Study of Compatibility Between Epoxy Resin and C4F7N/CO2 Based on Thermal Ageing

Fluorinated nitrile (C4F7N) is a potential SF6-alternative gas in Gas-Insulated Transmission Line (GIL) due to its lower impact to global warming and excellent dielectric strength. To ensure the long-term physical and chemical stability at the interface between C4F7N/CO2 gas and epoxy resin assembly in GIL, laboratory thermal ageing tests on the material compatibility were carried out. In order to evaluate the compatibility, the authors set up a gas-solid compatibility test platform in this paper. Thermal ageing tests of C4F7N/CO2 and epoxy resin were set up at different temperatures. Also, the groups of SF6 and He gas were adopted to evaluate the influence of temperature. The compatibility between the gas and solid insulating materials in contact was evaluated in terms of the changes of insulation performance after over long period of tests. The changes of gas compositions and solid contents were also assessed. Dielectric spectroscopy, surface flashover voltages, surface morphology, and chemical elements of epoxy resin and gas composition before and after the ageing tests were compared. The surface insulation of epoxy resin decreased only after ageing reached 160 degrees C, when a small amount of C3F6 and trimer of C4F7N were found. Under the normal operation of GIL (below 90 degrees C), the compatibility of epoxy resin with 9 % C4F7N/91 % CO2 is as good as epoxy resin with SF6.