A Macroscopic Inception Criterion for the Upward Leaders of Natural Lightning

The increased use of electronic equipments in day-to-day life as well as the steady increase in the height of the structures have considerably increased the lightning threat. As a result, a suitable lightning protection system has become very essential. For a reliable evaluation of the protection efficacy the process involved with the final bridging needs to be accurately ascertained. This requires tracing of the inception as well as the propagation of the upward connecting leaders from both the protection system as well as the structure being protected. Owing to the complexity of the problem, only the macroscopic models seem to be practical. As a first step in this direction, the present work has developed a model capable of ascertaining the inception of the upward leaders from both the air termination network as well as the structure itself. In this, the discharge activities around the prospective inception regions are represented by a corona envelope, which is followed by a streamer. Using the works based on the long air-gap switching surge breakdown experiments it is shown that the streamer in the model must attain a critical length for the inception of a leader. This critical length is shown to be sensibly independent of gap-geometry and the electrode radii when varied below the critical radii. The applicability and the stability of the model is demonstrated with a few salient examples.