Runaway power oscillations and core saturation: A motor starting with soft starter of a Tyre Industry's Banbury Mixture Motor of rating 400kw, 660v, 3ph, 50hz. The recorded RMS graph view, lasting totally about 6secs, shows high oscillations at the starting instant with the 3phae system voltage and motor currents, which lasted for a longer time than the usual time of a few milliseconds. Thereafter the system voltage and motor currents did not droop back to their rated values, which happens with normal motor starting.