Control of inductive load switching transients

Voltage transients are inevitable when switching in MV and HV networks. Overvoltages up to a level of 3 p.u. are quite normal and acceptable in relation to insulation coordination. Only in very specific cases, extra precautions are needed in order to limit the probability and/or level of unacceptable overvoltages, irrespective of the arc-quenching medium. The new edition 3 of the IEC 62271-110 standard on inductive load switching demands both stalled motor switching and shunt reactor tests for MV breakers. Apart from overvoltages beyond the withstand capability, also voltage surges with high steepness and even internal resonances are considered to be a possible cause of failed dry-type transformers. This implies that transformer modeling plays a crucial role when studying these phenomena. The question is raised whether the transformer standards should be revised on the insulation versus overvoltage / resonance issue.