Space Charge Characteristic of Nano-composite Film of MgO/LDPE under DC Electric Field

This paper deals with the effect of magnesium oxide (MgO) nano-filler to stabilize internal electric field under DC voltage application. A low-density polyethylene (LDPE) film containing the MgO nano-filler (nano-composite film) was subjected to space charge measurement by applying DC voltages. The pulsed electroacoustic method was employed for the measurement. In addition, conduction current under the corresponding conditions was measured and correlated with the space charge evolution.

When the average DC field was as low as 80 kV/mm, very little space charge was observed with the “non-filled" film, whereas a positive space charge was observed with “filled" film. The density of the positive space charge in the vicinity of the anode was higher compared to that in the bulk. The more distant the position from the anode, the lower the charge density. The conduction current under the same condition was found to be lower with higher content of the MgO nano-filler. The conduction current determined by the space charge in the vicinity of the anode was calculated for the specimen with each content of MgO nano-filler, and good agreement between the estimated current and the measured one was found. It is concluded that the MgO nano-filler seems to trap the positive space charge in the vicinity of the anode and suppresses conduction current by reducing the local field at the anode.