As explained in Section III, there is also an effect of the neglected
flux transients at the moment the fault occurs, giving a
breaking torque caused by the transient short circuit currents.
As shown in Fig. 5(a), this causes a reduction of speed before
the almost linear increase during the fault. In the particular case
of a machine with high losses and low inertia, the effect of this
breaking torque is significant and can be seen as increased critical
clearing time from the simulations, even though the critical
speed at fault clearing is slightly overestimated by the simplified
calculations.With these effects taken into account, the accuracy
of the critical clearing time for the proposed calculations is still
within 10–15%, with the highest deviations for the SVC.