UPFC:

Among the available FACTS devices, the Unified Power Flow Controller (UPFC) is the most versatile one that can be used to improve steady state stability, dynamic stability and transient stability The UPFC can independently control many parameters since it is the combination of Static Synchronous Compensator (STATCOM) and SSSC. These devices offer an alternative mean to mitigate power system oscillations.

Static Var Compensator (SVC):

Static var systems are applied by utilities in transmission applications for several purposes. The primary purpose is usually for rapid control of voltage at weak points in a network. Installations may be at the midpoint of transmission

interconnections or at the line ends

Thyristor Controlled Series Capacitor (TCSC):

TCSC is one of the most important and best known FACTS devices, which has been in use for many years to increase the Power Transfer as well as System Stability.

Static Synchronous Series Compensator (SSSC):

The SSSC is one of the most recent FACTS devices for power transmission series compensation. It can be considered as a synchronous voltage source as it can inject an almost sinusoidal voltage of variable and controllable amplitude and phase angle, in series with a transmission line. The injected voltage is almost

in quadrature with the line current. A small part of the injected voltage that is in phase with the line current provides the losses in the inverter. Most of the injected voltage, which is in quadrature with the line current, provides the effect of inserting

an inductive or capacitive reactance in series with the transmission line. The variable reactance influences the electric power flow in the transmission line.

International Journal of Computer Applications (0975–887) Volume 8 –No.4

, October 2010

Comparison of FACTS Devices for Power System Stability Enhancement

by D.Murali,, Dr.M.Rajaram, and N.Reka

Link : http://www.ijcaonline.org/volume8/number4/pxc3871701.pdf

From the applications of different Facts Devices We can observe that the

Thyristor Controlled Series Capacitor (TCSC) is the simplest Device that can be used to increase the Power Transfer as well as System Stability. Power Transfer Capacity can be increased by decreasing the difference between Sending end and Receiving End Voltages and also by decreasing the Transfer Reactance. TCSC does both because it effectively reduces the series Line Reactance..For the same amount of Power Transfer, increase of Max.Power Transfer Capability ( Es * Er ) / X automatically reduces the Initial Power Angle and Leads to increased Power Angle Stability Margin, both for Steady State and Transient Stability. By reducing the Line Reactance the Receiving End Voltage also Increases..

Except Thyristor controlled Shunt capacitor ,all the Facts Devices can do both the Functions better. Thyristor controlled Shunt capacitor also Decreases the difference between the voltages at both ends, but does not reduce the Line Reactance.

UPFC seems to be the Best for both the purposes.

People do not cover both aspects but only one on which they are concentrating.

The exact effect on the other has to be studied, but there will be improvement on the other also.

Dr.P.S.

Thank you professor.