Radio interference characteristic of ultra-high voltage AC transmission lines by using stochastic modeling

For developing ultra-high voltage (UHV) AC power transmission systems, it is important to precisely estimate and to limit the radio interference RI) level of power lines. Based on the stochastic characteristics in amplitude and repetition rate of induced corona current, by using the probability theory and mathematical statistics, we establish a stochastic model for the wide-sense stationary random process of corona discharges. Then combining the stochastic model with model-propagation-analysis method, the RI levels under three-phase UHV AC transmission lines are calculated. The results of the calculation based on stochastic model method and International Council on Large Electric Systems (CIGRE) excitation function are compared with that based on semi-empirical method and some other excitation functions. The stochastic model based on different excitation functions is also adopted to simulate the RI levels under finite test lines with two opened terminations. The results indicate that with the same average maximum gradient on conductor surface and the same conductor type, the number of corona discharge per unit length is one of the main reasons that causes the difference between different excitation functions. It is also concluded that for a long test line, the effect of standing wave on RI field strength is negligible in the middle of the line, but obvious near both terminations: for a 10-km line, the maximum difference in RI field strength is 2.78 dB, between the peak value of the standing wave near the ends and the steady value near the middle of the line.