Optical Imaging-Based 3D Reconstruction of Electrical Tree in Polypropylene Cable Insulation Under Mechanical Bending

This study proposes a nondestructive optical imaging-based three-dimensional (3D) reconstruction method to analyse electrical tree propagation in polypropylene (PP) cable insulation under mechanical bending. The technique combines focus-stacked optical imaging with a feature fusion algorithm to segment in-focus regions across depth layers, enabling 3D reconstruction of electrical trees in PP homopolymer (PPH), block copolymer (PPB) and elastomer-blended (PP/TPE) samples. The results demonstrate that mechanical bending accelerates electrical tree propagation in PPH, and that degradation channels transition from a branch-like to a straight-stick morphology, tending to grow directionally towards stretched regions. With a bending radius of 10 mm, the breakdown time drops from 297.0 min for the undeformed samples to 6.3 min. PPB and PP/TPE delay the time to breakdown by 70.6% and 171.2%, respectively, highlighting their superior resistance under bending stress, which is attributed to maintaining elasticity rather than yield deformation under bending stresses. This study provides a novel tool for evaluating the electrical tree resistance of PP composites under the mechanical stress, guiding the development of recyclable high-voltage direct current cable insulation.