This book introduces the concepts of more electric aircraft and aviation electrical appliances, as well as the aviation experimental platform of vacuum switches, the interruption characteristics, frequency characteristics and post-arc breakdown characteristics of intermediate frequency vacuum switches, etc. It is the first monograph on protection electrical appliances, vacuum interrupter in aviation variable frequency power system. This book includes a lot of experimental process and chart analysis for readers to understand and provides references for practical engineering problems. This book could be used as references for engineers and technicians working on electric power systems in aircrafts.