The effect of surface roughness on corona-generated electromagnetic interference for long-term operating conductors

This paper presents a research of the surface roughness effects on corona-generated electromagnetic interference of long-term operating conductors. The detailed surface morphologies and roughness of typical long-term operating conductors were measured and analyzed. The radio noise measurement system based on the corona cage was discussed and the actual radio noise generated by the conductor in the measured cage was obtained, based on the parameters of the corona cage and the measured data. The radio noise tests were carried out under both dry and wet conditions. Under two types of conditions, the corona intensity was higher on the long-term operating conductors contrasted to the new conductors as a result of the anomalistic surfaces of the long-term operating conductors. The rate of decrease of corona inception voltages between the long-term operating conductors and new conductors was discovered to increase with the raise of surface roughness degree Ra in linear relationship. Approximate linear relation was also discovered between the averaged radio noise deviation and R_a. The rate of decrease of corona inception voltages under wet conditions was slightly higher (about 1%) than that under dry conditions. The difference between the radio noise of long-term operating conductors and that of new conductors was larger (1.3 dB) under wet conditions compared to dry conditions.