Main Issues In The EMI Protection On Wireless Electronic Facilities From Adjacent UHVDC Power Lines

The UHV power transmission lines, which have long distance and high capacity, are the solid foundation and core of UHV power grid construction in China. However, in the planning, design and construction of current UHVDC projects, how to avoid the electromagnetic interference(EMI) on adjacent wireless electronic facilities has become an important issue puzzling the routing choices of UHVDC power lines. In this paper, the two key problems of this EMI, the radio reradiation interference and the magnetic interference, were studied:the theories of reradiation interference on radio station and magnetic interference on geomagnetic observation station were analyzed; the corresponding mathematical models with theirs solution methods were presented; the calculation process of EMI protecting distance between various types of wireless electronic facilities and UHVDC power lines was designed; and the correction system of magnetic interference on the geomagnetic observation from UHVDC power lines was developed.The main contents are as follows:Using the electromagnetic scattering theory, the generation mechanism of reradiation interference from power lines was analyzed; the surface and wire electric field integral equation(EFIE) of reradiation interference were soluted. Based on the Hallen method and antenna theory, the equivalent principle of wire model, and the reasons for its increasing error at high frequency were researched. In order to embody the structure of angle-steel effectively while assuring the continuity of induced current on steel tower, three-dimensional surface simulation model of UHVDC angle-steel tower based on triangular element was presented. Using the RWG base function and Galerkin's method, method of moments(MoM) was applied to calculate the surface EFIE. In order to acquire the impact from auxiliary angle-steel, the wire model and surface model of angle-steel tower with or without auxiliary angle-steel were established using Numerical Electromagnetic Code(NEC) with its source code improved. The results showed that the surface model should be adopted at higher frequency, such as 16.7 MHz and over, while choosing 0.1 dB as the deviation allowable value. Considering the calculation's accuracy and speed, using the wire-surface modle of UHVDC power lines is suggested. According to the scaled model experiment in Kangxi Prairie(in Beijing) and the short-wave direction-finding interference from vertical grounding object experiment, the proposed model and its solution method were verified by the comparion between calculation results and experiment results.By analyzing the current solution method of reradiation interference protecting distance, the resonance frequency was shown to be the key of protecting distance calculation. Normally, the frequency of interference has maxima on "N-wavelength loop resonance frequency" and "λ/4 resonance frequency", based on which the induced current on power lines and interference values under vertical polarization plane wave were calculated. Because the excitation of broadcasting antenna was replaced by vertical polarization plane wave and the frequency bandwidth was extended, the results showed that, at middle-wave frequency, the extremum interference occured on "1-wavelength loop resonance frequency" and "3-wavelength loop resonance frequency", but not strictly on "λ/4 resonancefrequency". When the frequency was in short-wave band,"N-wavelength loop resonance frequency" was not fitting. After further study of the impact on resonance frequency from conductor, ground wire, number of towers and tower spans, the conclusion of<IEEE guide on the prediction, measurement, and analysis of AM broadcast reradiation by power lines>-the reradiation interference from power lines is mainly decided by the reradiation from induced current on the loop consisted from tower, ground wire and ground below 1.7MHz-was validated; a new conclusion, the reradiation interference is mainly decided by electromagnetic scatter from power towers in short wave and above, is proposed. As a result, a more appropriate calculation method of protecting distance was proposed.Analyzing the principle of geomagnetic observation instrument and the characteristics of interference on geomagnetic observation from DC power lines, the Z-component of geomagnetic field is mainly impacted. The magnetic field calculation model of current on polar conductor, and the model of ground current in infinite homogeneous soil and in layered soil around earth electrode field were established. The calculation results showed that the interference was mainly related with the imbalance current on conductors of DC power lines. Consquently, the soil conditions and the ground current could be ignored in the calculation. Therefore, three-dimensional current magnetic field calculation model of power lines based on the geocentric coordinate system was presented, with the towers as points and the tower spans as line segments.The geomagnetic observation point coordinate system with observation point as coordinate origin was constructed, and then the unit vector expression equations, which represented each axis of observation point coordinate system in geocentric coordinate system, were deduced. Based on the definition of space vector dot product, the calculation equation of space current magnetic field vector projected on the direction of Z-component verctor was acquired. Therefore, the "Interference on geomagnetic observation from DC power lines correction system" was developed; the idea of system development and the database construction were introduced. The geomagnetic observation interference experiment was accomplished by station observation combined with field observation. The results showed that the proposed mathematical model and solution methods had considerable accuracy...