One of the most important insulating components for developing a 154 kV superconducting fault current limiter (SFCL) is post insulator, which supports 154-kV SFCL modules in a cryostat. In order to design an optimum post insulator, the top priority is to determine the creepage distance of post insulator. In our previous research, surface flashover voltages along smooth glass fiber reinforced polymer (GFRP) rods immersed in liquid nitrogen (LN2) were experimentally investigated. To reduce the cryostat volume, ribbed post insulators with increased creepage path were then considered. However, due to difficulties with producing ribbed GFRP post insulators, ribbed specimens were made of polytetrafluoroethylene instead. Four kinds of test specimens were prepared to determine the position and the number of ribs attached to the surface. From the experimental results, it was found that the ribbed insulator has shown better insulation performance in LN2 and number of ribs could affect the surface flashover voltage of post insulator. Consequently, ribbed model for 154-kV SFCL post insulator was designed and successfully tested. Finally, real 154-kV SFCL system with newly designed ribbed post insulator was installed and Basic Impulse Level (BIL) test and ac required withstand voltage were successfully carried out.