Aging and lifespan prediction of busbar connection in GIS: a detailed study in SF6 free dry air atmosphere

This study investigates the aging behaviour of copper busbar connections in SF6-free Gas Insulated Switchgear (GIS). Driven by environmental concerns related to use of SF6 gas, the long-term performance of these connections under dry air with high oxygen levels was evaluated through extensive aging tests. Conducted in a specially designed tank, the tests simulated real-world thermal stresses and oxygen interaction with busbar surfaces. Different bolted connections, including bare silver-plated copper busbars, were studied. Oxygen diffusion is one of the major causes that can lead to degradation of current carrying joints. Therefore, oxygen diffusion within the busbars was monitored and analysed from surface to depth before and after thermos-oxidative aging. A non-steady state diffusion prediction model was used. Experimental results were compared with mathematical modelling to assess the effect of oxygen diffusion. Results indicated that even though oxygen diffusion significantly impacts the surface condition and microstructure of the material post-aging, the performance of electrical joints in the experiment did not degrade due to oxygen diffusion in both bare and silver-plated copper connections. This was validated through temperature rise, conductivity, and resistance measurements. The predictive model provides valuable insights for GIS using dry air as an insulating medium. The study shows that long-term oxygen diffusion in copper and silver does not create detrimental effects, as diffusion is restricted to the surface, preserving bulk material properties.