In the pioneering era of electricity, the production was carried out in direct current and the distribution took place in direct current for the small distances. Only towards the end of 1800,there was a rapid transition to alternating current with the three-phase system, allowing the operation of high-efficiency static transformers and, therefore, the transmission and distribution at a considerable distance.
Electricity distribution is the last phase in the delivery process, after production, transformation and transmission. It is carried out through a network system of the aerial type and the underground type, arriving to the end users.
These network systems include High Voltage power lines (between 36kV and 1000kV), Medium Voltage lines (between 10 and 24kV) and Low Voltage lines (between 0.23kV and 1kV).
These systems include the generations of energy by means of thermal combustion plants (coal or gas or oil power plants), by exploiting the flow of rivers (hydroelectric power plants) or the wind power (wind generators) or the energy latent in the air (photovoltaic generators) or the production of gas from bio masses, using transformation plants HV/MV (primary cabins), MV/LV (secondary cabins).