Development of the hottest DC transmission technol

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The development of DC transmission technology and its role in China's electricity

China's electricity is facing an unprecedented development situation Because DC transmission has the characteristics of long transmission distance, large transmission capacity and flexible control, DC transmission projects under operation, construction and planning have undertaken and will soon undertake the main power transmission tasks in the west to East power transmission and North-South mutual supply, and will play an important role in the future national alliance. Doing a good job in the research, planning and construction of DC transmission is an important task for China's power development in the future

with the rapid development of national economy and power industry, China's electricity is facing an unprecedented development situation. By the end of 2003, the installed capacity of power generation in China had reached 384million kW and 191million kwh. The total installed power generation capacity and annual power generation are second only to the United States, both ranking second in the world. In China's electric structure, except for the northwest electric power, which is mainly 330 kV, other regional electric power has formed a 500 kV main frame

1. Development and characteristics of DC transmission technology

HVDC transmission technology has emerged since the 1950s. After half a century of development, it has become a mature transmission technology. More than 60 HVDC projects have been successfully put into operation in the world, including 2 in the 1950s, 5 in the 1960s, 15 in the 1970s, 30 in the 1980s, and there is no need to identify whether they are recyclable, and 10 in the 1990s. Entering the 21st century, China has successively put into operation the Tianshengqiao Guangzhou (Tianguang) DC transmission project and the Three Gorges Changzhou (Sanchang) DC transmission project

HVDC technology started in the 1950s, but its breakthrough development was in the 1980s. With the development of thyristor technology and the needs of modern electricity development, 30 DC transmission projects were built all over the world in the 1980s, and DC transmission has played an important role in electricity. During this period, 14 back-to-back projects were constructed; The Inga Sabah project in Zaire with a transmission distance of 1700 km has been built; The transmission project of Itaipu hydropower station in Brazil with voltage level of ± 600 kV has been completed. The control and protection technology of DC transmission has been further developed and improved. After entering the 1990s, with the rapid development of power electronics technology, computer technology and control theory, HVDC technology has become increasingly perfect and its reliability has been improved

China's DC transmission technology was also developed in the 1980s, and the Zhoushan DC transmission project (± 100 kV, 100 MW, 55 km) independently developed by China and the Gezhouba Shanghai (hereinafter referred to as GESHANG) ± 500 kV DC transmission project representing the world's advanced level at that time were completed. In the 1990s, Tianguang DC transmission project and Sanchang DC transmission project began to be constructed. Tianguang DC project was put into operation in December 2000, and bipolar in June 2001; The three constant DC transmission project was put into operation in May, 2003. In 2001, the Three Gorges Guangdong (hereinafter referred to as "San Guang") DC transmission project and Guizhou Guangdong (hereinafter referred to as "Gui Guang") DC transmission project were started, and the San Guang DC project was officially put into operation in June 2004; Guiyang Guangzhou DC project was put into operation in September, 2004

compared with AC transmission, DC transmission has obvious advantages and characteristics: ① large transmission capacity; ② The size and direction of transmission power can be quickly controlled and adjusted; ③ The input of DC transmission system will not increase the short-circuit current capacity of the original power system, nor will it be limited by the system stability limit; ④ The corridor width of the DC overhead line is about half of that of the AC line, which can make full use of the resources of the line corridor; ⑤ The DC cable line has no problem of capacitive current in the AC cable line, no magnetic induction loss and dielectric loss, basically only the core resistance loss, and the insulation voltage is relatively low; ⑥ When one pole of the DC transmission project fails, the other pole can continue to operate and give full play to its overload capacity, that is, it can not reduce or reduce the transmission power loss; ⑦ DC itself has a modulation function, which can respond according to the requirements of the system, damp electromechanical oscillation and low-frequency oscillation, so as to improve the transient stability of the power system; ⑧ It can adjust the AC voltage of the system through the reactive power control of the converter station; ⑨ Large electricity is interconnected through DC transmission (such as back-to-back mode), and the two electricity will not interfere with and affect each other, and power support can be carried out quickly

DC transmission technology is suitable for long-distance and high-capacity power transmission, which can transmit power beyond 2000 km, and the power transmission capacity of a DC project can exceed 3 million KW; It is suitable for network interconnection between power systems and power transmission of giant hydropower and thermal power bases. These are exactly what China needs in the development of electricity

2. The current situation and overall strategy of China's electricity industry

in addition to Taiwan, China has formed six trans provincial electricity regions in Northeast China, North China, Northwest China, East China (including Fujian), central China (including Sichuan and Chongqing) and South China, and four independent provinces in Shandong, Hainan, Xinjiang and Tibet. In addition to the 330 kV main frame of northwest power, other inter provincial power and Shandong power have built 500 kV main frames. Hong Kong power and Macao power are respectively connected with Guangdong power by 400 kV and 110 kV, thus connected with southern power; Central China and East China power have been interconnected through the GESHANG DC transmission project; Northeast China and North China, North China and central China have realized interconnection through AC 500 kV; Central China and southern China power have realized interconnection through the three Guangzhou DC transmission project; Northwest and central China power will realize interconnection through Lingbao DC back-to-back project in 2005; The joint plan between Hainan and Guangdong will be realized in 2006. At present, the situation of the all China Federation is advancing rapidly, and it can basically realize the all China Federation except Xinjiang, Tibet and Taiwan around 2006

because China's energy resources are mainly concentrated in the west, while the main load is in the Middle East. According to the characteristics of resource distribution and load, it is decided that the west to East power transmission is an important strategy for China's power development in a period of time. The overall development strategy of China's electricity in the future is: power transmission from the west to the East, mutual supply between the north and the south, and nationwide connection

