Calculation of Ion Flow Field Around HVdc Bipolar Transmission Lines by Method of Characteristics

The ion flow fields around high voltage direct current (HVdc) transmission lines due to corona are nonlinear, which can be simulated by calculating the electric field distribution and ion density distribution iteratively. In this paper, an application of the method of characteristics is presented to calculate the ion densities around bipolar HVdc transmission lines based on a pair of first-order partial differential equations of the ion densities. The electric field is calculated directly by accumulating all the contributions from the ions in the air and charges on the conductors. No large-scale system of equations needs to be solved, which means that the requirement for computer memory is low, and the method is suitable for large-scale calculation. The results are in good agreement with the measured data.