High-Voltage Power Transmission Projects Are Booming Around the World

High-voltage power transmission systems are more important today than ever before because power generated at renewable energy sites in remote locations must often be transmitted to distant load centers. Several state-of-the-art projects being done around the world are reviewed below.

The majority of major electric power transmission lines in the U.S. are 115-kV, 230-kV, or 500-kV alternating-current (AC) lines. These high-voltage lines are crucial for efficiently transmitting large amounts of electricity over long distances.

The primary reason for using high voltages is to minimize power losses during transmission. In accordance with the equation P = V x I, where P is power (watts), V is voltage (volts), and I is current (amps), higher voltages allow lower currents for the same amount of power transmitted. This is important because all conductors, including transmission lines, have some inherent resistance (R, ohms) that impedes the flow of electric current. This resistance causes a voltage drop along the line and dissipates power in the form of heat.

Because V = I x R, the power equation can be rewritten P = I2 x R. This shows that the power loss is proportional to the square of the current flowing through the conductor. Therefore, because higher voltages allow lower currents for the same amount of power transmitted, the I2R losses are significantly reduced.

Lower current also provides an economical benefit during construction because smaller conductor cross-sections can be used, reducing material and construction costs while still minimizing losses. The growth of renewable energy sources, such as wind and solar farms, which are often located in remote areas, has increased the demand for high-voltage transmission to integrate these resources into the grid. Thus, using high voltages is important for multiple reasons.

Ultra-High-Voltage Systems

In China, constructing ultra-high-voltage (UHV) power lines (Figure 1), both AC and direct-current (DC), has been a priority. In April 2024, at the 26th World Energy Congress in Rotterdam, Netherlands, a representative from State Grid Corporation of China (SGCC) told POWER that the company had already commissioned 19 UHV (1,000-kV) AC transmission projects, one UHV (±1,100-kV) DC transmission project, and 15 UHV (±800-kV) DC transmission projects.

1. Technicians are shown here working on the construction of the cross-Yangtze River transmission line of the Wuhan-Nanchang 1,000-kV ultra-high-voltage (UHV) alternating-current (AC) project in Qichun County, Huanggang City, Hubei Province, China. Courtesy: State Grid Corporation of China

The most impressive project on SGCC’s resume is its Zhundong Anhui South ±1,100-kV DC project, also known as the Zhundong-Wannan project. The project starts at the Zhundong (Changji) converter station in Xinjiang and ends at the Anhui Wannan (Guquan) converter station, passing through Xinjiang, Gansu, Ningxia, Shaanxi, Henan, and Anhui provinces. The total length of the line path is 3,304.7 kilometers (km, 2,053.4 miles). The transmission capacity is 12 GW at a voltage of ±1,100 kV. SGCC says it is “the world’s highest voltage level, largest transmission capacity, and farthest transmission distance ultra-high-voltage project,” and claims it can reduce coal consumption in East China by about 38 million tons annually.

The Zhundong Anhui South project was considered an important element of China’s Belt and Road Initiative (BRI, see sidebar “The Belt and Road Initiative”). The project provides significant economic, social, and environmental benefits for the region. It was the second UHV power transmission project to export electricity from Xinjiang. It bundles the delivery of thermal power, wind power, and solar power from Xinjiang’s energy base to ensure a more reliable power supply and reduce air pollution in East China. The stimulation of Xinjiang’s economy also played a very important role in the project.

The Belt and Road Initiative

China’s “Belt and Road Initiative,” also known as the “New Silk Road,” is a massive infrastructure project launched by China in 2013 to build a vast network of transportation routes, energy pipelines, and other infrastructure across multiple continents. The “Belt” component was focused on plans to revitalize a series of ancient overland trading routes connecting Europe and Asia, built largely by the Chinese. The “Road” element, meanwhile, was designed to establish new sea trade infrastructure along the old Marco Polo route—a maritime silk road connecting China, Southeast Asia, Africa, and Europe. The new route was expected to be longer, avoiding the Malacca Strait, while incorporating fueling stations, ports, bridges, industry, and infrastructure through Southeast Asia and into the Indian Ocean.

ABB supplied technology and equipment valued at more than $300 million for the Zhundong Anhui South project. Among the items delivered by ABB were advanced converter transformers and components such as bushings and tap changers. It also supplied the HVDC converter valves, DC circuit breakers (see sidebar “Environmentally Friendly High-Voltage Equipment”), wall bushings, and capacitors, as well as providing system design support. Nanjing Electric won the bid for nearly 400,000 pieces of high-tonnage DC tempered-glass insulators of 550 kiloNewtons (kN) and above. Among the items it supplied were more than 20,000 pieces of 840-kN DC products.

