Power transformers are static devices transferring electrical energy between two circuits with separate systems of alternating voltages, by means of electromagnetic induction. They are used to connect power networks and components with different voltage levels. Transformers are essential components for the transmission, distribution, and utilization of electric power in large power grids, which are facing increasingly demanding requirements for power quality, integration of renewable sources and demand side management. Transformers benefit from the recent technological developments in components, design and construction.