为研究树冠火条件下的导线-板电极空气间隙直流击穿特性，搭建松树木垛火与树冠火条件下5 m导线-板电极空气间隙击穿放电试验平台，研究两种火焰形态不同燃烧阶段的燃烧特性与间隙直流击穿特性，分析火焰高度与间隙击穿电压的关系，并通过回归分析给出拟合表达式。研究结果表明：不同燃烧阶段，树冠火对导线-板电极空气间隙绝缘强度影响程度不同；最大火势阶段，松木木垛火平均击穿电压梯度为104.5 kV/m，松木树冠火平均击穿电压梯度为84.7 kV/m，分别为同海拔下空气间隙平均击穿电压梯度的38.9 %与31.6 %；松木木垛火与树冠火的间隙平均击穿电压梯度与火焰高度有良好的线性关系，对比松木木垛火与树冠火间隙直流击穿电压值，火焰区的温度与高度导致的火焰特性差异对间隙绝缘强度的影响弱于烟雾区中烟雾颗粒特性差异对间隙绝缘强度的影响。研究结果可为输电线路山火短路击穿风险评估提供指导。

In order to study the DC breakdown characteristics of the conductor-plane air gap under the crown fire conditions, a 5 m air gap conductor-plane breakdown test platform is set up. The combustion characteristics and the DC breakdown characteristics of the air gap of pine crib fire and crown fire at different combustion phases are studied. The relationship between the flame height and the breakdown voltage of the gap is analyzed and fitting equations are given through regression analysis. The results show that: at different combustion phases, the crown fire has different impacts on the insulation strength of the air gap between the conductor and the plane; at the maximum combustion phase, the average breakdown voltage gradient of the pine crib fire is 104.5 kV/m, and the average breakdown voltage gradient of the pine crown fire is 84.7 kV/m, which is 38.9 % and 31.6 % of the average breakdown voltage gradient of the air gap at the same altitude, respectively. The average breakdown voltage gradient of the gap has a good linear relationship with the flame height. Comparing the DC breakdown voltage between the pine crib fire and crown fire, the influence of the difference in flame characteristics between the temperature and height of the flame zone on the insulation strength of the gap is weaker than the influence of the difference in the characteristics of the smoke particles in the smoke zone on the insulation strength of the gap. The results could provide guidance for risk assessment of short-circuit breakdowns on transmission lines under forest fire conditions.