A new method to group the most effective preventive controls for a set of critical contingencies and select the promising groups considering cost and effectiveness is proposed. This methodology is based on a sensitivity analysis of the maximum loadability point with respect to voltage controls and on a hierarchical clustering analysis. Considering not only the effectiveness of the control elements but also their availability, the methodology design a set of controllers to eliminate all critical contingencies. The methodology was successfully tested in a reduced south-southeast Brazilian system composed of 107 buses.