Electrical insulation characteristics of liquid nitrogen-impregnated laminated paper-insulated cable

The liquid-nitrogen-cooled superconducting cable using a high-temperature superconductor is considered to have good potential as a means of transmitting large high-density electric power in the next generation. The authors consider the design of insulation for a 66-kV high-temperature superconducting cable based on the measurement of the electrical insulation characteristics of liquid-nitrogen-impregnated laminated-paper-insulated cable using the existing cable insulating paper. Three kinds of insulating paper were almost the same in AC breakdown strength, which decreased in proportion to the insulation thickness. The value was 30 kV/mm at 8 atm in the 66-kV model cables (PPLP, insulation thickness 4 mm). It was clarified that the PD (partial discharge) inception voltage was about 20 kV/mm, which is lower than the breakdown voltage of liquid nitrogen. From the point of view of long-term deterioration, the designed voltage should be lower than the PD inception voltage. Therefore, a design stress of 15 kV/mm for 66-kV cables appears possible