Air density influence on the strength of external insulation under positive impulses: experimental investigation up to an altitude of 3000 m a.s.l

Abstract

This paper summarizes the research carried out to investigate the dependence of the strength of external insulation on air density, with particular reference to positive polarity impulses, generally of major interest for design and testing.New tests were carried out up to an altitude of about 3000 m a.s.l., with particular attention to the influence of air density on the strength and on the discharge process.It was found that, for positive switching impulses, the variation of the breakdown voltage with air density is more marked at lower density values. This trend is not fully taken into account by current correction methods.A refined correction approach is proposed to account for the above mentioned aspects, with special attention to high altitudes.

Proposal for a General Atmospheric Correction Method of Breakdown and Withstand Voltages of Air-Gap Insulated Configurations Based on a Streamer–Leader Differentiated Model of the Breakdown Process

“…were conducted [13,14]. The results provided SI-specialized variants of m(G) and m(G, δ), through which the correction of switching impulse voltage can be adequately applied in a range of 0.7…”

“…The dependence of m(G, δ) on electrode configuration could be quantified using an empirical approach in [13], and a verifying, analytical determination in [14]. Using the gap factor K of Equation (11) (confer Appendix B.2), the configuration can be considered.…”

“…This is achieved by correcting the co-ordination withstand voltage of equipment U cw using Equation (13).…”

“…Until today, measurements have shown that air density is the atmospheric parameter with the highest impact on the breakdown voltage. Thus, in some publications, the influence of air humidity is neglected (e.g., [13,14]) (confer Appendix B.1).…”

“…For some basic configurations, first qualitative findings on the behavior and ratio of the streamer and leader lengths were gathered (illustrating the atmospherically dependent changes of the ratio between the streamer and leader parts) [13,21].…”