Anne Bondiou-Clergerie

Fundamental processes in long air gap discharges

The development of atmospheric lightning is initiated and sustained by the formation in virgin air of ‘streamer corona’ and ‘leader’ discharges, very similar to those observed in laboratory long sparks. Therefore, the experimental and theoretical investigations of these laboratory discharges have become of large interest to improve the physical knowledge of the lightning process and to develop self-consistent models that could be applied to new protection concepts. In the present paper the fundamental processes of the subsequent phases of long air gap discharges are analyzed, from the first corona inception and development to the leader channel formation and propagation. For all these processes simulations models are discussed that have been essentially derived and simplified by the authors, in order to develop sequential time-dependent simulation of the laboratory breakdown, with both positive and negative voltages. The possibility of extending these models to the case of natural lightning is discussed in the companion paper, presented in this same volume. To cite this article: I. Gallimberti et al., C. R. Physique 3 (2002) 1335–1359.

A simplified model for the simulation of positive-spark development in long air gaps

This paper presents a new modelling of positive-discharge development, based on new simplifying assumptions. It presents these assumptions, which are deduced from the existing theoretical models and concern mainly the coupling between the leader corona and the corona region. This model has been validated through the comparison of simulations with experimental results in the reference configuration of a rod - plane gap subjected to various positive impulse voltages. It has also been used to simulate the discharge behaviour with perturbations of the applied potential form.

The lightning swept stroke along an aircraft in flight. Part I: thermodynamic and electric properties of lightning arc channels

During a lightning strike to an aircraft in flight, the lightning channel becomes deformed in the airflow and displaced along the aircraft, a so-called swept stroke. The deformation and the displacement are caused by the interaction between the aerodynamic flow and the plasma properties of the channel together with the properties of the surface. The main part of the lightning current is a continuous current with a magnitude of hundreds of amperes and a duration of hundreds of milliseconds. The objective of this article is to analyse the properties of the lightning channel during this continuous current phase in order to parametrize them; this parametrization is used in a companion paper (Larsson et al J. Phys. D: Appl. Phys. 33 1876-83) for complete swept-stroke simulations. A model of the thermodynamic evolution of a lightning channel during its continuous current phase is developed and numerically solved. In this model, the channel is assumed to have axial symmetry. A quantitative analysis of the influence of failing axial symmetry is also included. The main conclusions are that the steady-state conditions are rapidly reached and that the channel can be considered to be a free-burning arc subjected to increased thermal losses due to transverse aerodynamic flow.

Numerical modelling of inhibited electrical discharges in air

The inhibited discharge is a discharge in which the input of energy into the discharge channel is limited by the presence of a large series resistance in the external circuit supplying the discharge current. One situation in which such a discharge occurs is in outdoor high-voltage insulation systems when the system is subjected to rain. The inhibiting resistance is caused by layers or runnels of water on the insulators surface. This paper concentrates upon the numerical modelling of the inhibited discharge. The core of the modelling is the interaction between the discharge itself and the external circuit which supplies the discharge current. Physical models of the corona streamer development, the propagation of the streamer-leader system and the final jump were used for the calculation of the discharge current. The calculations show that propagation of the streamer is not influenced by a large series resistance, whereas the propagation of the streamer-leader system and the final jump may be significantly inhibited.

The lightning swept stroke along an aircraft in flight. Part II: numerical simulations of the complete process

During a lightning strike to an aircraft in flight, the lightning channel gets deformed in the airflow and displaced along the aircraft, a so-called swept stroke. The deformation and the displacement are caused by the interaction between the aerodynamic flow and the plasma properties of the channel together with the properties of the surface. We give a theoretical analysis and a numerical modelling of the swept-stroke processes. Some numerical simulations of the swept stroke are presented and the results are compared with existing experimental data with satisfying agreement.

New Investigations of the Mechanisms of Lightning Strike to Radomes Part I : Experimental Study in High Voltage Laboratory

The main purpose of the experiments described here is the analysis of the mechanisms of radome protection with lightning diverters of various types and sizes. A high voltage arrangement and associated diagnostics have been implemented to perform a quantitative study of the inception and propagation mechanisms of the corona and leader discharges that precede the final breakdown. It is shown that ambient humidity plays a significant role on the discharge process and that the nature of the discharge initiated from the strip is very different depending on the strip type. Segmented strips are more likely to allow energetic discharges to propagate from an internal antenna leading to radome puncture.

New investigations of the mechanisms of lightning strokes to radomes. Part II : Modeling of the protection efficiency

Experimental studies of the mechanisms of lightning strokes to radome have shown that the protection efficiency can be related to the ability of diverter strips to initiate stable leaders before inception of energetic discharges take place inside the radome. A model based on a 3D code for electric field calculation is used to compute the threshold of these different processes and deduce the optimum strip height for a given internal electrode configuration. The results of this model are successfully compared to experimental estimation of optimum protection.