The problem of restoring power systems after a complete or partial blackout is as old as the power industry itself. During early stage of primary restoration process, unexpected over-voltage may happen during power equipment energization. Such an overvoltage might damage some equipment and delay power system restoration. Switching of those devices produce transients that need to be carefully studied and, if required, limited. In this book, overvoltages caused by switching operation in transformers, transmission lines, and shunt reactors are studied and estimated. In order to study temporary overvoltages during transformers and shunt reactors energization, a harmonic index is used to reduce number of simulations by applying analytical or knowledge-based rules to discard a number of system configurations before an actual time-domain simulation is carried out. Also based on this harmonic index, a new approach to harmonic overvoltages reduction during transformer energization via controlled switching is introduced. Artificial neural network is addressed in this book, in order to evaluate the switching overvoltages due to power equipment energization.