Daily increase of the demand for electrical power and the restructuring of the power sector set the main objective of the power system management and control: a safe and reliable power supply with minimum costs and maximum availability. This objective is attained in the optimum way by connecting power systems. Large power systems are formed, which operate on the verge of their technical capabilities in order to minimise costs and losses. One of the significant problems in their safe management and control is the dynamic stability – the larger the system, the more marked this problem. The investigation covers large modern power systems and the role of the HEP Transmission System Operator as the main business entity in power system management and control, dynamic problems and a mathematical model for the analysis based on the eigenvalue analyses, dynamic equivalents of external power systems and optimal linear management and control, issues related to subsynchronous resonance, static and dynamic characteristics of the 1st and the 2nd zones before reconnection, the procedure of power system connecting and power efficiency results. The thesis provides a mathematical model and a theoretical consideration of the problem of dynamic characteristics of connecting two large power systems: the 1st and the 2nd Pan-European synchronous zones. Practical implementation of the project has provided valuable scientific and practical insights, which were presented at international and national conferences and professional meetings. Calculations, measurements and results of the power system connecting are used in projects of further expansion and connection of the Pan-European power system.