Investigation of the dependence of DC insulation resistivity of ultra-clean polyethylene on temperature and electric field

The present work aims at determining the dependence of the dc insulation resistivity on temperature and electric field for a super-clean low density polyethylene (LDPE) used in manufacturing modern high voltage ac cables. Resistivity measurements were made using relatively thick (- 2 mm) samples at different temperatures and dc electric fields. Based on the present experimental data, a mathematical model for the relationship between the insulation resistivity ofthe polymer, temperature and electric field was determined using: i) computer curve fitting techniques, ii) Artificial Neural Networks (ANN) method. Comparison between the present results and previous measurements, using less clean grades of LDPE, indicates that the inherent dependence of the dc insulation resistivity of LDPE on temperature and electric field has not been appreciably improved by using an ultraclean polymer. It is concluded that the successful utilization of LDPE for HVDC cables will require the modification of such dependence.