In case of an electrical blackout, it is essential for Transmission System Operators and Electric Utilities to be able to restore the network as fast as possible. To do so, available power generating units have to energize the nearest ones, which in turns, will be able to energize the whole network. This implies to power up overhead lines, transformers, reactances and underground cables.A transformer which is energized is likely to temporarily absorb a significant amount of reactive currents. Depending on the surrounding network, these currents can go together with significant overvoltage: this specific type of resonance caused by the non-linear inductance of the transformer and the capacitance of the network is known as ferroresonance.Depending on the power source, the voltage restoration can be of two types:-sudden, which means that the energization is carried out by closing the transformer circuit breaker on a network which voltage level is imposed by the islanded unit;-or gradual, which means that the voltage of the power source is gradually increased. This is possible when the generating unit has black start capability.This last type is considered less critical as it gives more time for the transformers to have their flux DC component back to zero.To be prepared to such events, voltage restoration scenarios are regularly tested. During one of these tests that will be fully presented in the paper, measurements carried out at several points along the energized network have shown significant inrush currents and overvoltages. Although the voltage source was gradually increased, the transformers residual fluxes did not have enough time to fully decay, this is the reason why some of the transformers had saturated.To understand what happened and quantify the risk of occurrence, the entire case has been modeled on EMTP-RV. The complexity of such a case can be explained by several factors:-Four transformers are energized at once. Their initial states of magnetization are unknown and independent from each other, as well as their magnetization characteristics;-The overhead lines are long and their electrical characteristics are known with a certain degree of accuracy;-As the voltage increase has to be simulated entirely in time-domain, the automatic voltage regulator and the generator of the power source have to be modeled precisely;-As it is well known that the results of such studies are extremely variable and dependent on the initial conditions, many simulations have to be performed to obtain robust results.To cope with all these uncertainties and constraints, a software developed at EDF, aiming at performing parametric and probabilistic studies with EMTP-RV, has been used. A few tens of thousands of EMTP simulations have been launched:-First to understand and explain the phenomenon (by an extended comparison between measurements and simulation results);-Then to precisely estimate the risk of damaging electrical components.Different voltage setpoints of the power source have been considered in the simulations to minimize the risk of damage as much as possible.