Maintenance resource planning for utility poles in a power distribution network

In this paper, we address the problem of maintenance resource planning for utility wood poles for a power distribution company. The poles are currently replaced with new ones either when they fail or are found in poor condition at regular inspections. As the poles age, a large number of failures might occur, yielding an unexpected increase in the demand for maintenance resources. Timely preventive replacement of poles is one strategy to prevent such an increase in maintenance demand. Therefore, changing the maintenance program such that poles whose ages exceed a threshold value are also replaced at regular inspections can reduce the number of failures in the future and consequently the unplanned demand for maintenance resources. However, determining the threshold age is challenging. To solve the problem, we assume that the failure time of poles follows a Weibull distribution and estimate its parameters by the maximum likelihood method from the available left truncated and right censored data. To justify the necessity of preventive replacement, we then use the delayed renewal process theorem to calculate the expected number of failures in any given interval in the future assuming poles are replaced only at failure. Finally, we propose a mathematical programming model to determine the threshold age ensuring that the expected number of failures in a given future interval is limited. The methodology developed in this paper can be used by any utility to limit the number of unplanned replacements.