Influence of internal residual mechanical stresses on local dielectric strength of EHV extruded XLPE cables

Internal residual mechanical stresses are not uniformly distributed in the cable insulation and form so-called flow patterns or frozen-in stresses. EHV cable samples were analyzed with respect to residual stresses, local breakdown strength and electrical treeing properties. Photoelastic observations have been carried out on the cable samples to investigate quantitative residual stresses. Breakdown strength, electrical tree inception voltage and tree propagation corresponding to the typical regions of the flow pattern have also been investigated and analyzed using Weibull distribution.