Electrical Power System Essentials

5.6 FLEXIBLE AC TRANSMISSION SYSTEMS (FACTS)

In the power system, the power flow follows the laws of physics. In the past, the possibilities to control the power flows in the system were limited; they were mainly based on mechanical devices, such as transformer tap changers and turbine governors. These mechanisms automatically introduce a limitation to the speed of control. Nowadays, FACTS devices are available that enable a greater flexibility in the operation of AC power systems (FACTS is an acronym for flexible AC transmission systems) [11,22,23,24,25]. FACTS devices are large power-electronic controlled devices and can do control actions at a considerable higher speed. Some of these devices are operated in a shunt configuration for reactive power and voltage control, whereas others are put in series to control the power flow. This gives the system operator flexibility and a certain degree of freedom in operating the system, which is of great value in the present-day market environment (see also Chapter 7 (Electricity Markets)).

In the previous sections we explained the operating principles of the most common FACTS devices:

• SVC – Static Var Compensator (Section 5.4.3 (Reactive power Injection))
• STATCOM – Static synchronous compensator (Section 5.4.3 (Reactive power Injection))
• TCSC – Thyristor-Controlled Series Capacitor (Section 5.5.2 (Controlling Reactive power Flows))
• SSSC – Static Synchronous Series Compensator (Section 5.5.2 (Controlling Reactive power Flows))
• UpFC – Unified ...