Solid insulation materials are the backbone for all kinds of outdoor insulation applications. Environmental stresses degrade every outdoor insulation material with the passage of time. Internal partial discharges and external surface tracking are the two major factors governing the health of outdoor insulation. Best outdoor insulation is the one having lowest level of partial discharge and highest resistance to tracking. Improvement in tracking resistance of polymeric insulation materials has been a concern of many researchers. This study investigates the improvement in partial discharge and tracking resistance of LDPE under the effect of three different nano fillers including SiO 2 , TiO 2 , TiO 2 @SiO 2 . A very little has been reported on the effect of these nano fillers on the tracking performance of LDPE. TiO 2 @SiO 2 is a novel core-shell nano filler. No study has reported the effect of these core-shell nano fillers on the partial discharge and tracking performance of LDPE. It has been observed in this study that core-shell nano fillers are much more efficient in improving partial discharge and tracking resistance of solid insulation materials than ordinary nano fillers.

In last two decades a promising performance improvement in the electrical insulation materials has been reported by many researchers using different nano fillers (NFs). In recent years another type of NFs called core-shell type nano fillers have shown even more attention than ordinary NFs. The coreshell NFs are a combination of nano particle core coated with outer nano layer of different material. The core-shell NFs combine the beneficial properties of two material with in one NF. Recently a few studies have reported a considerable improvement in the dielectric properties of epoxy by utilising TiO 2 @SiO 2 core-shell NFs. The TiO 2 @SiO 2 particles have a core of TiO 2 coated with an out layer of SiO 2 at nano level. This study investigates the improvement in tracking performance of silicone rubber (SiR) using TiO 2 @SiO 2 core-shell nano particles which has not been reported previously. The tracking immunity of low (below 1%) and high (above 1%) filler concentrations of nano TiO 2 @SiO 2 incorporated into SiR was investigated according to IEC 60587. The results showed that an optimum percentage of 0.6 wt% of TiO 2 @SiO 2 imparts best immunity to silicone rubber against tracking.