Electrotechnical Features and Theoretical Modelings of the 100-m 22.9-kV/50-MVA BSCCO Cable System

Because of a much higher power density than a conventional underground cable, several high-temperature superconductor cables with different voltages and designs have been developed worldwide and demonstrated in a power grid. The 100-m 22.9-kV/50-MVA BSCCO cable system developed for long-term demonstration has been tested during phase I of three years, after being installed at Gochang Test Yard in Korea first: initial cooling, engineering properties, and its reliability. In this paper, we particularly focused on its dielectric and transport current characteristics investigated under high voltage up to 30 kV or large current, experimentally and theoretically. The results show that the dielectric parameters such as permittivity and loss tangent are similar to a conventional oil filled cable. However, the impedance is one fifth of a concentric neutral cross-linked polyethylene insulated cable with a similar conductor size. In addition, separate estimation of ac loss in the conductor and shield, which has not been clear yet, is also established: the shield's loss is evaluated directly from the shield lead, but the conductor's loss indirectly through the virtual-voltage lead. Then this conductor's loss at the rated current may raise its temperature to a coolant by a few degrees. The lumped circuit model shows that the three-phase shield suggested in our cable system can sufficiently cancel magnetic field generated from any variation of a power load in an actual grid. Finally, the theoretical models based on a home-written code and a commercial package are in good agreement with their corresponding experimental results.