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January 1, 2012

Getting Peak Returns out of Peaking Turbines

By Joe Zwers

Other Technologies

Utilities are taking a variety of approaches to economically providing reactive power from existing generation sources. In each of these cases, the company uses a synchronous self-shifting clutch from SSS Clutch Co. of New Haven, Del., or SSS Gears Ltd. of Sunbury-on-Thames, England.

With the clutch engaged, the turbine is used to bring the generator up to synchronous speed, at which point it connects to the grid. If power is needed, the turbine continues to drive the generator. During off-peak times, however, the turbine can be shut down. As the turbine slows below the speed of the generator, the clutch automatically disconnects the turbine and generator and the generator draws just enough power from the grid to keep it synchronized and generating reactive power. Later, when peaking power is needed, the turbine is again brought online, and when it reaches the speed of the generator, the clutch links the two, and the turbine again provides the power needed for generation. A more detailed description of the synchronous condenser operation is found in a recent article in POWER describing the retrofit of an existing combustion turbine.

In Western Australia, power generation has moved away from the population center of Perth, where three-quarters of the population lives, to the coal mines, aluminum plants, and a wind farm hundreds of kilometers from the city. This lowers generation costs, but because some of the local generation facilities were decommissioned, this led to stability problems in the Perth metropolitan area. Western Power Corp. modeled its system requirements and decided to use a peaking station near Perth, Verve Energy's 576-MW Pinjar Gas Turbine Power Station, as a source of reactive power. GE Frame 6 units at the site were outfitted with clutches, allowing them to operate as synchronous condensers to stabilize the load coming from the more economical, but remote, generating stations, and allowing the transmission line to transport more real power (kW).

Lafayette Utilities System in Lafayette, La., purchases most of its power, but it bought four 50-MW GE LM6000 turbines to provide peaking and emergency power in case there was a problem with the grid. Two of the turbines have clutches, allowing the generators to provide reactive power to stabilize the grid and import more power when the units are not needed to produce electricity.

The same approach can be used with steam turbines. For half the year, BC Hydro operates six steam turbine generators near Vancouver to provide the city with power. The rest of the year the power comes from hydroelectric plants. When the steam turbines are shut down, the generators are used to stabilize the voltage coming from the hydro plants, improving the power factor to the point where BC Hydro could sell more power over interconnects to the U.S.

—Joe Zwers is a freelance writer based in Glendale, Calif., specializing in business and technology.