Turbogeneradores

ID: 664

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The Turbogenerator – A Continuous Engineering Challenge
C. Ginet, R. Joho, Member, IEEE, M. Verrier

Abstract— Since the 1901 invention of the cylindrical rotor for a
high-speed generator, the turbogenerator has been used for converting the steam turbine and gas turbine power into electrical power. Today a wide array of turbogenerators between 50 MVA and 1300 MVA in full-speed(two-pole) design is available. The nuclear power plant business is covered by halfspeed (4-pole) designs with a range up to 2000 MVA. Today, the main drivers for design uprates are cooling design and insulation technology. The design development is supported by FEM and CFD, which in future will get linked with mechanical design tools. The future is characterized by new needs regarding power,efficiency and stability, and the commercial availability of emerging material technologies.

I. INTRODUCTION ince the 1901 invention of the cylindrical rotor of Charles Brown for a high-speed generator, the turbogenerator has been the unique solution for converting steam turbine power into electrical power. The continuously transposed stator bar, invented by Ludwig Roebel in 1912, opened the doorfor large scale winding application. Up to the 1930ies the generators were designed in 2-, 4- and even 6pole, in accordance with the speed optimums of the steam turbines in those days. The 1920ies ended with impressive power generation plants, having generator units in the 100 MVA range (see Fig.1). The stator winding insulation consisted in the beginning of plied-on mica-paper, compounded byShellac varnish, later substituted by asphalt. Voltages were up to 12 kV.

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In the early 1930ies two European manufacturers were introducing 36 kV stator windings, thus eliminating the machine transformer. All such designs were suffering of continuous heavy electrical discharges, and were soon discontinued. After a 60-year time-out, a manufacturer surprised the world in 1998 with a cable-basedhigh-voltage generator up to 400 kV. However again, the cable technology was not ready for turbogenerator requirements, and a breakthrough for commercial application was not achieved. In the 1930 US manufacturers were introducing hydrogen as coolant. When combined with direct conductor hydrogen cooling in the rotor, and later in the stator, this allowed a considerable increase in specificutilization and efficiency. By early 1960 the unit ratings were achieving 500 MVA. At that time deionized water cooling in the stator winding was introduced. Around 1960 all major manufacturers changed their insulation system to mica tape with synthetic resin impregnation, a technology for thermal qualification at 155°C, and which has been lasting into these days. By end of the 1960, with the powersemiconductors becoming mature, the dc machine excitation (Fig.2) was superseded by the static excitation, and by an ac exciter machine with rotating diodes.

Fig.2. DC-exciter on the left, replaced by static thyristor on the right

Fig. 1. Hellgate USA, 1928, 2 x 80 MW, with external generator fan

C. Ginet and R. Joho are with ALSTOM (Switzerland) Birr M. Verrier is with ALSTOM (France) Belfortconstantin.ginet@power.alstom.com

The 1970ies brought again a tremendous growth in unit ratings, going along with the introduction of nuclear power. Units of 1200 MVA at 3000 rpm and 1600 MVA at 1500 rpm at up to 27 kV were designed and put in operation. The rotor diameters were arriving at their physical limits. Water-cooling of the rotor winding was introduced. Along with plans for 2000 MVAand beyond, superconducting rotor windings and stator air-gap windings were studied. However, in early 1980 the market focus was shifting to gas turbine technology, with some 100 MW beginning to grow into the area of large power plants, and initiating a new round of uprating the simple and robust air-cooling technology in the 300 MVA range by 1996. The generator has for a long time been developed...