Study of Surface Flashover and Breakdown Characteristics in Liquid Nitrogen for SFCL Application

With the rapid development of commercial use of superconducting fault current limiters (SFCLs), higher and higher voltage use is being taken into consideration. Insulation property is crucial and limits the development at high voltage level. G10, as an excellent insulation material for cryogenic use, can be applied in high voltage SFCL module. Based on the fundamental design of SFCL module in Shanghai Jiao Tong University, flashover characteristics of G10 in LN₂ are researched to design the SFCL module. In addition, ac breakdown strength of SFCL module terminals is investigated to design module distance to ensure insulation safety and do not make SFCL too large. Simulations are conducted to study the theoretical electric field distribution. Partial discharge voltage and ac surface flashover breakdown voltage of different electrodes are measured. SFCL module terminal electrodes and triangle-plane electrodes are applied. How the surface flashover breakdown strength would be affected is studied by changing the electrode gap. Breakdown strength property of SFCL module terminal is also studied by altering the distance of electrodes. The experiment results show that gas gap and surface length do influence the partial discharge charge and flashover breakdown voltage. Bubbles also affect breakdown strength between terminals. These results are conducive to design SFCL module.