Electric power industry have always try to provide reliable electricity to customers and at the same time decrease system costs. High Voltage circuit-breakers are an essential part of the power network. This study has developed a maintenance and replacement scheduling model for high voltage circuit-breakers that minimize maintenance costs while maintaining the acceptable reliability. This model, quantify the effect of maintenance on reliability. A mixture weibull distribution is used to system’s failure rate function and a hybrid hazard rate recursion rule based on the concept of age reduction factor and hazard rate increase factor is built up to model system reliability. The model is based on sequential imperfect maintenance policy. Whenever the equipment reliability reaches the threshold R, an imperfect preventive maintenance (PM) is performed on the equipment. The optimal reliability threshold R is determined by minimizing the maintenance cost per unit time in the residual life of the system. Finally, the model is applied on Esfahan Regional Electric Company circuit-breakers and a maintenance and replacement scheduling is presented. Keywords: High Voltage circuit breaker, Preventive maintenance, Imperfect m, Reliability, Mixture weibull distribution, Hybrid hazard rate function.
