الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The voltage generated by power stations has a sinusoidal waveform with a constant frequency. Distortion in Voltage can lead to problems affecting the operation of electrical and electronic devices. Sensitive loads, like electronic equipment and nuclear installations, need pure sine wave shape, constant frequency and symmetrical voltage with a constant RMS value. Power quality issues have become an increasing concern with the increase of sensitive loads. Many crucial production processes face huge economical losses with improper quality in the distribution system. Some of power quality problems are voltage sags, voltage swells,voltage unbalance, harmonics distortion and short interruption.Voltage sags can occur more frequently than any other power quality phenomena in the power distribution system. Voltage sag is produced by a magnitude change in sensitive loads with or without a phase shift in the supply voltage. The voltage temporarily drops to a lower value and returns back again after a certain period of time. The causes of voltage sags on the line such as short circuit faults, motor starting and transformer energizing will cause short duration increase in current. Despite their short duration, such events can cause serious problems for a wide range of equipment. There are different methods to mitigate voltage sags, but Flexible AC Transmission Systems (FACTS) device is considered the most efficient method. There are many types of FACTS such as Solid State Transfer Switches (SSTS), Distribution Static Compensators (DSTATCOM),and Dynamic Voltage Restorers (DVR). DVR can provide an effective solution to mitigate voltage sag by establishing the appropriate predetermined voltage level required by the loads to protect sensitive equipment. It is a series connected power electronic based device. It has the advantages of lower cost, smaller size and fast dynamic response to disturbances. It can restore the sensitive load voltage within a few milliseconds and hence, avoid any power disruption to that load. ABSTRACT This work presents the DVR to mitigate the voltage sag on sensitive load. The nuclear research reactor is the case study for mitigation of voltage sags problems. The controls of the compensation voltage are based on the DVR control and an improvement of DVR using Proportional Integral controller (PI controller) to mitigate the voltage sag in distribution network are carried out. Different types of faults are applied in medium and high voltage system. The simulation results are modeled by using MATLAB/SIMULINK to examine the improvement of the proposed technique over the DVR control.