Space charge formation and conduction current of MgO/LDPE nanocomposite under DC ramp field

To understand the space charge formation of nano-sized magnesium oxide (MgO)/low-density polyethylene (LDPE) nanocomposite materials, the space charge and the conduction current up to the breakdown has been investigated under increasing DC ramp field. A negative charge was dominated in the 0 phr sample. A positive charge was dominated in nanocomoposite sample. The field increment (= the maximum field - the average field) of the 0 phr increased with increasing average field and then was saturated with a few rises and falls before the breakdown. In the 1 phr sample, after showing the peak, the field increment turned to decrease with further increase of the average field. In the 2 phr and more, the clear decrease of the field increment was not observed due to a few positive charges. The conduction current of 0 phr sample and 5 phr sample increased monotonically with a increase of the average field. The conduction current of the 1 phr and the 2 phr showed great increase under one average field. From these results, it was considered that the homo space charge effect at the anode brought by charge trapping effect of MgO nano-filler controlled the space charge formation and the space charge influenced to the conduction current under a high field.