DC ion-currents in AC conductors in hybrid AC/DC transmission

This publication presents the results of a series of laboratory investigations on the DC ion current coupling between nearby AC and DC conductors, which is an important consideration in the design of hybrid AC/DC transmission towers. The corona activity depends on the surface condition of the conductor. Whether or not the conductors produced corona was controlled by selectively wetting them. This allowed a distinction of the observed effects into field interactions and space charge interactions. One key result is that the presence of an AC field alone does not have any effect on the DC ion current coupling. Corona activity on the AC conductor, however, may significantly increase DC ion current components in both conductors. Another important finding is that the DC current in the AC conductor for the case of corona activity on both conductors was significantly larger than the sum of the DC currents based on corona activity on either conductor individually. This indicates that the bipolar space charge environment between a coronating AC and DC line plays an important role in the ion current coupling.