The Benefits of High-Voltage Direct Current (HVDC) Power

For the past century, alternating current (AC) systems have been the global standard for electrical transmission to businesses, applications, and homes. However, over the last several decades, High-Voltage Direct Current (HVDC) has emerged as a viable complement to AC power transmission, with the ability to connect asynchronous AC grids and allow power transmission across long distances with minimal losses.

This is essential for applications such as offshore wind farms, which can operate at considerable distances from where the power they generate is needed. In this way, HVDC technology is on course to unlock the full potential of Europe’s offshore resources and increase the efficiency and compatibility of energy systems across the world. Andreas Berthou explains the benefits of this transmission system.

 

Figure 1: Offshore wind

 

AC vs DC

AC transmission has established itself as the preferred global platform over the past century, due to the convenience of transformers in stepping voltage up or down as needed, as well as being easier to interrupt than DC grids. However, high-voltage AC transmission has a number of limitations, including shorter distance constraints and transmission capacity, as well as the impossibility of connecting two AC power networks of different frequencies.

Owing to a number of innovations over the years, HVDC transmission is now primed to supplant AC transmission, with HVDC offering an improved capacity for distance transmission and higher efficiency over those distances. While AC transmission is impossible between two networks of different existing energy infrastructures. This precise power flow allows new energy sources to be integrated seamlessly into power grids without the volatility that such integration can introduce to frequencies, HVDC transmission can connect networks that operate on any frequency or voltage. This allows renewable energy from various sources to be easily integrated into existing power grids, facilitating an efficient transition to renewable energy sources. HVDC transmission is reliable and easy to control, providing instant and precise control of power flow for new and existing grids. HVDC can expand the energy networks, making them more stable.

HVDC is more environmentally friendly than AC, providing more energy per square metre over greater distances more efficiently than AC systems, as well as lower losses and less space requirements. This increased efficiency reduces the carbon footprint of HVDC compared to AC, with losses being reduced from around 5-10% in AC transmission to around 2-3% for the same application in HVDC.

 

Figure 2: DC overhead lines

 

What is HVDC?

HVDC, pioneered by Hitachi ABB Power Grids in the 1920’s, and commercially established in the 50’s, differentiates itself from AC transmission systems through electrical current converter technology, converting AC to DC to more efficiently transmit across large distances with fewer transmission lines needed. HVDC is also commonly used to connect asynchronous AC networks, stabilising the surrounding grid while increasing grid capacity and affording greater control over power flow. HVDC systems use high-power semiconductor valves, tuned specifically by Hitachi ABB Power Grids for their applications.

 

 

Figure 3: HVDC light valves

 

 

HVDC is the method of choice for subsea electrical transmission and long-distance power transmission, owing to its ability to send large amounts of electricity across greater distances than AC transmission, with minimal losses. Offshore wind is becoming increasingly important, with WindEurope estimating that Europe’s offshore wind capacity will reach 450GW in 30 years, and HVDC transmission is an essential part of connecting remote offshore wind farms to the cities and areas where this electricity is used. To enable this integration with offshore energy, a hybrid HVDC breaker designed by Hitachi ABB Power Grids was recently tested by KEMA Laboratories as part of the EU-funded “Progress on Offshore Meshed HVDC Transmission Networks” project. Using optimized power semiconductors developed in-house by Hitachi ABB Power Grids, this breaker overcomes existing technical limitations by allowing the HVDC transmission system to maintain power flow even if there is a fault on one of the lines, breaking the direct current on the line and isolating the fault. 4

Another important development is HVDC Light®, a voltage-sourced converter solution pioneered by Hitachi ABB Power Grids in 1997, recently hailed by the World Economic Forum as “one of the greatest global energy innovations” of the last decade. HVDC Light provides more secure power control and quick power restoration, and allows long-distance underground high-voltage transmission, enabling easier transition to renewable energy in urban areas.

 

The future of HVDC

While AC fulfils an important role for energy transmission across shorter distances and to the end-user, HVDC technology is a more viable energy transmission solution in our increasingly connected global energy ecosystem. HVDC’s efficiency across long distances will be an essential part of global renewable energy solutions, seamlessly integrating clean energy into existing power infrastructures and ensuring that renewable energy is accessible and affordable.

 

Figure 4: HVDC Classic valves from North East Agra multiterminal link in India

This potential is already being shown through large-scale global developments using HVDC in renewable energy systems. Hitachi ABB Power Grids is supporting China in building the Zhangbei HVDC grid in the Beijing-Tianjin-Hebei area, the first grid installation of its kind in the world. When completed, this grid is expected to provide the area with a consistent supply of renewable energy through the integration of remote wind, solar and hydro energy, and could facilitate the adoption of similar systems in Europe and the US. Just last month Hitachi ABB Power Grids announced a major project with Scottish and Southern Electricity Networks (SSEN) Transmission, part of the UK energy giant SSE plc, to enable Europe’s first multi-link VSC HVDC connection. The link, which will connect Shetland to the UK transmission system for the first time, will enhance security of power supply and help transmit wind power generated on the islands, contributing to the UK’s decarbonization target of bringing all greenhouse gas emissions to net zero by 2050.

Another exciting HVDC project is the Dogger Bank development in the UK, consisting of three wind farm projects in the North Sea. The development will be the UK’s first offshore wind application of HVDC and is expected to power 4.5 million homes when completed in 2030. These developments not only represent the massive potential HVDC has for the future of the energy industry, but they are playing an essential role in strategies to reduce global warming and contributing to the UN Sustainable Development Goal of increasing access to reliable and affordable energy for all.

 

This article originally appeared in the Bodo’s Power Systems magazine.

 

About the Author

Andreas Berthou received his Bachelor Of Science in Mechanical Engineering at Chalmers University of Technology, then Master Of Science in Business Management at Napier University. He work as a Senior Vice President, High Voltage Cables at ABB.