RESEARCH ARTICLE Determining the optimal inspection rate of circuit breakers equipped with condition monitoring devices using new maintenance Markov model Ali Karimabadi 1 | Mohammad Ebrahim Hajiabadi 2 | Ebadollah Kamyab 3 | Ali Asghar Shojaei 1 1 Department of Electrical Engineering, Neyshabur Branch, Islamic Azad University, Neyshabur, Iran 2 Department of Electrical and Computer Engineering, Hakim Sabzevari University, Sabzevar, Iran 3 Research Center, Khorasan Regional Electricity Company (KREC), Mashhad, Iran Correspondence Dr. Mohammad Ebrahim Hajiabadi Department of Electrical and Computer Engineering Hakim Sabzevari University Sabzevar, Iran Email: ebrahim.hajiabadi@gmail.com Peer Review The peer review history for this article is available at https://publons.com/publon/ 10.1002/2050-7038.12272. Abstract Nowadays, the maintenance scheduling of equipment has been highly improved using condition monitoring (CM) systems. This paper determines the optimal inspection rate of circuit breakers equipped with CM using a novel mathematical procedure. To achieve this goal, in the first step, it is necessary to quantify the effect of CM on the early detection of minor failures of the equipment. Therefore, a mathematical formulation is provided to categorize and model the failures of the equipment based on their severity. Moreover, a new concept termed predictive maintenance (PDM) rate will be introduced and formulated in this paper. The PDM rate is applied in the maintenance pro- cess as the smart inspection rate of the equipment. In the second step, this paper proposes a new combined preventive and predictive maintenance Mar- kov model. By developing the formulation of the proposed Markov model, an optimization problem is formed. In this optimization problem, the annual maintenance cost serves as the objective function and the inspection rates rep- resent the decision variables. The comprehensive statistical study on the fail- ures of 400kv-CB of KREC in Iran and the implementation of the proposed method indicates that the CM and optimal inspection of the CB not only enhances the lifetime of the CB by 19.48 years but also lower the annual main- tenance cost by 19%. List of Abbreviation and Symbol: μ´ i , outage rate of false detection state i; μ I´i , outage rate of smart inspection state i; μ Ii , outage rate of inspection state i; μ M´i , outage rate of smart minor maintenance state i; μ Mi , outage rate of minor maintenance state i; μ MM´i , outage rate of smart major maintenance state i; μ Mmi , outage rate of major maintenance state i; A s , the number of failure type y occurred with Sensor detection; A x , factor failure type x of equipment; A y , factor failure type y of equipment; C I , average cost per inspection activity; C M , average cost per minor maintenance activity; C MM , average cost per major maintenance activity; C R , average cost per equipment replacement; f F , frequency of occurrence of equipment replacement; f i , frequency of occurrence of each state in the maintenance model; f Ii , frequency of occurrence of the ith inspection state in PM; f 0 Ii , frequency of occurrence of the ith inspection state in the proposed Markov model; f Mi , frequency of occurrence of the ith minor maintenance state in PM; f 0 Mi , frequency of occurrence of the ith minor maintenance state in the proposed Markov model; f MMi , frequency of occurrence of the ith major maintenance state in PM; f 0 MMi , frequency of occurrence of the ith major maintenance state in the proposed Markov model; n s , the number of failure type x occurred with Sensor detection; n x , the number of failure type x occurred; n y , the number of failure type y occurred; P f,d , probability of false detection of CM; P S , available probability of sensor s; q ii , transfer rate between same state; q ij , transfer rate between different state; Q m , failure probability of sensor m; Q n , failure probability of sensor n; λ x , failure rate of equipment; π i , outage probability of state i. Received: 16 April 2019 Revised: 23 September 2019 Accepted: 4 November 2019 DOI: 10.1002/2050-7038.12272 Int Trans Electr Energ Syst. 2020;e12272. wileyonlinelibrary.com/journal/etep © 2020 John Wiley & Sons, Ltd. 1 of 22 https://doi.org/10.1002/2050-7038.12272