Medium voltage cable designs for 100km DC superconducting power transmission line using experimental data of Ishikari Project

Main two merits of the DC superconducting power transmission line are low loss and zero resistance of the cable. Since it is a small system, its system cost will be lower than the copper cable system finally. The loss of the DC superconducting power transmission line depends on the heat leak from the cryogenic pipe and the COP of the refrigerator, therefore the main subject is to minimize the electric power consumption of cryogenic refrigerator system, and we should realize low heat leak from the cryogenic pipe, and high COP of the refrigerator is required. At the same time, low circulation power of liquid nitrogen is necessary. The heat leak of cryogenic pipe lower than 1 Watt/meter was realized in Ishikari project in 2016 in very low pressure drop of the cryogen circulation. We also should pay attention on the temperature rise of the cable for a longer transmission. The temperature rise is only ∼0.03 K/km in Ishikari project because of the radiation shield structure. Therefore, we could construct 100km transmission line basically, and the cooling stations are located at both ends. We investigate several parameters of the cable designs, and its voltage will be 25kV, and the current is available up to 10kA. Because of this, we can connect the power stations to the distribution substations directly, and we can omit high voltage substations. Medium voltage power converter was proposed and is developed for renewable energy system. Finally, we can realize the main two merits of DC superconducting power transmission line.