Abstract
This study presents an experimental methodology to investigate interfacial electrical treeing at solid-solid interfaces under AC voltage stress. Using coplanar needle electrodes combined with full-frame imaging and partial discharge (PD) detection, the influence of contact force (150 – 350 N), surface roughness (grit sizes #180-#2000), and sanding direction on tree inception and growth was systematically examined for a silicone rubber (SiR)-epoxy interface. Rough surfaces sanded with grit sizes #180 and #320 caused flashover before treeing could initiate, whereas smoother surfaces prepared with #500 and #1000 grit promoted stable tree growth. Using #500 and #1000 grit sandpapers, single-branch tree structures were observed at contact forces of 150 N and 350 N, while branch-bush structures emerged at 250 N. Tree growth time to reach 80% of the gap exhibited a non-monotonic trend, peaking at intermediate force (mean 132 min at 250 N) and significantly decreasing at higher force (mean 50 min at 350 N). This phenomenon is attributed to higher inception voltages and stronger tip fields at elevated contact forces, promoting faster, predominantly single-branch propagation with fewer interruptions.