الفهرس 
chapter 1Only 14 pages are availabe for public view
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Abstract
The relationship between power quality and protective rrelay is cleary appeared in this study. Voltage sags are widely recognized as one of the most important power quality issues facing many industrial customers especially induction motors. Different types of voltage sags (symmetrical and unsymmetrical) cause an increase in current levels, when applied to induction motor loads and may lead to overcurrent relay tripping depending on motor characteristics, motor load, sag characteristics, and relay setting.
In this thesis, an overcurrent relay used for motor loads protection has been simulated to be tested under different type of sags with different severities, both the voltage sag testing signals and the relay model under test are completely simulated . therefor, a proposed algorithm is used to apply wide range of sags with different magnitudes and duration to the relay model, search for the overcurrent peak levels and their durations, and finally describe the relay response in the form of current sensitivity curves and number of relay tripping signals which could be used in relay design. If the survive of motor in service is very important in a certain industrial process, the overcurrent relay could be readjusted, or another function like voltage monitoring technique could be added to the overcurrent protection system.