The interconnections between the national power systems was developed parallel to networks of each country. Originally, the interconnections used to get outside help in case of failure could affect the security of a country national electricity supply. In electrical power networks small oscillations appear from time to time. These oscillations concern the quantities determining the equilibrium point of the system, and following which, system stability and system behaviors are influenced. To improve system behaviors and dynamic stability it is necessary to minimize these transient states. The objective of our study is, first, to check the static stability of the high voltage power to small perturbations of electrical network. In this context, we present a study based on the modal analysis of the linearized system. The results of this analysis allow us to obtain the optimal placement of power regulators PSS injected at the input of voltage regulator AVR based on the matrix of participation. The calculation of these parameters is performed by the regulators method residues. In this paper, the study is structured around one main objective: to have a real interconnection Tunisia-Libya with a stable, efficient and solider operation.