Loss Characteristics of the Polygonal YBCO Conductors with a NiW Magnetic Substrate

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The single- and double-layer polygonal conductors were tested, to understand loss of the 154- and 22.9-kV YBCO-NiW cables in the power grid of Korea Electric Power Corporation (KEPCO). Especially in YBCO-NiW, there is also an iron loss of NiW besides AC loss of YBCO, and so the loss is very complex. For reliability of our loss data, we tried a statistical treatment for several losses measured after compensating an inductive voltage at the same current first. Then distribution of flux around YBCO caused by NiW’s reluctance was investigated for different arrangements of YBCO (Y) and NiW (N): the YN and NY ones. Finally, influence of perpendicular magnetic field on conductor loss was also examined through two polygonal conductors, whose wires’ numbers are ten and five, respectively. The results show that the loss in a single-layer YBCO-NiW conductor is constant regardless of inductive compensation, as might be expected. But a double-layer conductor has dispersive loss properties at the same current: this is due to external AC magnetic field applied to an outer layer. And loss flux distribution in the conductors strongly depends on NiW arrangement because of its reluctance. Then differently from BSCCO, the loss measured for a polygonal YBCO-NiW conductor does not depend on its wires’ number. Thus, difference between the experimental and numerically calculated losses gets gradually large with increasing the number of wires. It can also be seen from the measured losses that in the single-layer conductor, they are identical to the sum of self-field losses in its YBCO-NiW wires. However, the losses of the double-layer NYYN conductor are greater than the total self-field losses of the YBCO-NiW wires. Furthermore, losses measured from two voltage leads, which are contacted to the inner and outer layers, well fit with each other.