HVDC links: Technology advances
Ultra-high voltages, smarter converters and record subsea links
What this tab covers The newest technologies in service or close to adoption, what each improves, and how the main options compare.The frontier is higher voltages and powers (UHVDC), voltage-source converters for offshore wind and weak grids, longer subsea links, and bulk procurement to secure factory slots.
Latest advances
±1,100 kV UHVDC in service · 2019LCC link of 12 GW over 3,293 km from Xinjiang to eastern China12
Improves: Up to 40% lower losses than conventional systems, according to the converter supplier
Voltage-source converters (VSC) in service · 2023IGBT-based modular multilevel converters that control active and reactive power independently6
Improves: Black-start capability and weak-grid support; 53 VSC projects existed in May 2023 and 102 more were planned to 2032
Very long subsea interconnectors in service · 2023Viking Link, 765 km of land and subsea cable between the UK and Denmark8
Improves: Joins two markets across the North Sea; expected to save about 600,000 tonnes of CO2 in its first year
400 kV subsea link, Bay of Biscay being deployed · 2028Two 1,000 MW HVDC links of about 400 km between Spain and France with four converter stations1617
Improves: Raises Spain to France exchange capacity from 2,800 to 5,000 MW
Framework procurement being deployed · 2025National Grid reserved converter and cable factory capacity through multi-year frameworks9
Improves: About GBP 24.6 billion of converter and GBP 21.3 billion of cable work
Comparing the options
| Option | Efficiency | Cost | Capacity or distance | Maturity |
|---|---|---|---|---|
| LCC HVDC overhead (±800 to ±1,100 kV)13 | About 3.5% per 1,000 km including converters (Xiangjiaba, calculated) | Cheaper converters than VSC | 6,400 to 12,000 MW per link | mature |
| VSC HVDC (overhead or cable)4816 | About 0.8 to 1% per converter station plus line or cable losses | Higher converter cost than LCC | 1,000 to 1,400 MW per link in recent subsea projects | mature |
| HVAC overhead (765 kV)18 | Higher losses on long routes | Cheaper below about 250 to 400 miles | About 2,400 MW natural loading per circuit | mature |
| HVAC cable4 | Charging current uses up capacity on long cables | No converters; HVDC cheaper beyond about 30 miles | Limited to short routes | mature |
HVDC is the only practical choice for long subsea links and the cheapest for very long overhead routes. Brattle puts the break-even with AC at about 700 km for new build; converting an existing AC corridor to DC can pay beyond about 200 km, or wherever capacity must rise by more than 60%. MISO's range is 250 to 400 miles.
Sources
- The world's most powerful transmission system facilitated by Hitachi ABB Power Grids Hitachi Energy, 2020
- China's SGCC commissions world's first ±1,100 kV UHVDC project Power Line Magazine, 2019
- Xiangjiaba - Shanghai (case study) Hitachi Energy, 2024
- Overview of HVDC Technologies and EPRI's HVDC Research (R. Adapa, presentation to ERCOT) EPRI / ERCOT, 2023
- HVDC Transmission: Multi-Value Planning Considerations and Experience The Brattle Group (for MISO), 2023
- National Grid announces commercial operations of Viking Link, the world's longest land and subsea interconnector National Grid, 2023
- National Grid awards HVDC supply chain framework contracts National Grid, 2025
- Hitachi Energy wins order for first subsea electricity interconnection between France and Spain Renewable Energy Magazine, 2023
- EIB supports with EUR 1.6 bn the strategic Bay of Biscay electricity interconnection between Spain and France European Investment Bank, 2025
- Discussion of EHV and HVDC (M. Tackett, MISO, presentation to ERCOT) MISO / ERCOT, 2023