Guide: The surface of the transmission line wire has certain defects on the surface of the wire due to the burrs caused by the manufacturing process and the fouling and corrosion of the long-term running wires, resulting in an increase in the electric field strength near the surface of the wire. When the electric field strength of the surface of the wire reaches the height of the corona field of the air, the air in the vicinity of the wire is ionized and corona discharge occurs.
Sound is closely related to people's daily lives. Sound can transmit energy and information. People talk through voice, express their feelings and carry out various activities. At the same time, inevitably there will be an unpleasant noisy, harsh sound, that is, noise, and noise in the frequency range of 20 Hz to 20,000 Hz is audible noise. Strong audible noise can interfere with normal language conversations and daily life, making people irritated and affecting people's sleep quality. If people work and live in a noisy environment that exceeds the limits for a long time, the health of the human body may be compromised.
Most of the environmental noise comes from random noise sources, such as the whistling of vehicles passing by, the construction of various power machinery and the noise of people in public places. With the construction of a large number of ultra-high voltage transmission lines, the audible noise generated by the line corona discharge has begun to attract people's attention as a noise source. In the design of the transmission line, the audible noise needs to be predicted according to the structural parameters of the conductor to ensure that the audible noise level is lower than the limit required by the environmental protection. Due to the higher voltage and large cross-section of the UHV transmission line, the existing audible noise prediction method is no longer applicable. How to realize the accurate prediction of the audible noise of UHV transmission lines has become a key issue to be solved in the design and construction of UHV transmission lines.
Generation and characteristics of audible noise on corona discharge of transmission linesIn the air, all kinds of sounds start from the vibration of the air, and audible noise is no exception. How is audible noise generated during corona discharge? What are the characteristics? These questions will be answered below.
Due to the burrs caused by the manufacturing process and the fouling and corrosion of the long-term running wires, the surface of the transmission line may have certain defects on the surface of the wire, resulting in an increase in the electric field strength near the surface of the wire. When the electric field strength of the surface of the wire reaches the height of the corona field of the air, the air in the vicinity of the wire is ionized and corona discharge occurs. The interaction between charged particles and air molecules generated by corona discharge causes air molecules to vibrate, which in turn produces audible noise on the transmission line.
The size of the audible noise of the transmission line is closely related to its operating voltage, line erection mode, wire splitting structure, wire cross-sectional area, wire surface state and atmospheric environmental conditions. During the corona discharge of AC and DC transmission lines, the resulting motion characteristics of charged particles are significantly different. Therefore, there are also significant differences in the audible noise characteristics produced by AC and DC transmission lines.
The audible noise of AC transmission lines generally consists of two parts: one is broadband noise, which is the main part of AC audible noise; the other is due to the cyclical change of AC voltage, which causes the charged particles near the wire to move back and forth to produce AC pure sound components. . The measured results show that the audible noise of the AC transmission line is small when it is sunny, and the surface of the wire is damp or attached with water droplets during rainy or foggy days. Corona discharge is strong and the audible noise is large. It is a consideration when designing the AC transmission line. major factor.
The DC transmission line has audible noise, no AC pure tone component, and only broadband noise. Since the effect of corona discharge on the negative conductor is much lower than that on the positive conductor, the audible noise of the DC transmission line is mainly derived from the corona discharge of the positive conductor. In rainy or foggy days, the corona discharge intensity of the wire is reduced due to the space charge accumulated near the wire, which acts as a uniform electric field on the wire surface, and the audible noise is reduced compared with the sunny day. The audible noise is large on sunny days, which is the main factor to be considered when designing a DC transmission line.
Limit value of audible noise for corona discharge on UHV linesIn order not to affect the normal life of people near UHV transmission lines, China has made clear the following audible noise limits for AC-DC UHV transmission lines:
The People's Republic of China power industry standard "1000 kV overhead transmission line electromagnetic environment control value (DL/T1187-2012)" stipulates: 1000 kV AC UHV line is 20 meters away from the edge projection, audible noise 50% statistics The value does not exceed 55 decibels.
