Achieving uniform surface treatment on large-area epoxy resin via a transparent water-tungsten wire mesh electrode DBD with integrated visual and distributed diagnostics

High-voltage electrical equipment operating in humid environments is prone to accelerated aging of insulating barriers and an increased risk of flashover, which threatens operational reliability. This study proposes an in-situ plasma-based protection strategy to achieve uniform hydrophobic surface modification of large-area insulating barriers. A large-area dielectric barrier discharge (DBD) surface modification device incorporating water–tungsten wire mesh electrodes was developed to homogeneous plasma and enable visual observation and distributed diagnostics. By systematically optimizing the applied voltage and argon (Ar) gas flow rate, homogeneous plasma discharge was achieved under optimal conditions of 12 kV and 1 L/min Ar flow, as verified through grayscale image analysis and spatially resolved optical emission spectroscopy. Using a nanosecond pulsed power supply at atmospheric pressure with hexamethyldisiloxane (HMDSO) as the precursor, a uniform hydrophobic coating was deposited on an epoxy resin (EP) laminate after 20 min of plasma treatment. The average water contact angle increased to 130.2 ± 3.9°, representing a 74.7% improvement compared with the original surface. Mechanistic analysis reveals that the observed enhancement in hydrophobicity results from the synergistic effects of increased surface roughness and the deposition of a dense silicon-containing coating. The combination of visual inspection and distributed diagnostic techniques has been demonstrated to be effective in ensuring uniform large-area treatment during the process.