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 allows power transmission between AC transmission systems that are not synchronized. 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. 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.
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