The designation of the "largest" High-Voltage Direct Current (HVDC) cable can be interpreted in terms of power transmission capacity or physical length. Currently, several remarkable HVDC cable projects stand out globally for their impressive scale and engineering.
HVDC Cables with the Highest Power Capacity
When considering operational HVDC cables designed for submarine or underground deployment (excluding overhead lines), the Western HVDC Link connecting Scotland and England holds a leading position in terms of power capacity.
- Western HVDC Link: This interconnector boasts a power rating of 2.2 GW (2,200 MW). It primarily consists of extensive subsea and underground cables, allowing for the efficient transmission of electricity across significant distances, supporting grid stability and renewable energy integration.
Other notable high-capacity HVDC cable links include:
- Xizang-Qinghai HVDC (China): This link, while incorporating some overhead sections, also utilizes significant underground HVDC cabling for its 2.2 GW capacity, designed to transmit power from the Qinghai-Tibet Plateau.
- North Sea Link: Connecting Norway and the UK, this interconnector has a power capacity of 1.4 GW (1,400 MW), facilitating energy exchange between the two nations.
The Longest HVDC Cables
When evaluating the largest HVDC cables by their physical span, several projects have pushed the boundaries of engineering to connect distant grids.
- Viking Link: This interconnector, linking the UK and Denmark, is one of the longest HVDC cables in the world. It stretches a remarkable 765 km (475 miles). The Viking Link is designed to transmit up to 800 MW of power, with a planned upgrade to 1,400 MW by 2025. It plays a crucial role in enhancing energy security and enabling the sharing of renewable energy resources between the two countries.
- North Sea Link: With a length of 720 km, this cable between Norway and the UK is another one of the world's longest HVDC interconnectors, just shy of the Viking Link's length.
Overview of Key HVDC Cables
Here's a comparison of some of the world's leading HVDC cable projects:
| HVDC Link | Primary Location/Connection | Power Capacity (MW) | Total Length (km) | Key Features |
|---|---|---|---|---|
| Western HVDC Link | Scotland - England (UK) | 2,200 | ~420 | Highest capacity submarine/underground cable link |
| Xizang-Qinghai HVDC | Qinghai - Tibet (China) | 2,200 | ~1,000 | Significant cable sections, high altitude |
| North Sea Link | Norway - UK | 1,400 | 720 | Longest interconnector when commissioned |
| Viking Link | UK - Denmark | 800 (1,400 by 2025) | 765 | One of the longest HVDC cables globally |
Note: The AC voltage at the conversion stations for the Viking Link is 400 kV in both Jutland (Denmark) and Bicker Fen (UK), which is the point where the alternating current is converted to direct current for transmission.
Distinguishing Cables from Overhead Lines
It's important to clarify that the term "cable" typically refers to insulated conductors designed for underground or submarine installation. Many of the highest-capacity and highest-voltage HVDC transmission lines globally are overhead lines, not cables. For example, China operates several Ultra-High Voltage Direct Current (UHVDC) overhead lines, such as the Changji-Guquan UHVDC link, which can transmit an astounding 12 GW at ±1100 kV. While these are part of HVDC systems, they are fundamentally different in construction and application from the submarine and underground cables discussed here.
The Importance of Large HVDC Cables
These large HVDC cable projects are critical for:
- Integrating Renewable Energy: Connecting offshore wind farms to mainland grids or transferring solar/hydro power from remote areas.
- Enhancing Grid Stability: Providing robust interconnections between different regions or countries, allowing for the rapid exchange of power to balance supply and demand.
- Reducing Transmission Losses: HVDC transmission is more efficient over long distances compared to AC, minimizing energy loss.
- Market Integration: Facilitating cross-border electricity trading, leading to more competitive energy markets.
As the world moves towards a more interconnected and renewable energy future, the development and deployment of increasingly powerful and longer HVDC cables will continue to be a cornerstone of modern power grids.