The power industry standard of the People's Republic of China “±800 kV UHV DC line electromagnetic environment parameter limit (DL/T1088-2008)†stipulates: ±800 kV DC UHV line is projected 20 m below the ground line of the positive line, corona on sunny day The resulting audible noise has a 50% value of no more than 45 decibels.
The design of the audible noise level of the transmission line must be predicted during the design of the UHV transmission line, and the conductor structure should be selected according to the prediction result. In order to ensure that the audible noise meets the limit requirements, if the emphasis is placed on reducing the audible noise as much as possible, such as increasing the number of multi-split wires or increasing the height of the transmission line to the ground, the construction cost of the UHV transmission line will be greatly increased. Therefore, it is very important to accurately predict the level of audible noise.
The prediction of audible noise in the initial stage of UHV transmission project mainly adopts the foreign empirical formula. Since the multi-split and large-section conductors used in UHV transmission lines have exceeded the applicable range of existing empirical formulas, the accuracy of audible noise prediction results It is questionable. In order to ensure the rationality and economy of transmission line design, the establishment of accurate audible noise prediction methods has strong technical and engineering requirements.
Prediction and analysis of audible noise of corona discharge on UHV linesIn order to obtain the characteristics of the audible noise of UHV transmission lines and establish an accurate audible noise prediction method, the most direct method is to use the UHV corona cage to observe the audible noise of the UHV true wire for a long time, and pass the statistics. Analyze the statistical characteristics and prediction methods of audible noise under different weather conditions for different structural forms, and provide guidance for the optimal design of transmission lines.
Based on the above research ideas, the research team carried out long-term testing of audible noise of DC UHV true wires for nearly 3 years, and established an accurate background noise rejection method and statistical analysis method for audible noise. On this basis, the prediction formula of audible noise of DC UHV transmission lines suitable for eight-segment and below conductors is summarized. The formula fully considers the influence law of different climatic conditions, and fills the large-section conductors with more than six divisions and 700 square millimeters or more. A blank for audible noise prediction methods. Through the measurement and calculation of the audible noise of the test line segment and the Hazheng high-voltage DC line, the correctness of the empirical formula proposed by the research group is verified.
The empirical formulas obtained by the research group have been applied in the high-voltage direct current transmission lines of Xizhe and Hazheng. The audible noise is lower than the limit standard during the environmental protection acceptance of the project, ensuring the environmental friendliness of the transmission lines and saving the construction of hundreds of millions of yuan. cost. This empirical formula is applicable to the prediction of audible noise of ±800 kV to ±1100 kV DC UHV transmission lines. Subsequent DC UHV transmission lines will not require a lot of repeated tests to verify the design of audible noise. Can save a lot of manpower and financial resources.
The research team used the same research ideas to conduct long-term tests on the audible noise of the AC UHV true wire in the corona cage, and summarized the audible noise of the AC UHV transmission line suitable for the twelve-split and below wires. Forecast formula. The formula is directly applied to the design of the 1000 kV AC UHV double-circuit line on the Huai River in China. The actual measurement results of the audible noise after the project is put into operation indicate that the prediction formula proposed by the research group is more than the result obtained by the foreign experience formula. To be accurate.
The development of UHV transmission technology has been adhering to the principle of “environmentally friendly, resource-saving, safe and reliableâ€, to achieve optimal design of UHV transmission lines, reduce the audible noise level of transmission lines, and create a good acoustic environment has become the development of UHV transmission technology. Inevitable demand. The research work on audible noise of UHV transmission lines still has a long way to go. In the future, it is necessary to supplement the audible noise prediction method with the influence of environmental factors such as temperature and humidity on audible noise, and realize the accurate prediction of audible noise under complex climatic conditions. , to provide further guarantee for the further optimization of UHV transmission line design.
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