Figure 2 shows a typical inrush current. The waveform displays a large and long lasting dc component, is rich in harmonics, assumes large peak values at the beginning (up to 30 times the rated value), decays substantially after a few tenths of a second, but its full decay occurs only after several seconds (to the normal excitation level of 1-2% of the rated current). In certain circumstances, some small changes of the excitation current are observable even minutes after switching a transformer in [4,5]