Technical Difficulty Analysis of UHV Transmission Lines

UHV transmission lines refer to the transmission of electric energy at the voltage level of ±800 kV and above DC and 1000 kV and above AC. UHV power transmission is developed on the basis of EHV power transmission, and its purpose is to continue to improve power transmission capacity, realize high-power medium and long-distance power transmission, and realize long-distance power system interconnection to build a joint power system.

1. Technical introduction of UHV transmission lines

The transmission power of a 1000 kV UHV AC transmission line is about 4 to 5 times that of a 500 kV line; the plus or minus 800 kV DC UHV transmission capacity is more than twice that of a plus or minus 500 kV line. At the same time, when the UHV AC line transmits the same power, the longest power transmission distance can be extended by three times, while the loss is only 25% to 40% of that of a 500 kV line. To transmit the same power, using a 1000 kV line for power transmission can save 60% of land resources compared to using a 500 kV line. Around 2020, the UHV backbone grid of the State Grid will be basically formed, and the inter-regional transmission capacity of the State Grid will exceed 200 million kilowatts, accounting for more than 20% of the country's total installed capacity. At that time, long-distance and large-capacity transnational power transmission from neighboring countries to China will become possible.

Regarding the economics of the UHV power grid, experts analyzed that by 2020, UHV can reduce the installed capacity by about 20 million kilowatts, save about 82.3 billion yuan in power construction investment; and reduce coal consumption for power generation by 20 million tons per year. The thermal power capacity of the north-south power transmission can reach 55 million kilowatts. Compared with the separate operation of the regional power grids, the annual coal cost will be reduced by about 24 billion yuan.

2. Construction planning of UHV transmission lines

China's ultra-high voltage transmission lines use 330 kV, 500 kV AC transmission lines and 500 kV, 800 kV DC transmission lines as the backbone grid. Five regional power grids and the Southern Power Grid have been formed across the country. Among them: the four regional power grids of East China, North China, Central China and Northeast China and the Southern Power Grid have formed a 500 kV main grid, and the Northwest Power Grid is building a 750 kV grid on the basis of a 330 kV grid. However, since the cross-regional power transmission of my country's power grid mainly relies on 500 kV AC and plus or minus 500 kV DC, the improvement of power transmission capacity is subject to many constraints such as technology, environmental protection, and land resources.

The UHV power grid can adapt to the long-distance large-capacity power transmission needs of 2,000 to 3,000 kilometers from east to west, and 800 to 2,000 kilometers from north to south, which is conducive to the development and power transmission of large coal power bases, large hydropower bases, and large nuclear power plant groups. The first, the 750 kV Guanting-Lanzhou East Power Transmission and Transformation Project, which was designed by the Northwest Electric Power Design Institute of the group company, has been operating safely and stably as of 2012, laying a solid foundation for the planned national UHV power grid.

At the beginning of 2008, the State Grid Corporation issued the "Opinions on Changing the Development Mode of the Power Grid and Accelerating the Construction of the Power Grid". , a strong national grid with coordinated development of power grids at all levels, and comprehensively promote the strategy of "one special and three major"; it is to completely solve the problems of lagging power grid construction and weak grid structure, adapt to the rapid growth of power demand, and realize the comprehensive and coordinated development of power grid and economic society; It is to fundamentally change the concept of local balance, promote the adjustment of power structure and layout optimization, and realize the optimal allocation of resources in a wider range..."

The "Opinions" for the first time publicly clarified the more detailed construction plan of the UHV power grid. District power grids, large coal power bases, large hydropower bases, and strong grid structures for major load centers. By 2020, 53 UHV AC substations will be built, with a transformation capacity of 336 million kVA and a line length of 44,500 kilometers; DC transmission will be built There are 38 projects, with a transmission capacity of 191 million kilowatts and a line length of 52,300 kilometers. The transmission capacity of UHV and cross-regional and transnational power grids has reached 373 million kilowatts. The technical equipment and operation indicators of the power grid have reached the international advanced level.…”

