Influence of Ambient Electric Field on the Corona Performance of HVdc Transmission Lines

Ambient electric fields produced by atmospheric electricity at the ground surface modify the electric-field distribution between the conductors and ground plane of HVdc transmission lines. Depending on their magnitude and direction, ambient electric fields may therefore contribute to variations in the overall corona performance of dc lines. A computational technique is developed in this paper to simulate ambient electric fields in the vicinity of HVdc transmission lines and evaluate their influence on the electric-field distributions on the surfaces of conductors and ground plane and determine the resulting pattern of flux lines. The computational technique is then applied to practical HVdc transmission-line configurations to determine the influence of ambient electric fields on radio interference (RI), audible noise (AN) performance, and onground-level electric-field and ion current distributions. The computational results are compared with some experimental data obtained on a dc test line and an operating dc transmission line.