Reliability

Combined cycle turbines have inherent reliability advantages over more traditional applications. STAG steam turbines operate at modest steam conditions that permit simpler designs, are smaller in size with less thermal expansion, and many drive simple air-cooled generators. The result is greater than 97 percent reliability.

Impulse Staging

High power density steam turbines are made possible by impulse staging. GE's steam turbines have fewer stages, more robust components and centerline support, and they are capable of fast cycling for rapid load changes.

Half the Number of Stages

Because impulse designs rely on wheel and diaphragm design, they can take more energy drop per stage than reaction turbines designed for equal pressure drop on both the fixed and moving blades. As a result, they harness more energy per stage and require about half as many stages.

Smaller Machines

We take advantage of this compact wheel and diaphragm construction and the shorter rotor length and combine the intermediate-pressure and low-pressure sections into a single intermediate-pressure/low-pressure casing on A configurations and into the combined high pressure/intermediate pressure section on D configurations, shrinking the size of the machines. In addition, having fewer stages permits generous spacing between stages allows us to use multi-toothed, spring-backed packings and more rugged components.

Fast Cycling

An additional advantage of impulse design is fast cycling. As the turbine load changes, steam temperature changes, creating rotor thermal stress. This can limit the rate at which a turbine-generator can change load, as well as the number of load cycles the rotor can tolerate. In our design, large radii wheel fillets and the small-diameter solid steel monoblock rotor reduce the concentration of thermal stress to permit rapid load changes.

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