Investigation of Asymmetrical Three Phase Current and Impedance Variation in the Grid Connection of a HTS Power Cable

When a 22.9 kV, 50 MVA HTS (high temperature superconducting) power cable was applied to a real power system and the system was being operated as part of the Icheon project, a current redistribution problem occurred in the shield layer. To clarify the reasons for this, the authors analyzed the characteristics of the current distribution and induced current ratio with a phase angle in the HTS power cable considering an asymmetrical three-phase current that flowed into the conducting layer and the impedance variation of the shield layer according to a grounding method using the PSCAD/EMTDC (power system computer aided design/elector magnetic transients DC) analysis program and vector calculation. It was found that the increases in the asymmetrical current flowing through the conducting layer of the HTS power cable and in the impedance of the shield layer affected the magnitude and phase of the induced current. In addition, depending on the grounding method used, a problem in which the zero current generated by the asymmetry affects the induced current and flows through the cryostat was found. The results obtained through the simulation analysis will provide valuable information for the installation and operation of HTS power cable systems in actual utilities.