Environmentally Friendly High-Voltage Equipment

Sulfur hexafluoride (SF6) gas has long been used in high-voltage switchgear components, such as circuit breaker interrupter chambers, gas-insulated substations, and instrument transformers, due to its excellent insulating and arc-quenching properties. However, while SF6 is a great gas for these applications, it is also a potent greenhouse gas (GHG) with a global warming potential (GWP) about 24,300 times that of carbon dioxide (CO2), according to the Intergovernmental Panel on Climate Change’s (IPCC’s) Sixth Assessment Report (AR6). That means that it is 24,300 times more effective at trapping infrared radiation than an equivalent amount of CO2. SF6 also has an atmospheric lifetime of 1,000 years, which is significant.

To address the environmental concern posed by SF6, manufacturers have been exploring alternative insulating and arc-quenching media for high-voltage components. According to Naeem Siddiqui, head of Offer Management—Switchgear Americas with Siemens Energy, there are only a few main alternatives currently being used, which include fluoronitrile (C4), fluoroketone (C5), and clean air.

“C4 and C5 still have a global warming potential, though minimized, and require reporting and incur a penalty for leaking,” Siddiqui explained. “As regulations change and requirements become stricter, C4 and C5 may fall under future greenhouse gas regulations. Clean air—being comprised of nitrogen and oxygen—is the only alternative that will never become restricted, as it is comprised of only natural components and has zero global warming potential, zero harmful effects,” he said.

Siddiqui also noted that with time and usage, C4 and C5 can produce byproducts, which themselves are harmful and affect the efficiency and safety of breaker functions. This also increases risks to maintenance workers. The byproducts of C4 include hydrogen fluoride (HF), carbon monoxide, and carbonyl fluoride (COF2). C5 byproducts also include HF and COF2. Both C4 and C5 Novec gasses are registered PFAS (per- and polyfluoroalkyl substances) and are in the same toxicity class as SF6.

Beyond the harmful gaseous byproducts attributable to C4 and C5, a published technical document suggests crystals may form during use that can alter the arc characteristics, thus creating safety and product efficiency concerns. In contrast, Siddiqui said the clean air approach has no byproducts, nor is anything created that would affect the efficiency or safety of the equipment or its maintainers.

“C4 and C5 are baby steps towards decarbonization, however, clean air is a full advanced step, being the only alternative to date that is completely greenhouse gas-free for the net zero future with no harmful byproducts or efficiency concerns nor any concerns of future regulations,” said Siddiqui.

Siemens Energy’s clean air breakers (Figure 2) have a vacuum interrupter and they are sealed for life; therefore, no maintenance is required. Today, circuit breakers rated up to 145 kV, and 40 kA and 63 kA, have been successfully designed and tested. A 245-kV breaker is in development and is expected be available by 2027. Siddiqui said once these are available, the products will cover about 75% of utility and industry breaker requirements. Still, higher voltage classes, including 420-kV and 550-kV designs, are next in line for development.

2. An installed Siemens Energy clean air vacuum circuit breaker is shown here. Courtesy: Siemens Energy

Because of the vacuum design, arc energy is lower in a clean air circuit breaker than in an SF6 breaker, which results in a much longer life. Extensive third-party testing found the clean air vacuum breaker lifetime could be double that of an SF6 breaker. Furthermore, the clean air design can operate in extreme cold temperatures (as low as –60C) without requiring external tank heaters—a very attractive benefit for customers in frigid climates.The solution has been well-received by the industry. “Siemens Energy has over 4,200 circuit breakers and gas-insulated switchgear from the clean air Blue portfolio contracted worldwide. Of these, 1,500 are in operation and to date have saved 4.4 million tons of CO2 emissions,” said Siddiqui.

Massive Brazilian Projects

The Belo Monte hydropower station is an 11.2-GW run-of-the-river hydroelectric power plant located on the lower reach of the Xingu River, in northern Brazil. Fully commissioned in November 2019, it is the second-largest hydroelectric plant in Brazil, behind only the Itaipu complex. It is also the world’s fourth-largest power plant.

While several major power plants are located in northern Brazil, 80% of the country’s electricity is used in southern and southeastern regions, many hundreds of kilometers away. Getting power from generating sites to major load centers is important for economic and social reasons.

Under the BRI, SGCC sought to develop projects outside of China, and Brazil was a country looking for help. In February 2014, SGCC formed a consortium in which it held a 51% share with Centrais Elétricas Brasileiras S.A. (Eletrobras), the leading electricity generation and transmission company in Brazil, as the other shareholder. The consortium won the bid for the Belo Monte Phase I UHV ±800-kV transmission project. It was SGCC’s first UHV transmission project in the Americas. The project included an ±800-kV transmission line traveling 2,084 km (1,295 miles) with converter stations at both ends. The total investment was estimated to be $2.47 billion, of which $1.26 billion was from SGCC. The project was put into operation in December 2017.

