Analysis of the losses in a turbine-generator rotor caused by unbalanced loading

Unbalanced loading of a turbine generator induces rotor currents at twice the supply frequency, with consequent heating of solid iron and other damping circuits, which limits the negative sequence capability of the machine. The paper presents a method for analysis of rotor current and loss distributions under these conditions. Methods are described for representing the slotted region, with its combination of solid iron teeth, wedges and damping windings, and the nonlinear behaviour of currents in the solid iron of the rotor. A noteworthy feature of the analysis is the ability to include the effects of transverse flexibility slits, cut in the unslotted portion, which can give rise to extremely localised heating. The accuracy of the analysis is demonstrated by application to a 500 MW generator for which test results are available.