Charlie Xu

September 2016

Introduction

Over the past few decades, China has achieved unprecedentedly high rates of economic growth, completely transforming its economy and increasing its GDP by almost tenfold. [1] This tremendous economic growth, coupled with rapid urbanization, has naturally resulted in a sharp rise in China’s demand for energy and electricity. Historically, China has used its waterways and railroads to supply the nation with energy, shipping billions of tons of coal [2] to light its urban centers, power its industry, and support its burgeoning economy. However, with its staggeringly high amounts of air pollution and the more widespread use of renewable energy technologies across the nation, China has been developing and deploying a more modern, more efficient way to ensure the steady flow of energy: high voltage direct current (HVDC) transmission.

HVDC transmission is not a novel idea. Since its first commercial deployment in Sweden in 1954, HVDC transmission has been used extensively for the long distance bulk transport of power. [3, 4] In a basic HVDC system, electricity from the grid, which utilizes alternating current (AC), is converted into DC via a converter station, transmitted through a cable at a voltage as high as 500 kV, and then converted back into AC using another converter station. [4] These HVDC cables can be suspended overhead through the use of support towers, buried underground, or laid underwater. [4, 5] Thus, HVDC transmission “enables the power flow to be controlled rapidly and accurately, and improves the performance, efficiency and economy of the connected AC networks” in a variety of environments. [4]

HVDC transmission can present significant advantages over high voltage alternating current cables (HVAC), which are currently used for transporting electricity through the grid. HVDC cables exhibit lower power losses than HVAC cables in all cases, and these cables are cheaper than HVAC cables. [5] Nevertheless, “it is also true that HVDC terminal stations are more expensive” [5, 6] given the complexity required for the conversion process. Thus, beyond a certain “break-even” distance (~600-800 km for overhead, ~50 km for subsea cables), HVDC transmission is the more economical choice. [5] As with any technology, however, there are some drawbacks to the use of HVDC cables. Since expensive converter stations are needed to transform the electricity from DC to AC, it is difficult to distribute power to the areas that the cable encounters between terminal stations. Furthermore, for projects under the aforementioned “break-even” distance, HVAC transmission is the more economical choice than HVDC transmission. [5, 7]

Given the efficiency of HVDC in bulk power transport, the Chinese government has invested heavily in HVDC transmission. [8, 9] As mentioned above, China’s demand for power has been rising dramatically, and it is expected to continue to rise in the future. According to the

State Grid Corporation of China (SGCC), the largest of China’s two state-owned utility corporations, China’s energy demand in 2030 will exceed 10 PWh, [8] representing an enormous challenge that the country needs to address. Furthermore, while the vast majority of China’s energy resources, both renewable and non-renewable, lie within its northern and western regions, the majority of its energy demand is concentrated in its eastern and southern regions. [8] Since the distances between energy bases and load centers can range from 800 to 3500 km, [8] transmission of power via HVAC cables would result in significant power losses. Therefore, the Chinese government has been developing a nation-wide HVDC cable system, which it hopes will be able to “change [its] energy development pattern, ensure energy security…and serve the economic and social development.” [10]

 

China’s HVDC Network

As mentioned above, China has been aggressively developing a fairly extensive HVDC network (see Figure 1). Interestingly enough, despite building two HVDC projects during 1987 and 1990, China did not construct any HVDC projects until 2001, most likely a consequence of China’s slow economic growth in that timeframe. [9] From that date to 2010, China began to steadily develop its HVDC transmission capability, as it planned, built, and put into commercial operation roughly one HVDC project per year. From 2010 onward, the Chinese government has accelerated the construction of its HVDC network, evidenced by multiple HVDC projects being put into commercial operation. As of 2013, China had completed 23 different HVDC projects and was planning the construction of 15 new HVDC projects. Furthermore, if China continues to deploy its HVDC grid as planned, by 2018, it will possess roughly 60% of the world’s installed HVDC capacity. [11]

Figure 1: List of Chinese HVDC Projects Pre-2013

[9] Source: Cao, Junzheng, and Jim Y. Cai. HVDC in China. Palo Alto: EPRI 2013 HVDC & FACTS Conference, 28 Aug. 2013. PDF.

[9] Source: Cao, Junzheng, and Jim Y. Cai. HVDC in China. Palo Alto: EPRI 2013 HVDC & FACTS Conference, 28 Aug. 2013. PDF.

