Electric fields, magnetic fields and their environmental effects of high-voltage transmission lines
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In recent years, in order to improve and strengthen the power grid structure, improve the safety and reliability of regional power supply, and provide power guarantee for regional development, my country's power industry has continued to develop rapidly and the scale of construction has continued to expand. Due to the large population base in my country and the relatively concentrated urban population, it is inevitable that high-voltage or even ultra-high-voltage transmission lines will enter densely populated areas. With the increasing living standards of our people, people have doubts about whether human exposure to electromagnetic fields will have harmful effects on health and daily life. Coupled with some one-sided reports, people have panic about electromagnetic fields to a certain extent. The main reason is that they lack the necessary understanding of electromagnetic fields. Drawing on relevant research results at home and abroad, combined with the daily practice of environmental impact assessment of high-voltage power transmission and transformation projects, the generation mechanism of electromagnetic fields of high-voltage AC transmission lines and their electromagnetic impact on the environment were studied. 1. The generation mechanism of electromagnetic fields around transmission lines. Stationary charges generate an electric field in the surrounding space, and moving charges (current) simultaneously generate a magnetic field in the surrounding space. When the frequency is very low, the electric field and the magnetic field are independent of each other and have no connection with each other. When the frequency is very high, the changing electric field and magnetic field can be converted into each other and have a quantitative wave impedance relationship, and electromagnetic energy can be separated from charges or currents and propagate into space in the form of waves. The power supply operating frequency (power frequency) of my country's power system is 50 Hz, which belongs to the extremely low frequency (ELF) 0~300 Hz, and its wavelength is up to 6 000 km. According to the theory of electromagnetic fields, it can be known that only when the scale of an electromagnetic system is equivalent to its working wavelength, the system can effectively emit electromagnetic energy into space. However, the size of the substation facility is much smaller than this wavelength, which does not constitute effective electromagnetic energy emission. The electric field and magnetic field around it are not interdependent and mutually transformable. Therefore, in actual work and environmental health research, power frequency electric fields and power frequency magnetic fields are usually discussed separately.
2 Factors affecting the levels of power frequency electric fields and power frequency magnetic fields around transmission lines. The potential difference between high-voltage power transmission lines (high potential) and the earth (zero potential) forms a strong power frequency (50 Hz) electric field; a certain power frequency magnetic field is generated when current passes through. Factors that affect the power frequency electric field intensity around transmission lines include: line operating voltage, line parameters (including wire diameter, number of split wires, split spacing), tower structure, phase sequence arrangement (when multi-circuit transmission lines are erected on the same tower or horizontally), etc. Factors that affect the power frequency magnetic induction intensity around transmission lines include: line operating current, tower structure, phase sequence arrangement (when multi-circuit transmission lines are erected on the same tower or horizontally), etc. a. The relationship between the power frequency electromagnetic field and the height of the transmission line to the ground. Figure 1 shows the power frequency electric field intensity distribution curve of the 220 kV triangular arrangement transmission line under different conductor heights to the ground. Figure 2 shows the power frequency magnetic induction intensity distribution curve of the 220 kV triangular arrangement transmission line under different conductor heights to the ground. It can be seen from Figure 1 and Figure 2 that under the transmission line, the power frequency electric field intensity and power frequency magnetic induction intensity both decrease as the height of the transmission line to the ground increases. b. The relationship between power frequency electromagnetic field and transmission line conductor layout. For single-circuit tower type, the conductor layout is divided into horizontal arrangement, triangular arrangement and inverted triangle arrangement. Figure 3 shows the lateral distribution of power frequency electric field intensity at a height of 1·5 m on the ground when 220 kV wires are arranged in different ways. Figure 4 shows the lateral distribution of power frequency magnetic induction intensity at 1·5 m on the ground when 220 kV wires are arranged in different ways. It can be seen from Figure 3 and Figure 4 that for 220 kV transmission lines, the power frequency electric field intensity and power frequency magnetic induction intensity generated under the horizontal arrangement and the triangular arrangement line are not much different. However, when the conductors are arranged in an inverted triangle arrangement, the maximum value of the field strength and the range of the high field intensity area are reduced.
I have the impression that the force post to leave a name has an impact, it seems to be within 30 meters, but I can’t find the original data, and I have been paying attention to this issue recently.