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GE turbine helps power co-op meet its demand.
By Ed Ritchie
When rapid growth in the northwestern states served by Basin Electric Power Cooperative created demands for more power generation, the utility looked for a flexible generator in the 100-MW range. The search led to a progressive product from General Electric (GE) that represents a breakthrough in design, engineering, and performance.
Basin Electric has a long history of expansion in serving its multistate customer base. It started in May 1961, when 67 distribution cooperatives from eight states met to form Basin Electric Power Cooperative, with headquarters in Bismark, ND. The Leland Olds Station, Basin Electric’s first power plant, came online in 1966 with 210 MW, followed in 1975 by another 440-MW plant located near Stanton, ND.
Since then, generating resources have grown to include three coal-based power plants, two peaking stations, nine combustion-turbine generators, and four wind turbines. Basin also buys the entire output of three wind farms owned and operated by FPL Energy.
Demand on the Rise
Basin’s engineers started seeing substantial growth in their load forecasts in 2002. By 2004, planning began in earnest for the new Groton facility. “We had increased demand from commercial, residential, and industrial growth,” recalls Daryl Hill, Basin’s news media coordinator. “Most of our forecasts are provided by our members, so they are out there looking at what’s coming down the road and the demand for electricity in the next several years.”
After researching the market, Basin found General Electric’s LMS100 gas turbine, a new offering that combined engineering from various GE turbine products. The LMS100 had impressive performance results in tests by GE but had yet to be tested in the field. Taking the first unit was a risk, says Dick Shaffer, Basin’s mechanical engineering supervisor and project coordinator, but the turbine’s features and GE’s reputation won out. Total cost of the project was $69 million, with GE supplying product and construction for a turnkey facility.
“We were looking at something in the LMS100 class that could deliver 100 megawatts, and we also looked at Rolls-Royce and Siemens,” notes Shaffer. “But the LMS100 had the best heat rate of any of them, and that was attractive to us. The best heat rate reduces the operating cost and use of natural gas, which runs about 40,000 pounds per hour under full load. So we get the best fuel per kilowatt-hour.”
The LMS100 was introduced in December 2003. According to GE, it represents some of the most extensive design and manufacturing collaboration in GE’s history, with four GE business units and three other companies participating in the development program. The unit was designed to provide an economical solution for a variety of dispatch needs by combining proven frame and aeroderivative gas-turbine technologies to achieve a thermal efficiency of 44%. Operating flexibility allows for peaking, mid-range and baseload operations with fast start times, load following, and cycling capabilities. It runs on natural gas or liquid distillate.
From Zero to 100 in Record Time
“The LMS100 produces 100 MW in just 10 minutes at 44% simple-cycle efficiency,” says Tom Walker, general manager, LMS100. “That represents a 10% efficiency improvement over other similar gas turbines in the 80- to 100-megawatt range. That is huge for the power-generation industry.”
“That’s good for peaking operation,” adds Shaffer. “Our typical agreement with dispatchers is that we will have additional power to them within half an hour of their call. When the grid is unstable it’s nice to be able to get our power online as quick as possible.”
According to Walker, Groton’s need for fast starts provides the ideal environment for a turbine based on aeroderivative technology. “LMSs are great for peaking because you can start and stop them as many times as you want without maintenance impact. That’s how aircraft engines are designed to operate. You can turn them on and off, unlike larger-frame designs where starting and stopping has a big maintenance impact. Their highest stress is when they start.”
Maintenance is critical because Groton was planned as an unmanned station that’s controlled remotely. Currently, Basin has nine gas combustion turbines in the Gillette, WY, area that are unmanned and operated from a power plant in North Dakota. Service for the turbines is done by staff members that travel a route to maintain the units.
In hot summers, Walker says, performance benefits from the unit’s intercooler technology. “The LMS100 increases in power up to about 75 degrees Fahrenheit and then falls off at a much slower rate than other gas turbines,” he explains.
Basin Electric saw the benefits immediately, adds Hill. “When we went live on July 1, we started running the heck out of it,” Hill says. “We put it online and had one of the hottest summers in a long time in this neck of the woods. We used our generation very hard and for the most part the LMS100 performed quite well.”
Stability in a Clutch
Another bonus for the new plant’s output comes from better power stability. Because the LMS100 is based on a three-shaft design, it maintains current frequency to a range of plus-or-minus 5%. The shaft design also enables the use of a clutch for running in synchronous condensing mode.
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| Basin Electric has a long history of expansion in serving its multistate customer base. |
The synchronous clutch is mounted between the output shaft of the turbine and input shaft of the generator,” says Shaffer. “If you want to operate in synchronous condensing, you can fire up the turbine and run the generator to synch idle speed, which is 3,600 rpm. It will either produce or consume reactive voltage from the system. By shutting your turbine down, the clutch allows the generator to continue rotating independently of the motor. At that point the generator is consuming electricity off the grid. If you want to go back into generation, you restart the turbine and switch to electrical generation, so it’s good for stability.”
The stability factor extends further into the area of fuel efficiency, notes Walker. The LMS100 can run at partial power, such as 50% load, while maintaining a 40% simple-cycle efficiency. “That 40% efficiency at 50% power is equal to or better than the highest-efficiency gas-turbine competitors,” says Walker. “At full load we go up to 44%. All of these specifications have been validated through our test site in Houston, Texas, and at the Groton facility.”
