Optimal Sizing and Placement of FCL for Restoring Recloser-Fuse Coordination in DG-Integrated Distribution System Using MOPSO Algorithm

Abstract

With the demand for a more reliable power supply and the decentralization of the power system, there is a high penetration level of distributed generators in the distribution system. Some merits of DG integration are power loss reduction, voltage profile improvement, reliability improvement, backup supply and so on. The high penetration level of DG in the distribution system has led to the large contribution of fault current by the DG units to the fault location. The problem with the fault current provided by the DG unit is that the proper coordination between protective devices such as recloser-fuse coordination is disturbed. To restore the protection coordination between recloser and fuse, the fault current needs to be reduced. The fault current can be reduced by using a fault current limiter. With the optimal planning of Fault Current Limiter (FCL), the protection-coordination between recloser-fuse can not only be maintained but also the cost associated with FCL installation can be reduced. This thesis is focused on minimizing the size and the number of FCL for maintaining recloser fuse coordination. Moreover, the FCL should also reduce the voltage sag in the distribution system during the fault condition. Because of the flow of large fault current, there is a large voltage drop along the distribution line which results in low bus voltage. Since FCL reduces the fault current, the optimal sizing and placement of FCL should also minimize the voltage sag. Thus, in this thesis, the four objective functions:- the reduction of the fault current through the protective device to restore recloser fuse coordination, the reduction of the size of FCL, the reduction of the number of FCL, and the reduction of voltage sag during fault conditions are considered. The optimization problem is solved by using the Multiple Objective Particle Swarm Optimization Method (MOPSO) which uses non dominated solutions found in the external repository to guide the flight of the particle in the search space. Unlike PSO which gives a single solution to the optimization problem, MOPSO provides a set of non-dominated solutions which are called Pareto optimal solutions. Out of many non-dominated solutions, the best solution for the optimization problem is the solution with the minimum number of FCL along with a minimum size that can restore the recloser fuse coordination as well as maintain the voltage sag during the fault condition. The optimal calculation of size, number and placement of FCL are considered for two test systems: Canadian Bench Mark Test System, and IEEE 69 bus test system. The iv optimization problem using MOPSO has been solved in MATLAB and the results are simulated and verified in ETAP software. For the Canadian Bench Mark Test System, only two FCLs with a total size of 3.093 pu was found necessary. The current minimization and voltage minimization indexes were 8.867 pu and 0.530 pu respectively. Similarly, for IEEE 69 bus system, 12 FCLs with a total size of 1.978 pu was found necessary. The current minimization and voltage minimization indexes were 28.276 pu and 0.492 pu respectively.