The Calculation Of Power Frequency Electromagnetic Field Under UHV AC Transmission Lines

At present, UHV AC Transmission Line is the highest level in China, with long transmission distance, high transmission capacity, saving transmission line corridors and reducing transmission losses. The construction of UHV transmission lines is beneficial to optimize the energy configuration, to improve the development and utilization efficiency, and also is the fundamental guarantee to meet the sustainable growth of power demand in the future. UHV power network is currently the focus of power grid construction in China. With the enhancement of social environmental protection consciousness, the effect of electromagnetic environment under UHV transmission lines becomes one of the problems to which people pay close attention. In this paper, UHV transmission lines electromagnetic environment was studied.Based on the charge simulation method (CSM), the calculation of power frequency electric field is established which take the corona discharge into account around the UHV transmission lines. The calculation results show that the corona discharge enhances the power electrical field. The comparison between calculation and measurement proved that this method is correct and effective. Some factors which have influence on the electrical fields were discussed, including lightning shield line, wire division distance, position arrangement of phase conductors, conductor height above ground, different stringing methods in single circuit lines and phase order arrangement in double-circuit lines, etc. The distribution of power frequency electric field was summarized, some kinds of ways to reduce electrical field were given:increasing wire to ground distance, reducing the space between different phase lines, inverted triangle arrangement in single circuit, reversed phase sequence in double circuit line.The two-dimensional calculation model of power frequency magnetic field under UHV transmission lines was build. The magnetic field under transmission lines with six kinds of phase conductor configuration was studied and the distribution features of them were analyzed by comparison. Some influencing factors in power frequency magnetic were studied, for example:load current, the distance of line to the ground, phase distance, different stringing methods in single circuit lines and phase order arrangement in double-circuit lines, etc. The effect on vertical component, horizontal component and synthesis component of power frequency magnetic field were analyzed quantitatively and some good advisory opinions to the UHV transmission line design would be given.The physical process of corona discharge was decrypted briefly and several characteristics of radio interference in UHV transmission lines were introduced. The calculation method of the conductor surface electrical field strength was studied seriously. The surface E-field of different UHV transmission line bundle conductors was calculated and studied. The relations between the distance of conductor to ground, middle phase, boundary phase conductors, sub-conductor radius and conductor surface field strength were investigated. Because there are more than 4 sub-conductors in UHV transmission line, the excitation function was recommended to calculate the radio interference under UHV transmission line. There were four kinds of UHV single circuit transmission line in the radio interference calculation model. In the result, the effect of sub-conductor radius was more obvious than stringing methods and conductor height above ground.