Due to the fact that the modeling of perturbations using zero mean Gaussian noises does not always provide a good description of the behavior of fluctuations, the problem of bistable dynamic power systems driven by Markov jump noise processes have been analyzed in this paper. An example of a discrete stochastic model will be presented to reflect perturbations in the switching events due to transformer tap changers. One of the most important features of this model is the capability to properly represent prevailing conditions leading up to voltage collapse scenarios.