3. The role and planning of DC transmission

the goal of quadrupling China's GDP by 2020 over 2000 and building a well-off society in an all-round way set by the 16th CPC National Congress makes the power industry face new development opportunities and challenges. It is predicted that the total installed capacity of power generation in China will reach about 600 million KW by 2010 and about 950 million KW by 2020. It is the basic task of China's power construction to send the electric energy of the newly-built power supply safely, stably, reliably and economically. On this basis, we should gradually improve the electrical structure and promote the National Alliance, which makes the development of electricity more challenging than the construction of power supply. How to choose the network structure, transmission mode, new transmission technology and voltage level in power construction is not only related to the power transmission capacity after the power supply is completed, but also related to a series of problems such as the safety and stability of the power system, engineering benefits, power market and power marketing. With its unique characteristics, DC transmission technology will play an important role in the future development of electricity in China

in the west to East power transmission project, DC transmission will play a very important role because it is suitable for long-distance transmission, large transmission capacity, easy to control and adjust; Because the research and development of ultra-high voltage (million volt voltage level) transmission in the world has not yet reached the practical stage, DC transmission is more important. For transmission projects with a distance of more than 1000 km, especially about 2000 km, in the next 10 to 20 years, the use of DC transmission will be almost unmatched

the electric interconnection adopts the AC connection mode, which has the advantages of simple implementation of the scheme, low investment, natural accident emergency support after power loss on one side and fast response speed on the other side. However, because of the natural "binding" between the latter two, the scope of AC synchronization is extended. When one power fails, it will affect multiple interconnected power, expand the consequences of the failure and reduce power quality; Moreover, it is very easy to cause the power of the tie line to fluctuate sharply, even to vibrate and break the weak links of the system, thus increasing the probability of a major accident of system stability destruction, which will be disastrous. This will affect the stability level of the two sides of the AC connection, other electricity synchronously connected with it and relevant connecting lines to varying degrees, and reduce the stability limit of the connecting line. When DC or DC back-to-back mode is adopted for electric interconnection, it can effectively isolate the interaction between interconnected alternating currents without mutual interference, and the accidents can be controlled within this range; DC connection will not increase the short-circuit current level of electricity; Using the modulation function of DC control can improve the stability of the interconnected system; The tie line has the advantages of simple power control and convenient dispatching management

the long-distance power transmission and DC transmission projects that have been put into operation in China are playing an important role in the west to East power transmission and the national connection, and often operate under the rated load. The transmission capacity of the three constant DC transmission projects, the three Guangzhou DC transmission projects and the Guiyang Guangzhou DC transmission projects are all 3 million KW, and the transmission distance is about 1000 km. The Lingbao back-to-back DC project of northwest power and North China power grid, which is under construction, has a transmission capacity of 360000 kW and will be completed and put into operation in 2005

China's west to East power transmission project can be divided into south channel, middle channel and north channel, all of which have multi circuit DC transmission projects. Nantong road has completed Tianguang and Guiyang Guangzhou DC transmission projects, and the second Guiyang Guangzhou DC transmission project is under construction; Taking the Three Gorges as the starting point, the middle channel uses HVDC to transmit power to East China power and South China power. Ge Shang and San Chang DC transmission projects have been completed, and the DC transmission project from the right bank of the Three Gorges to Shanghai is under construction; The north channel has also begun to build DC transmission projects. The typical DC transmission project of North-South mutual supply is the three Guangzhou DC transmission project, which not only transmits 3million kW power from the Three Gorges to Guangdong, but also realizes the interconnection of central China power and southern China power. In the plan of the all China Federation, there are multi circuit DC projects, especially the back-to-back interconnection of regional electricity

at present, there are more than a dozen DC transmission projects with clear power transmission direction and scale, and the power transmission scale is mostly more than 3million kW. In 2004, the construction of the Three Gorges Right Bank to Shanghai DC transmission project and the Guizhou Guangdong second circuit DC transmission project has been started, with a transmission capacity of 3million kW, a transmission distance of about 1000 km, and a voltage of ± 500 kV. They will be put into operation in 2007

during the "Eleventh Five Year Plan" period, the following DC transmission projects will be built: the Xiaowan Hydropower Station Guangdong DC transmission project, with a voltage level of ± 500 kV or ± 600 kV, a transmission capacity of 3 million KW, and a transmission distance of ﹤ 1500 ~ ﹤ 1600 km; The DC transmission project from Deyang, Sichuan to Baoji, Shaanxi has a voltage grade of ± 500 kV, a transmission capacity of 1.8 million KW and a transmission distance of about 600 km; Ningxia Yinnan Tianjin DC transmission project, with voltage level of ± 500 kV and transmission distance of 1200 km; The North Shaanxi Shandong DC transmission project has a voltage level of ± 500 kV, a transmission capacity of 3 million KW, and a transmission distance of about 1000 km

from 2010 to 2020, more than ten DC transmission projects will be built, with longer transmission distance and greater transmission power. With the development of Jinsha River, after the completion of Xiangjiaba, Xiluodu, Baihetan, Wudongde and Guanyinyan Hydropower Stations, the power will be mainly transmitted to central China power and East China power, and the transmission distance will reach about 1000 km and 2000 km. With the development of Lancang River, Nuozhadu Hydropower Station will send power to Guangdong after its completion, and the power transmission distance will exceed 1500 km. When the power transmission distance exceeds 1500 km, ± 600 kV needs to be considered

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