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Flexible AC Transmission System
Alternating current transmission systems incorporating power electronics-based and other static controllers to enhance controllability and increase power transfer capability
Constraints on Useable Transmission Capacity
• Dynamic:
– Transient and dynamic stability
– Subsynchronous oscillations
– Dynamic overvoltages and undervoltages
– Voltage collapse
– Frequency collapse
• Steady-State:
– Uneven power flow
– Excess reactive power flows
– Voltage capability
– Thermal capability
FACTS Controllers
• Static VAR Compensator - SVC
• Thyristor Controlled Series Compensator - TCSC
• Thyristor Controlled Phase Angle Regulator - TCPAR
• Static Synchronous Compensator - StatCom
• Solid State Series Compensator - SSSC
• Unified Power Flow Controller - UPFC
US FACTS Installations
Power Flow Control
• Power transfer between areas can be affected by adjusting the net series impedance.
• Transmission line capability can be increased by installing a series capacitor which reduces the net series impedance
UPFC Capabilities
• Increase transmission line capacity
• Direct power flow along selected lines
• Powerful system oscillation damping
• Voltage support and regulation
• Control of active and reactive power flow at both sending- and receiving-end
Operation
• Reactive power is generated or absorbed by the shunt inverter to control bus voltage
• Reactive power is generated or absorbed by the series inverter to control the real and/or reactive power flow on the transmission line
• A portion of the real power flow on the transmission line is drawn from the bus by the shunt inverter to charge the DC capacitor.
• Real power is inserted into the line through the series inverter