Reliability assessments of electrical power substations have been traditionally performed assuming that the failure and repair processes are stationary and making a great simplification on the protective systems modeling. Thus, in order to improve the level of detail of these assessments, this paper presents a method that combines the modeling of failures and repairs as stochastic point processes and a procedure of sequential Monte Carlo simulation for computing the reliability indexes. Its main features are: i. It can manage time varying rates, a necessity for those scenarios considering improvement/deterioration of component reliability, preventive maintenance and repair process performance. ii. It allows the explicit representation of the protective systems, its operating sequence and the effect of their failures. iii. It does not require an exhaustive list of operating states as other methods do. Of course, this improvement in modeling detail has a price; it is the long computational time required by the simulation.