Effects of electric field distribution and water drop ejection on flashover of icicles in plane-to-plane gaps

Ice morphology was established from field failure observations on electrical insulators, considering partial and full bridging conditions. Small scale laboratory simulations showed an important effect of droplet ejection on the probability of flashover. During the experiments, factors including applied water conductivity, icicle length, combinations of air gap and icicle length and duration of melting period were investigated using typical in-service stress levels. According to the experimental results, applied water conductivity and icicle length affected the residual ice layer resistance. Flashover voltage decreased by 33% as the conductivity increased from 150 μS/cm to 750 μS/cm and reduced by 10% as icicle length declined from 6 to 4 cm for constant 2-cm air gap. Fully bridged icicles required extra energy for ice melting, leading to higher flashover voltage compared to partially bridged icicles of the same morphology. A single 3-cm air gap had 14% higher flashover voltage than a pair of 1.5 cm air gaps.