The urgent need to decrease greenhouse gas emissions and enable clean energy transition has driven the power industry to seek compact and eco-friendly solutions for power transmission. Gas Insulated Switchgear has been a key technology in this regard, using Sulphur Hexafluoride gas as an insulating medium. However, is a potent greenhouse gas with high global warming potential, necessitating the search for more environmentally friendly alternatives.
Siemens Energy has proposed "Clean Air" as a substitute for inside high voltage. Clean Air, also called Synthetic Air is a homogeneous mixture of 80% N2 and 20% O2. However, due to its lower electrical strength compared to SF6, the GIS design with Synthetic Air as the insulation gas requires optimization and newer insulation techniques to maintain compactness and reliability.
The goal of this thesis is to analyse the breakdown strength of Synthetic Air as a substitute for SF6 inside the High Voltage GIS and examine the performance of its breakdown strength with dielectric coatings on the surface of the electrodes.
Initially, experimental studies were conducted to investigate the breakdown strength of Synthetic Air under various pressure ranges. Comparisons with compressed air reveal that Synthetic Air demonstrates similar electrical breakdown strength.
Next, the study focused on understanding the influence of dielectric coatings on the breakdown behavior of Synthetic Air for applications in GIS. Methodical optimization of coating thickness and air gap distance were done to effectively minimize the electric stress inside the air gap. The test setup was designed with electrodes coated with neat epoxy and the AC breakdown tests were performed. Compared to the uncoated electrodes, the coated electrodes showed significant improvement in breakdown strength.
Though the coated electrode did not breakdown at the voltage at which the uncoated electrodes broke down, with higher voltages, a new phenomena of surface flashover was observed. The observations of surface flashovers across the dielectric coatings demonstrated the ability of these flashovers to travel longer distances at remarkably low voltage ranges. This research concluded by postulating two hypotheses to explain the observed surface flashover phenomena. These hypotheses were researched and analyzed using FEM simulations and experimental investigations.