HVDC (High-Voltage Direct Current)
Transmission technology that carries bulk power as direct current, with lower losses over long distances and the ability to link asynchronous grids.
High-voltage direct current (HVDC) transmission converts AC to DC at a converter station, carries it over overhead lines or cables, and converts it back. It avoids the reactive charging current and skin effect that limit long AC links, especially subsea cables, where AC becomes impractical beyond roughly 50 to 100 km.
Converter types:
- LCC (line-commutated): thyristor-based, highest ratings (up to 12 GW at ±1,100 kV on China's Changji–Guquan line, 3,300 km), but requires a strong AC grid and cannot black-start.
- VSC (voltage-source): IGBT-based, controllable reactive power, can supply weak grids and offshore wind farms, and supports black start. Typical ratings 1 to 2 GW per link.
Losses are typically about 3% per 1,000 km on the line plus 0.7 to 1% per converter station (LCC lower, VSC slightly higher), compared with 6 to 8% per 1,000 km for comparable AC (ABB, Siemens Energy). The break-even distance against overhead AC is often quoted at 600 to 800 km because converter stations are expensive.
HVDC is central to China's UHV network, North Sea interconnectors, offshore wind connections and Germany's north-south corridors (SuedLink, 4 GW).
Related terms
All terms →- Interconnector
A transmission link, AC or HVDC, that connects the grids of two countries, regions or market zones and allows electricity to be traded between them.
- Transmission and distribution losses
Electricity lost as heat and through non-technical causes between power plants and end users, usually expressed as a share of energy supplied.
- Offshore wind
Wind turbines installed in seas or large lakes, usually on fixed foundations in water up to about 60 m deep, exploiting stronger and steadier winds than onshore sites.
- Curtailment
Deliberate reduction of a generator’s output below what it could produce, usually wind or solar, because of grid, market or system constraints.
- Reactive power
The component of AC power that oscillates between source and load without doing net work, needed to sustain magnetic and electric fields and control voltage.
- Grid-forming inverter
An inverter that sets its own voltage and frequency reference, behaving like a voltage source that can stabilise weak grids and provide synthetic inertia.