last highlighted date: 2024-11-25
Highlights
- Most HVDC links use voltages between 100 kV and 800 kV.
- HVDC lines are commonly used for long-distance power transmission, since they require fewer conductors and incur less power loss than equivalent AC lines
- The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden (ASEA) and in Germany.
- between Gotland and mainland Sweden in 1954.[2]
- High voltage is used for electric power transmission to reduce the energy lost in the resistance of the wires. For a given quantity of power transmitted, doubling the voltage will deliver the same power at only half the current:
HVDC in 1971: this 150 kV mercury-arc valve converted AC hydropower voltage for transmission to distant cities from Manitoba Hydro generators.- Comparison with ACAdvantages A long-distance, point-to-point HVDC transmission scheme generally has lower overall investment cost and lower losses than an equivalent AC transmission scheme
- Although HVDC conversion equipment at the terminal stations is costly, the total DC transmission-line costs over long distances are lower than for an AC line of the same distance
- HVDC requires less conductor per unit distance than an AC line, as there is no need to support three phases and there is no skin effect
- Depending on voltage level and construction details, HVDC transmission losses are quoted at 3.5% per 1,000 km (620 mi), about 50% less than AC (6.7%) lines at the same voltage
- This is because direct current transfers only active power and thus causes lower losses than alternating current, which transfers both active and reactive power.
- Specific applications where HVDC transmission technology provides benefits include
- Undersea-cable transmission schemes (e.g. the 720 km (450 mi) North Sea Link, the 580 km (360 mi) NorNed cable between Norway and the Netherlands,[20] Italy’s 420 km (260 mi) SAPEI cable between Sardinia and the mainland,[21] the 290 km (180 mi) Basslink between the Australian mainland and Tasmania, and the 250 km (160 mi) Baltic Cable between Sweden and Germany[22]).
- Endpoint-to-endpoint long-haul bulk power transmission without intermediate taps, usually to connect a remote generating plant to the main grid (e.g. the Nelson River DC Transmission System in Canada).
- Increasing the capacity of an existing transmission line in situations where additional wires are difficult or expensive to install.
- Power transmission and stabilization between unsynchronized AC networks, with the extreme example being an ability to transfer power between countries that use AC at different frequencies.
- Stabilizing a predominantly AC power grid, without increasing prospective short-circuit current.
- Integration of renewable resources such as wind into the main transmission grid. HVDC overhead lines for onshore wind integration projects and HVDC cables for offshore projects have been proposed in North America and Europe for both technical and economic reasons.
- Generally, vendors of HVDC systems, such as GE Vernova, Siemens and ABB, do not specify pricing details of particular projects; such costs are typically proprietary information between the supplier and the client
- For an 8 GW 40 km (25 mi) link laid under the English Channel, the following are approximate primary equipment costs for a 2000 MW 500 kV bipolar conventional HVDC link (excluding way-leaving, on-shore reinforcement works, consenting, engineering, insurance, etc.) • Converter stations ~£110M (~€120M or 1.6M/km; €2m or $2.5m/mile)
- Almost all HVDC converters are inherently capable of converting from AC to DC (rectification) and from DC to AC (inversion), although in many HVDC systems, the system as a whole is optimized for power flow in only one direction.
- Line-commutated converters Most of the HVDC systems in operation today are based on line-commutated converters (LCCs).
- A major drawback of HVDC systems using line-commutated converters is that the converters inherently consume reactive power. The AC current flowing into the converter from the AC system lags behind the AC voltage so that, irrespective of the direction of active power flow, the converter always absorbs reactive power, behaving in the same way as a shunt reactor.
