DC breakdown characteristic on LDPE/MgO nanocomposite influenced by DC prestress

To understand the space charge formation of low-density polyethylene (LDPE)/nano-sized magnesium oxide (MgO) nanocomposite materials, the breakdown strength and the space charge formation influenced by DC prestress were investigated. DC breakdown strength (Fb) of LDPE decreased with increase of DC prestress. A packet-like charge was observed under DC pre-stress. When the applied field turned to a ramp field from a constant field, the space charge decreased with incase of applied field. A packet-like charge, enhancing the local filed in bulk, might bring to many dissociated carrier. Therefore, it was considered that DC-Fb of LDPE decreased with increase of DC pre-stress field because bulk of LDPE became more conductive condition by generation of a packet like charge. On the other hand, DC-Fb of LDPE/MgO nanocomoposite increased with increase of DC pre-stress field. In case of MgO content of 1 phr, a packet-like charge was not observed under DC pre-stress field and a little positive space charge was formed in the bulk The positive charge decrease gradually with increase of ramp filed. When the MgO content was 5 phr, little space charge was observed under DC constant or ramp fields. The MgO nanofiller may trap the space charge, and the homo space charge in the vicinity of electrodes suppressed the carrier injection.