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Aiming at the complexity of the structure in the end region of large turbogenerators, 3-D mathematical and physical models of nonlinear transient eddy current field are given by taking a 330-MW water-hydrogen-hydrogen-cooled turbogenerator for example. Both nonlinearity of B-H curve and noncontact structure between the copper screen and press plate, as well as the evolvent of stator end windings, were taken into consideration. When the copper screen thickness is different in the end region of the generator, 3-D transient electromagnetic field and losses of metal parts were calculated under no-load and rated-load conditions by finite-element method. The metal part losses, which were obtained from transient electromagnetic field, were applied to the thermal field as heat sources. Temperatures of copper screen were gained after the thermal field was calculated in the end region. The calculated results coincide well with the measured data.