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ABSTRACT
This paper provides a summary of FACTS Fundamentals and its system. The overall process for system studies and analysis associated with FACTS installation projects and the need for FACTS controller models is also discussed. Finally, an introduction to the basic circuits of several FACTS controllers is provided with a focus on their system performance characteristics. FACTS is applicable in parallel connection or in series or in a combination of both. The rating of shunt connected FACTS controllers is up to 800 Mvar, series FACTS devices are implemented on 550 and 735 kV level to increase the line transmission capacity up to several GW. The performance of two parallel FACTS devices – the SSSC and STATCOM has been examined in terms of their ability to provide damping to a power system. Simulation results indicate that both the devices are capable of providing additional damping of oscillation.
I. INTRODUCTION
Electric power systems are among the most complex outcomes of engineering, being the result of the interconnection of a huge number of different devices. Safe and reliable operation of such systems is mainly the result of real-time action of several control devices, which ensures proper operation of the whole system both in steady-state and after an equilibrium condition is perturbed by sudden contingencies. Guaranteeing proper operation of electric power systems is therefore the problem of maintaining system's stability. Although many power systems were firstly devised several years ago, they are still continuously growing in complexity and extension. Many analysis and control tools share with electric power systems the same long history of research
and practical application. Despite this long tradition, the continuous evolution in technologies has strongly affected power systems. In the past three decades, power system stabilizers (PSSs) have been extensively used to increase the system damping for low frequency oscillations. The power utilities worldwide are currently implementing PSSs as effective excitation controllers to enhance the system stability. However, there have been problems experienced with PSSs over the years of operation. Some of these were due to the limited capability of PSS, in damping only local and not inter area modes of oscillations. Flexible AC transmission systems (FACTS) have gained a great interest during the last few years, due to recent advances in power electronics. FACTS devices have been mainly used for
solving various power system steady state control problems such as voltage regulation, power flow control, and transfer capability enhancement. As supplementary functions, damping the inter area modes and enhancing power system stability using FACTS controllers have been extensively studied and investigated. Generally, it is not cost-effective to install FACTS devices for the sole purpose of power system stability enhancement. In this work, the current status of power system stability enhancement using FACTS controllers was discussed and reviewed.
II. TYPES OF FACTS
1. Static VAR Compensator (SVC)
The static VAR compensator (SVC) is generally designed to operate in both inductive and capacitive continuous compensation (shown in fig.1). The TCR serves as the controller basis for the conventional SVC used for reactive power compensation for either voltage regulation or power factor correction. It is known that the SVCs with an auxiliary injection of a suitable signal can considerably improve the dynamic stability performance of a power system .In the literature, SVCs have been applied successfully to improve the transient stability of a synchronous machine . Then, the low frequency oscillation damping enhancement via SVC has been analyzed . It is shown that the SVC enhances the system damping of local as well as inter area oscillation modes. Self-tuning and model reference adaptive stabilizers for SVC control have been also proposed. The transient ability and steady state power handling capacity can be increased by using SVC at the intermediates buses of the long lines.SVC is the faster in response than synchronous condensers.
Fig.1 Static Var Compensator (SVC)
2. Thyristor-controlled Series Capacitor (TCSC):
The thyristor-controlled series capacitor (TCSC) is also based on the TCR which was first developed for shunt connection (fig.2). When the TCR is used connected in series with the line, it has to be always connected in parallel with a capacitor because it is not possible to control the current if the equivalent of the transmission line and the sources is a current source.