UHV transmission is the most advanced transmission technology in the world. We all know that electricity is transmitted by wires. We use electricity everywhere in our homes, factories, shops, schools, and hospitals, all of which are imported through the grid. Electricity in the grid is generated from power plants. We may or may not have seen power plants, and that's okay because most of them are built far away from us. To transmit the electricity from the power plant to the grid, and then through the grid to our homes, factories, shops, schools, and hospitals, this is "power transmission".
On January 11, 2016, the Zhundong-Wannan (Changji, Xinjiang-Xuancheng, Anhui) ±1100 kV UHV DC transmission project started construction. This is the UHV transmission project with the highest voltage level, the largest transmission capacity, the longest transmission distance and the most advanced technology in the world.
1. Characteristics of UHV transmission
Transmission of electrical energy using voltage levels of 1000 kV and above. UHV transmission is developed on the basis of EHV transmission, and its purpose is to continue to improve transmission capacity, realize high-power medium and long-distance transmission, and realize long-distance power system interconnection to build a combined power system.
UHV power transmission has obvious economic benefits. It is estimated that the power 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.
2. Current status of UHV transmission
Because China needs long-distance and large-capacity transmission of electric energy. Anyone with basic geography knowledge and an understanding of China's national conditions knows that China has a large population of about 1.4 billion, and most of the population is concentrated in the central and eastern regions. Because the economy in the central and eastern regions, especially the coastal areas, is relatively developed, and the production and living conditions are better, while the western and northwestern regions have more mountains and less land, the conditions are relatively difficult, the population distribution is relatively small, and the economy is not as developed as the central and eastern regions.
The central and eastern regions with a relatively developed economy and a large population will inevitably consume more energy, mainly because they need more power supply. As mentioned earlier, electricity comes from power plants.
What do power plants rely on to generate electricity? In China, power plants mainly rely on coal or hydropower to generate electricity, and a small amount of nuclear energy is also used to generate electricity. Those that use coal to generate electricity are called thermal power plants, those that rely on hydropower to generate electricity are called hydropower plants, and those that use nuclear energy to generate electricity are called nuclear power plants. In other words, if you want to be able to generate electricity, you must have coal or hydropower resources, and nuclear power generation only accounts for a small part.
However, China's coal reserves are mainly in the northwest, such as Shanxi, Shaanxi, eastern Inner Mongolia, Ningxia and parts of Xinjiang, and the central and eastern provinces have very little coal reserves. Hydropower resources are mainly distributed in the western region, the middle and upper reaches of the Yangtze River, the upper reaches of the Yellow River, and the Yalong River, Jinsha River, Lancang River, and Yarlung Zangbo River in the southwest.
As a result, the central, eastern and coastal areas need a large amount of power supply, but have no resources for power generation. The coal and hydropower resources that can be used for power generation are far away in the western region thousands of kilometers away. How to solve this energy problem?
3. Solutions for UHV transmission
Therefore, the country adopts two strategies of coal transportation and electricity transmission. One is to transport part of the coal in the west to the port (Datong-Qinhuangdao) by rail, and then ship it to Jiangsu, Shanghai, Guangdong and other places, referred to as coal transportation; the other is to use coal and hydropower resources in the west to generate electricity locally, and then Transmission lines and grids send electricity to the central and eastern regions, referred to as transmission.
Let's look at the strategy of coal transportation first. First, the coal dug out of the coal mine must be loaded onto the train, travel thousands of kilometers to the port, and be unloaded on the wharf for temporary storage. It is then loaded onto a 10,000-ton ship for long-distance transportation by sea to the destination port, and coal has to be unloaded and stored. Finally, it is loaded on trains and other means of transportation before being transported to the local thermal power plant coal storage yard, where it is unloaded and stored for later use. The entire process of coal transportation has to go through three loadings and three unloadings, as well as storage in the middle, and transportation means such as trains and ships are used, so the transportation cost is very high, and the transportation cost is often higher than the cost of buying coal in the coal mine. After technical and economic calculations by experts, in China, if the distance between the coal mine and the power plant exceeds 1,000 kilometers, it is not very cost-effective to adopt the coal transportation strategy.