With regards to those projects constructed between 2001 and 2010, there are some general commonalities. The vast majority of the HVDC projects are designed for bulk transport of power, given the distance spanned by the projects and the high power capacity of the cables themselves. [9, 12] In addition, many of these projects, such as the Tianshengqiao-Guangzhou project and the Three Gorges-Changzhou project, carry electricity generated through hydropower, demonstrating hydropower’s central importance in China’s energy economy. [13] However, there are also several HVDC projects that span a much shorter distance and have a much lower voltage capacity than the others. [9] China has termed these cable projects as “back-to-back” projects, which are designed to connect two otherwise unconnected AC electricity grids. [9, 12] Thus, during this period of time, the Chinese appears to have been interested not only in long-distance bulk transport of power, but also in crafting a stronger, more connected grid.

In addition to being the first year of an apparent acceleration in HVDC deployment, 2010 was also the first year that the Chinese government constructed and began to commercially operate the world’s first ultra-high voltage direct current (UHVDC) projects. While the basic principles and uses governing UHVDC cables are the same as those for HVDC cables, UHVDC cables are able to transmit power at a voltage (generally 800 kV) higher than the 500 kV used for regular HVDC cables. Thus, UHVDC cables are able to transmit far more power than standard

HVDC cables, making them well-suited for addressing China’s persistent rise in energy consumption. Indeed, according to ABB, the Xiangjiaba-Shanghai UHVDC cable project can direct up to 7400 MW of power from China’s massive Xiangjiaba hydroelectric dam toward China’s leading economic powerhouse of Shanghai. [14] Moreover, the Yunnan-Guangdong cable project, which has a maximum power capacity of 5000 MW, transmits electricity from several hydroelectric dams in Yunnan Province to industrial centers within Guangdong Province as well as the megacities of Guangzhou and Shenzhen. [15]

Both China’s need for greater transmission capacity and its great interest in UHVDC technology are evident by the projects that China intended to build between 2013 and 2015 (see Figure 2). Of the fifteen aforementioned projects, eleven of them span very large distances and have high power capacities, indicating that they are intended for large-scale bulk power transport. [9] Moreover, out of these eleven projects, ten of them utilize UHVDC cables, with one of the ten utilizing UHVDC cables that can achieve voltages up to 1100 kV. Thus, it is very likely that China will continue to invest heavily in the deployment of UHVDC transmission as well as research to further increase the maximum voltage (and therefore the maximum amount of power that can be carried through that cable) for UHVDC cables.

Figure 2: List of Chinese HVDC Projects Between 2013-2015

xu-2

Source: Cao, Junzheng, and Jim Y. Cai. HVDC in China. Palo Alto: EPRI 2013 HVDC & FACTS Conference, 28 Aug. 2013. PDF.

The remaining four HVDC projects, however, differ both in inherent properties and applications of the cables. Most HVDC projects, both in China and around the world, use line commutated converters (LCC), which are most efficient for transmitting high capacities of power over long distances. [16] However, other projects require voltage-sourced converters (VSC), which allow for the “independent control of active and reactive power” as well as “the capacity to supply weak or even passive networks.” [18] These attributes of VSC-HVDC transmission make it ideal for “small power applications,” [19] such as offshore wind farms, or the electricity grids of islands. [16, 17, 19] China’s first VSC-HVDC project integrates the Nanhui wind farm with its surrounding electricity grid, and the three VSC-HVDC projects currently being constructed are all designed to connect the electricity grids of islands to mainland China. [9, 19, 20] It is likely that VSC-HVDC transmission will be used more frequently in China as it seeks to not only connect island communities to the general grid, but also connect future offshore wind projects to the main grid. [21]

The exact cost of an HVDC project is generally difficult to determine, given that each project has different factors (e.g. transmission distance, rated power) that will need to be taken into account. However, general estimates can be provided based on knowledge of previous projects. For instance, the Southern Hami-Zhengzhou HVDC line is a massive project, extending a total distance of 2200 km as it travels from Xinjiang province in the northwest down to Henan province in central China. [22, 23] Utilizing 800 kV cables, the line can supply up to 8000 MW of energy. [9] Furthermore, as one of China’s large-scale HVDC projects, the lines are suspended aboveground. Given these factors, the project ended up costing 23.4 billion yuan (~3.5 billion USD), [22, 23] or roughly 1.8 million USD/ km. Moreover, the recently constructed LingzhouShaoxing HVDC line, which extends from Ningxia Province to Zhejiang Province, [24] incurred similar costs. Like the Southern Hami-Zhengzhou line, the Lingzhou-Shaoxing line uses 800 kV cables and can supply up to 8000 MW of energy; however, the Lingzhou-Shaoxing line is a bit shorter, spanning 1722 km. [25] Due to these reasons, the project cost 19.5 billion yuan (~2.9 billion USD), [25] or roughly 1.7 million USD/km. As China (and other nations) more aggressively develops its HVDC network and discovers cheaper, more efficient methods and materials, it is very likely that these costs may be lower in the future.

