Optimised design of rotor field winding of a turbogenerator using both thermal and electromagnetic FE methods

The paper describes the optimisation of the rotor field winding of a turbogenerator. The aim of the optimisation is to obtain better performance of the generator by reducing the rotor losses and to reduce manufacturing and material costs of the rotor. The main part of the calculation involves the determination of the no-load characteristic of the various different designs in order to calculate the rated rotor current and rated rotor losses. These calculations are performed using a 2D magnetostatic finite element package. Because the cross-section of both the copper conductors and of the cooling channel at the bottom of the slot is altered, also a 2D thermal finite element calculation is performed to check if the temperature rise of the winding remains acceptable. The optimisation results in a design that has less turns than the original design, rotor losses are reduced and the saturation level in the solid rotor is reduced. The measurements and calculations for both the old and the optimised design are compared and are found to be in good agreement