Taking the challenge
Several test cases were examined at Cherokee Station. They spanned several layers of complexity, beginning with a simple example of how data integration works at the equipment level and then moving to more complex analyses at the system level.
Optimizing PM. As part of the test, software from SmartSignal and Meridium was used to predict the longevity of the seals of Boiler Feed Pump 3A. The current probability of seal failure was determined to be 18.8%. Based on historical performance data and assuming normal operating conditions, the software calculated that the probability of failure would rise to 54.6% in 200 days. Although the seals are expected to fail every 318 days, by taking into account the differences between unplanned and planned maintenance costs, the software determined that the optimal PM interval for seal work is 274 days. A key number like that can be used to prioritize critical tasks during planned outages for scheduled maintenance.
Equipment performance data from SmartSignal were used to determine if the seals of pump 3A were healthy enough at the 274-day point to further extend the PM interval. In this case, new mean-time-between-failures statistics were generated to refine the optimum PM time. Additional information from SmartSignal was combined with Meridium's reliability-centered maintenance analysis to reduce time to repair and to determine equipment criticality and appropriate overhaul intervals.
Minimizing failure costs. The same boiler feed pump was analyzed as part of a system model that also included pumps 3B and 3C. The model assumes that two pumps run simultaneously, with the third serving as a spare to ensure that Unit 3 can always operate at full load. In calculating predictions for the next 1,000 days, the SmartSignal and Meridium software determined that total failure-related costs for the period would be approximately $100,000. A more-detailed analysis of the data indicated that both the 3B and 3C pumps could be expected to fail during the period, but not at the same time.
By predicting failures that can be expected over a fixed period, the system model improves operational planning. For example, $100,000 in failure costs for this system are more than justified by the revenue generated during a 1,000-day run of a generating unit. Alternatively, the analysis may suggest performing critical tasks during shorter outages during off-peak windows as a way to minimize costs while maximizing generation. When this system model is evaluated in the context of a larger system model (for the entire four-unit Cherokee plant, for instance), it may even become feasible to postpone some scheduled outages.
Making output more predictable. The system model also defines the probability of maintaining a desired generation level during any given month. A Weibull analysis of data on Cherokee Unit 4 from January 2003 to December 2004 indicated that the unit's median monthly generation is 192,802 MWh. Building on this analysis, the software tools were used to optimize planned maintenance and reduce system operating risk. Using historical generation data, the condition of the equipment and system can be used to predict future generation based on reliability improvements made at the plant.
Improving operations. The pilot PM project developed dynamic views of all assets in Units 3 and 4. For example, the view of an asset called "Cherokee 3D Mill" now includes the mill's location, work histories, SmartSignal Watch Lists, condition results, previously performed tasks, documented recommendations, and reliability analyses performed on it. The system also can document and manage inspections, calibrations, thickness measurements, and recommendations. At Cherokee Station, Meridium adapted its APMS tools to respond to SmartSignal alerts. Providing a single view of an asset facilitates rapid analysis by plant operators.
Reducing unplanned downtime. During the pilot, generation availability data, Maximo data, and SmartSignal data were analyzed together to further facilitate operator analysis. With all data residing in one integrated system, alerts from SmartSignal can be verified and acted upon more rapidly. Other benefits include the potential for maximizing reliability through root-cause and failure-and-effect analyses. Finally, the integration allows a user to not only measure confidence levels of calculation results but also to more confidently make decisions to defer maintenance. The bottom line—as is usually the case when technology is leveraged in a power plant—is a reduction of unplanned downtime.
Boosting employee productivity. When O&M analysts work off-site, they might be unaware of the external factors that may be creating condition-based alarms. The software integration achieved by the pilot PM program created a more efficient and sustainable system for analyzing problems.
For example, remote analysts were capable of being informed—at the beginning of their shift—of all activities planned for the plant for the day that could produce an alarm. They could obtain that information as easily as by querying a database listing all calibrations due or overdue for monitored equipment. Examples of calibration tasks scheduled for the Cherokee plant were included in the pilot demonstration. A similar query could give the analyst a view of all work activities scheduled for that or any other day, week, or month.
When there is a new alarm, an analyst may want to verify maintenance work in progress on the machine being analyzed. This was demonstrated at Cherokee by having an analyst select a query that returned the Watch List Log, which includes links to associated work histories on the same machine that occurred within seven days of the SmartSignal log date.
When more detailed history is needed, the Meridium application enables a hyperlink to multiple options that include the Watch List Log detail, the asset data sheet, and the work order associated with that entry. The ability to see all events and information related to a specific asset and an entire system, and to monitor work performed on a remote plant, dramatically improves employee productivity.
Final results
By hosting the pilot PM project, Xcel Energy learned that it could potentially save $1 million at Cherokee Station by reducing maintenance and fuel expenses and maximizing generation revenue. That the pilot project was able to draw that conclusion in just a few months made it a complete success.
"When you think about 'utility innovations,' those are two words you don't normally put together in the same sentence, said Xcel Energy's Chairman, President, and CEO Dick Kelly in his Edison Award acceptant speech. "But I think in the future you'll look to companies like Xcel Energy, and whether you're addressing environmental challenges, customer service issues, or whatever it may be, hopefully you'll see innovative techniques that enhance the business and improve its day-to-day operations."
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