PFAS-Free Ablative Insulation for Circuit Breakers

Polytetrafluoroethylene (PTFE) is a critical element of gas breaker insulation due to its tendency to ablate into an insulating gas rather than char and degrade. However, PTFE is a type of per-and polyfluoroalkyl substance (PFAS), materials which are gradually being phased out due to environmental and health concerns. This has led to a series of replacements which are themselves PFAS materials and thus also concerning. As such, it is critical to find PFAS-free alternatives for PTFE in this application, particularly ones that replicate its ability to ablate and form a quenching vapor. Here, alternatives for PTFE insulation for switchgears were investigated for their thermal and electrical stability. The materials of choice were Delrin, Nylon, and LDPE. In this work, these commercially available materials were studied as a baseline for future work involving a chloro-polymer-based composite material. Thermal stability was examined via thermogravimetric analysis (TGA) and electrical stability was examined via arc tracking resistance measurements. Delrin behaved the most similarly to PTFE in terms of arc tracking by not charring, though it was much less thermally stable, degrading at much lower temperatures. Additionally, these alternative polymer materials were directly compared to PTFE and an alumina reference in a small-scale ablation test. Delrin ablated the most readily under these conditions and had multiple ablation events from a single arc. It also caused the largest increase in arc voltage due to the insulating gas it generated, making it the most effective at absorbing the arc's energy.