Advantages of HVDC Over AC Transmission
The most common reason for choosing HVDC over AC transmission is that HVDC is more economic than AC for transmitting large amounts of power point-to-point over long distances. A long distance, high power HVDC transmission scheme generally has lower capital costs and lower losses than an AC transmission link.
Even though HVDC conversion equipment at the terminal stations is costly, overall savings in capital cost may arise because of significantly reduced transmission line costs over long distance routes. HVDC needs fewer conductors than an AC line, as there is no need to support three phases. Also, thinner conductors can be used since HVDC does not suffer from the skin effect. These factors can lead to large reductions in transmission line cost for a long distance HVDC scheme.
Depending on voltage level and construction details, HVDC transmission losses are quoted as about 3% per 1,000 km, which is less than typical losses in an AC transmission system.
HVDC transmission may also be selected because of other technical benefits that it provides for the power system. HVDC schemes can transfer power between separate AC networks. HVDC powerflow between separate AC systems can be automatically controlled to provide support for either network during transient conditions, but without the risk that a major power system collapse in one network will lead to a collapse in the second.
The combined economic and technical benefits of HVDC transmission can make it a suitable choice for connecting energy sources that are located remote from the main load centres.
Specific applications where HVDC transmission technology provides benefits include:
- Undersea cables transmission schemes (e.g., 250 km Baltic Cable between Sweden and Germany, the 600 km NorNed cable between Norway and the Netherlands, and 290 km Basslink between the Australian mainland and Tasmania).
- Endpoint-to-endpoint long-haul bulk power transmission without intermediate 'taps', for example, in remote areas, usually to connect a remote generating plant to the main grid, for example the Nelson River DC Transmission System.
- Increasing the capacity of an existing power grid in situations where additional wires are difficult or expensive to install.
- Power transmission and stabilization between unsynchronised AC networks, with an extreme example being the ability to transfer power between different countries that use AC at differing frequencies. Since such transfer can occur in either direction, it increases the stability of both networks by allowing them to draw on each other in emergencies and failures.
- Stabilizing a predominantly AC power-grid, without increasing prospective short circuit current.
Read more about this topic: High-voltage Direct Current
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