Time Based Preventative Maintenance Policies for Circuit Breakers with Multiple Failure Types

The reliability of critical components within large test facilities, such as the Unitary Plan Wind Tunnel (UPWT), is a paramount concern, due to the significant impact of component failures which result in facility downtime and subsequent schedule increases. Testing is on the critical path of multiple aircraft and spacecraft development projects, therefore, a component failure affects not only the test facility but also many development programs which require testing prior to attaining key milestones in order to stay on schedule. Vacuum circuit breakers, which actuate electrical power during wind tunnel operations, are critical single point of failure components. The breakers have several failure mechanisms and associated repair processes. This paper models the recurrent failure and subsequent maintenance events throughout the operation life of vacuum circuit breakers as a trend renewal process. The model parameters are estimated using the maximum likelihood method. Subsequently, a generalized maintenance policy is constructed which maximizes the availability of the UPWT system. The policy establishes optimal preventative maintenance scheduling for individual circuit breakers given their unique failure history.