From the view of environmental compatibility, we attempt to develop switchgear without using SF6 gas. As an electrical insulation gas, we focused our research on the compressed air and pure N2, because of their minimum global warming potential. In this paper, we verified the impulse breakdown and impulse partial discharge characteristics under various non-uniformity of electric field. The experimental result shows that the breakdown voltage (BDV) of air is higher than the BDV of pure N2 gas under highly non-uniform gap condition. On the other hand, the discharge inception voltage of air and N2 were almost the same. Furthermore, first partial discharge (PD), leader discharge and its transition to the breakdown were successfully observed through the measurement of discharge current and light emissions under impulse voltage application.