A Study on Acoustic Emission Signal Feature Extraction with Varying Radii of Curvature of Tree Needle Tips in Epoxy Resin

In this study, epoxy resin samples with four types of tree needle electrode curvature radii (1, 5, 40, and 100 μm) were fabricated. To investigate the electrical degradation process, tree image signals were captured using a microscope under an applied voltage of 18kV at 60Hz from tree initiation through progression to final breakdown. Concurrently, partial discharge (PD) occurrences and the corresponding acoustic emission (AE) pulse waveforms were measured using AEwin software. A larger radius of curvature (r) indicates a blunter tree needle tip, which theoretically decreases the maximum electric field intensity at the tip. Experimental results using the fabricated samples confirmed that as the radius of curvature increased (1→ 5→40→100μm), the time to tree breakdown significantly increased. Furthermore, a larger radius of curvature prolonged the initial tree inception time, whereas a smaller, sharper radius shortened it. The AE signal data, generated by the propagation of AE pulses from the PD source, was analyzed. By utilizing the AE waveform amplitude and pulse counts, distinctive signal features were extracted for each degradation stage: tree initiation, progression, pre-breakdown, and breakdown. These features effectively enable the characterization and analysis of the insulation degradation state and its underlying mechanisms.