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.