**3. Basic Information about the Slovak Electricity System**

On the territory of Slovakia, the beginning of the electrification of the territory relates to the operation of the first hydroelectric power plants in the Central and Northern Slovakia at the end of the 19th century, which gradually merged into local systems. The first brown-coal-fired steam power plant, with 12.0 MW installed capacity, was put into operation in Handlova more than 100 years ago and became the primary source of the regional system in the area between Handlova and Prievidza. In 1949, a brown-coal-fired power station in Novaky with an installed capacity of 178 MW was commissioned. In 1963, a new 110 MW unit was put into operation in Novaky, connected to the Bystricany substation, and then connected to the already highly developed Czech electricity system through the 110-kV substation Liskovec in the north of Moravia. The operation of the first system power plant guaranteed the security of electricity supplies to Slovakia, which, until then, had been mainly supplied by electricity from a hydroelectric Vah river cascade which reliability was limited by the potential of the Vah's hydro energy. At present, the electrical system is an infrastructure property of high value with thousands of resources, tens of thousands of kilometres of superior and distribution air and cable lines, appliances, and safety features of the power grid. The electrical system facilities have made electricity continuously available throughout the country, and it serves the development of the economy and the population of the Slovak Republic.

It is important that a balance of production and consumption of electricity is always maintained in order to guarantee the safety and reliability of the electrical system operation. The frequency and voltage offset reflects the difference in electricity production and consumption, while the higher the power production and lower the power consumption, the frequency increases, and vice-versa. If the frequency (49.8–50.2 Hz) and voltage offset is exceeded, their life span would be reduced and their own protections would start to be disconnected from the system. According to the current load, the difference in MW production and consumption may cause local outages in the supply of electricity, which in the undesired process ends with the disruption of the system. Disturbances in the system spread at a speed that goes beyond the possibilities of human perception. Therefore, each regulatory area must have a system of protection and management of the electricity system that prevents the spread of faults and controls the production of resources and consumption of consumers in the nodes, while real controlling the operation of the power system of the Slovak Republic (SR) is provided by the "Slovenska elektrizacna prenosova sustava" (SEPS Inc., Zilina)/Slovak Electricity Transmission System.
