Line-commutated converters (LCC) used mercury-arc valves until the 1970s, or thyristors from the 1970s to the present day. Voltage-sourced converters are made with switching devices that can be turned both on and off. Line-commutated converters (HVDC classic) are made with electronic switches that can only be turned on. However, all HVDC systems built since the 1940s have used electronic (static) converters.Įlectronic converters for HVDC are divided into two main categories. Early HVDC systems, built until the 1930s, were effectively rotary converters and used electromechanical conversion with motor- generator sets connected in series on the DC side and in parallel on the AC side. HVDC converters can take several different forms. In such schemes, power flow in the non-preferred direction may have a reduced capacity or poorer efficiency. Others, for example those designed to export power from a remote power station such as the Itaipu scheme in Brazil, may be optimised for power flow in only one preferred direction. ![]() Some HVDC systems take full advantage of this bi-directional property (for example, those designed for cross-border power trading, such as the Cross-Channel link between England and France). A complete HVDC system always includes at least one converter operating as a rectifier (converting AC to DC) and at least one operating as an inverter (converting DC to AC). A complete converter station may contain several such converters in series and/or parallel to achieve total system DC voltage ratings of up to 1,100 kV.Īlmost all HVDC converters are inherently bi-directional they can convert either from AC to DC ( rectification) or from DC to AC ( inversion). HVDC converters capable of converting up to two gigawatts (GW) and with voltage ratings of up to 900 kilo volts (kV) have been built, and even higher ratings are technically feasible. HVDC is used as an alternative to AC for transmitting electrical energy over long distances or between AC power systems of different frequencies. ![]() An HVDC converter converts electric power from high voltage alternating current (AC) to high-voltage direct current (HVDC), or vice versa.
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