Charge transport and space charge dynamics in EPDM/2D-nanoclay composite dielectrics

Composite dielectrics with two types of 2D-nanoclays (i.e., Kaolinite and Talc) incorporated in ethylene propylene diene monomer (EPDM) as the polymer matrix exhibit distinctly different electrical performances for high-voltage direct current (HVDC) cable insulations. This study investigated electrical conductivity and space charge as the key electrical characteristics of DC cable insulation in conjunction with dielectric spectroscopies. The findings of this study revealed that the composite dielectric with Talc 2D-nanoclays significantly suppressed space charge and thus minimized electric field distortion to less than 9% under 20 kV/mm at both measured temperatures of 25 °C and 50 °C with thermal gradient. In addition, the activation energy of electrical conductivity for the composite dielectric with Talc 2D-nanoclays is 0.45 eV which is notably lower than that of the composite dielectric with Kaolinite 2D-nanoclays, 0.95 eV. Based on the experimental results, the microstructural characteristics of composite dielectrics were discussed to provide insights into charge transport and space charge dynamics in the composite dielectrics. The charge transport mechanism attributed to the electronic and ionic conduction was explained, and the reasons for space charge accumulation were discussed. The larger interfacial area of 2D-nanoclay particles, the uniform and oriented distribution of 2D platelet-like nanoclay, and the smaller difference between the bandgap of polymer and 2D-nanoclay particles contribute to controlling the charge transport and suppressing the space charge accumulation in the composite dielectrics. Charge dynamics from the dielectric spectroscopy based on the Dissado-Hill model analysis confirms the explained mechanism.