Design of Distance Protection Scheme for an 11kv Distribution Feeder

Abstract

Electrical power system has a high impact on the services of the society and in order to ensure healthy operation of the power system, adequate protection systems are required to mitigate the effect of faults as faults are inevitable in power systems. This research work majors on the application of a distance protection scheme to transmission lines in order to identify a fault and issue a trip command to clear the fault in the least possible time. In power systems, load flow analysis is regarded as the mother of all engineering studies, thus it is imperative to perform a load flow to determine the existing state of the power system network, that is, bus voltages, phase angles, active and reactive power flow through various branches and loads under steady state conditions as well as line losses. Maximum and minimum short-circuit analysis were also required to determine the fault currents at various buses thereby ensuring adequate selection of protective devices. The method of distance protection scheme used was a three-stepped distance protection scheme in which the transmission line was segmented into three zones; 70%, 90% and 100% and the discrimination between each zone was 200ms in order to ensure proper coordination of the protective devices. It was observed that some of the buses were suffering from the effect of under-voltage, thus, capacitor banks were employed for voltage improvement thereby preventing overload. The software used for modelling and analysis is known as Electrical Transient Analyzer Program (ETAP).