FACTS Flexible Alternating Current Transmission Systems

Increased demands on transmission, absence of long-term planning and the need to provide open access to generating companies and customers have created tendencies toward less security and reduced quality of supply. The FACTS technology is essential to alleviate some but not all of these difficulties. The FACTS technology opens up new opportunities for controlling power and enhancing the usable capacity of present, as well as new and upgraded, lines. The possibility that current and therefore power through a line can be controlled enables a large potential of increasing the capacity of existing lines. These opportunities arise through the ability of FACTS controllers to control the interrelated parameters that govern the operation of transmission systems including series impedance, shunt impedance, current, voltage, phase angle and the damping of oscillations. This report is an overview of the existing FACTS devices. It is mainly a summary of [1], [2], [3] where more extensive elaborations on FACTS devices can be found. The IEEE definition to these devices are given in italic in the corresponding sections.