Breakdown Characteristics of Rod-Plane Gap in an Ethanol Flame

The wildfires nearby high-voltage transmission lines are frequently reported to induce outages in many countries. Less research addresses the role played by individual characteristic factor (i.e., high temperature, intense heat, etc.) of wildfires in triggering phase-to-ground flashovers of transmission lines. Aiming at this, systematic laboratory experiments are performed to reveal the breakdown characteristics of rod-(ring-like) plane gap in clean ethanol flames. By setting different scenarios of pure air gap, nonbridged and bridged gaps by ethanol flames, the breakdown voltage, average breakdown strength, and leakage current with various gap spacings are measured and analyzed. Results show that the flame centerline positions at a height of 4.0-6.0 cm are regarded as the main reaction zone. The breakdown processes of rod-plane gaps in ethanol flames are the combined results of diverse discharge patterns. Compared with the pure air case, the breakdown voltages are decreased by 27.8%-70.5% in the nonbridged gap and by 68.3%-77.1% in the bridged gap by ethanol flames, and their corresponding levels of average breakdown strengths decrease to 45.7% and 27.6%, respectively. Under the alternating current (ac) electric field, the coupled effects of electric field force, thermal buoyancy, and ionic wind together promote the formations of streamer channels in ethanol flames. Finally, the high-temperature flame itself is found to be the most dominant factor in influencing the breakdown.