الفهرس 
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Abstract
With the exacerbation of climate problems and the increase in global warming,it was necessary to turn to renewable energy sources. Hence the use of Distributed Generation (DG) as a way to supply power has increased in abundance recently. The impacts due to the use of DG units must be discussed.Therefore, this thesis presents a study of distributed generation effect on the transients phenomena in electrical distribution systems. Firstly, the impact of DG units on the distribution power system is given. DG definition, classification, advantages and disadvantages are discussed. The contribution of DGs for reducing emissions is presented. Also, the methods used to obtain the optimum size and location of DG units are explained. Moreover, the methods that used to avoid DG disadvantages are compared. There are increasing interest to study the ferroresonance phenomenon, due to the various problems it causes to power quality and the destruction of network parts, insulators and consumer devices. As the ferroresonance leads to a significant increase in voltage or/and current with harmonic presence, both of which represent a threat to the stability of the electrical network and its parts. The influence of ferroresonance on the distribution system is crucial because the distribution system is the network’s closest part to the consumer, and the customer is affected by the power system problems. Secondly, this thesis presents the role of DG in contributing to ferroresonance investigation reduction in the distribution sector. A new method for ferroresonance suppression in distribution system is introduced as a novel technique based on a negative sequence component. Theii proposed method is based on High Ohmic Reactor Shunt Limiter (HOR-SL). The proposed HOR-SL reduces the ferroresonance in Distribution System (DS) by no more than 10.5 msec. Furthermore, this thesis presents a new method to mitigate the ferroresonance in DS integrated with multi-DGs. This is based on RLC Shunt Limiter (RLCSL). It is relied on the negative sequence detector to connect the RLC-SL to the system in the cases of ferroresonance. A comparison between the different methods of ferroresonance suppression is given and it can be seen the efficiency of the proposed methods over others.