EHV transmission technology paper 20 17

UHVDC transmission has many advantages, such as long transmission distance, large capacity, flexible control, convenient dispatching, low loss, less occupied transmission corridors and so on, which provides favorable power and energy conditions for the rapid development of various fields in China. The following is my paper on UHV transmission technology 20 17, I hope you can get some insights from it!

EHV transmission technology paper 20 17 EHV transmission line key technology analysis

Abstract: This paper mainly studies three key points in UHV transmission lines, namely corona effect, overvoltage and electromagnetic field. On the basis of meeting the operation requirements of power grid, UHV transmission lines need to consider many ecological, safety and impact issues. Based on the study of these problems and drawing lessons from advanced experience, this paper analyzes how to solve these problems in the design and construction of UHV transmission lines.

Keywords: UHV；; Transmission line; Corona; overvoltage

China Library Classification Number: TM7 14.2 Document Identification Number: a document number:

Since electric energy cannot be stored on a large scale, its production, transmission and use must be completed at the same time, which determines the importance of electric energy transmission. According to ohm's law, in order to reduce the loss in the transmission process, on the one hand, the resistance is reduced, on the other hand, the voltage is increased. Due to the imbalance of resource distribution and economic development in China, the development of China's power grid has to adopt large-scale long-distance transmission, so UHV transmission has become an inevitable choice for the development of China's power grid [1]. This paper takes UHV transmission lines as the research object, and introduces the key technologies of UHV transmission.

1 UHV transmission problem

In China, UHV transmission refers to AC 1000kV and DC? 800 kV transmission engineering and technology. EHV transmission is produced to meet the needs of long-distance and large-capacity transmission, and its technical basis is the mature application of EHV transmission technology. According to the operation and design experience of EHV transmission, three key problems, corona effect, insulation requirements, electromagnetic field and its influence, must be deeply studied and solved in the application and development of EHV engineering technology [2-4].

1) corona problem. In bad weather, when the electric field intensity on the surface of UHV conductor exceeds the critical value, the surrounding air molecules will ionize to form positive and negative charged particles, and the ion collision recombination process will produce photons and corona discharges. The hazards of corona discharge include power loss, noise and signal interference. Because of the high voltage level, the corona phenomenon of UHV lines is more serious than that of EHV lines, so it is necessary to choose the number and structure of wires reasonably to minimize the influence of corona discharge.

2) electromagnetic field problem. Power frequency electric and magnetic fields will be generated around and on the ground by transmission lines. Due to high voltage and high current, the electromagnetic field influence of UHV transmission lines has become the focus of public attention, especially on the surrounding buildings, people's production and life.

3) Overvoltage problem. Overvoltage problem refers to induced overvoltage caused by lightning strike, direct lightning overvoltage and overvoltage caused by various operations. All kinds of overvoltage in UHV power grid are similar to those in UHV power grid, but there are great differences in characteristics. The overvoltage of UHV power grid will determine the insulation level and the design of insulation system, and directly affect the construction cost and operation reliability.

2 The main conclusions of the research on UHV power grid

On the basis of in-depth research on three key issues, a large number of conclusions are drawn, mainly in the following aspects.

On the basis of improving transmission capacity and reducing line impedance, how to reduce audible noise and meet environmental protection requirements has become a key factor to be considered in UHV line design. The line design should be carried out according to the standard of audible noise, and the interference level to signals (broadcast and TV signals) should reach satisfactory results, and the corona power loss should be reduced as much as possible.

2) Power frequency overvoltage and operating overvoltage become the key to the selection and design of insulation system. Therefore, how to limit power frequency overvoltage has become an important issue in UHV transmission. The operating overvoltage level can be limited by shunt reactor, lightning arrester, switching resistor and line segmentation.

3) The ground power frequency electric field intensity under the EHV transmission line and the edge of the line corridor can be designed to be at the same level as the EHV transmission line, and the transmission line designed according to the audible noise standard will form an electric field intensity similar to the EHV transmission line, and its environmental impact is also at the same level as the EHV transmission line. Therefore, the problem of electromagnetic field is no longer the key to line design, but the adverse ecological impact and public acceptance should be considered.

Three key technologies of UHV transmission line

In order to solve the important problems existing in UHV power grid, based on a lot of research and experiments, UHV power grid was built and put into operation. In operation, some problems have been further solved and become the key to the operation of UHV power grid. Now, the key problems in transmission lines are analyzed.

