The development of a new range of hydrogen cooled generators

The increased usage of combined cycle plants in power generation has created a market trend for turbine generators of mid range unit size. To remain competitive manufacturers have had to improve the specific output of the machines, leading to increases in the magnetic and electric loadings. Although there has been some improvement in iron loss figures, saturation flux densities have reached a plateau. Consequently output is predominantly controlled by the electric loading, which is in turn limited by the temperatures experienced in the generator. A major contribution to the competitiveness of any design is to use a more effective but simpler ventilation system. In this case indirect cooling of the stator armature winding (heat transfer through the electrical insulation) with hydrogen as the cooling gas, has been employed. The inclusion of radical changes in the design, compared with earlier machines, made it difficult to extrapolate and the alternative of building an evolutionary prototype would have been prohibitively expensive. However, the development was made possible by employing advanced computational techniques including both computational fluid dynamics (CFD) and finite element analysis (FEA) supported by model test rigs as well as operational experience.