This paper deals with the problem of voltage collapse in power systems by presenting a decentralized secondary voltage control. For this purpose the coordination between the joint voltage control available in the generation plants is used to control the voltage level at the transmission system by adjusting a compensation impedance. By using this approach, the generation plants become more sensitive to the system operating and configuration conditions. A sensitivity-based methodology to identify the most effective plants and the impedance value associated is presented. Some examples meant to explore the potential of the methodology are presented and discussed with the help of real systems.