We study positive streamers in air propagating along polycarbonate dielectric plates with and without small-scale surface profiles. The streamer development was documented using light-sensitive high-speed cameras and a photo-multiplier tube, and the experimental results were compared with 2D fluid streamer simulations. Two profiles were tested, one with 0.5 mm deep semi-circular corrugations and one with 0.5 mm deep rectangular corrugations. A non-profiled surface was used as a reference. Both experiments and simulations show that the surface profiles lead to significantly slower surface streamers, and also reduce their length. The rectangular-cut profile obstructs the surface streamer more than the semi-circular profile. We find quantitative agreement between simulations and experiments. For the surface with rectangular grooves, the simulations also reveal a complex propagation mechanism where new positive streamers re-ignite inside the surface profile corrugations. The results are of importance for technological applications involving streamers and solid dielectrics.

We investigate the propagation of positive streamers along a profiled dielectric surface in air at atmospheric pressure. Results from experiments and two-dimensional planar low-temperature plasma fluid simulations are presented and analysed. The test object consists of a disk-shaped high voltage electrode and a dielectric slab with 0.5 mm deep corrugations. The corrugated surface has a 47% larger surface area than the smooth reference surface. The experiments and simulations are performed at voltage levels that lead to either gap-bridging or arrested streamers. In both experiments and simulations, the streamers take a longer time to reach the ground electrode when propagating along the profiled surface than along the smooth reference surface. Also, arrested streamers stop closer to the high voltage electrode when a profiled surface is used. Streamers propagate closely along the surface profile in the simulations, which suggests that the observed surface profile effect is mainly a result of elongated streamer channels. Compared to the streamers propagating along the smooth surface, the elongated streamers on the profiled surface have less residual voltage at the streamer front to drive the streamer advancement.

Streamer behaviour near dielectric surfaces is an important characteristic of air-solid electrical insulation systems. Accurate predictions are important for dielectric design, but dynamic aspects such as surface charging during streamer propagation are not well understood. A drift-diffusion model is used here to simulate positive streamer behaviour in non-uniform fields. The 2D-planar simulation domain includes air gaps between a tip of a HV electrode and a dielectric barrier laying on a grounded plane. The resulting surface charge distributions approach saturation charge conditions, i.e. zero normal electric field on the air side of the boundary. Such charging behaviour was also reported in lightning impulse (LI) experiments. The simulations are also aligned with empirical streamer propagation range estimates. It is demonstrated that saturation charge levels are reachable within a few tens of nanoseconds of exposure to positive streamer channels. Ion drift is shown to be the dominating mechanism of surface charging during positive streamer propagation, although photoemission also plays an important role. Discharge suppression by streamer-deposited surface charge is also demonstrated. Furthermore, the influence of back discharges at the LI tail on the surface charge distribution is shown. Simulating realistic streamer surface charging behaviour with arbitrary electrode and dielectric shapes is an important step toward first principles discharge prediction models.

Surface charge on dielectric surfaces can alter the field conditions of insulation systems substantially. In this work, lightning impulse experiments are compared with a simulation model for surface charging in rod-barrier-plane geometries. The model is based on the saturation charge assumption, i.e. zero normal electric field in air pointing onto the dielectric surface, which prevents further charging. This hypothesis holds well for most geometries, as long as there are no leader discharges or restrikes (also known as back discharges). Restrikes are discharges that occur on the lightning impulse tail when the active electrode is close to zero potential. A method is proposed to compute the charge distribution after a restrike. Furthermore, the model can predict discharges on both sides of the barrier. Saturation charge fields can be computed efficiently, so the results are encouraging for dielectric design applications. This is the accepted version of an article published in

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