 Michael Faraday D.C.L, F.R.S, in 1831 published a paper on his discovery of electromagnetic induction which is the time rate of change of the magnetic flux with a coil induces a voltage in that coil, the amplitude of the induced voltage is proportional to the velocity of flux linkages with the coil.With normal operation a step-up autotransformer would have flux linkages at the supply frequency; in the case of a very fast dv/dt at the instant of contact separation, the voltage induced into the redundant windings of the first starting stage, will be extremely large.This basic principle explains the source of the destructive transient voltage in the Korndörfer motor starter apparatus.