Electrical evaluation of the AC losses in a BSCCO cable with an HTS shield

Abstract

In general, a high temperature superconductor (HTS) cable has a conductor and a shield encircling it. This structure causes electrical evaluation of AC loss in the HTS cable to be very difficult. Thus it is not clear yet. Using two voltage leads attached to the conductor and shield, respectively, we evaluated not only their AC loss but also the cable’s total loss. To experimentally elucidate our electrical evaluation presented in this work, first we measured the total loss of the 100 m/22.9 kV BSCCO cable by calorimetry, especially around 77 K. Besides the same 5 m cable sample as above, another cable model with a thin insulator was also tested electrically, and they were compared with two numerical models: a non-twisted polygon model and a twisted cylinder model. The results show that, according to the insulator thickness between a conductor and a shield, their magnetic interaction becomes very different. For the 100 and 5 m cables, their normalized total AC losses measured from calorimetry and electrical evaluation correspond well to each other, regardless of operating temperatures. Moreover, the numerical analysis shows that the total AC losses measured for the 5 m sample and cable model fit with the numerically calculated ones. Besides, the conductor’s AC losses measured for both the cables agree well with the numerical ones, regardless of their insulator thickness. This is because a conductor in an actual cable is inside a shield, and so does not receive any effect of the shield’s magnetic field. These experimental and theoretical results support the view that our electrical evaluation for the total and conductor losses is reliable. However, unlike the results for the total and conductor losses, the shield’s experimental loss is not in good agreement with any of the theoretical ones from either the non-twisted polygon model or the twisted cylinder model.