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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.

This paper presents a dielectric simulation approach for predicting withstand voltage of air insulated power devices. The paper gives an overview of typical evaluation procedures for the basic discharge stages including inception, streamer propagation and leader transition. For selected test arrangements, we compare the results of lightning impulse tests with simulations. The simulations utilize a new approach that combines the well-established empirical procedure with numerical computations for arbitrary geometries. We introduce a new formulation for evaluation of saturation charge density, which enables a revision of the streamer inception conditions due to surface charging and an estimation of the leader transition characteristics including the surface capacitance.

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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