Validation and testing played a key role in Groton’s development, and GE took the unusual measure of building a complete power plant at their Houston manufacturing facility. It has a full-load test capability; but instead of being connected to the grid, it uses a series of load banks to dissipate the power generated by test units. The facility also provided training for GE’s engineering staff prior to the installation and shakedown at Groton. “We accomplished our reliability tests and our installation procedures beforehand,” Walker recalls. “Our field service reps gained experience at the Houston test site, and that was invaluable.”
A Steep Learning Curve
According to Shaffer, it was a good thing that GE came prepared because the learning curve was “very steep. Both GE and our staff are learning a lot,” says Shaffer. This is serial number one so we’re going through some growing pains that I wouldn’t expect on the second unit. GE has been very responsive to our needs and that was one of the incentives to build this unit.”
The worst situation Shaffer remembers was a time when Groton was offline and, as luck would have it, two of the co-op’s other baseloaded units went down the same day. At that point, Basin had to buy power from outside resources to maintain service.
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| The 100-MW LMS 100 provides a single, economical solution for a variety of dispatch needs. |
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Both parties agree that the incident was unusual, and Walker says that overall reliability is strong because GE has leveraged all the pieces from its other technologies, including proven aircraft engines that have millions of hours of operation on them. “Even though it had a few bumps in the road, we have been there every step of the way and have an onsite rep there through the first year of operation, as well as remote monitoring and diagnostics to keep our eye on everything that’s going on. With these resources, as soon as we see any kind of trip event or burp in the system we are all over it, doing analysis and making adjustments as required.”
Walker and GE had to make many adjustments due to the weather in the Dakotas. The schedule mobilized the construction team in late August 2005, and construction continued into North Dakota’s harsh winter, where it’s not unusual to see temperatures of -15°F to -20°F. “Trying to build a power plant for the first time in that kind of weather was extremely challenging and caused some delays,” Walker recalls.
Shaffer adds that since Groton was the first commercial installation of an LMS100, his team expected to encounter unforeseen challenges. Some were related to weather, such as complications of the initial foundation work due to an extremely high water table caused by heavy spring rainfall. In another instance, cold temperatures ruptured heat-exchange tubes located in the intercooler heat exchanger, due to some water being trapped in the tubes, which had been shipped in February.
Cold temperatures also required additional heat tracing to protect against freezing. The heat tracing along with insulation is used to prevent freezing of water lines and instrumentation inside and outside the unit. When the LMS100 is operating, water is injected into the combustor to reduce emissions of nitrogen oxide. Heat tracing and insulation is also used on motorized air and gas valves and actuators that are located outside; otherwise, the valves won’t operate during extreme cold weather. The site is designed to operate at -30°F.
During the design stages, the project went through numerous drawing revisions, but additional requirements for materials such as pipe, conduit, and cable weren’t included in the revisions. Finally, Shaffer notes that the critical package instrumentation has triple redundancy, an approach requiring triple the work for calibrating and triple the source for control issues on startup and commissioning. Moreover, the sophisticated control system demanded constant communication with offsite entities. Nonetheless, Shaffer sums up the installation as “not that much different than any other project of its nature.”
Obviously, LMS100 unit number one has proved itself, because the second unit is on its way. Less than six months after Groton went into commercial operation, Basin signed a contract for the installation of a second simple-cycle, gas-turbine generator to join the first unit at the South Dakota power plant. The second LMS100 is nominally rated at 95 MW and will operate as a simple-cycle, peaking/mid-merit unit. Like the first unit, the next LMS100 will be fueled by natural gas from the Northern Border Pipeline and is connected to the existing substation operated by the Western Area Power Administration.
Walker notes that in a second installation there’s an opportunity to take advantage of a modular approach. But truly substantial savings could come from scaling up to three or more systems that could take advantage of sharing equipment for covering redundancy.
Peaking is again the priority for the second LMS100, and much of it is related to backing up the inconsistency of Basin’s growing wind resources. Basin has close to 136 MW of wind resources. It owns four turbines in North Dakota and two in South Dakota. Additionally, the co-op buys the entire production of three independent wind farms operated by FPL Energy in North Dakota and South Dakota.
“We are being forced into increasing our renewable resources, such as wind,” explains Hill. “But that’s not reliable, so we need to have backup capacity. The LMS100s are very good because they start up quick and you can follow the load with them quite efficiently. So in the future we’re probably going to be chasing wind with them. Reliability is the biggest challenge of wind; it is still tough to accurately predict availability and capacity. Company engineers are gaining experience about how to incorporate wind as a resource and work closely with FPL in scheduling their output.”
For now, Basin expects the new unit to come online in June 2008, and the co-op is also looking at other sites in South Dakota to work in conjunction with the site in North Dakota, which has a baseload power plant. “We are seeing growth that’s increasing quite fast from what we’ve experienced in the past,” says Hill. “It was quite stable over that last 10 years, but now it’s taking off again. It’s very apparent that we’re going to need more generating capacity not only in peaking but in baseload as well.” The next step is a coal-based plant currently under development near Gillette. Plans call for construction to start late this year so that operations can begin in 2011.
Ed Ritchie specializes in energy, transportation, and communication technologies.
DE - May/June 2007
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