The "Opinions" also re-emphasized some plans during the "Eleventh Five-Year Plan" period, "...the UHV AC test demonstration and UHV DC demonstration projects will be fully completed, the North China-Central China-East China UHV synchronous power grid will be initially formed, and 750,000 kilometers in the Northwest will be basically completed. volt main grid, the company's business area has been fully connected to the Internet, and a major breakthrough has been made in transnational power cooperation. The company's grid investment in the "Eleventh Five-Year Plan" is 1.215 billion yuan. By 2010, the company's 220 kV and above AC and DC lines will reach 389,000 kilometers. The electric capacity reached 1.64 billion kVA, the cross-regional and cross-border transmission capacity reached 85 million kilowatts, and the exchange power reached 380 billion kwh. Gaoling back-to-back, China-Russia DC back-to-back projects were completed and put into operation in 2008. Lingbao back-to-back expansion, Huainan- The Shanghai UHV line project and the Nanyang UHV station expansion main transformer project were completed and put into operation in 2009. Speed up the construction of the Xiangjiaba-Shanghai ±800 kV DC demonstration project and ensure that it will be put into operation in 2010. Start the construction of Jinping-Sunan ±800 kV VDC, Ningdong-Shandong ±660 kV DC, Sanhu Erhui, Debao, Huliao, Shanxi-Jiangsu, etc. ±500 kV DC, Qinghai-Tibet ±400 kV DC and other projects.  …” For the State Grid in 2008 According to the company's construction plan, the data shows that in 2008, 32,000 kilometers of AC and DC lines of 330 kV and above, with a transformation capacity of 190 million kVA, are planned to be put into operation. billion. Among them, 17,000 kilometers of UHV, 750 kV and inter-regional power grids are planned to start construction, with a transformation capacity of 100 million kVA, and 2,450 kilometers of lines are planned to be put into operation, with a transformation capacity of 16.2 million kVA.

The State Grid Corporation also released brief operating performance data for 2007. Data show that in 2007, the State Grid Corporation completed 225.4 billion yuan in fixed assets investment, including 213 billion yuan in power grid investment; 60,000 kilometers of 110 (66) kV and above AC lines started construction, and 54,000 kilometers were put into operation; construction of substation capacity started 270 million kV Ann, put into production 210 million kVA. Completed electricity sales of 1974.2 billion kWh, main business income exceeded one trillion yuan, and profits and taxes exceeded one hundred billion yuan.

In 2008, the planned investment in power grid construction was 253.2 billion yuan, with a year-on-year increase of more than 10%. At the same time, according to the adjusted "Eleventh Five-Year Plan" total investment target of 1.215 billion yuan, we estimate that in 2009, it can still maintain more than 10% The growth rate, that is, the investment will reach about 285 billion yuan, and in 2010 it will be basically the same as in 2009.

3. Technical difficulties of UHV transmission lines

For AC UHV, there are two main technical key points: one is to manufacture an adjustable shunt reactor, and the other is to develop a double-break circuit breaker with a voltage level of 1000 kV. These two key technical problems have been basically solved. For the DC UHV power grid, the key to its technical research is the development of 6-inch thyristors. Japan has developed a 6-inch thyristor, and my country has a certain foundation for the development of a 6-inch thyristor. The significance of the UHV AC test and demonstration project in southeast Shanxi-Nanyang-Jingmen of my country is that it will truly realize full voltage, full capacity, and long-distance power transmission.

In addition, for my country's power grid equipment manufacturing industry, China's construction of UHV power grids is undoubtedly a huge boost to my country's national industry. China began to develop UHV power grids in 2006, which shows that China has the courage to solve UHV, a worldwide problem.

On August 9, 2006, the National Development and Reform Commission issued the "Reply on the Approval of the UHV AC Test and Demonstration Project from Southeast Shanxi to Jingmen" (Fagai Nengli [2006] No. 1585), officially approved the High-voltage AC test demonstration project. According to the State Grid Corporation of China, the UHV line has a total length of 654 kilometers, a declared cost of 5.857 billion yuan, and a dynamic investment of 20 billion yuan. It starts from Changzhi Substation in Shanxi Province, passes through Nanyang Switching Station in Henan Province, and ends at Jingmen Substation in Hubei Province. If it is fully rolled out across the country, the future investment will be more than 406 billion yuan, and the supporting dynamic investment will reach more than 800 billion yuan. The total investment is equivalent to 3 to 4 Yangtze River Three Gorges projects. This huge project has not been included in the outline of the national "Eleventh Five-Year Plan".

From August 19th to 26th, 2006, the UHV test project was grandly laid in Changzhi, Shanxi, Nanyang, Henan, and Jingmen, Hubei. On October 30, the State Grid Corporation of China held an oath mobilization meeting for the construction of the Jindongnan-Nanyang-Jingmen 1000 kV UHV AC test project in Shanxi, Henan and Hubei.

In 2016, the first UHV line entering Beijing - the Ximeng-Beijing East-Shandong 1000 kV UHV AC project will be completed and put into operation, and will transmit 1 million kilowatts of electricity. The National Development and Reform Commission approved the Beijing East UHV Station supporting 500 kV power transmission and transformation project to cooperate with UHV power transmission into Beijing.

China has a vast territory, and two-thirds of the exploitable hydropower resources are distributed in the northwest and southwest regions. Most of the coal resources are stored in the north of the northwest region and the west of the North China region, while the load centers are mainly concentrated in the eastern coastal regions. Due to the uneven distribution of power resources and load centers, with the development of the power system, the research and development of UHV transmission will also be put on the agenda.