Technological and Policy Advancements

The development of such an HVDC grid has both prompted and been propelled forward by notable innovations and ideas in technology and policy alike. After listing UHVDC development “in the 11th Five-Year and 12th Five-Year Plan, the Action Plan for Air Pollution Prevention and Control and the energy development goal of the 12th Five-Year Plan,” [10] China has steadily directed its research centers and manufacturing base to create HVDC transmission technology of greater quality and in greater quantities. Technologically, China continues to discover new methods and techniques to improve its HVDC transmission, while it also institutes policies that enable the continued and steady production of more HVDC transmission components.

First and foremost, China’s pioneering efforts in developing, constructing, and deploying

UHVDC transmission technology has enabled it to make significant strides in cultivating its own HVDC network. Given that China is the first country to begin the widespread development and deployment of 800 kV UHVDC transmission cables, it comes as no surprise that China is already working on 1100 kV UHVDC technology. At the end of 2010, China recognized that projects having to span distances greater than 2500 km would experience economically unfavorable transmission losses, even with 800 kV UHVDC technology. [26] Thus, the SGCC decided to set 1100 kV as the next target voltage level for UHVDC technology, initiating the ZhundongSichuan (also known as Zhundong-Chengdu) pilot project. [9, 26] China has steadily worked on this project, utilizing research used in developing previous projects to push HVDC technology to its limits. Moreover, China has also established contracts with Siemens, ABB, and NR Electric to provide the various components needed for yet another 1100 kV UHVDC project: the ChangjiGuquan project. [27, 28, 29]

Of course, these projects and China’s HVDC network as a whole would not have existed without dedicated scientific research and testing into electric transmission, something that China has actively supported. Within China, there are two major organizations that have propelled

Chinese scientific research in HVDC technology: the SGCC and the Chinese Electric Power

Research Institute (CEPRI). Due to its control over most of China’s electricity grid, the SGCC has naturally invested in improving HVDC technology. In 2013, the SGCC formed the State Grid Smart Grid Research Institute (SGRI), an institution designed to conduct research on equipment pertaining to the development of a smart grid. [30] Within the SGRI, there exist three laboratories that focus on improving, among others, HVDC technology. [31] The Electric System Power Electronics Laboratory performs tests on various HVDC converter valves, which are a crucial component within an HVDC converter station. Moreover, the DC Power Grid

Technology and Simulation Laboratory confronts the technological challenges of integrating

HVDC technology into the grid as a whole, while the State Energy HVDC Technology and

Equipment Research Center explores various methods of developing more efficient HVDC and

UHVDC equipment technologies. [31]

Working in direct affiliation with the SGCC, CEPRI is a comprehensive, multi-discipline research institution dedicated to all aspects of electric power research, [32] thus serving as the main R&D center for the SGCC. To accelerate technical research into HVDC technology, CEPRI created three world-class labs for the purpose of testing UHVDC technology, which are the UHVDC Test Base in Beijing, the UHV Transmission Tower Test Base in Hebei, and the High Altitude Test Base in Tibet. [33, 34] The UHVDC Test Base has been especially prolific, having, as of 2015, achieved “52 major technological innovations” and “set 15 records.” [34] These innovations include improvements in overvoltage suppression, general reliability, and real time DC protection, to name a few. [34] Through these centers, both at the SGCC and the CEPRI,

China has truly created a world-class research and testing platform for HVDC technology. [8, 11]

The improvements in HVDC technology derived from such scientific research have been implemented at a massive scale, due to forward-thinking Chinese policy. As it began to build its HVDC network, the Chinese government naturally had to purchase equipment from and rely on the expertise of European companies like ABB and Siemens that had the necessary understanding of the HVDC field. However, in signing its deals with these companies, the Chinese government also made sure that these companies had to partner with local companies, thus ensuring a transfer of skills and knowledge. [11, 35] Such a policy has produced great benefits for China. Currently five Chinese engineering firms (e.g. NR Electric, Power Electronics

Research Institute, Xi’an Electric) have sufficient HVDC experience, [11] such that they could possibly develop projects even outside of China. [35] Moreover, these Chinese companies have begun manufacturing HVDC components. For instance, Power Electronics Research Institute (PERI) manufactures 90% of thryistors (a crucial component within an HVDC converter transformer) used in Chinese HVDC projects, while the converter valves and converter transformers of Xi’an Electric (also known as China XD Group) have been included in many

Chinese HVDC projects. [11] Thus, China has been able to not only cultivate a strong manufacturing base for HVDC technology, but also slowly substitute imported components with domestically produced, cheaper parts. [9, 35] Thus, through its shrewd policy of information sharing, the Chinese government has been able to create new jobs, lower the cost of its HVDC projects, and become more self-sufficient in creating said HVDC projects.

