# Surface Discharge Mechanism on Epoxy Resin in Electronegative Gases and Its Application
## 5 Conclusions  
This study investigated the surface discharge characteristics of epoxy resin in compressed gases, namely SF\({}_{6}\), dry air, and N\({}_{2}\), in a non-uniform electric field. Among the different gases, SF\({}_{6}\) and dry air, which are electronegative gases, revealed better insulation performances compared with N\({}_{2}\), owing to their electron attachment ability. The effect of electronegative gases on surface flashover voltages, varying with the pressure in these compressed gases, was analyzed in detail through the processes of electron attachment and electron detachment. Electron attachment induced an increase in the surface flashover voltage of the electronegative gas. Electron detachment seemed to result in saturation of the voltages as the pressure increased. A surface discharge mechanism that includes electron attachment, electron detachment, and secondary electron emission (SEEA and photoemission) was proposed for an analysis of the surface flashover voltages, which varied with the gas pressure. From this mechanism, it was found that the physical phenomena governing the behavior of electrons, including electron attachment, electron detachment, and electron scattering, are related to an improvement in the dielectric strength of the mixed gas. Based on these findings, techniques for improving the dielectric strength of mixed gases were discussed from a physics and engineering point of view. The discussions and knowledge of the physics behind gas discharge suggest the possibility of a new insulating gas to replace SF\({}_{6}\). To discover and develop the new insulating gas, theoretical and experimental attempts to understand the effects of varying the pressure on electron attachment and electron detachment are required. In addition to such attempts, the insulation characteristics of gases and mixed gases and their discharge mechanisms under DC and AC voltages must specifically be identified. This study contributes to explorations attempting to expand the knowledge of physics that governs gas discharge. The physical information obtained from the results of this study can be used to secure improved surface insulation performances by using the technique of mixing insulation gas in the surface insulation design of SF\({}_{6}\)-free high-voltage equipment.  
**Author Contributions:** Conceptualization, H.P., D.-Y.L. and S.B.; Investigation, H.P., D.-Y.L. and S.B.; Supervision, S.B.; Writing--original draft, H.P., D.-Y.L. and S.B.; Writing--review & editing, H.P., D.-Y.L. and S.B. All of the authors were involved in the preparation of the manuscript. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, grant number 2017R1D1A3B03035693. This work was also supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government (MOTIE) (No. 20192010107050).  
**Conflicts of Interest:** The authors declare no conflict of interest.