The progressive increase of renewable energy sources (RES) share during past decade strongly reflects on power system operating conditions. Romania is the South Eastern European country with the largest RES generating capacity. This paper proposes a novel method for assessing the impact on national power systems operation of integrating high shares of RES. Specifically, the method addresses first a variability analysis of RES production, based on historical records over 10 years for the Romanian power system. Wind energy is selected as the RES with the widest confidence interval, thus generating the largest power output fluctuations. Further, different simulation scenarios are defined in terms of variable wind energy share. The values obtained are integrated in a scaled simplified model, implemented in PSS/E. The impact of generating sets based on wind energy employment on voltage magnitude and transient time is assessed in fault conditions. Considering that the simulation scenarios defined comprise variable wind energy generation shares, this study emphasizes the impact of its dynamics on power systems. Simulation results highlight the negative influence of increasing wind energy share on the analyzed quantities. The outcomes of this research can suggest a particular analysis approach useful in studying power systems operation. (C) 2019 Elsevier Ltd. All rights reserved.