Dielectric response of sPP and XLPE insulations at high temperatures and electric fields

An attractive application for polypropylene is as high voltage AC or DC cable insulation. The main driving force for using polypropylene is the simpler production technique avoiding degassing treatments, as well as the higher melting temperatures compared to the conventional cross-linked polyethylene (XLPE) Large spherulites are not formed in sPP insulations making this insulation particular attractive. The dielectric response has been measured using miniature cables in frequency domain, using a method based upon measurements of capacitance and dielectric loss. The cables were energized up to 20 kV in the frequency range of 10 mHz to 100 Hz in the temperature range of 30 to 130 °C. It is shown that sPP has significant lower dielectric losses than XLPE and is less sensitive to water absorption in the low frequency regime. However, both insulations showed no field or temperature dependence of the losses close to power frequency.