Risk-Based Assessment of Unplanned Outage Events and Costs for Combined-Cycle Plants

Unexpected outages and maintenance costs reduce plant availability and can consume significant resources to restore the unit to service. This paper describes a survey and analysis of unplanned outage events for 388 combined-cycle plants, based on 164 D/E-Class and 224 F-Class gas turbines. The 15-year timeframe included over 3000 unit-years of data. The causes and durations of forced outages and unscheduled maintenance were identified, and overall reliability and availability were established for each class of plant. Costs to restore the unit to service for each main outage cause were estimated, as were net revenues lost due to unplanned outages. A statistical approach to estimated costs and lost revenues provides a risk-based means to quantify the impact of unplanned events on plant cash flow as a function of class of gas turbine and plant subsystem. The risk-based assessment defines the range of probable costs of unplanned outage events.