Technical and economic aspects of using a long submarine HVDC connection for frequency control

Several new submarine HVDC connections between the hydro-dominated Norwegian power system and the thermal-dominated UCPTE system of Western Europe are being planned, giving a total transfer capacity of approximately 3000 MW. Both existing and new HVDC exchange agreements are based mainly on the pumped storage principle, where Norwegian hydropower is exported during peak load, while surplus energy can be imported during off-peak periods. This paper focuses on an additional benefit of these HVDC connections: the possibility to supply frequency control in the thermal power system of northern UCPTE. Typical costs related to frequency control in thermal generating units are estimated, giving a strong economic motivation for this possibility. Furthermore, it is shown that the substitution of thermal frequency control reserves with a long submarine HVDC connection is possible without additional equipment or extensive control strategies, and without causing large disturbances in neither the thermal nor the hydro system.