4. Economic benefits of UHV transmission lines

UHV power transmission has obvious economic benefits. It is estimated that the transmission capacity of one 1150 kV transmission line can replace 5-6 500 kV lines, or three 750 kV lines; it can reduce tower materials by one-third, save conductors by one-half, and save including The cost of the power grid in the substation is 10-15%. The 1150 kV UHV line corridor is only about a quarter of the corridor required by the 500 kV line with the same transmission capacity, which will bring significant economic and social benefits to countries and regions with dense population, precious land or difficult corridors.

UHV transmission lines with a voltage level of 1000 kV need to use multiple split wires, such as 8, 12, 16 splits, etc. The cross-section of each split wire is mostly more than 600 square millimeters, which can reduce the loss caused by corona discharge And radio interference, television interference, audible noise interference and other adverse effects. The height of the tower is about 40-50 meters. The double-circuit parallel line towers are as high as 90-97 meters. Many countries are focusing on the development of new tower structures in order to reduce the size of towers and reduce the cost of lines. The former Soviet Union, the United States, Italy, Japan and other countries have started to plan and construct 1000 kV UHV transmission lines, and the transmission capacity of a single circuit line is generally 6 to 10 million kilowatts. For example, the former Soviet Union is stepping up the construction of large energy bases such as Ekibastuz, Kansk-Achinsk, and Tyumen oilfields. It already has a thermal power plant with an installed capacity of 6.4 million kilowatts, and plans to build a power plant with an installed capacity of 20 million kilowatts. Giant hydropower stations and nuclear power stations with large installed capacity. These energy bases are about 1,000-2,500 kilometers away from the power load center, and need to use 1,150 kV, ±750 kV DC, and even 1,800-2,000 kV for power transmission. The former Soviet Union has built a 1150 kV transmission line with a length of 270 kilometers, which doubles as an industrial test line. It started trial operation in 1986 and continued to build a 1150 kV transmission line with a length of 1236 kilometers. A 1150 kV UHV power grid will be formed by the end of the 20th century. The power system under the jurisdiction of the Bonville Power Bureau in the United States predicts that 60% of thermal power plants will be built in the east of the Cascade Mountains by the end of the 20th century, and about 32 million kilowatts of power will need to cross this mountain range to transmit electricity to the western load center. 1100 kV voltage level is used for power transmission. Each line is about 300 kilometers long and has a transmission capacity of about 10 million kilowatts. Italy plans to use 1,000 kV UHV lines to transmit electricity from thermal power plants and nuclear power plant bases along the Mediterranean Sea such as Pisa to industrial areas such as Milan in the north. Japan selected a 1,000 kV double-circuit parallel UHV transmission line to transmit electricity from the Shimokita giant nuclear power plant to Tokyo, with a length of 600 kilometers and a transmission capacity of 10 million kilowatts. These UHV transmission lines are all planned to be completed in the 1990s.

5. Putting into operation of UHV transmission lines

The United States, the former Soviet Union, Japan and Italy have all built AC UHV test lines and conducted a large number of AC UHV transmission technology research and tests. In the end, only the former Soviet Union and Japan built AC UHV lines.

5.1 The former Soviet Union: On the basis of previous studies, the construction of 1150 kV AC UHV lines began in 1981, which are 494 kilometers from Ekibastuz-Kokchetav and Kokchetav-Kustan Chennai is 396 kilometers. In August 1985, the world's first 1150 kV line, Ekibastuz-Kokchetav, was operated under rated operating voltage with load, and then extended to Kostanay. On January 1, 1992, through reconnection, the central dispatching department of Kazakhstan lowered the voltage of the 1150 kV line section to 500 kV for operation. During this period, the operation time of the Ekibastuz-Kokstanay line section and the substation equipment at both ends reached 23,787 hours at the rated working voltage, and the Kokchitav-Kostanay line section and Kostanay The running time of the substation equipment at the rated working voltage reached 11379 hours. From 1981 to 1989, the former Soviet Union also successively built 1,500 kilometers of UHV lines, with an overall scale of 2,400 kilometers. All step down to 500 kV operation.

5.2 Japan: In the autumn of 1988, the construction of 1000 kV UHV line started. On April 28, 1992, the 138-kilometer line of the West Gunma Main Line from the Nishi Gunma Switching Station to the Higashi Yamanashi Substation was completed. In October 1993, the 49-kilometer line of the South Niigata Main Line from the Kashiwazaki Kariwa Nuclear Power Station to the West Gunma Switching Station was completed. As for the UHV line, the two UHV lines have a total length of 187 kilometers. Since 2000, both have been operated at a voltage of 500 kV. In 1999, the East-West Corridor completed the construction of the 194-kilometer South Iwaki Main Line from the South Iwaki Switching Station to the East Gunma Switching Station and the 44-kilometer East Gunma Main Line from the East Gunma Switching Station to the West Gunma Switching Station. Two sections of UHV lines The total length is 238 kilometers. A total of 426 kilometers of UHV lines have been built in Japan. Due to the small size of the country, Japan’s UHV lines all adopt the method of double-circuit paralleling on the same pole.