Negative sequence losses in turbine generator rotors

Negative sequence currents are induced in the rotor of a turbine generator when there is imbalance in the three phase armature currents. By adopting surface impedance boundary conditions to represent the rotor steel, three dimensional finite element methods can be used to determine the effect of barriers to the current flow caused by transverse balancing slits and gaps between slot wedges or dampers, with realistic computational resources. Total loss is largely unaffected by these barriers but loss distribution may be modified by more than 10% from a model where they are ignored. The dampers play a vital role in reducing the total loss.