Increasing the utilisation of the Finnish 400 kV grid

The Finnish power system is a part of the synchronous Nordic Power System (Nordel). The transmission capacity of the Finnish 400 kV grid is defined by Nordel´s dimensioning criteria. As an owner of the bulk of the grid IVO Transmission Services Ltd. (IVS) is searching for means that allow the 400 kV lines to be operated closer to their thermal limits. The problem being maintaining the voltages in case of severe faults, we concentrated on comparing different reactive power producing components, both thyristor-controlled and mechanically switched devices. The best alternative turned out to be the fixed series compensation of certain lines which gives a capacity increase of some 30% in the worst bottleneck of the grid. The total cost (including the losses) of this solution is considerably lower than that of building new lines. The new FACTS technology was also considered but the extra cost associated with controllability would not be justified in our case