Surface flashover characteristics of fluorinated polyimide films in liquid nitrogen

With the emergence of superconductor technology, high temperature superconducting (HTS) power devices are quickly being developed. Among them, the HTS cable is receiving considerable attention and application in power systems due to high capacity and low loss. To develop a HTS power cable system, the terminal technology is essential component. The HTS cable terminations must withstand a temperature as low as 77K So, it is necessary to study the termination insulation materials and electrical properties at cryogenic temperature. Polyimide film (PI) and liquid nitrogen (LN2) have been used as insulation material and coolant in HTS cable systems. Surface flashover may lead to degradation and breakdown of HTS cable termination insulation. To optimize the insulation design of HTS cable termination, the method of direction fluorination was used for modulating the electrical properties and restraining the surface discharge of the PI film. In this paper, the surface flashover characteristics of original and fluorinated PI were investigated under 50 Hz AC voltages in LN2. The results show that the direction fluorination of PI film can improve the surface flashover strength.