A two-scale maintenance policy for protection systems subject to shocks when meeting demands

•Activations of a protection system for meeting demands may act as shocks.•A shock may result in an increase in the failure rate of the system.•We propose a new maintenance policy for protection systems: the KMT policy.•KMT policy is based on two scales: 1. time (system age), 2. number of met demands.•The two-scale based policy outperforms the corresponding one-scale based policies. We propose a model for a two-scale hybrid inspection and preventive replacement policy for protection systems subject to shocks due to meeting demands. The policy guides periodic inspections and also considers both the age of the system and the number of demands met as parameters for decision-making on preventive replacement. We considered a non-repairable single-component protection system that is subject to demands that arrive according to a Homogeneous Poisson Process. The activation of the system on demand acts as a shock that increases the failure rate of the system with a given probability. We also considered that inspections are imperfect: they may result in false positives and false negatives. We evaluated the performance of the policy in terms of the cost-rate and rate of unmet demands. Our numerical analysis shows the strategic role of inspections and demonstrates the following: 1. The greater the effect of shocks the more beneficial is the two-scale policy relative to a one-scale policy; 2. The proposed policy performs well when the rate of demands varies over time. These findings are important to practice because they show that maintenance policies for protection systems should be less time based and more use based.