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Top1. Introduction
In developing countries like India, there is an unpredictable growth in industrial as well as commercial power demand. Thus, it becomes a challenging task to supply reliable and secure power to the consumer. With the increasing demand for electricity and the growth of power transfer, the power system becomes increasingly more difficult to operate, and more insecure owing to unscheduled power flows and higher losses.
The optimal power flow (OPF) is a power flow problem in which certain controllable variables are adjusted to minimize an objective function such as the total cost of active power generation and/or the losses, while satisfying physical and operating limits on various controls, dependent variables and function of variables (Kothari & Dhillon, 2004). OPF is a very large, non-linear mathematical programming problem and hence took years to develop efficient algorithms for its solution. The first person to introduce the concept of OPF problem (OPF) was Dommel and Tinney in the year 1968 (Dommel & Tinney, 1968). The OPF solutions are carried out to determine the optimum operating state of a power network subjected to physical and operational constraints (Enrique, Claudio, Hugo & Cesar, 2004). As introduced by Hingorani in 1988, with the rapid development of self-commutated semiconductor devices, it is possible to design power electronic equipments known as the Flexible AC Transmission Systems (FACTS) devices (Hingorani, 1988) to get secure power flow solutions. The objective of using FACTS devices in power system is to bring systems under control and to transmit power according to the ordered of the control centers, and also allowing the increasing of the usable transmission capacity to its maximum thermal limits. Using FACTS devices, the voltage magnitude of a particular bus of interest, the phase angle as well as the line impedances of a transmission system can be controlled.
The increasing demand in the power generation gives rise to the need for constructing new transmission lines and to transfer more power in the existing lines. But the cost for the erection of towers, providing insulators, drawing conductors, etc., i.e., the conventional means of adding new transmission lines is always expensive. Thus the only feasible option seems to be the increase in the power transfer capability of the existing transmission lines. This can be achieved using FACTS devices within the network.
Among the various FACTS devices, TCSC is one of the most effective measures for increasing the transfer capability of the transmission system, enhancing the stability of power system. TCSC devices are used for reducing the line reactance of the transmission system. The reduced value of transmission line reactance helps to enhance the active power flow in the line. This enhances the transmission system, thereby allowing transfer of the desired power at right line.