Ion flow simulations of HVDC conductors under rainy conditions

During the last years, more and more renewable power generation units have been connected to the European power grid, creating demands for higher transport capacity as well as longer transport distances. Plans for the construction of HVDC and hybrid HVAC/HVDC corridors in Europe lead to an increased interest in the corona behaviour of direct current overhead lines. Within the scope of this paper, simulations and measurements are conducted to analyse the accuracy of the used simulation tool for rainy conditions, which is constituting an important study case since corona intensity is significantly increased during periods of precipitation. Especially, charge generation at the conductor surface and its influence on total corona current as well as on the ion current distribution at ground level under rainy conditions are investigated. As a result, the idea that a single onset field strength can describe the entire V-I characteristic of an overhead line under rainy conditions is challenged. It is shown that a field dependent correction factor for the onset field strength can improve the accuracy of simulations considerably. Additionally, in order to improve the simulated current distribution at ground level, a method to inversely calculate charge generation profiles is introduced.