Relay replacement strategy based on the least unit life cycle cost with minimum maintenance model

Protection device is repairable system, and its routine maintenance is Minimum Maintenance. With the number of maintenance increasing, both the reliability of relay and the economy of maintenance are decreasing. Therefore, it should be replaced at a proper time. The optimal replacement strategy was studied based on relay reliability and maintenance economy according to field data. It first constructed a minimum maintenance model. Then, based on the constructed model, it formulated the replacement strategy as an optimal problem with the objective of least unit life cycle cost. Finally, it obtained the optimal replacement cycle for a field-operating relay with the proposed strategy. In addition, in order to simulate the actual situation with more accuracy, it considered the double protection in the proposed strategy.