Four Categories of FACTS Devices

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The FACTS device concept was introduced by the Electric Power Research Institute in the late 1980. Since then facts devices have become more and more popular in power systems. Before the introduction of FACTS conventional power flow control techniques were there but they were not fast enough, need to be manually operated and lacked proper co-ordination leading to acceptance of FACTS devices. As years pass by more and more advancement in FACTS technologies are evolving.

FACTS controllers can be divided into four categories based on their connection in the network - Shunt Controllers, Series Controllers, Combined Series-Series Controllers and Combined Series-Shunt Controllers. These type of controllers are connected in shunt with the transmission line. Shunt controllers are of variable impedance type, variable source type or a combination of both. They inject current into the system at the point of connection and thereby inject or absorb reactive power and hence regulate voltage at the point of connection. Thyristor Controlled Reactor (TCR), Thyristor Switched Reactor (TSR), Thyristor Switched Capacitor (TSC) and Static Synchronous Compensator (Statcom) are the common shunt controllers. Series controllers are connected in series with the transmission line. They decrease the overall effective series transmission impedance from the sending end to the receiving end and thereby control the power flow. Static Synchronous Series Compensator (SSSC), Thyristor Controlled Series Capacitor (TCSC), Thyristor Switched Series Capacitor (TSSC), Thyristor Controlled Series Reactor (TCSR) and Thyristor Switched Series Reactor (TSSR) are some of the common series controllers.

Combined Series-Series controllers are connected in series with neighbouring lines with a DC link in between them. They control power flow through the installed lines and are also capable of exchange of active power between neighbouring lines. The Interline Power Flow Controller (IPFC) is one such controller Combined Series-Shunt controllers are the most versatile and powerful device among the FACTS device family. They are connected both in series and shunt with the transmission lines. Depending on its main control strategy they can act as shunt and/or series compensator, a power flow controller, a voltage regulator or a phase shifter. Unified Power Flow Controller (UPFC) is one such controller. In this work voltage stability improvement is focussed and hence the shunt FACTS device SVC is used here.

A. Static Var Compensator (SVC)

SVC is a shunt-connected static reactive power generator or absorber which can maintain or control specific parameters of the electrical power system (typically bus voltage). They are called static because they dont have any rotational components

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