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Although there are many studies on application of FACTS unit, especially application of reactive power generating unit for power system to enhance voltage stability amplitude and transient stability as considered, the evaluation and selection of suitable power generating unit (STATCOM or SVC) as well as optimal compensation size in the analysis of steady and transient state is not paid attention to. This article studies the above described issues to give a solution to install reasonable reactive power generating source (kind of Var source, location, size) for the power system. The analysis will be based on the technical factors rather than economic ones. 500kV grid system in Vietnam will be used in the calculation until 2015. To deeply evaluate, the implementation plan of reactive power compensation was only studied for 500kV grid in the South, where the load demand is large and can be dramatically increased. The results of power flow calculation, the analysis of characteristics of PV, OPF, and transient stability were studied through PSS/E-30 software.

Abstract-The power system stabilizer (PSS) is a control device provides a maximum power transfer and optimal power system stability. PSS has been widely used to damp electromechanical oscillations that occur in power systems due to disturbances. If no adequate damping is available, the oscillation will increase result in instability case. Shunt static var compensator (SVC) and Static Synchronous Compensator (STATCOM) is also used to improve system stability. This paper focus on the significant of SVC-PSS and STATCOM-PSS to improve the transient stability of power system in various abnormal condition. This paper shows the simulation result of model for different fault condition with PSS and without PSS, with SVC and without SVC, with STATCOM and without STATCOM, and show how the Statcom and SVC help to improve the stability when PSS is fail to maintain the stability.

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Many of papers refers to study of application for Flexible Alternative Current transmission Systems (FACTS). Especially for using reactive compensators for 500kV power system in order to increase the static voltage stability margin and transient stability enhancement have considered. This paper presents a simulation model of the Static Synchronous Compensator (STATCOM) is developed to study its dynamic characteristics. The developed STATCOM is connected at the Point of Common Coupling (PCC) of the Doubly Fed Induction Generator (DFIG) wind turbine system connected to the weak distribution grid for steady state and dynamic voltage regulation purpose. The purpose of this paper is to solve the above problems in order to suggest a solution of the appropriate shunt compensator for a reality 500KV power system. Simulation results have shown that STATCOM helps to keep the steady state terminal voltage of the DFIG system to its rated voltage during the entire operation region of the DFIG. STATCOM maintains the fast voltage regulation (or voltage restoration) at the PCC during step change in reactive load causing voltage swelling or sagging. STATCOM does this by dynamically exchanging the reactive power with the power grid. The results of this work are of certain practical significance and applicable value.