Study On Electromagnetic Environment Impact From Ultra-High Volta Multi-circuits Transmission Lines On The Same Tower

With China's rapid economic development, the increasing and imbalanced electricity load, the structure of the existing power grid can not meet the rapid economic development, the characteristics of the energy resources and load distribution also determine that China is bound to construct high-capacity, long-distance backbone grid of UHV power transmission system. Ultra-high voltage (UHV) transmission projects have been included in the "Twelfth Five-Year" plan on March,2011. During the "Twelfth Five-Year" period, the state will invest over 500 billion yuan into a "three vertical and three horizontal " backbone grid of UHV AC. UHV transmission will optimize resource allocation in a wider range, reduce transmission costs, improve transmission efficiency, and conserve land occupied.This paper studied the electromagnetic environment problems of UHV multi-circuit lines, so as to provide references and recommendations for optimizing the structural design of the lines, provide technical data support for public to understand electromagnetic effects of the lines scientifically, objectively and accurately, and eliminate the doubts and misunderstandings of the public for electromagnetic pollution caused by UHV transmission lines. The main work and contents of the paper are as follows:(1) According to the theoretical calculation model of electromagnetic environment parameters, we developed a computer-aided analysis software of the frequency electric field, frequency magnetic field and radio interference near the high-overhead lines using the language of PowerBuilder. The software has a rich and flexible man-machine interface, which can simulate multi-voltage, multi-loop and multi-phase arranged transmission lines, and calculate frequency electric and magnetic field and display the various curves conveniently. The development of the computer-aided analysis software about UHV electromagnetic environment is part of the results of creative work.(2)Use the software to study the rules of changes in each of the parameters (tower, wire height, phase space, phase arrangement, split wire number, split space, split wire diameter, et al) used in UHV multi-circuit lines which affect the electromagnetic environment. In accordance with the rules, we give the relevant measures to reduce the electromagnetic environment effects, so as to provide advice and technical data support for engineering design and construction of high voltage at the initial stage of China's.(3) According to the simulation results, it is proposed that in the design process of UHV transmission lines, raising the line height, reducing the phase space, reducing the split wire space, and using tower of triangular arrangement of phase conductors (cat-head type tower) can effectively reduce the effects of the frequency electromagnetic fields and radio interference under the line, can also reduce the width of the line corridor which has practical significance on the conservation of land resources.(4)For new UHV double-circuit, multi-circuit lines, frequency electric field,which is the main effect of the electromagnetic environment, phase conductor arrangement of reverse phase sequence can effectively reduce the level of frequency electric field of the lines, the maximum reduction of the field compared with the same phase sequence is up to 20%.(5)The results showed that the number of split wires affects the radio interference large. With the number increasing, the radio interference value below the line significantly reduces, while the electric field strength within the region that is 30 miters from the line center increases significantly (outside the region the effect is weak). Therefore, for region that is sensitive to radio interference and is outside 30 miters from the line center, it can be considered to reduce radio interference by increasing the number of split wires during engineering design and construction of the lines.