What about power transmission? To use coal and hydropower in the west to generate electricity locally, it is enough to build thermal or hydroelectric power plants locally. Of course, it costs money to build a power plant, especially to build a hydropower plant, but this is a one-time investment that will last for many years. Then it is necessary to build transmission lines to send electricity to the central and eastern regions.
4. Benefits of UHV transmission
The UHV transmission capacity is large, the power transmission distance is long, the line loss is low, and the land occupation is small. The capacity of the 1 million volt AC UHV transmission line to transmit electric energy (technically called the transmission capacity) is five times that of the 500,000 volt ultra-high voltage transmission line. So some people make the analogy that EHV power transmission is a provincial road, at most it is a national road, while UHV power transmission is an "electric power highway".
As we all know, after the rapid development in recent years, China's expressways have basically formed a network extending in all directions. However, China's UHV power transmission "electric power highway" has just completed a test and demonstration project at the end of 2008, and the total length of the line is only 640 kilometers. Therefore, it will take a long time to build the UHV power grid, which is an electric highway network, and will inevitably spend a lot of manpower, material resources, and financial resources in order to allocate energy resources conveniently, quickly, and efficiently across the country.
In power engineering technology, there is a term called "economic transmission distance", which refers to the most economical transmission distance of a transmission line of a certain voltage level, because the transmission line itself also has losses while transmitting electric energy, and the line is too long and the loss is too great It doesn't make sense economically.
The economical transmission distance of a 500,000-volt ultra-high voltage transmission line is generally 600-800 kilometers, while a 1-million-volt ultra-high-voltage transmission line has increased voltage and reduced line loss, and its economical transmission distance has also increased, reaching 1,000 to 1,000 kilometers. 1,500 kilometers or even longer, so that the aforementioned problem of transferring energy from the west to the central and eastern regions can be solved.
The construction of transmission lines also requires land, which is called "line corridor" in engineering. As mentioned earlier, building a 1 million volt UHV transmission line can support five 500,000 volt ultra-high voltage transmission lines, and the land occupied by the line corridor is only equivalent to two 500,000 volt transmission lines, so relatively speaking, the construction of UHV Transmission lines can occupy less land, which is especially beneficial to the central and eastern regions where land resources are scarce.
Of course, UHV power transmission, especially the construction of UHV power grid, has many benefits. It can firmly connect China's power grid, so that different power plants built in different locations (such as thermal power plants and hydropower plants) can support and complement each other. Promote the intensive development of coal resources and water resources in the west, reduce the cost of power generation; ensure the growing power demand in the central and eastern regions, and reduce the environmental pollution caused by the construction of thermal power plants in densely populated and economically developed areas; Harmonious economic and social development in resource-intensive and economically underdeveloped areas.
5. Historical status of UHV transmission
UHV transmission lines with a voltage level of 1000 kV need to use multiple split wires, such as 8, 12, 16 splits, etc., and 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 1,000-kilovolt 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-scale energy bases such as Ekibastuz, Kansk-Achinsk, and Tyumen Oilfield. 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 to 2,500 kilometers away from the power load center, and need to use 1,150 kV, ±750 kV DC, and 1,800 to 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.
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 areas. 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.
6. The world project of UHV transmission
6.1 1150kV project in the former Soviet Union
In the 1970s, the former Soviet Union began the research work on 1000kV UHV AC power transmission and transformation technology. In August 1985, the Ekibastuz-Kokchetaf line (497km) and two 1150kV substations (boost station), and put into industrial operation according to the system rated voltage of 1150kV.
