2D Fluid Simulations of the Interaction Between Streamers and Dielectrics: Characteristics of Surface Charge

Charges accumulating on the surface of insulators under dc voltage are regarded as potential hazards for HVDC apparatus. Here, we investigate the surface charge characteristics due to streamers interacting with dielectrics, including inception beside the dielectric, attaching to and propagation over the dielectric surface. The numerical model is based on the Afivo-streamer code1, and extended to include dielectrics2. Surface charge is calculated by summing up the electron and ion fluxes at the interface. For positive surface discharges, positive charge accumulates on the dielectric around streamer heads. But the amount of charge is quite small, even with secondary electron emission (caused by ions and photons) with a coefficient of up to 0.5. On the other hand, when the positive surface streamer is long enough, the electric field behind the head returns to a lower level, electrons diffuse back to the dielectric, thus, the surface charge becomes negative. For negative discharges, electrons attach to the dielectric surfaces, surface charge is negative, and the amount of charge can be dozens of times higher than for positive surface discharges. The maximum negative surface charge is present near the streamer head.