Impact of New Flexible Load Operation and Grid Codes on Turbine Generators with a Focus on End Windings

摘要

The integration of renewable energy sources with preferred feed in the high voltage transmission system results in fundamental changes in the global and local load regime of the European transmission grid. New power plant operation demands need to be defined for conventional units. The turbine generator as the key electrical component of the plant will face new operational stresses created by the more flexible grid behavior. To handle this novel situation, the Agency for the Cooperation of Energy Regulators (ACER) of the European Commission in Brussels has elaborated a new European grid code called the European Network Code for Transmission System Operators including Requirements for Generators ENTSO-E NC RfG. This is a framework of requirements covering the spectrum of the different national grid codes. The new European Network Code requires higher flexibility in the operating conditions of the power plant generator to maintain a secure power supply and grid stability. The consequences of this new network code for currently operating generators in power plants and especially for the design and manufacture of future generators are set forth in this paper. The correlation between individual grid code requirements, extrapolated mechanical utilization stresses and affected generator components is demonstrated with examples. In a comparison of different designs of turbine generators, the effects of individual grid code requirements on specific components such as the stator core, windings, bearings and shafting train are presented based on qualitative analysis. The impact of fast load changes on the stator bars is further investigated based on FEM analysis of the stator end windings. Possible mitigations and solutions are presented for generators which have been in service for many years and are now confronted with the new grid demands.