Compatibility between C4F7N/CO2and Epoxy Resin in Electro-thermal Environment

Fluorinated nitrile (C ₄ F ₇ N) is a potential SF ₆ -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 between C ₄ F ₇ N/CO ₂ gas and epoxy resin assembling in GIL, laboratory tests on the material compatibility under electro-thermal stresses were done. In the tests, a platform of electro-thermal acceleration test in a gas closed high pressure chamber was used. The conditions of the electro-thermal acceleration were set to the maximum allowable values (70°C-5kV/mm) which are commensurate to the normal operation conditions of GIL. The tests lasted for 1000 hours. Moreover, the conditions of the thermal acceleration tests under 70°C were also set up. The compatibility between the gas and solid insulating materials in contact is evaluated in terms of the changes of insulation performance after long tests. The changes of gas compositions and solid contents were also assessed. It was found that the surface flashover voltages decreased after electro-thermal acceleration tests. In contrast, the surface flashover voltages increased after only thermal acceleration tests, indicating that the deterioration of insulation was affected by the electric field. Results showed that there was no evidence of reaction between the epoxy resin and C ₄ F ₇ N/CO ₂ under the experimental conditions.