The paper proposes two automatic voltage controllers for the South Korean power system. Simulation results from detailed Korean power-flow models show that the controllers can provide significant improvements in security, quality and efficiency of power system voltage monitoring and control. Operating within a time scale ranging from tens of seconds to a few minutes, the controllers can act upon voltage alarms and voltage insecure conditions to maintain prescribed voltage profile and adequate VAR margins. The control actions include continuous adjustment of generator VAR outputs as well as switching of discrete VAR support devices such as shunt capacitor banks. This paper extends an earlier discrete version of the controller developed at Washington State University and tested at Bonneville Power Administration into a hybrid voltage controller. This paper tests the implementation and application of the previously developed discrete as well as the proposed hybrid controllers in Korean p...