Abstract
The propagation of a positive streamer and its basic mechanisms are analysed in order to find the conditions that an equivalent simplified model must satisfy. Considering the energy balance in the development of secondary avalanches around the streamer tip, an equivalence criterion is derived and used in the formulation of a single-avalanche model. This model reproduces the streamer propagation through a series of successive equivalent avalanches which develop in front of the streamer tip. A number of computer programs have been prepared in order to calculate macroscopic measurable quantities. A first comparison between experimental and computed results shows a satisfactory agreement.