What is High-voltage direct current?
[[Image:HVDC Europe.svg|thumb|right|350px| {{legend|#F80E34|Existing links}} {{legend|#10BF45|Under construction}} {{legend|#0E25F8|Proposed}} Many of these transfer power from renewable sources such as hydro and wind]] [[File:Nelson River Bipoles 1 and 2 Terminus at Rosser.jpg|thumb|HVDC transmission line in [[Canada]]]] A '''high-voltage direct current''' ('''HVDC''') is a [[Electric power transmission|transmission system]] which uses [[Direct current|direct electric current]] (DC) to transmit [[electricity]]. It is more efficient over long distances than the usual [[Alternating current|high-voltage alternating current]] (HVAC). ==History== HVDC was first demonstrated in 1882 in [[German Empire|Germany]]. The technology was further developed during the 1930s in [[Sweden]] and [[Nazi Germany]]. Early commercial uses were in the [[Soviet Union]] and Sweden in 1951. ==Technical details== ===Converter=== [[File:Pole 2 Thyristor Valve.jpg|thumb|HVDC converter]] The converter in HVDC system converts AC electricity to DC electricity or vice versa. Converting AC to DC, it acts as a [[rectifier]]. Converting DC to AC, it acts as an [[inverter]]. Types of HVDC converters: * Line-commutated converters (LCC) * Voltage-source converters (VSC) ===Converter transformer=== [[File:Transformateur du complexe La Grande.jpg|thumb|HVDC converter transformer]] The [[transformer]] at the converter station ensures that the station is isolated from the AC system connected to the HVDC system. It also provides the correct voltage level which will be converted to DC voltage. ===Harmonic filter=== Because [[Power system harmonics|harmonics]] are always produced in electronic equipment, harmonic filters are used at the AC terminal of the converter. The DC harmonic filters can also be used at the DC line after the AC/DC conversion. ===Electrode=== The [[electrode]] provides a ground return path for line current in monopolar configuration and unbalanced current in bipolar configuration. ==Configurations== ===Monopole=== [[File:H