Eddy currents and flux distributions of short circuited turbine generators following field suppression tests

The transient performance of turbine generators following a field suppression test with the generator on short circuit is obtained from design data using electromagnetic field calculations. The stator currents are replaced by an equivalent current sheet lumped into the stator slots. Currents in the stator windings are taken to depend on rotational voltages, but currents in the field winding, damper wedges and solid rotor depend on the rate of change of the magnetic field. Induced eddy currents, currents in the machine windings and flux distributions are obtained iteratively in a step by step calculation using the Newton-Raphson technique. The problem is nonlinear and saturation in steel is allowed for within each element. The effect of the short circuited stator windings on the generated eddy current patterns is shown. The calculated values compare well with the experimental results on a 333 MVA turbine generator.