Network Reconiguration for Reliability Worth Enhancement in Distribution System by Simulated Annealing 161 Network Reconiguration for Reliability Worth Enhancement in Distribution System by Simulated Annealing

The distribution system is an important part that provides the final links between the utility and the customers. Most distribution systems in practice have a single-circuit main feeder and are radially configured. The radial distribution system is widely used because of its simple design, generally low cost and supportive protection scheme. This configuration suggests from a reliability point of view that all components between a load point and the supply point must work and therefore poor reliability can be expected as the failure of any single component causes the load point to be disconnected. The reliability in a distribution system can be improved by network reconfiguration, which is accomplished by closing normally-open switches and opening normally closed switches (Brown, 2001). These switches play an important role in reducing interruption durations in the event of a system failure. Two types of switches are normally installed along the main feeders and laterals: sectionalizing switch (normally closed switch) and tie switch (normally open switch). The former is a device that isolates a faulted part from the system so that the healthy part can still be electrically supplied. The latter is a device that recovers loads that has been disconnected by transferring some of the loads to other supporting distribution feeders without violating operation and engineering constraints (Chowdhury, 2001). Apparently, different network configurations due to an alteration of the switch statuses provide different services to the customers. A great deal of work has been done on network reconfiguration (also known as feeder reconfiguration) in distribution systems mainly in the context of active power loss reduction because the cost of MW loss occupies considerable amount of operating cost in the system and therefore small amount achieved from loss reduction is still attractive for electric power utilities. A number of methods have been proposed to solve feeder reconfiguration for loss minimization, such as integer programming (Sarma & Prakasa Rao, 1995) and artificial neural network (Kashem et al., 1998) and simulated annealing (Chang & Kuo, 1994). The reconfiguration problem in this case are normally subject to power balance equations, bus voltage upper and lower limits, line carrying capability of the feeders and radial topology of the network. Other constraints may be taken into account, for example, load balancing 8