Computation of transient electromagnetic torque in a turbogenerator under the cases of different sudden short circuits

A method for the computation of the transient electromagnetic torque in turbogenerators is given in which the iron saturation and the relative motion of the rotor and stator are taken into account. This method is based on the finite-element computation using a dynamic model coupled with the equations of external electric circuits. To avoid the airgap mesh distortion caused by the movement of the rotor, moving boundaries are introduced in the airgap. An example is given that involves the computation of the distribution of transient magnetic field and the electromagnetic torque of a 200-MW turbo-generator following different types of sudden short-circuits. The computed results agree with the measurements very well