Inspection and preventive maintenance optimization of electrographite brushes for a hydrogenerator unit in the Brazilian interconnected power system

The possibility of shutdown due to the wearing of carbon-brush collectors is a major concern on turbine-generators and one of the most frequent motives for preventive maintenance. This paper introduces an approach to estimate the optimal inspection and maintenance periods of carbon-brush collectors used in hydrogenerator units through an algorithm procedure based on sequential Monte Carlo simulation. The approach is characterized by the probabilistic representation of brush wearing and associated emergency stops using real data from a hydroelectric generator unit; the stochastic modeling of inspection as well as preventive and corrective maintenance activities; and the application of a conditional value-at-risk indicator dictated by contracted thresholds of generation unavailability. The approach has been tested with real data from a Brazilian electric utility, providing information on how to safely reduce the number of maintenance periods per year, thus further improving the availability of the generating units. For the generator unit under analysis, optimal values have been found using inspections and preventive maintenances each 0.0192 and 0.8290 years, respectively, considering the expected costs of the worst 3% simulated scenarios.