Dielectric Characteristics of PPLP With Various Pressures and Intervals Between Butt Gap

Superconducting cables are one of the most promising applications among several high voltage superconducting power apparatuses owing to its low energy loss and high power capacities. Superconducting cables system consists of four parts: the termination, the joint box, the core, and the cooling system. The core is responsible for power transport, and is insulated with polypropylene laminated paper (PPLP) to ensure a high dielectric strength in the presence of liquid nitrogen (LN₂). The insulation layer of the core is fabricated by winding PPLP in multiple layers. It is inevitable that butt gap filled with LN₂ is generated in this process. Currently, many studies on the dielectric characteristics of PPLP according to various intervals between butt gap under 0.1 MPa and those with fixed butt gap according to various pressures have been conducted. A study on determining a proper interval between butt gap according to pressure in order to develop reliable superconducting cables under high pressure should be performed because superconducting cables system in power grid is operated under high pressure. This study focuses on the evaluation of the dielectric characteristics of PPLP with interval between butt gap at various pressures. In addition, dielectric experiments on V-t characteristics for a mini-model cable are conducted and experimental results are analyzed by the inverse power model.