Space charge characteristics of LDPE nanocomposite/LDPE insulation system

Two kinds of insulation systems with nanocomposite have been fabricated by co-pressing low-density polyethylene (LDPE) and nano-titania doped LDPE (TiO₂-LDPE) films. The three-layer systems considered are TiO₂-LDPE/LDPE/TiO₂-LDPE (namely, NLN) and LDPE/TiO₂-LDPE/LDPE (namely, LNL). Space charge distributions under different applied electric fields were measured by the pulsed electro acoustic (PEA) method. The charge transport characteristics and the interface space charge formation as well as the effect of nano-TiO₂ concentration have been systematically discussed. The results show that heterocharges and homocharges are formed at the LDPE/TiO₂-LDPE polymer interfaces in the system NLN and LNL, respectively. The nature of the interfacial charge has been explained in term of the interfacial polarization theory combined with conductivity and permittivity of the materials. Additionally, the recombination between charges influences the amount of the interface space charge. However, the NLN system always stores more charges than LNL, which was explained by the change of the effective electric field caused by the formation of the interface space charges. The results obtained would provide experimental support for optimizing high voltage direct current power cables.