Characterization of partial discharge with fluorinated polyimide films in high temperature superconducting cable insulation

Abstract

High temperature superconducting (HTS) cable has now reached the stage where their application in power systems is in the process of being implemented. Polyimide film has been used as an insulation in HTS cable systems with the advantages of low temperature resistance, good mechanical properties and excellent dielectric properties. Due to the organic properties of polyimide, the breakdown of the films is one of main problems to the safety and reliability of HTS cable. Partial discharge (PD) events may lead to material degradation and total breakdown. Our recent researches have shown that fluorination as a chemical modification technology can influence the surface charge behaviors thus influence the PD characteristics of modified polyimide films. In this paper, the effect of fluorination time on the partial discharge and breakdown characteristics of fluorinated polyimide films have been carried out. Samples were surface fluorinated in a laboratory vessel at about 328 K (55 °C) using a F2/N2 mixture with 20% F2 by volume and 0.05 MPa (500 mbar) for 15, 30, 45 and 60 minutes, respectively. Atomic force acoustic microscope (AFM) was used to detect the surface topography of the samples. The PD characteristics results showed that the partial discharge quantity decreases with the fluorination time increasing from 0 min to 45 min and increases with the fluorination time increasing from 45 min to 60 min.