The lack of investments and the ecological matter have limited the expansion of the transmission system. This reality, together with the load growth, makes the electric systems to work heavy loaded. This new condition can lead to situations of voltage collapse. Methods for evaluation the transmission network loading became necessary and indispensable for understanding system performance under these conditions and for making possible secure operation. Analytic tools have been used to evaluate the voltage security of the system in real time. If it is evaluated that the system is not sufficiently secure in relation to voltage, control actions can be determined, in order to move the state of the system for a secure operation point. However, these tools are not the only need. The same control actions that can move away the system from a situation of voltage instability, can also have opposite effect and contribute for worsening the problem, perhaps leading to system collapse. Therefore, it is necessary the development of computational tools to evaluate the adequacy of these control actions. In this work it is proposed a computational tool, based on the linearized set of power flow equations, including equations for voltage control and limits, for the evaluation of the effect voltage control actions. Indexes that allow the evaluation whether the control action is adequate or not are obtained. The indexes can also evaluate the interdependence among the controls, because besides indicating the effect of the control action on the voltage of the controlled bus, they can also indicate the effect on the other voltage controlled buses. The indexes can be calculated in an extremely fast way, and are appropriate for use in real-time operation.