Comparative analysis of impacts of discrete droplets versus continuous streams on discharge characteristics at various electrode distances

Accumulated rainwater may form discrete droplets or continuous streams, both of which degrade the electrical insulation performance of outdoor equipment. The distinct effects of discrete droplets and continuous streams on the gap discharge characteristics remain unreported. Using a customized rod–plane short air gap (25–70 mm) alternating current discharge experimental platform, this study systematically investigates the modulation mechanisms of droplets and streams, along with their distinct electrohydrodynamic and morphodynamic behaviors, at various electrode distances. Increasing the initial velocity of the rainwater induces a droplet-stream transformation, with both droplet formation and phase transition, which accelerates the decay rates of the critical discharge voltage (Vc) and breakdown voltage (Vb). For gaps smaller than 47.5 mm, rainwater droplets/streams attain their maximum length (Lmax) under the critical discharge conditions, before contraction precedes complete breakdown. The Lmax values of water streams substantially exceed the droplet dimensions, corresponding to reductions of 51.8% and 38.5% in Vc and Vb, respectively. Droplets transition from spherical to pear-shaped before elongating into bar-like structures under maximum stretching during critical discharge, whereas streams maintain stable bar-like profiles. Conductivity variations induce nonmonotonic Lmax behavior, with an initial increase in 37.0 ± 3% before declining with rising conductivity, whereas the discharge voltage decreases proportionally before stabilizing above 3000 μS/cm. When the electrode distance exceeds 47.5 mm, stream disintegration occurs before the critical discharge. Intensifying the applied voltage reduces the stream length, diminishing the morphological distinctions between droplets and streams until the discharge voltages converge at a gap distance of 70 mm (±5% variation).