Static series compensators applied to very long distance transmission lines

Flexible ac transmission systems are discussed for the power-flow control of lines that are a little longer (about 2,700 km at 60 Hz) than half the wavelength of the power system's frequency. These very long lines do not need reactive power compensation to function properly and, if they are uncompensated, they present, in several important respects, much better behavior than lines with a length above 300 km with conventional reactive compensation. Small series compensation can be used with the GCSC (gate-turnoff thyristor--controlled series capacitor) to control large quantities of active power transmitted by very long lines. A new control strategy is presented for the GCSC, which proves to be efficient, simple and robust. The theoretical principles are confirmed by computer simulations.