In this paper, the new methodology for the determination of circuit breakers (CB) replacement time has been proposed. The methodology is based on statistical analysis of condition monitored data and the impact on substation reliability. Influence of CB removal on substations reliability is presented together with cost justification of such investment. Using statistical data of 427 CBs gathered in past 10 years, Weibull probability distribution of contact resistance for breakers on both overhead and underground feeders and voltage levels of 35 kV and 10 kV is determined. Substations reliability is calculated using minimal path and minimal cuts method. With this methodology influence of CB’s condition on substations reliability can be observed by using real field data. Example of calculation is shown on 35/10 kV substation. Substation reliability calculation is carried out for 5 different scenarios of CB removal with their expenses. At the end, discounted investment costs for each action and period of 5 years are calculated and are shown in table. For this substation final results are showing best scenario with removal CB’s on power transformers.
