Study of electromagnetic phenomena in the end region of large turbo-generators - Testing tools for the 125 MW turbo-generator

This work aims to improve the knowledge of electromagnetic phenomena that occur in the end region of large turbo-generators. The goal of this work is to evaluate the axial magnetic flux density with regard to the operating conditions (such as active or reactive power) in order to prevent potential deterioration of the stator. Indeed, the axial magnetic field is known to induce hot points or voltages between laminations that may cause insulation breakdown and thus stator faults. An experimental apparatus in real scale has been designed and built. Its purpose is to study precisely the following phenomena: losses, axial magnetic flux density penetration, voltage across adjacent voltages. Finite element simulations (FEM) are also used: their advantages and drawbacks are discussed, and the results are compared with the experimental measures. The whole end-region of a turbo-generator is also simulated. Finally, a simple model of the axial magnetic flux is proposed. Its parameters are based on the results of the FEM model, but it may be used in real time to evaluate the axial magnetic flux density of any operating point. (author)