Sandwiched structure effect on space charge characteristics of alumina/polyethylene nanocomposites

In the recent decades, the phenomena of space charge accumulation in the high voltage direct current (HVDC) insulation have been attracted more attention. In this paper, the novel sandwich-structured low-density polyethylene (LDPE) nanocomposites filled with nano-sized Al
₂
O
₃
particles were prepared by layer-by-layer hot pressing method. For comparison, the homo-dispersed LDPE composites with nano-Al
₂
O
₃
were also prepared. Morphology, breakdown strength, space charge distribution and electrical conductivity of the specimens were investigated. Morphologies of the composites were characterized by scanning electron microscopy (SEM), and their space charge profiles were measured by pulsed electro-acoustic (PEA) method. SEM images showed that there are no obvious interfaces between the adjacent layers. The breakdown strength of the sandwich-structured LDPE nanocomposites is higher than that of the homo-dispersed ones. Besides, the charge profiles indicated that space charge suppression of the sandwich-structured LDPE composites was better than that of homo-dispersed ones. Under the electrical field of 50 kV/mm at 70°C, the conductivity of homo-dispersed nanocomposite almost approaches to 1.0 × 10
^-11
S/m, which is almost four-fold over that of 1%N/LDPE/1%N (i.e, 2.5 × 10
^-12
S/m). It was concluded that the excellent electrical insulating properties of the sandwich-structured nanocomposites were attributed to the traps existing on the interfaces, which could effectively inhibit the charge injection.