Power system problems solved by FACTS devices

AC power transmission started in the late 19th century from low voltage levels and restricted supply areas and changed over time towards larger distances and higher power transfers. Increased transmission voltages have been one important measure making systems capable of meeting growing demands. While in the early days power systems had high reserve capacities economical and environmental constraints gradually increased loading of existing systems closer to their power transfer limits. Long transmission distances, fast changing high power loads and growing interconnection of local area networks imposed new challenges to power transmission like untolerable voltage fluctuations due to load changes, power oscillations, stability issues or unequal load sharing of parallel transmission paths resulting in unnecessary bottlenecks. As the most obvious signs of that changes blackouts of smaller and even larger system supply areas occured. Today power systems face new requirements associated with tremendous changes of the established generation and load structure due to adding renewable energy generation partially replacing conventional power plants at distant locations. New electronically controlled system components were developed and installed to overcome such power system problems. The paper discusses devices for FACTS (Flexible AC transmission systems) like SVCs, TCSCs and VSC-based systems providing fast reactive power compensation and fast controlled active power transfer as key technologies for enforcing power systems and making them able to meet the requirements of today and tomorrow.