigation methods are discussed.