Compressed air exhibits excellent insulating properties

making it a promising environmentally friendly alternative to SF6 gas. Investigating the charge characteristics at gas-solid interfaces and the evolution of discharges in air is crucial for improving the design of environmentally friendly electrical insulation systems. In this study

a bilayer insulator composed of polyethylene terephthalate (PET) film and silicone rubber was designed. A gas-polymer surface discharge optical monitoring and charge measurement platform was constructed to measure charge density

potential

and electric field distribution. The results indicate that the bilayer insulator

with PET film coating the silicone rubber

significantly reduces the discharge phenomena between the probe and the polymer measurement surface. Under a positive impulse voltage

the boundary between leader and streamer discharges is located approximately 20 mm from the high-voltage electrode. Under a negative impulse voltage

this boundary gradually moves toward the ground electrode as the voltage increases. In the impulse voltage range of 12.5 kV to 16 kV

the boundary for charge density between leader and streamer discharges is between 350 and 680 pC/mm²

the transverse potential boundary is around 9 kV

and the longitudinal potential boundary is between 6 kV and 8 kV. In the negative impulse voltage range of -9.5 kV to 17.5 kV

the boundary for charge density is between 500 and 600 pC/mm²

the average field strength in the streamer region is between 1.0 kV/mm and 1.6 kV/mm

and the field strength in the leader channel is between 0.15 kV/mm and 0.20 kV/mm.