Challenges in calculation and design of large synchronous generators

Large Synchronous Generators are the fundamental machines in nuclear, fossil and alternative energy generation. Large 4-pole turbo-generators reach 2191 MVA with torques of 12.6 MNm. This torque-level is even small in comparison with the Three Georges hydro generators, which have less speed and reach up to 96MNm. The market of both kinds of machines is a very limited one. The backbone of the energy market is given by gas-turbine-and wind-turbine driven generators. Beside smaller asynchronous and synchronous generators up to 6 MW, which are driven by the wind-turbine over a gearbox, direct drives are used with large synchronous generators either with permanent magnets or a field winding in the rotor. Generators with large numbers of machines per year as well as extreme large generators are based upon highly sophisticated design and calculation methods. Salient 4-pole synchronous generators for instance must be very reliable and optimized in design due to the number of machines, which are going into application each year. The development process is based for all large synchronous generators on analytical and numerical calculation methods. Numerical field calculation is a powerful tool for the design in these electrical machines. Developed methods and programs enable the skilled engineer to solve challenging field problems, which occur in reality. Analytical methods are nevertheless the backbone to calculate synchronous generators as a whole or to evaluate design modifications close to a verified design point.