Abstract: A series compensator, connected in series to an AC transmission line, for compensating for an electric amount, such as a voltage, current, phase or impedance, of the AC transmission line, comprises a first capacitor and a second capacitor connected in series to each other and connected to the AC transmission line, and a compensation current generator connected in parallel to the first capacitor. This structure eliminates the need for a bypass transmission line to simplify the main transmission line structure, has an enhanced current controllability, reduces harmonics to be generated and realizes an economical way of ensuring a large compensation amount.

Abstract: A series compensation generator SCG is installed in a transmission line that links various substations SS and the transmission capability of the system as a whole can be increased by regulating the equivalent reactance of the transmission line. Series compensation generator SCG generates a voltage of which the phase angle is shifted substantially 90° in relation to the current flowing in the transmission line, and it also generates a voltage that compensates the voltage drop due to the equivalent reactance. Also, when an electrical fluctuation phenomenon (power oscillation) occurs in the transmission line, it is possible speedily to suppress the power oscillation by detecting the power fluctuation of the transmission line and controlling the compensating voltage of series compensation generator SCG so that it suppresses that power fluctuation.