This paper presents a methodology in order to evaluate the security of electrical industrial systems considering security, quality, reliability and availability factors and the system response to sudden disturbances such as short circuit and harmonics.The models proposed using the probabilistic networks theory: Bayesian Networks and Generalized Stochastic Petri Nets. The obtained results allow the identification of hidden failures and erroneus coordination of protection. The models are tested on the IEEE 493 system proposed by the IEEE Gold Book.