الفهرس 
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Abstract
This research outlines the principle of a novel protective technique for short
lines against earth faults. Such technique is based on injecting a precalculated high
frequency signal at the relay location and using appropriate Intel 80386-DX
microprocessor to initiate tripping for lagging circulating high frequency current in
the earth fault loop.
The following topics have been included in details in the present thesis :
Conventional Distance Relays, operating theory, their characteristics and
drawbacks.
Microprocessor based relays, system architecture and different algorithms used
for transmission line protection.
Novel algorithm for short lines protection against earth faults.
Laboratory realization by applying earth fault on line simulator protected by
the 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 earth
faults detection using the proposed algorithm and the associated subroutines.
Investigation for the ranges of frequency used for practical transmission lines
of different operating voltages.
SlDDD1ary for the digital filter algorithms presented in chapter 2.