Breakdown of air at elevated temperatures

Abstract

High- and medium-voltage systems operating in extreme industrial environments require optimized dielectric insulation to ensure safety and equipment reliability. While traditional research focuses on room-temperature standards or pressurized gases like SF6, establishing guidelines for unsealed equipment demands a deeper understanding of atmospheric air under severe thermal stress.
To address this gap, this thesis evaluates the dielectric breakdown strength of air at elevated temperatures using a dedicated high-temperature test setup. Designed to simulate open, unsealed operational environments, the setup reaches temperatures up to 800 degrees Celsius and measures precise breakdown voltages up to 70 kV peak for inter-electrode gap distances up to 8 cm. Experimental results showed that across the tested temperature ranges, dielectric breakdown was predominantly density-related. Furthermore, combining elevated temperatures with variations in electrode shape and gap distance mostly did not produce any distinctive additional effects, proving that geometric field stress profiles remain largely invariant under thermal scaling. Finally, a finite element modelling methodology in COMSOL Multiphysics has been described that evaluates localized electric field and thermal distributions. Based on the electrode geometries and empirical breakdown measurements, estimations are made on localized peak electric field strengths at discharge initiation. Simulations show that COMSOL accurately calculates electric field strengths, proving that combining numerical modelling with high-temperature experimental findings provides a highly useful and reliable approach for determining the breakdown strength of high-voltage configurations in extreme-temperature environments.