The present article is aimed to discuss the various operational and control aspects of interconnected power systems. The structure of present day power systems is discussed and it is followed by the identification of automatic generation control (AGC) problem among the overall control of interconnected power systems. The article describes the duties and functional areas of AGC in a power system. The relevant aspects of frequency deviations and associated operating controls, structure of frequency control loops and functions of typical AGC system are described. Keywords: Interconnected power systems, EHVAC/DVDC transmission links, Control function hierarchy, Subsystems, Primary, secondary and emergency control
