This paper proposes a methodology to measure the impact on power systems caused by the massive installation of Wind Power Plants (WPP) based on the computation of the system loadability by analyzing the PV curves in different scenarios of participation of WPP, considering the probabilistic behavior of the wind through the point estimate method (PEM). This methodology is implemented in the IEEE 39 Bus New England test system by comparing the probabilistic loadability margin between an initial case without WPP and several cases with different percentages of WPP participation, between 9% and 33% of total system generation capacity.