Abstract
This study examines the effect of severe mechanical bending on the AC breakdown voltage of Polypropylene Thermoplastic Elastomer (PP-TPE) cable insulation. AC breakdown tests were conducted on 30 kV PP-TPE cables bent around a 50 mm diameter cylinder which stands for a bending radius of 0.71 times the cable diameter. This induced up to 47% longitudinal strain in the insulation, well beyond the 20% yield point. Weibull analysis revealed a reduction in characteristic breakdown voltage from 303 kV (unbent) to 268 kV (bent), corresponding to a 12% reduction. Optical microscopy of the insulation at the breakdown site showed breakdown channels surrounded by electrical trees and stress-whitened material, indicating a coupling between mechanically induced stress whitening and electrical failure mechanisms. Although the sharp bending, far beyond the recommended maximum, introduced stress whitening and reduced the breakdown voltage, the reduction in breakdown stress was significantly smaller than previously reported for XLPE cables.