In July 2015, while Phase I was still in progress, SGCC independently won the bid for Phase II of the project. That $3.14 billion deal was ultimately financed, constructed, and operated solely by SGCC. The Phase II project starts at the Belo Monte Hydropower Plant and extends to Rio de Janeiro in the southeast, covering a total length of 2,539 km (1,578 miles). SGCC says it is “the world’s longest ±800-kV DC transmission line project.” The Belo Monte Phase II project was the first overseas project using Chinese UHV technologies and was considered a signature project under the BRI.

The Belo Monte Phase II UHV transmission project crosses three regions with very different topography and climate. It traverses 81 cities and five Brazilian states through diverse terrain that contains rainforests, hills, wetlands, and grasslands. The line also crosses 13 large rivers. The complex ecological system and great cultural diversity along the path made things even more difficult for a company operating on foreign soil. Yet, the Chinese and Brazilian workers involved in the project rose to the task. They braved high temperatures, strong winds, violent thunderstorms and other severe weather events, and still managed to complete the project 100 days ahead of schedule in March 2019, with zero safety accidents reported.

SGCC isn’t done constructing projects in Brazil either. In April, the company announced it had signed an agreement for the Graça Aranha-Silvania ±800-kV UHV DC power transmission project (Northeast Bipolar I). It called the deal “the largest transmission concession project” in Brazil’s history.

The 5-GW project involves the construction of 1,468 km (912 miles) of ±800-kV UHV DC transmission lines with converter stations and synchronous condensers at both ends, as well as related AC projects. The project will bring together and transmit clean energy such as wind power, solar energy, and hydropower from the northeast and north of Brazil through the states of Maranhão, Tocantins, and Goiás, to meet the electricity needs of about 12 million people, including in the Federal District of Brazil, where the capital is located. It is planned to be put into operation in 2029, with a concession period of 30 years.

Significant Projects Elsewhere

In June, German transmission system operator (TSO) Amprion awarded two major HVDC cable projects—Korridor B V49 and part of the Rhein-Main-Link project—to Sumitomo Electric. The combined deals have a total project value of more than €3 billion. At the same time, Sumitomo Electric announced the acquisition of 90% of the shares of Südkabel, a well-known German high-voltage cable manufacturer. Sumitomo Electric plans to also invest €90 million in Südkabel’s Mannheim, Germany, facility to increase its cable production capacity.

Amprion and Sumitomo Electric are currently proceeding with the A-Nord HVDC project connecting a 300-km link in Germany between Emden and Osterath near Dusseldorf. The two additional projects (Figure 3) will be implemented as part of a long-term strategic collaboration between the two companies. Korridor B V49 will connect approximately 300 km between Wilhelmshaven and Hamm, and the part of the Rhein-Main-Link project that is included in the deal spans about 650 km in length. Both projects will form part of Germany’s critical power transmission infrastructure, designed specifically to bring renewable power generated in the North Sea to the country’s major consumer areas.

3. The A-Nord high-voltage direct-current (HVDC) project is being constructed today. Korridor B V49 and part of the Rhein-Main-Link project are large-scale projects planned for completion by 2033. Courtesy: Sumitomo Electric

The 525-kV HVDC cable for these new projects, which Sumitomo Electric said is “the most technologically advanced transmission cable in the industry,” will be manufactured in Südkabel’s factory in Mannheim. The projects are expected to be completed by 2033.

Meanwhile, in May, Hitachi Energy was selected by Marinus Link Pty. Ltd. (MLPL) to supply an HVDC project that will augment the connection between mainland Australia and Tasmania’s grid. The approximately 345-km (214 mile) cable route HVDC system will enable the flow of renewable power in both directions between the Victorian and Tasmanian states. The connection will enable the Tasmanian state to import excess supply of solar and wind produced in Victoria, while reserving its hydro and storing the extra energy. Clean hydropower can then feed the mainland grid when it is needed most, acting as a large battery for the nation. Moreover, Hitachi Energy said it will strengthen the security of supply in the Australian power grid, which is increasingly being generated by intermittent renewable resources.

Hitachi Energy will supply its HVDC Light voltage source converter (VSC) stations as part of the project. Upon completion, the Marinus Link will have a total capacity of 1.5 GW.

In the Netherlands, GE Vernova and Seatrium Ltd. have been awarded a third contract by TenneT TSO B.V. for the construction of a 2-GW HVDC electric transmission system. The HVDC system will support TenneT’s goal of installing 40 GW of offshore wind energy in the German and Dutch North Sea. The contract announced in June will serve the Nederwiek 2 offshore wind farm, located approximately 95 km (59 miles) off the coast of the Netherlands. The project is slated to begin in June 2024, with commissioning expected by 2031.

Aaron Larson is POWER’s executive editor.

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