Two main factors to the effect of nonlinear characteristics of turbo-generator

By the means of finite element method (FEM), the nonlinear characteristic curves and magnetic field distribution of a 300 MW turbine generator under normal or abnormal operating condition are obtained, it is found that the iron saturation and magnetic field distortion are two main factors which cause the nonlinear phenomenon. When the power angle is given, different exciting currents will result in different magnetic leakage field distribution and as a result affect the rotor iron saturation degree. Thus in order to produce a certain E ^delta, the required value of resultant current I_Sigma will vary with the change of saturation status; besides, with a large power angle, the magnetic field distortion will lengthen the air-gap part of the main magnetic path and then influence the value of air-gap voltage E_delta