Keeping combustion turbines spinning at power plants across Xcel Energy’s service territory is critical to maintaining reliability and minimizing costs. One of the challenges to meeting that goal is scheduling planned outages to maintain and overhaul the turbines, to avoid equipment problems and failures.
The outages must be done quickly to reduce downtime, and that requires careful planning to ensure all needed parts and equipment are available onsite. That used to involve keeping an extensive—and expensive—stock of parts on hand at multiple sites across the fleet.
Working with Key Suppliers
Starting in 2012, however, Xcel Energy began working closely with key suppliers to create an exchange program for combustion turbine (CT) spare and replacement parts. The industry-first program has led to improvements in Xcel’s procurement and management of parts in its growing CT fleet (Figure 1), and has cut expenses by millions of dollars, resulting in savings for customers.
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| 1. A long-time fixture on the Mississippi River. Xcel Energy’s High Bridge Generating Station in St. Paul, Minnesota, was built in 1923, and operated for most of its life as a coal-fired plant. The facility—which takes its name from the nearby bridge across the Mississippi River—was replaced with a natural gas-fired combined cycle generating plant that began operating more than a decade ago. The plant’s combustion turbines (CTs), with generation capacity of 530 MW across three units, are part of Xcel’s CT parts exchange program. Courtesy: Xcel Energy |
Previously, the sourcing of components for a CT overhaul required the purchase of additional sets of spare parts, which were held in corporate inventory and ready for change-out after about 12,000 hours of operation—the manufacturer’s recommended overhaul interval.
The turbine parts were removed for inspection and a qualified supplier refurbished the parts, which were then returned to the company and held in inventory for the next overhaul. The cost of the refurbishment was covered through a plant’s operations and maintenance (O&M) budget, and the process was repeated for two or three cycles, after which the parts were no longer able to be rebuilt. At that point they were retired, sold as scrap, and a new set purchased to maintain the “remove and rebuild” rotation process.
Managing Inventory
The process for procuring and managing the extensive inventory of CT parts was labor-intensive, complex, and costly. In late 2011, a team of employees set out to explore more efficient and cost-effective alternatives. After researching options, the team came up with a plan to shift responsibility for keeping needed turbine parts on hand and available.
The new parts exchange program, launched in 2012, involved building close partnerships with vendors and manufacturers to improve communication and standardize processes. Planning and proactive engagement with all parties has mutual benefits in terms of costs and efficiency of operations. In the first three years of the CT parts exchange program, Xcel Energy successfully completed 15 scheduled overhauls on a variety of turbine brands.
The company’s CT fleet (Figure 2) continues to grow in order to meet increasing demand. There are more than a dozen natural gas-powered generating units in the program, and the program will expand as the company’s gas fleet expands.
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| 2. Moving from nuclear to gas-fired power. The Fort St. Vrain Generating Station in Platteville, Colorado, operated as a nuclear power plant until 1989. It was decommissioned from 1992 to 1996, and repowered in stages from 1995 to 2009 as a natural gas-fired plant. It is among the gas-powered plants benefiting from Xcel Energy’s CT parts exchange program, which launched in 2012. Courtesy: Xcel Energy |
Overhauls have been completed on schedule and within budget since the inception of the program, which has significantly reduced expenses compared to historical practices, and has provided a more consistent overhaul process.
All overhauls have been completed successfully with a team composed of members from Xcel Energy, Power Systems Manufacturing (PSM), and Mitsubishi Hitachi Power Systems Americas (MHPSA)—the spare parts exchange vendors.
Additional Benefits
There are additional benefits as a result of the CT parts program, including other process improvements and operational benefits, such as additional equipment inspections, fuel-nozzle replacements, and operations analysis. The partners also hold regular post-outage reviews to discuss each overhaul, and what works—and what doesn’t—for all parties. In addition, the partners brainstorm new process-improvement ideas to enhance the long-term relationships between the company and its CT vendors.
Since completing the parts agreement, the company team has negotiated long-term service agreements for the existing General Electric, Siemens, and Mitsubishi turbines, and created a new parts exchange program with General Electric for the two newest natural gas-fired units at Cherokee Generating Station near Denver.
The biggest challenge with the program is gaining an understanding of the new process versus the old “way we have always done it” mentality, and ensuring that all parties involved in the overhauls are aware of the agreement details.
Since the implementation of the CT parts exchange program, Xcel Energy has successfully standardized the project scope for inspections and overhauls on its entire CT fleet, along with improved parts performance and extended warranties. The effort allows for extended time between outages, eliminating the need for an entire set of inspection intervals—saving more time and money, and improving the operating availability for the units.
Plans for the future include developing long-term service agreements for overhaul labor and inspection services. Those agreements will promote a further streamlining of the overhaul process; a consistent maintenance management procedure that is easy to forecast, implement, and manage; and ongoing and significantly reduced CT overhaul costs.
—Steve Mills is vice president of operations for Xcel Energy.