Upward leader inception criterion considering gas kinetic process and heat conduction

Modelling of upward leader inception is important for calculating lightning shielding failure rates of transmission lines. The leader inception model proposed by Gallimberti I. has been widely adopted for about 30 years and applied in the analysis of unstable upward leader inception. However, the gas kinetic process and heat transfer via conduction are not considered in this model. Theoretical analysis and simplified simulation show that the gas density variation and heat conduction cannot be neglected. In this paper, the gas kinetics and heat conduction have been considered, and a simplified one-dimensional thermofluid dynamics (1D-TFD) model has been proposed as an upward leader inception criterion. A Mach-Zehnder interferometer was set up to observe the gas density variation in leader channel and the channel expansion. Experimental results indicate that the gas density reduction in leaders is significant, and the calculation of the channel diameter expansion has a good agreement with that obtained by experiments.