Field and temperature dependent conductivity of syndiotactic polypropylene effect of temperature and electric field

Syndiotactic polypropylene (s-PP) is an extrudable polymer with properties which should make it highly suitable as high voltage cable insulation, including high AC breakdown strength, flexibility and a high melting point. However, for HVDC applications it is important to improve the knowledge of charge transport phenomena which control the field distribution. This paper presents electrical conductivity measurements performed on Rogowski shaped test objects and model cable. The polarisation and depolarisation currents were measured at the temperatures 60, 80, 100, and 120 °C with an applied electric field varying from 6 to 20 kV/mm. The electrical conductivity was calculated based on the quasi-steady polarization current. The field dependence of the conductivity was found to be non-linear for the entire field range. The temperature dependence for Rogowski shaped objects with painted silver electrodes followed an Arrhenius law with activation energy of approximately 1.68 eV, which is similar to values reported for XLPE. For model cable with polymeric semi-conductive electrodes the average activation energy was also 1.68 eV. In addition the estimated conductivity was also fitted to the Poole-Frenkel and hopping conduction mechanisms.