To provide reactive VAr control in order to support the power supply system voltage and to filter the harmonic currents in accordance with Electricity Authority recommendations, which prescribe the permissible voltage fluctuations and harmonic distortions, reactive power (VAr) compensators are required.
Static var compensator (SVC) is a shunt connected static var generator or absorber whose output is adjusted to exchange capacitive or inductive current to maintain or control specific parameters of the electrical power system (typically bus voltage). At least four different types of static Var compensator (SVC) are available.
In case increasing the power is required the series compensation is the most appropriate selection as Fig. 8.11 depicts. The most important supplement of shunt compensator is to increase the power stability of the system. The phase-shifting compensator has a great potential for symmetrical systems under exceeding or unpredictable phase differences.
The most widely used device is SVC first installed in 1970s and it is known that the total installed SVC compensator capacity is over than 100.000 MVA. It is also noted by literature that over than 700 conventional series compensation plants are installed worldwide that are capable to compensate around 350.000 MVA total power.
Capacitor provides reactive impedance that causes proportional voltage to the line current when it is series connected to the line. The compensation voltage is changed regarding to the transmission angle δ and line current. The delivered power P S is a function of the series compensation degree s where it is given by
The PST are the most common compensators used in power flow control . The drawbacks of this device such as higher footprint and maintenance requirement have promoted the alternative compensators as UPFC) , IPFC , and DPFC . Although the UPFC was known for a long time, it is installed for testing and improvement applications.