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

To understand the space charge formation of low-density polyethylene (LDPE) / nano-sized magnesium oxide (MgO) nanocomposite materials, the space charge and the conduction current were simultaneously measured up to the breakdown under increasing DC ramp field. A negative charge was dominated in the sample without nanofiller (0 phr sample). A positive charge was dominated in nanocomoposite sample. The field increment (= the maximum field - the average field) of the 0 phr sample increased with increasing average field and then was saturated with many small rises and falls and finally 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. The conduction current of 0 phr sample and 5 phr sample increased monotonically with increase of the average field. The conduction current of the 1 phr sample showed great increase under one average field, and the field increment at the average field turned to decrease. From these results, it was considered that the homo space charge effect at the anode brought by charge trapping effect of MgO nanofiller controlled the space charge formation and the space charge influenced to the conduction current under a high field.