Influence of Various Voltage Leads on AC Loss Measurement in a Double Layer BSCCO Conductor

We have operated the two 22.9 kV/50 MVA HTS cable systems installed at Gochang Test Yard and Icheon Substation of Korea Electric Power Corporation (KEPCO), respectively; they have a double layer conductor and a single layer shield, consisting of BSCCO and YBCO-NiW wires. In general, the ac loss of a multilayer cylindrical conductor like the KEPCO HTS cables is evaluated from the conductor's current and the loss voltage of a lead soldered onto its outermost layer. To experimentally investigate what the voltage lead on the outermost layer picks up in this study, we prepared a double layer BSCCO conductor sample, and attached the four voltage leads of the outer, inner, contactless, and total leads. Then its ac loss for these leads was examined for different layer current distribution, and finally compared with a numerically calculated one. The results show that the outer-lead, which is often used in the double layer conductors, takes only the outer layer's loss voltage like the contactless-lead. Therefore, for ac loss evaluation of our double layer sample, a new voltage lead, total-lead, is presented besides the conventionally used outer-lead. The total-lead best fits with the numerical calculations, regardless of layer current distribution. However, the outer-lead is not suitable, especially for nonuniform distribution, although it still now is valid only for uniform distribution.