3. 1 corona and its solution to corona problems, such as audible noise, radio signal interference, corona loss, etc., are closely related to the electric field intensity on the line surface. The voltage of UHV transmission line is high, and the amount of charge on the conductor is large, so the surface field strength is also large. In order to control the surface field strength of the conductor, the number of conductor splits in UHV transmission lines is more, and the diameter of sub-conductor is much larger than that of UHV transmission lines. Under certain operating conditions, the key factors affecting the surface field strength of conductor are line structure and climatic conditions. The line structure includes conductor structure, number of splits, sub-line diameter, distance and pole surface field strength. However, the influence of climate on ground field strength is very complicated, which generally needs to be studied through experiments. For audible noise, according to the national noise standard, the audible noise of UHV transmission lines shall not exceed 55dB(A). It is equivalent to the noise limits of Class 1 standard daytime and Class 2 and 3 standard nights in GB3096- 1993 "Standard for Environmental Noise in Urban Areas". For radio interference, the interference level of EHV transmission lines can be equivalent to that of EHV transmission lines by properly selecting the number of conductor splits and the diameter of sub-conductors. The corona loss of UHV transmission lines is related to many factors, the most important of which is meteorological conditions. Because corona loss mainly comes from bad weather, the influence of electric field intensity on conductor surface is also manifested through the loss of bad weather. Considering that people are most concerned about the annual average corona loss and maximum corona loss, and the corona loss in bad weather may be hundreds of times that in good weather, and the weather reasons in different sections of long-distance transmission lines may be different and complicated, the calculation of corona loss is extremely scattered, so corona loss has been studied for many years, and there is no internationally recognized estimation method so far.

3.2 Power frequency electric field and magnetic field power frequency electric field are affected by transmission line layout, distance to ground, phase-to-phase distance, number of splitting elements, phase sequence transformation, etc. Among them, the influence of ground wire on electric field is related to the distance between ground wire and phase conductor and the height between phase conductor and ground. The farther the conductor is from the ground, the lower the electric field intensity on the ground. When the distance between the conductor and the ground increases to a certain extent, the electric field intensity that can be reduced is limited and the economic investment will be great. In contrast, reducing the number of split wires can obviously reduce the ground field strength, but at the same time, it will increase the surface field strength of wires and increase radio signal interference and audible noise. 2.3 Overvoltage and its limit operating overvoltage are the important basis for determining the insulation level of UHV transmission lines, and three types of operating overvoltage are mainly considered, namely closing, breaking and grounding short-circuit overvoltage. Among them, the only way to solve the positive overvoltage caused by short circuit to ground is to use metal oxide arrester (MOA) near both ends of the line. Therefore, the core of limiting the operating overvoltage is how to limit the overvoltage in the process of opening and closing, and its goal is to limit it below the level of1.6 ~1.7pu. The main methods include using MOA, circuit breaker closing resistance and controlling the closing phase angle of circuit breaker. In recent years, the manufacturing level of MOA has been continuously improved, and its ability to limit overvoltage has been continuously enhanced, which has become the main means to limit operating overvoltage at present. The closing resistance of the circuit breaker is shown in figure 1. When closing, the auxiliary contact should be connected first, and then the main contact should be closed after a period of time (closing resistance access time) to limit the closing overvoltage. The closing phase control technology is to close the voltage near the zero crossing point to reduce the operating overvoltage caused by closing. Figure 1 Schematic diagram of opening and closing resistance of circuit breaker

4 conclusion

This paper mainly studies three key points in UHV transmission lines, namely corona effect, overvoltage, electromagnetic field and their influences and solutions. It should be noted that the problems of UHV transmission lines are far more than these aspects. For example, for the safety of overhead lines, vibration, tension and other reasons need to be considered, as well as the structure of transmission lines, as well as economic current density and heating conditions. In the construction of China's UHV power grid, it not only draws lessons from foreign advanced experience, but also combines China's national conditions and the characteristics of power system development, which has considerable particularity. Only on the basis of long-term operation practice and further in-depth research can we give full play to the advantages of UHV power grid.

Xin Zhongguo 196 1 19 was born in September. He is an undergraduate production management engineer and is now the manager of Gongzhuling Rural Power Co., Ltd.

Liu Zhenya. UHV power grid [M]. Beijing, China Economic Press, 2005.

2 Du Yuqing. Introduction of Japanese 1000kV UHV transmission line design [J]. north China electric power technology, 1993.73 Chen Yong, wan qifa, gu Lili, etc. Discussion on the structure of UHV conductor and tower in China [J]. High voltage technology, 2004, 30(6), 38-465438. Italy is considering the possible impact assessment of the new restrictions on human exposure to magnetic fields, CIGRE, 2002 seseion, 369- 106.

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