Pascal Ortega

Influence of negative ions on the humidity effect on the first corona inception

The first corona inception in a divergent electric field is affected by atmospheric parameters. The effect of humidity is a little-debated question and a summary review is first proposed in this paper. Then we present experimental results performed in two different high voltage laboratories. Those two laboratories are located at different latitudes (Germany and northern Argentina) in order to put in evidence the effect of humidity on the inception voltage. At high humidity levels, the standard deviation of the probability distributions is clearly reduced whereas the influence of humidity upon the mean values is made up by quite a large discrepancy in the data. Nevertheless, the critical volume model allows the experimental probability distributions to be calculated with the proviso that the negative ion density directly involved in the primary electron production rate is field dependent and not constant as previously assumed. The calculations show that the total negative ion density is exponentially linked to the humidity.

Charge–voltage relationship of the first impulse corona in long airgaps

This paper investigates the relationship between the charge Qi of the first impulse corona and the associated inception voltage Ui for a1 m point–plane airgap submitted to impulse voltages. Experimental studies under both polarities are reported; the Qi–Ui characteristics obtained allow empirical quadratic relationships between these two quantities to be derived. A physical interpretation is proposed by considering the established characteristics of the first impulse corona. The Gauss and Amp` laws can be applied and the quadratic Qi–Ui relationship is justified by the present model.

Impulse breakdown voltages of air gaps: a new approach to atmospheric correction factors applicable to international standards

In the design of high-altitude high-voltage transmission systems and in the optimization of the reliability of power sources in aeronautical environments, it is important to have reliable data concerning the effect of air density and humidity on reducing air insulation performance under local conditions. This is helpful also in the modeling of discharges and lightning in mountainous regions. This paper describes a systematic laboratory investigation of the combined effects of humidity and gas density on the breakdown strength of a 0.2 m rod/plane air gap that is subjected to positive-polarity lightning impulses, using a test chamber to reproduce the conditions commonly found in such regions. The results show that there are appreciable deviations between the measured humidity and air density correction factors and those of the 1973 and 1989 IEC Standards when extended to low air density. The paper proposes the adoption of a radically different correction procedure, based upon the influence of density and humidity on streamer propagation field, and including the effect of the high gradient in the anode region.

Generalization of the quadratic charge-voltage relation of impulse corona in air

On the one hand, a quadratic relationship between the charge Qi of the first corona and the associated inception voltage Ui has been recently put in evidence for a 1m point-plane air gap submitted to impulse voltages. On the other hand, different models have been proposed to evaluate that relation for coaxial geometries and conductor-plane also submitted to impulse voltages. The aim of this paper is to put in evidence the quadratic charge-voltage relations for all the configurations and to discuss how the assumptions made for one configuration can be exported to the other electrodes geometries.