Experimental investigation of air insulation characteristics under AC voltage in smoky conditions due to remote wildfire considering the impact of humidity

Wildfire smoke introduces fine particulate matter into the atmosphere, altering the insulating properties of air used in HV AC transmission systems. This study experimentally evaluates how wildfire smoke affects air-gap insulation under controlled laboratory conditions. A sealed smoke chamber was used to measure breakdown voltage, partial discharge inception voltage, phase-resolved discharge behavior, and partial discharge time-frequency characteristics at varying smoke and humidity conditions. Breakdown measurements using sphere–sphere gaps showed no significant deviation across all smoke conditions. In contrast, partial discharge inception voltage in needle–plane gap increased consistently with smoke density, rising by nearly 100% at the highest concentrations. Phase-resolved partial discharge patterns and partial discharge indicators show that smoke suppresses negative polarity discharges at low voltage, whereas at higher voltage it enhances partial discharge activity and increases pulse rate. Time–frequency analysis further revealed waveform-shape changes under combined smoke–humidity conditions.