What are FACTS devices and how do they improve power system performance?

FACTS (Flexible AC Transmission Systems) use power electronics for dynamic control of transmission parameters. Devices include: SVC and STATCOM (shunt compensation for voltage control), TCSC and SSSC (series compensation for power flow control), UPFC (combines series and shunt for comprehensive control), and IPFC (coordinates multiple lines). Benefits include: increased transfer capability, improved stability, power flow control, and reduced losses. FACTS enables better utilization of existing infrastructure but requires significant investment and coordination with protection systems.