Modelling of negative breakdown streamer in topologies with air/dielectric interfaces

The stable operational performance of high voltage power and pulsed power systems requires coordination of insulating topologies which include gas (air)/ solid dielectric interfaces. One of the straight-forward approaches to such insulation coordination is the analysis of the electrostatic field distribution and minimisation of the field strength in critical regions including triple points. However, this static approach does not take into account breakdown and transport characteristics of gases such as ionisation and attachment, the mobility of charge carriers, their concentration and dynamics. Also, in the electrostatic approach, the polarity of the applied voltage does not affect the field magnitude, thus there are no polarity effects in the Laplacian electrostatic models.
A number of publications have reported on the development of breakdown streamer models based on the Poisson equation, the charge continuity equations for positive and negative ions and electrons. In such approaches, ionisation and attachment coefficients for specific gas(es) are used to model the development and propagation of the breakdown streamer(s).
The work presented in this paper is focused on the development of the streamer breakdown model in air in topologies which include air/solid dielectric interfaces using COMSOL Multiphysics. The model is tested using a standard negative point-plane configuration, which allow the Paschen curve to be obtained and compared with the typical Paschen characteristic(s) of air available in the published literature.
The investigation explores the breakdown characteristics of several practical topologies which include air/solid dielectric interfaces with dielectric materials of different permittivities (from 2 to 10) and at different air pressures (up to 5 bar). The results obtained and the model which has been developed can be used for optimisation and insulation coordination in power and pulsed power high voltage systems.