This work presents the observation and analysis, in steady state and dynamic performance, of the phenomenon already observed in real operation conditions of the Brazilian Electric System, which is the opposite relationship between the controlled value and the target value. In this case, even if the resources have margin to keep the voltage controlled, this is not useful. For example, the reduction in the turn ratio on load tap changer transformer, with the aim of increase in the controlled voltage, result in its reduction, until the tap changer limit is reached or the system is led to the collapse. To demonstrate the existence of this problem, steady state and dynamic performance simulations were done, and the voltage control effect by on load tap changer transformer and static var compensator , current situations in a power system. Several situations where is possible verify the operation region changing was demonstrated. For steady state analysis was used a load flow algorithm and, for the dynamic analysis, a time domain simulation. In the simulations with on load tap changer transformer, it was possible to verify the existence of the reverse effect of the voltage control action in the static and dynamic analysis. In the simulations using static var compensator, a divergence was found between the results in the two analyses.