Comparison of stator and rotor induced transients in solid rotor turbine generators

The eddy current distribution arising from stator and rotor decrement tests are calculated in the cross -section of a 333 MVA 4-pole generator. The stator winding is represented by an equivalent current sheet, voltages in it being calculated from a two-axis consideration of the air-gap field, Coupling equations for the field in the machine and the windings are formulated with the nodal method and eddy currents and field distributions are obtained in a step-by-step calculation using a Newton-Raphson technique. Saturation of the steel is allowed for within each element. Results are shown for the eddy current distribution when the machine is excited (i) from the 3-phase supply and (ii) from the field winding, and the excitation is suddenly removed. The eddy current patterns generated indicate the different nature of these two transient conditions and confirms the need for d-axis equivalent circuits containing a representation of damping circuits asymmetrical to the field and stator winding.