Modal Components in Multiphase Transmission Line Radio Noise Analysis

Modal components are customarily used in transmission line radio noise calculations [1-4]. Complete modal transformation [5] produces attenuation and phase constants (losses and velocities of propagation) within the modes. In order to fully utilize this technique, the frequently adopted assumption of random phase relation between the modes at the point of recombination is replaced by a more exact approach in this paper. The correlation of the modes is found mathematically and compared with approximations discussed in the literature [3, 4]. To the authors´ knowledge, the analysis presented here closes a gap in the literature on the subject. Its practical importance is most evident for unsymmetrical corona conditions, as they may exist on double-circuit ac and dc lines, and wherever the contributions from the phases shall be calculated separately.