In the 19th century, at the dawn of the electric era, high voltage AC transmission system (50/60 Hz) was chosen at the expense of DC transmission (0 Hz) (see Electricity network). Nevertheless, high voltage DC is used to transmit electrical energy over long distances, including under the sea, and to interconnect different frequency networks (eg in Japan, for interconnection between 50 Hz network in the north and 60 Hz network in the south).
And the situation continues to evolve. Indeed, the need to interconnect countries to ensure trade in electricity (eg interconnection Nemo Link® in the North Sea and interconnection ALEGrO) and the relocation of electricity production plants (eg wind farm in the North Sea) involve the development of electrical connections on long distances, which are more effective in DC. Moreover, in Belgium for example, trains, excluding high speed train, also operate in DC.
Note: Detailed information on the challenges of transport in both AC and DC power are available at Electricity network.