Large 4-pole generator design

An important economic trend has been the increased use of gas-turbine generating sets, together with combined-cycle schemes for high efficiencies. This has led to development of larger sizes of 4-pole generators with ratings up to 6O MVA or more, for use with geared gas turbine and also steam turbine sets where traditionally a more-expensive 2-pole generator would have been employed. The design of such a set requires considerable expertise in a number of fields, including extensive electromagnetic and mechanical analysis, with particular reference to transient analysis of various system electrical fault conditions and the mechanical response of the complete turbine-gearbox-generator shaft system. In addition, system studies may indicate that generator subtransient reactances require to be increased, in order to limit fault currents and to reduce the switchgear ratings and costs. It is also particularly important, for units of this size, that design features are incorporated to enhance the set integrity, and to assist operational installation, commissioning, operation, performance, monitoring and maintenance. The following aspects of the design approach are discussed: EM design, dynamic response, mechanical design, protection, and testing.