An early method of HVDC transmission was developed by the Swiss engineer René Thury and his method, the Thury system, was put into practice by 1889 in Italy by the Acquedotto De Ferrari-Galliera company. The first long-distance transmission of electric power was demonstrated using direct current in 1882 at Miesbach-Munich Power Transmission, but only 1.5 kW was transmitted. Pylons of the Baltic Cable HVDC in Sweden

History Electromechanical systems Schematic diagram of a Thury HVDC transmission system HVDC in 1971: this 150 kV mercury-arc valve converted AC hydropower voltage for transmission to distant cities from Manitoba Hydro generators. Practical conversion of power between AC and DC became possible with the development of power electronics devices such as mercury-arc valves and, starting in the 1970s, power semiconductor devices including thyristors, integrated gate-commutated thyristors (IGCTs), MOS-controlled thyristors (MCTs) and insulated-gate bipolar transistors (IGBT). These advantages led to early low-voltage DC transmission systems being supplanted by AC systems around the turn of the 20th century. Transformers made AC voltage changes practical, and AC generators were more efficient than those using DC. Transformers are used to change the voltage levels in alternating current (AC) transmission circuits, but can't pass DC current. High voltage cannot readily be used for lighting or motors, so transmission-level voltages must be reduced for end-use equipment. While power lost in transmission can also be reduced by decreasing the resistance by increasing the conductor size, larger conductors are heavier and more expensive. Power = ( voltage ) ⋅ ( current ) = ( 2 ⋅ voltage ) ⋅ ( 1 2 ⋅ current ) using half the current at double the voltage reduces the line losses by a factor of 4. Before the Chinese project of 2019, the longest HVDC link in the world was the Rio Madeira link in Brazil, which consists of two bipoles of ☖00 kV, 3150 MW each, connecting Porto Velho in the state of Rondônia to the São Paulo area with a length of more than 2,500 km (1,600 mi). Early commercial installations included one in the Soviet Union in 1951 between Moscow and Kashira, and a 100 kV, 20 MW system between Gotland and mainland Sweden in 1954. The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden ( ASEA) and in Germany. This improves the stability and economy of each grid, by allowing the exchange of power between previously incompatible networks. HVDC also allows the transfer of power between grid systems running at different frequencies, such as 50 and 60 Hz. Since the power flow through an HVDC link can be controlled independently of the phase angle between source and load, it can stabilize a network against disturbances due to rapid changes in power. HVDC also allows power transmission between AC transmission systems that are not synchronized. HVDC lines are commonly used for long-distance power transmission, since they require less conductor and incur fewer power losses than equivalent AC lines. With this dimension, intercontinental connections become possible which could help to deal with the fluctuations of wind power and photovoltaics. However, a 1,100 kV link in China was completed in 2019 over a distance of 3,300 km (2,100 mi) with a power capacity of 12 GW.

Most HVDC links use voltages between 100 kV and 800 kV. Electric power transmission system Long distance HVDC lines carrying hydroelectricity from Canada's Nelson River to this converter station where it is converted to AC for use in southern Manitoba's gridĪ high-voltage direct current ( HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for electric power transmission, in contrast with the more common alternating current (AC) transmission systems.

Underground 200 amp service wire