Analysis on the Dielectric Characteristics of Solid Insulation Materials in $\hbox {LN}_{2}$ for Development of High Voltage Magnet Applications

Several types of solid materials are used in the development of high voltage superconducting magnet systems as the former and insulation barrier. The solid insulation materials used in cryogenic applications require excellent dielectric characteristics as well as robust mechanical characteristics. In this study, the dielectric experiments for three types of solid insulation materials, including glass fiber reinforced plastic (GFRP), epoxy (Stycast 2850FTJ), and Bakelite in liquid nitrogen (LN₂) at 77 K temperature are performed. Each experiment on the solid insulation materials is performed according to the type of applied voltage (lightning impulse and ac voltage) and the system pressure (0.1 ~ 0.4 MPa). Also, experiments considering the stacking effect of insulation sheets are performed. All electrical breakdown voltages are observed when the solid insulation materials are fully penetrated. Electrical breakdown experiments on GFRP and Bakelite sheets according to the number of stacking are performed and the results are compared. The relationship between the dielectric characteristics of solid insulation materials and the distribution of electric field intensity is calculated and analyzed by the finite elements method (FEM). The results revealed that the dielectric characteristics of solid insulation materials in LN₂ are directly affected by the distribution of electric field intensity and the number of stacking sheets.