الفهرس 
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Abstract
The Voltage stability problem has an attractive role for electrical power engineers and utility COMPANICS to make sure of system secure operations This problem is mainly a reactive power planning problem The voltage instability may arise when the generated reactive power is insufficient to meet the load demand therefore, this thesis concerns with avoiding this phenomenon by designing a proposed control relict titan the prediction or detection of the Phenomenon lo be able to do Ibis design, it necessitates to study the voltage stability phenomenon first then it is essential to choose the most convenient model of the power System The different models are studied and the sensitivity model is chosen to deal with the problem as a static problem the internal sources of reactive power should be utilized completely to coves the load requirements as the power system growing Increases, the Planning of reactive power overall the system it difficult to some extent in the case it is better to decompose the system into subsystem (subareas) which can be considered as voltage Control areas The cloistered algorithm is applied for this purpose When the internal reactive power source are insufficient w feed the demand ،increase, the external source must be involved the SVCa arc used as external reactive power sources Their locations ,are determined according to both participation factor and participation of each bus and each subarea, respectively Consequently, the coordination between the internal and external sources of reactive power is takes into consideration with a goal of avoiding the risk of voltage collapse in power system this coordination is the basic idea which the technique of proposed controller is built Upon This technique coordinates between the reactive power of exaction system and that of static var cornpensators (SVCs) The method starts with the decomposition of system into several voltage control areas (Vt As) When a reactive power deficiency occurs in a certain Area the excitation system, response first to supply the required reactive power by increase Reactive generation of synchronous generators to its Upper limit. If more reactive power is needed within the specific area to recover voltage instability. a SVC will be inserted by a Switching controller in order to increase the reactive power reserve This controller receives in actuating signal when the terminal voltage is will wieatisfcto1y, By this technique, it is possible to fully utilize the excitation systems reactive power, and to deign the economic size SVCs to recover voha1e instability the application of the proposed technique on the New England 39 hut system proves its efficiency in controlling voltage instability.