6.2 1100kV substation in Japan
Japan's 1000kV power system is concentrated in Tokyo Electric Power Company. The construction of 1000kV power transmission and transformation projects began in 1988. In 1999, two 1000kV transmission lines with a total length of 430km and one 1000kV substation were completed. The 1000kV transmission line to the southern Tokyo area is called the South-North Line (190km in length), the South Niigata Main Line, and the West Gunma Main Line; the second line is a 1000kV transmission line connecting power plants on the Pacific coast, called the East-West Line (length 240km ), East Qunma Main Line, and South Qingcheng Main Line.
6.3 Italy 1050kV test project
In the 1970s, Italy and France were entrusted by the Western European International Power Generation and Supply Federation to conduct demonstration work on the selection of AC 800kV and 1050kV transmission schemes in the European continent. After that, the Italian UHV AC transmission project carried out basic technology research and equipment manufacturing under the auspices of the state. After a series of work, the 1050kV test project was completed in October 1995. Until December 1997, it was carried out at the system rated voltage (nominal voltage) of 1050kV for more than 2 years, and certain operating experience was obtained.
6.4 Jindongnan-Nanyang-Jingmen 1000 kV UHV AC test demonstration project
On January 6, 2009, the 1000 kV AC power transmission and transformation project independently developed, designed and constructed by my country with independent intellectual property rights - Jindongnan-Nanyang-Jingmen UHV AC test demonstration project successfully passed the trial operation. This is China's first UHV AC transmission line, which marks a major breakthrough in my country's long-distance, large-capacity, low-loss UHV core technology and localization of equipment. Safety and a reliable supply of electricity are of great importance.
6.5 "Anhui Electricity Transmission to East" project
My country's first double-circuit UHV AC transmission project on the same tower - "Anhui Electricity Transmission to the East" project starts from Huainan, Anhui in the west, passes through southern Anhui and northern Zhejiang to Shanghai, with a total length of 656 kilometers and a total of 1,421 iron towers. Completed and put into operation. After the project is completed, it will be able to transmit more than 50 billion kilowatt-hours of electricity each year, which is equivalent to building six thermal power stations with a million-kilowatt class for Shanghai.
7. Development prospects of UHV transmission
On September 25, 2013, the world's first 1000 kV double-circuit UHV AC project on the same tower - Anhui Electricity Transmission to East China was officially put into operation. So far, the State Grid has completed two 1000 kV AC projects and two ±800 kV projects The DC project marks new achievements in my country's UHV construction. Liu Zhenya, former chairman and party secretary of the State Grid Corporation, said: "The State Grid is building two ±800 kV DC projects, and at the same time is developing ±1100 kV DC technology and equipment. The transmission capacity can reach 13.75 million kilowatts, and the economic transmission distance is 5000 kilometers. Kilometers will create conditions for the construction of trans-regional, transnational and transcontinental power transmission channels. For example, Africa and the Middle East can be connected, and South America can form a large power grid."
The State Grid has also established a systematic UHV and smart grid technical standard system. It has formulated 356 enterprise standards, 90 industry standards, 44 national standards, and compiled 19 international standards. UHV AC voltage has become an international standard voltage.
In this regard, Klaus Uhler, chairman of the International Electrotechnical Commission (IEC), pointed out: "Like China, many countries in the world have uneven distribution of energy resources. For example, Germany needs to transmit wind power from the north through UHV. To the south. At the same time, UHV can reduce the loss of long-distance power transmission, and has broad application prospects in other regions of the world. China's UHV transmission technology is at the leading level in the world. As an international standard voltage, China's UHV AC The voltage standard will be promoted to the world."
In addition, Joachim Schneider, chairman of the German Association of Electrical Engineers (VDE), also said: "We need long-distance power transmission. For the challenges faced by Germany and other countries after abandoning nuclear weapons, UHV is a good solution." According to reports, India China, Brazil, South Africa and other countries are actively promoting the construction of UHV AC and DC projects, among which Brazil will adopt my country's UHV technology.