Novel strategies for identifying voltage control areas in large power systems are proposed. These are founded on the modal energy levels and the instantaneous energy of oscillatory modes for determining voltage control areas of large power systems. The modal energy levels are used for identifying the minimum number of areas into the grid, and the minimum number of control buses per area in order to make a suitable secondary voltage control into the system. The energy levels are conceived regarding the topology of the grid and the dynamic analysis. Then, the instantaneous energy is provided by the Taylor-Fourier transform (TFT), which is taken into account for determining a set of sensible buses during the transient behavior. Both strategies are applied in the New England power system corroborating the applicability and the validity of the proposition.