Voltage stability has recently become a challenging issue in many power systems. The distribution systems are reconfigured with a view to reduce the system losses and offer a better voltage profile for the utilities. This paper presents a new fuzzy based reconfiguration algorithm that enhances voltage stability and improves the voltage profile besides minimising losses, without incurring any additional cost for installation of capacitors, tap-changing transformers and related switching equipments in the distribution system. Test results on a 69-node distribution system reveal the superiority of this algorithm.
Progressive increase in energy demands and rapid depletion of the existing generation and transmission resources due to various economic, environmental and regulatory changes have evolved a new type of problem, referred to as voltage instability or voltage collapse in power systems. Voltage collapse is generally triggered by large disturbances such as loss of generation, transmission lines or transformers and characterized by a slow variation in system operating point due to the inability of the network to meet the increasing demand for reactive power in such a way that the voltage magnitude gradually decreases until a sharp accelerated change occurs. Many utilities around the world have experienced major blackouts caused by voltage instabilities (Arya et al., 2008, Kundur, 1993, Salama et al., 1999 and Taylor, 1994).
In recent years, the distribution systems experience a sharp increase in load demand on account of the extensive growth of the utilities. Besides, with the advent of deregulation in the power industry, there is a greater focus on managing the network assets efficiently rather than reinforcing the network’s capacity. The operating conditions are thus more and more closer to the voltage stability boundaries. In addition, distribution networks are subjected to distinct load changes everyday. In certain industrial areas, it is observed that under certain critical loading conditions, the distribution system suffers from voltage collapse (Prada & Souza, 1998). Hence there is an urgent need to explore ways to enhance voltage stability (VS) in distribution systems.
Network reconfiguration is a process of altering the topological structure of the distribution feeders by changing the open/close status of the sectionalising and tie-switches. During normal operating conditions, networks are reconfigured for loss reduction to reduce system real power losses, and achieve load balancing in order to relieve the network overloads. The voltage stability of the distribution systems can be enhanced, if the loads are rescheduled more efficiently by reconfiguring the network, that allows to smoothen out peak demands, improve the voltage profile and increase the network reliability. Although there are many research papers discussing the reconfiguration algorithms for loss minimisation of distribution systems (Carpaneto and Chicco, 2008, Carreno et al., 2008, Chang, 2008, Enacheanu et al., 2008, Sivanagaraju et al., 2008 and Zhu et al., 2009), hardly any work related to improvement of voltage stability through reconfiguration is reported (Kashem et al., 2000, Sahoo and Prasad, 2006 and Sivanagaraju et al., 2004).
In the last three decades, fuzzy logic has found its role in many interesting power system applications, such as, load forecasting, power system stabilizer design and reactive power control (Momoh & Tomsovic, 1995) because of its usefulness in reducing the need for complex mathematical models. Fuzzy logic employs linguistic terms which deal with casual relationships between the input and output variables. It becomes easier to manipulate and rig out solutions, particularly where the mathematical model is not explicitly known or is difficult to solve.
A new fuzzy based algorithm that uses the voltage stability index suggested in Chakravorty and Das (2001), for enhancing the voltage stability of a radial distribution system through network reconfiguration is proposed in this paper. This method attempts to improve the voltage profile and reduce the system losses in addition to enhancing voltage stability. The method is tested on a 69-node radial system and the results are compared with that of the methods suggested in Sahoo and Prasad, 2006 and Sivanagaraju et al., 2004.
A new fuzzy based reconfiguration scheme has been developed for radial distribution system with a view to enhance its voltage stability. This approach coined using a simple VSI has been found to improve the voltage profile and reduce the system losses. The elegant nature of the algorithm besides serving to eliminate additional infrastructural cost, will go a long way in enabling it to be suitable for on-line applications for systems of any size.
