Some fundamentals on treeing breakdown in inorganic-filler/LDPE nano-composite material

A nano-composite material of magnesium oxide (MgO) added to a low-density polyethylene (LDPE) was subjected to electrical tree breakdown investigation. The LDPE without nano-fillers was lower in breakdown voltage than the LDPE added with nanofillers. The breakdown voltage was increased by increase of nano-filler concentrations in LDPE. This result much coincided with the result on tree inception voltage which was increased when the concentration of filler in LDPE was increased. It is considered that fillers would create such an obstruction to the tree bridging the counter electrode. However, even the tree had bridged the counter electrode; the breakdown was not always immediately to occur. There would be so-called timelag between "bridging" and "final breakdown". The time-lag to breakdown was increased with the nanofiller concentrations in LDPE. It is considered that the polymer nano-composites are more resistive against partial discharges than their base material.