Power Engineering - Siemens Westinghouse introduces US single-shaft combined cycle reference power plant

Siemens Westinghouse introduces US single-shaft combined cycle reference power plant

14 April 2004 - Siemens Westinghouse says it has developed a 1S.W501G Single-Shaft Combined Cycle Reference Power Plant to meet the needs of the US power market.

The 400 MW-class design allows the plant not only to be operated at over 58 per cent net efficiency during periods of high demand, but also to compete in the traditional "one-hour-forward" trading market that is served today only by simple cycle gas turbines. The latter is achieved by designing the plant with fast-start capability, which also dramatically reduces start-up emissions as well as fuel and water consumption.

Driven by the requirements of the US power market, suppliers of power plants are challenged to provide both plant efficiency and operating flexibility. The future market will also likely require power plants to be capable of increased power density by means of a single gas turbine based combined cycle plant. Paramount for plant efficiency is a highly efficient gas turbine and a state-of-the-art bottoming cycle, which must be well harmonized. Furthermore, operating and dispatch flexibility require a bottoming cycle that has fast-start, shutdown and cycling capabilities to support daily start and stop cycles.

In response to these requirements Siemens developed the single-shaft 1S.W501G combined cycle reference power plant. This highly efficient nominal 400 MW-class plant is equipped with proven Siemens components, including the W501G gas turbine, a hydrogen-cooled generator, a KN steam turbine and a Benson once-through heat recovery steam generator (Benson-OT HRSG). The single-shaft arrangement further improves net plant efficiency.

The 1S.W501G single-shaft combined cycle reference power plant represents a logical step in the evolution of 60Hz combined cycle power plant designs. It combines the proven performance of the 400 MW-class, 50Hz single-shaft 1S.V94.3A plant with the fast-start plant features demonstrated at the Cottam Energy Center in England. These include the Benson-OT HRSG, the Siemens patented turbine stress controller (TSC), a modern water treatment system with condensate polisher, an integrated steam conditioning system, high-capacity steam bypass systems, upgraded automation and provision of an auxiliary boiler and mechanical vacuum pumps. This design results in typical start-up times that are twice as fast as existing combined cycle plants.

Another unique feature of all Siemens single-shaft combined cycle power plants is the application of a synchronous self-shifting clutch between the center-arranged generator and the steam turbine. In addition to simplifying the start-up procedure, this provides high operating flexibility by allowing the gas turbine to be operated in a simple cycle mode with the steam turbine disengaged from the shaft train.

Siemens' single-shaft plants have been in successful operation since the mid-1990s in both 50 and 60Hz applications worldwide. The 1S.W501G combined cycle reference power plant is the design of choice for 60Hz operators requiring highly efficient plants with unprecedented operating flexibility.

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