Corona Current Coupling in Bipolar HVDC and Hybrid HVAC/HVDC Overhead Lines

Abstract

This paper investigates the corona generated ion-flow environment in bipolar HVdc and hybrid ac/dc transmission systems. The emphasis is on the dc ion current magnitude in the conductors. In dc conductors, this constitutes the corona power loss, while in ac conductors, this quantity is primarily of concern due to the risk of transformer saturation. Existing prediction methods are compared to full-scale test data from the literature and new laboratory measurements. It is shown that the bipolar HVdc and hybrid ac/dc ion-flow phenomena are similar in the sense that mutual space-charge-related surface field enhancements are a dominant factor in the determination of the total conductor ion currents. Furthermore, in a hybrid ac/dc environment, the existence of a net dc ion current stemming from the ac conductor is verified and explained. Limitations of existing prediction methods are demonstrated and recommendations for future work is given.