This paper proposes a voltage and reactive power control methodology, which is motivated towards implementation in the KEPCO power system. The main voltage control devices are generators in continuous type and make sure capacitors and reactors in discrete type. Effects of control devices are evaluated by pure reactive power reserve that is exactly to guarantee generator's reactive power margin for severe conditions. The control targets are each of critical buses of local subsystems that are decided by electrical distance in the whole system. The control objectives are to keep the voltage profile and to guarantee the reactive power reserve within constraints with the limit of generator output A robust control strategy is proposed to make the control feasible and optimal for severe contingency cases indicate that the proposed control methodology is much more effective than conventional voltage control scheme in the KEPCO system.