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A Flexible Alternating Current Transmission System (FACTS) is a family of Power-Electronic based devices designed for use on an Alternating Current (AC) Transmission System to improve and control Power Flow and support Voltage. FACTs devices are alternatives to traditional electric grid solutions and improvements, where building additional Transmission Lines or Substation is not economically or logistically viable.
In general, FACTs devices improve power and voltage in three different ways: Shunt Compensation of Voltage (replacing the function of capacitors or inductors), Series Compensation of Impedance (replacing series capacitors) or Phase-Angle Compensation (replacing Generator Droop-Control or Phase-Shifting Transformers). While other traditional equipment can accomplish all of this, FACTs devices utilize Power Electronics that are fast enough to switch sub-cycle opposed to seconds or minutes. Most FACTs devices are also dynamic and can support voltage across a range rather than just on and off, and are multi-quadrant, i.e. they can both supply and consume Reactive Power, and even sometimes Real Power. All of this give them their "flexible" nature and make them well-suited for applications with unknown or changing requirements.
The FACTs family initially grew out of the development of High-Voltage Direct-Current (HVDC) conversion and transmission, which used Power Electronics to convert AC to DC to enable large, controllable power transfers.[1] While HVDC focused on conversion to DC, FACTs devices used the developed technology to control power and voltage on the AC system. The most common type of FACTs device is the Static VAR Compensator (SVC), which uses Thyristors to switch and control shunt capacitors and reactors, respectively.
- ^ EPRI High Voltage Direct Current (HVDC) Transmission Reference Book EPRI, Palo Alto, CA: 2017. 1020401.