A Study on Sectionalizing and Coordination of Protective Devices and Voltage Drop Compensation of Rural Distribution System

Abstract

Methodologies are presented in this thesis to study the coordination among the protective devices and voltage drops at different points of a radial distribution system. Maximum and Minimum values of currents due to different types of faults occurring at various points of the distribution system are calculated. The inverse time relays and fuses are modeled by nonlinear time current relations. The definite time relays are modeled by constraint conditions. Impedance model for the radial distribution system is considered to find the fault currents. The effectiveness of the protection scheme is studied using different sets of minimum and maximum values of fault currents for all concerned fuses and relays acting as primary and backup protective devices. In the case of any miscoordination or improper coordination the CT plug multiplier setting and relay time dial setting are proposed to adjust. The optimal coordination of the radial distribution system is calTied out using two- phase technique. In phase I, the constraints for protecting the lines and equipment of the distribution system for primary and back up protection is tested for feasibility of the constraint conditions for protection. In this phase the relay and fuse time-current characteristic curves arc superimposed to visualize and ensure coordination graphically. Phase II endeavors to find out the optimal settings of relays to ensure minimum power interruption. Voltage drops under specified loading at different points are calculated to have an idea about the condition of power at different distribution points of the feeder. As case study, the radial distribution feeders of the Topshidanga 33/11 KV S/S and the Baganchra 33/11 KV S/S, under Jessore PBS-I, a project of Rural Electrification Board is considered for study on sectionalizing and coordination of protective devices and voltage drop compensation. The proposed methodology is tested in a Pentium III PC-based digital computer environment.