With the increasing insertion of renewable sources, the evaluation of the performance of electrical systems has become critical, given the intermittency of these energy resources combined with network equipment failures. This work presents the use of probabilistic power flow, based on Monte Carlo simulation and the cross-entropy method, to estimate the risk of inadequacy of electrical quantities, such as overload problems in electrical branches or undervoltage in buses. The objective is to determine, in a precise and computationally efficient way, the probability of the system not meeting operational criteria, considering load, generation and transmission uncertainties. The method is applied to the IEEE RTS 79 test system and also in a modified version with the inclusion of a wind farm and the results are widely discussed.