Microprocessor based digital protective scheme for short lines

This research outlines the principle of a novel protective technique for shortlines against earth faults. Such technique is based on injecting a precalculated highfrequency signal at the relay location and using appropriate Intel 80386-DXmicroprocessor to initiate tripping for lagging circulating high frequency current inthe earth fault loop.The following topics have been included in details in the present thesis :Conventional Distance Relays, operating theory, their characteristics anddrawbacks.Microprocessor based relays, system architecture and different algorithms usedfor transmission line protection.Novel algorithm for short lines protection against earth faults.Laboratory realization by applying earth fault on line simulator protected bythe suggested microprocessor based scheme.This thesis also includes three appendices detailing the following points :A The developed software, using the assembly language, to perform the earthfaults detection using the proposed algorithm and the associated subroutines.Investigation for the ranges of frequency used for practical transmission linesof different operating voltages.SlDDD1ary for the digital filter algorithms presented in chapter 2.