A method for the reliability analysis of power system has been develop
ed that includes the behaviour of the system during a disturbance. The
power system is modelled as an electrical network in which branches a
re removed and inserted by stochastic events, generated by a Monte Car
lo simulation. This method considers short circuits followed by an int
erruption of the protection, in stead of just the removal of a compone
nt. By using a maximum-permissable voltage sag as an interruption crit
erion the method can be used for industrial power systems with sensiti
ve loads. The (correct and incorrect) behaviour of the protection, age
ing of components, and the influence of preventive maintenance are als
o included in the method. An example of the use of the method is given
: a power system feeding four industrial plants. The influence of plan
t voltage solidity and of preventive maintenance in the feeding networ
k are investigated. Both turn out to have considerable influence.