Introduction to `FACTS´

In recent years, environment, wayleave and high cost problems have delayed the construction of new transmission. This has highlights the need to change the traditional system concepts and achieve better utilisation of existing lines. The authors gives an overview of flexible AC transmission systems (FACTS) technology which is based on the use of power electronic controlled devices for allowing transmission circuits to be used to their maximum thermal capability. In particular the FACTS devices aim principally to control the three main parameters directly affecting AC power transmission namely voltage, phase angle, and impedance. None of the FACTS devices is new in basic concept but the use of advanced power electronics has revolutionised the design and engineering of them. HVDC is a parallel technology using advanced power electronics and is not normally included as a FACTS technology