Rocks & mirror
Encyclopedia of Marine and Energy Technology

Direct Current (DC)


This is electrical current that does not alternate, the electrons flow through the circuit in one direction. As a result, DC does not generate reactive power. This means that, in a DC system, only real (or active) power is transmitted, making better use of the system’s capacity. In order to transmit electrical power as DC, the alternating current generated in the power plant must be converted into DC. At the other end of the process, the DC power must be converted back into AC, and fed into the AC-transmission or distribution network. The transmission of DC current has very low losses. In the conversion between the two forms of power, known as rectification, incurs additional power losses and so it is worth while only when these losses are less than would be incurred by AC transmission, i.e., over very long distances (~1000 km for overhead lines, ~100 km for underwater).