Improvement on the corona model of ultra high voltage alternating current transmission lines

In designing lightning insulation margin of substation equipment in China, the attenuation and distortion of intruding wave caused by corona in the transmission lines is neglected, thus making too strict insulation requirements on the electrical equipment, what´s more, the impulse corona has a great impact on the shielding failure and lightning resisting level of ultra high voltage alternating current (UHV AC) transmission line, making it necessary to study the corona effect of UHV AC transmission lines. In this paper, a corona model is put forward in which the coupling among the wires and corona in the overhead ground wire are taken into consideration and the capacity changes of wire to ground is taken into consideration as well after conducting the parallel connection between corona capacity and air capacity in the ionization zone then carrying out the series connection with the air capacity in none-ionization zone so as to simulate the corona. Such model is more favorable to the actual conditions of corona discharging. The lightning shielding failure ATP-EMTP corona model in the UHV AC transmission line, to which the corona mentioned above, is added will be established. The results show that corona has the impact on the wave passing through the transmission line, causing the attenuation and distortion of amplitude and slope of lighting wave, thus improving the shielding failure and lightning resistance level of the transmission line.