Facts Devices and HVDC - An Overview

FACTS DEVICES AND HVDC
Flexible AC Transmission Systems (FACTS)
According to IEEE,” FACTS is a power electronic based systems and other static equipment that provide
control of one or more AC transmission system parameters to enhance controllability and increases power
transfer capability.” They are electronic based devices that provides fast voltage regulation and control of
power flow thus improving transfer capability of the system. There are three types of transmission lines
classified under compensation namely; uncompensated, series compensated and shunt compensated
transmission lines.
Series compensated transmission line
FACTS is used for series compensation by modifying the impedance whereby line reactance is reduced so
as to increase real power transmitted.
Real power; Ps = V 2
| X | sinδ and reactive power ; V 2
X ( 1−cosδ )
Series compensation application includes fixed series capacitor (FSC), Thyristor controlled series
capacitor (TCSC), thyristor protected series capacitor (TPSC) and Thyristor switched series reactor
(TSSR).
Transmission Line with Shunt Compensation.
FACTS is shunted in the power system to operate as current controlled source. This compensation
scheme is of two types namely; shunt capacitive compensation (SVCs & STATCOM) for power factor
correction and shunt inductive compensation(shunt reactor)
Static VAR compensator (SVCs)
SVCs has no moving parts and provides fast response reactive power on high voltage transmission
network. It regulates p.f, harmonics and transmission system stability. Components of SVC includes
thyristor controlled reactor (TCR), thyristor switched capacitors (TSC), mechancically switched capacitor
(MSC) and harmonic filters. Simplified SVC is as shown in the figure below.