Future Prospects

Given the successes that it has achieved thus far in the HVDC space, China will continue to improve HVDC technology and grow its HVDC network. With regards to its scientific research, China is mainly interested in increasing the amount of power that can be transmitted through an HVDC cable, aiming to accomplish that goal through two approaches. The first approach entails increasing the voltage that an HVDC cable can accommodate, which will also have the benefit of reducing transmission losses, while the second involves increasing the current carrying capacity of the cable. [34] These increases in voltage and current will necessitate larger, heavier transformers, which will be very difficult to transport by land routes. [34] Therefore, in order to ensure that any improvements in voltage or current carrying capacity are fully utilized,

“an on-site modular assembly technique” [34] will need to be developed. Moreover, Chinese researchers are also interested in increasing the AC voltage of the grids that are connected by HVDC cables. [34]

These goals are, in no small part, motivated by China’s future plans for its HVDC network. China’s interest in 1100 UHVDC technology stems from its desire to utilize its energy resources in Xinjiang Province and Tibet through HVDC technology. [26] Xinjiang Province contains the most fossil fuel reserves than any other province and ranks second in terms of wind energy and solar energy resources. [37] On the other hand, Tibet, while lacking in fossil fuels, possesses vast hydroelectric and geothermal energy resources. [38] Seeing as these two are the westernmost provinces of China, far from the cities and industrial centers of eastern and central China, any HVDC project seeking to take advantage of these resources will require extremely high voltages to be economically feasible. Therefore, as China refines its 1100 kV HVDC transmission technology, it is very likely that China will build future HVDC projects that will connect Xinjiang and Tibet to its central and eastern provinces. Moreover, China will likely continue to build HVDC projects that will service its major population centers (e.g. Shanghai, Guangzhou), so as to keep up with the ballooning energy demand.

U.S. Implications

The United States can learn much from China’s experience with HVDC technology, as it does share similarities with China as a whole. According to the Energy Information Administration, the United States is expected to face a 24% increase in electricity generation between 2015 and 2040, [39] which also may rise if more electric vehicles head onto American roadways. By facilitating the steady flow of electricity from energy resource-intensive regions to energy demand-intensive regions, an HVDC network would enable the U.S. to take full advantage of energy resources that might otherwise be underutilized at a regional level. Moreover, similar to China, the U.S. is anticipating a higher penetration of renewables within its electricity grid in the future. Therefore, an HVDC network would help mitigate the renewables intermittency problem, as electricity from other areas could be supplied during times when renewable energy sources are not generating electricity at full capacity (e.g. nighttime for solar). Such optimization of the U.S. electricity grid could also reduce as much as 80% of carbon dioxide emissions from the U.S. electricity sector. [40]

Naturally there would also be major differences between the Chinese approach and any potential U.S. approach to developing an HVDC network. In the U.S., power companies wishing to construct transmission lines (including HVDC lines) must negotiate right-of-way agreements with the owners of every single property that the lines would pass through, a process that would add more costs to a nationwide HVDC network. Moreover, since a large-scale HVDC network in the United States would likely have to be buried underground, due to both the right-of-way situation and safety reasons, the cost for a U.S. HVDC project would be higher than an equivalent one in China.

Nevertheless, China’s example shows that it is indeed possible for the U.S. to construct a large-scale nationwide HVDC network, given that a few factors are present. First and foremost, the political will for such an undertaking is absolutely crucial to the creation of a national HVDC network. Given the scale and capital-intensive nature of such a project, the federal government would need to be fully committed to the network’s development to ensure that it is implemented successfully. Moreover, implementing a “knowledge-sharing” policy similar to China’s would accelerate the construction process by building U.S. expertise in HVDC technology. Moreover, such a policy would help build a manufacturing base in the U.S. for HVDC equipment and components, adding new jobs and contributing toward economic growth.

Conclusion

China has faced extraordinary challenges in the energy realm, and it has developed unprecedented solutions to meet those challenges. Confronted with quickly burgeoning energy demand and great distances between its energy resources and energy loads, China decided to craft an HVDC cable network, an “energy superhighway” system that would connect the nation and address its energy problems. While initial progress was slow, China quickly accelerated the development of its HVDC network, fueled by economic growth and smart policy. In its eager pursuit of a more effective, more cohesive HVDC network, China has pioneered new methods and new technologies, contributing such innovations as 1100 kV UHVDC technology and VSCHVDC. Indeed, today, China is leading the world in HVDC development and has fully incorporated HVDC transmission as a core tenet of its energy policy, a testament to the importance and usefulness of the technology. As more countries face an increasing need to optimize their energy system and confront rising energy demand, they would do well to look at China for a glimpse of how HVDC technology can help create a more efficient and more resilient electricity grid.

 

 

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