Abstract A method for the reliability analysis of power system has been developed that includes the behaviour of the system during a disturbance. The power system is modelled as an electrical network in which branches are removed and inserted by stochastic events, generated by a Monte Carlo simulation. This method considers short circuits followed by an interruption of the protection, in stead of just the removal of a component. By using a maximum-permissable voltage sag as an interruption criterion the method can be used for industrial power systems with sensitive loads. The (correct and incorrect) behaviour of the protection, ageing of components, and the influence of preventive maintenance are also included in the method. An example of the use of the method is given: a power system feeding four industrial plants. The influence of plant voltage solidity and of preventive maintenance in the feeding network are investigated. Both turn out to have considerable influence.