Series capacitors facilitate long distance AC power transmission

For transmission of large amounts of electric power, AC in the overwhelming majority of cases is the established as well as the most cost effective option at hand. In cases of long distance transmission, care has to be taken for safeguarding of synchronism as well as stable system voltages, particularly in conjunction with system faults. With series compensation, the viable distances of AC power transmission become sufficiently large to eliminate altogether the issue of distance as a limiting factor for AC transmission in most cases. Thus, series compensated AC power interconnectors transmitting bulk power over distances of more than 1.000 km are a reality today. Series compensation, likewise, is an efficient means for minimizing the amount of transmission lines needed for a certain power transmission capability of an interconnector. With series capacitors, the capability of already existing power lines can be increased considerably, thereby decreasing the need for building of new lines in cases where the need for power transmission capability in a system is growing. Installing of series compensation, as a rule, is also less costly as well as less time consuming than building of new lines. The paper will present some basic mechanisms for series compensation in power grids, some salient design features as well as recent operational experience of series capacitors for improving of interregional power transfer in a cost-effective and environmentally friendly way.