On in a Hot Minute

Twelve, actually—that’s how long it takes to fire up a combustion turbine gas plant and tie it to the power grid. These not-so-secret weapons in TVA’s generating arsenal come online quickly to meet peaking power demand on the coldest days.

JANUARY 10, 2018—We’ve seen our share of frigid days and nights this winter, and TVA’s power has been there for every little notching up of the thermostat. That’s thanks to a diversified portfolio that includes plenty of generating assets—including combustion turbines, which are in their glory on the coldest (and hottest) days of the year.

“A combustion turbine plant is a peaking plant,” explains John Moberly (pictured below), site manager at Marshall Combustion Turbine Plant in Calvert City, Ky. “That means when the base load electrical grid has reached its peak and they need additional megawatts, they call on us to provide more power.”

Moberly and his six-man crew can do that very quickly. “CT plants are easy on, easy off,” he explains. “We can tie to the system in 12 minutes, and have our maximum load online in just 17.” Considering that this plant has eight units capable of generating up to 92 MW each under cold winter conditions, that’s a lot of power.

man talking outside in front of equipment

Generally speaking, CT units are used short-term, as they are a responsive, versatile, high-reliability but relatively higher-cost form of generation. However, the Marshall team logged a record-breaking seven 24/7 days between December 31 and January 7, keeping the units online to keep the Valley warm during the coldest snap of the season to date.

“January 2nd was the tenth highest winter peak of all time for TVA, with a demand of 31,740 MW at 8:00 a.m. C.S.T. at an average Valley temperature of 11 degrees F,” says Allen Clare, vice president of Hydro and Gas Operations. “Employees at our CT sites which are normally only staffed weekdays on day shift, braved the cold temperatures and staffed several of our sites around the clock to ensure system needs were being met. That day the CT plants supplied 11% of the total load served.”

Let the Cold Winds Blow

With warmer weather moving in for now, Marshall CT Plant is offline and doing corrective and preventive maintenance. “There’s never any shortage of that,” says Kurt Johnson (pictured below), a site technician who keeps up a furious pace (when not catching up on his sleep). “We do a lot of maintenance and modifications—there is plenty of work to go around.”

man looking at screens in a control room

Marshall Combustion Turbine Plant is a star performer, having churned out over 400,000 MWh of generation across 400 starts in 2017, with a reliability rate of 99.999 percent. The plant is used not only to meet demand from highs and lows in temperature, but to compensate for any other disturbance in TVA’s generation system. “Anytime something comes offline unexpectedly elsewhere in the system, TVA is required to make up the difference,” Moberly explains. “CT plants are a great solution for grid disturbance recovery.”

They’re also a key asset for TVA, according to Clare. “Natural gas generation has taken on a larger role in the TVA generation mix as we move toward a more balanced portfolio,” he says. “Our simple cycle units are relied on for their quick-start capabilities to meet demands during peak times, as well as for backup power needs when our larger base-loaded plants aren’t available.”

Plus, CTs offer some side benefits. “They’re very environmentally friendly whether we are using natural gas or diesel, because they burn clean,” notes Moberly. “And we can also offer voltage support when needed.” In addition, Marshall is the only site at TVA that has 100 percent LED lighting, from floodlights to flashlights.

Pride, at this plant, runs high. “We are happy to run around the clock to whenever needed to ensure that the nine million people we serve can go to the thermostat and turn up the heat,” Moberly says. “We know we’ve doing our part in helping TVA in its mission to serve the people of the Tennessee Valley.”

How Do Combustion Turbines Work?

Combustion turbines work a lot like jet engines. A compressor draws air into the engine, pressurizes it and shoots it into the compression chamber, where either natural gas or diesel fuel is injected and heated to 2,000 degrees F. The high-pressure, heated gas stream then expands through the turbine section where it drives a generator, which generates electricity. TVA has nine combustion turbine plants located throughout the valley, with 87 units between them.