| At the beginning of 2005, after carefully analyzing the current situation and characteristics of energy supply, State Grid Corporation of China (SGCC) has put forward the strategic objective of developing UHV backbone network so as to achieve energy resources optimization and ensure national energy security. From then on, domestic many scientific research institutions and manufacturers have been doing in-depth research on UHV transmission and transformation technologies. Both the scheme and the important technical specifications have been worked out. The technical feasibility of UHV AC transmission has also been evalued. However, with the global economic development and people's increasing environment awareness, the electromagnetic environment problems caused by power transmission lines are paid more and more attention. At the same time with the voltage rating turning into UHV level, electromagnetic environment has become the critical factor which determines the structure and constructing cost of the transmission lines. Therefore, this dissertation focuses on the research about electromagnetic environment problem of UVH AC transmission lines, mainly including power frequency electric field, power frequency magnetic field, audible noise and radio noise. With the prediction and analysis of electromagnetic environment parameters for major tower and conductor type of preliminary design of UHV transmission lines in China, it can be a reference to the UHV transmission lines optimization design and will be of significance to eliminate the worries about electromagnetic environment problems of UHV transmission lines. The main contributions of the dissertation include the following.(1) Firstly, based on the accuracy verification of different mathematical models for calculating the conductor surface voltage gradient in engineering, it is pointed out that, the successive image method has higher accuracy and its maximum error is less than the engineering allowable limits, suitable for the design and electromagnetic environment research of UHV transmission lines. The conductor surface voltage gradient of 1000kV UHV AC single-circuit and double-circuit lines on the same tower are calculated by the successive image method and its influencing factors are analyzed in detail, such as height above ground, number and radius of subconductors, layout of phase conductors, phase order of double-circuit lines and so on. Then some advice about UHV transmission lines design is proposed, regarding the effects of reducing the conductor surface voltage gradient. Secondly, the mathematical model of the power frequency electric field under UHV overhead transmission lines is established on the basis of the successive image method. The distribution characteristic of spatial power frequency electric field under overhead transmission lines is analyzed by computer aided computation program and then the expression of ground electric field intensity is deduced. Especially, it is shown that conductor height above ground, number and radius of subconductors in bundle, position arrangement of phase conductors, phase order arrangement in double-circuit lines, etc. have different impact level on the magnitude of electric field. Summarization about the effects of above-mentioned influencing factors can be a reference to the UHV transmission lines optimization design in China. Thirdly, based on the foreign research results of UHV transmission lines and combined with the domestic design experience of EHV transmission lines, it is suggested that the maximum threshold value of ground electric field intensity is taken as the principle for selecting the minimum bundle conductor ground clearance of UHV AC transmission lines. And the minimum bundle conductor ground clearances of 1000kV UHV AC single-circuit and double-circuit lines on the same tower are calculated according to the control indices of ground electric field for different regions. The influences of operating voltage, phase spacing, bundle conductor structure, phase conductor configuration, phase order arrangement on the minimum ground clearance are studied. The obtained conclusions will be of significance to economical run and investment economization of UHV transmission project.(2)The mathematical model of power frequency magnetic field under UHV AC transmission lines is established. To adapt various operating conditions, the current variable in this method is handled in time domain, instead of the usual frequency domain. The magnetic field of 1000kV UHV AC single-circuit and double-circuit lines on the same tower are calculated by computer aided analysis software and the regularities of their variation due to the variation of parameters of the model are also analyzed by comparison. From distribution and attenuation rules of power frequency magnetic field, some ways have been found to reduce the magnetic field and some suggestions are proposed for construction of UHV transmission lines. On the other hand, this dissertation makes an analysis for the fact that almost all electromagnetic environment standards in China abuse the technical term "Electromagnetic Radiation", thus causing a current of fear in the public for no reason, and recommends to use equivalently International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines for limiting exposure to time-varying magnetic of UHV transmission lines which is internationally well accepted as national standard for electromagnetic environment.(3) Audible noise (AN) produced by corona discharges is one of the more important considerations in the design of UHV AC transmission lines, which will greatly affect the electromagnetic environment and the technical economical index of transmission lines, etc. So it will be of very important practical significance that making scientific researches on AN prediction from 1000kV UHV AC transmission lines. According to the AN cumulative distribution, frequency spectrums, and lateral profiles, quantitative relationship of the model with sound pressure level and sound power level is deduced, which it will provide the theory basis for AN prediction. To overcome the limitation of current prediction formulas, a novel machine learning technique, i.e. relevance vector machine (RVM) for AN prediction is presented in this dissertation. The RVM has a probabilistic Bayesian learning framework and has good generalization capability, as a result it can yield higher prediction accuracy and more universal application arrange. Based on the RVM regression prediction model, the AN from 1000kV UHV AC single-circuit and double-circuit lines on the same tower in China are calculated, and it is shown that the line configurations are rational and satisfied with the request of audible noise standard.(4) Radio noise (RN) produced by corona discharges is also one of the more important considerations in the design of UHV AC transmission lines, which will greatly affect the electromagnetic environment and the technical economical index of transmission lines as the same to AN. So it will be of very important practical significance that making scientific researches on the prediction and assessment of RN from UHV AC transmission lines. According to the RN's generation mechanism, some statistic characteristics are adopted to express the RN level produced by transmission lines, which it will provide the theory basis for RN prediction. To overcome the limitation of the current prediction formulas, a novel RN prediction model based on modal analysis method is presented in this dissertation and it is fitted for the transmission lines whose conductor bundle number is more than 4. With the established prediction model, the RN level from 1000kV UHV AC single-circuit and double-circuit lines on the same tower in China are calculated, and it is shown that the line configurations are rational and satisfied with the request of radio noise standard.
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