This book presents a synthesis of various results about heat transfer of power semiconductor devices and electrical apparatus, and includes topics on thermal analysis of toroidal transformers and fast fuses used to protect power semiconductor devices, heat transfer of high breaking capacity fuses, busbars, current paths from power circuit breakers and thermal analysis of sliding contacts. Some mathematical models to study the heat transfer of busbars during transient conditions and sliding contacts with double contact points, are proposed. Starting from the fact that at high speeds of electric traction vehicles, the pantograph-catenary's system has separation areas and electric arc appears, the possibility of power transfer from the line contact to the main electric motor through the sliding arc column, has been investigated. The book as a whole gives a comprehensive treatment of thermal modelling and numerical simulations of power semiconductor devices and assemblies, electrical equipment, and applies alike to researchers, experts, engineers, university specialists and students which study theory, design or operate with power electronic devices and electrical apparatus.