G. Bacchiega

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 Crystal Ball Gazing with Electrostatic Precipitators: V-I Curves Analysis

Have you dreamed about knowing what happens inside an electrostatic precipitator (ESP) without opening it? Well, the main defects can be revealed using voltage — current curves. When the unit is operating, it is impossible to intervene in the electrofilter. Many parameters can be used to demonstrate an increase in dust emission levels which might result in a malfunctioning of the ESP itself or of other components of the unit. When the external elements of the electrostatic precipitator have been eliminated, attention can be focused on the Electrostatic precipitator itself. If a diagnosis can be performed “in state” before shutting down the unit, valuable gains can be made in time and efficiency during the maintenance operation. V-I curves constitute an invaluable aid, indeed, they are the signature of the ESP itself and are more precise than the maximum recorded voltage and current points. The voltage-current curves were obtained in experimental pilot conditions and in an industrial situation to demonstrate the four main defects most commonly encountered in ESP. the fouling of the emissive wires; the misalignment of plates and wires; insulators problems; the presence of back-corona.

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.