Currents Induced in the Inner Stator Frame of Large Turbogenerators by the End-Zone Field

A method is described, based on 3-dimensional field calculations, for calculating the eddy-currents induced in the inner stator frame by the end-zone field; these currents are an order of magnitude greater than those caused there by yoke saturation, and their mechanism is explained through the calculation results for given alternative designs; it is based mainly on the shielding of the end-zone field. The eddy currents are limited mainly by the inductances; the effect of resistivity should be less than 15%. The design having the outer housing and inner frame electrically insulated from each other appears less satisfactory than the more usual design where the parts are electrically connected.     

Identification of parameters for superconducting generators havingfree or fixed outer rotor, based on tests and calculations

The generator, with its concentric and in part solid and conductive parts, is represented by a shell model, and the parameters of the system of equivalent windings are first obtained approximately using a two-dimensional analytical field calculation. The effect of the finite length, which is neglected in this field calculation, is taken into account by variation of the model geometry and material conductivity so that Nyquist plots of the model impedances are optimally matched to those of the real system. The resulting machine model is checked and confirmed by comparing the simulation results with test measurements. It is further shown that an outer damper cylinder (that is free to rotate independently) provides significant mechanical relief of the shaft line during transient processes