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After the synchronous interconnection of Turkish Power System to ENTSO-E CESA (former UCTE) System, inter area oscillations in the range of 0.15 Hz are prone to occur, according to simulation studies. Therefore, some preventive measures should be considered in order to ensure stable operation of the network after the interconnection. This study summarizes the effects of following measures based on computer simulations: 1) Retuning of power system stabilizers (PSS) of the important power plants in Turkey, 2) Controller modification of static VAR compensators (SVC) existing in steel melting arc furnaces that are supplied directly from the transmission system, 3) Controller modification of ±50 MY AR STATCOM which is designed for voltage regulation, 4) Application of breaking resistors as a backup measure in case of malfunctioning of the other solutions. In addition to individual analysis of each measure, their combined contribution is also analyzed. A load flow scenario, in which Turkey exports 900 MW to ENTO-E CESA System, is utilized as a reference scenario. In simulations, Turkish grid is represented in detail and a reduced representation of ENTSO-E CESA network, which consists of 75 nodes and 133 lines, is utilized. The results show positive contribution of each measure to system damping performance.The study includes comparison of each preventive measure's contribution level and conclusive recommendations.

The Turkish TSO (TEIAS) has been leading a project that aims the synchronous interconnected operation of the Turkish Power System and the ENTSO-E CESA (former UCTE) System. For this purpose, this study concentrates on the specific problems related to the electromechanical systems of large size hydroelectric power plants regarding low frequency inter area oscillations, which are prone to occur once the interconnected operation is established. The expected frequency of inter area oscillations after interconnected operation is close to 0.15 Hz, which is in the frequency range of the speed governing structures of turbines, as explained in the first two sections of the thesis. In the third section, the nonlinear turbine governor model used throughout the study is explained. In the following part, the governor parameter tuning study with regard to the defined performance objectives is explained. Afterwards, the effect of the retuned governor settings of the sample hydroelectric power plants on a simple multi machine power system is shown.Following that, the system wide effect of removing the sources of negative damping, which are strongly dependent on the governor settings of the major hydroelectric

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