The electrical energy system, including production, networks and electricity use is a traditional engineering field and a basic infrastructure of modern society. As a result of the ongoing revolutionary change, it is playing an increasingly important role as the basis for various energy systems when they are electrified. Renewables energy sources have an essential role in mitigating climate change and in preventing the climate crisis. Heating, transportation and industrial processes are also increasingly electrified. The main goal of future smart grids is to enable energy- and resource-efficient and sustainable electric energy system and the market by integrating distributed intermittent renewable electricity energy generation, energy storages, electric vehicles and demand response into the entire electricity system and to function reliably as one of the society’s most critical infrastructures.