Comparison Between PD Inception Voltage and BD Voltage of PPLP in $\hbox {LN}_{2}$ Considering HTS Cable Insulation

With the rapid development of world economics, demand for electricity in metropolitan areas has increased dramatically. The high-temperature superconductivity (HTS) cable is one of the most promising technologies for solving the bottleneck of the transmission system. However, power system planners have not yet considered the HTS cable as a mature technology due to its weak insulation characteristics with respect to those of conventional power cables. The electrical insulation design is one of the major issues for HTS cable. It is evident that the insulation in the dc cable should be investigated further at this time. For the insulation design of the HTS cable, it is necessary to investigate the breakdown (BD) characteristics and the partial discharge (PD) inception voltage of the liquid nitrogen (LN₂)/polypropylene laminated paper (PPLP) composite insulation system. In this paper, BD voltage and PD inception voltage of PPLP immersed in LN₂ was compared under ac and dc stresses. Various kinds of PPLP specimens considering the different layers and the butt gaps were prepared. The PD inception voltage was measured in a shield room according to IEC 60270. Consequently, it was investigated that characteristics of the PD inception voltage and the BD voltage was rather different when ac and dc voltages were respectively applied in LN₂, and these results could be used for the insulation design of ac and dc HTS cables.