AC Loss Measurement of an HTS Cable Model With a Shield Through Virtual and Contactless Voltage Leads
We have been investigating, in a power grid of Korea Electric Power Corporation, 22.9- and 154-kV high-temperature superconductor (HTS) cables, in which a conductor and a shield are coaxially arranged. Because of the shield opposite to the current of the inner conductor, electrical evaluation of ac loss in these actual power cables is very difficult. Nevertheless, our previous work proposed its concept through two contact voltage leads, i.e., nominal conductor lead and shield lead soldered to the conductor and the shield, each by assuming a virtual lead, which cannot be really put on the conductor's surface. However, it is still uncertain in some ways. Thus, through installing contactless voltage leads and the virtual lead into an HTS cable model, in this paper, we clarify what the contact voltage leads pick up and what the relationship is between the conductor lead/shield lead and the virtual lead, which is directly set up on the conductor's surface of our model. The results show that the ac losses measured from the voltage leads (virtual lead/shield lead) contacted to the conductor and shield always fit well with those of their corresponding contactless voltage leads. According to Faraday's law, this implies that each contact voltage lead picks up the lossy flux of the conductor and shield and the lossy voltage induced along specific closed paths, i.e., contactless leads, encircling them, respectively. Then, losses from the virtual lead of the inner conductor are unchangeable regardless of the outer shield, but losses of the shield lead depend on not only the amplitude of the conductor's current but also its direction. Finally, the losses of the conductor lead, including the conductor and shield, are equal to the addition or subtraction of the virtual lead and shield lead, although it is influenced by their current transportation mode.