In order to explore the method of improving the DC dielectric properties of crosslinked polyethylene for HVDC cable

a small amount of nano-TiO

2

（0.1%

0.5%

1%） were added into the crosslinked polyethylene matrix for DC cable using the melt blending method. The effect of surface modification on the dielectric properties of XLPE/TiO

2

was studied. Moreover

the dispersion of TiO

2

was observed by SEM

and the crystallinity

the conductivity at different tempera

tures

space charge injection characteristics and DC breakdown field strength of XLPE and XLPE/TiO

2

nanocomposites were tested. The results show that surface modification can improve the TiO

2

nanoparticle dispersion

the addition of nano-TiO

2

to XLPE for DC cable can increase the crystallinity

conductivity activation energy and DC breakdown field strength

reduce the conductivity and suppress the injection of positive charges

and surface modification using a coupling agent can make these effects more significant. It is suggested that the nanoparticles act as nucleating agents

leading to the increase of crystallinity

and the coupling agent modification made the particles and matrix more close to further increase the crystallinity. The improvement of conductivity and space charge characteristics is mainly due to the effect of interaction area formed by nano-TiO

2

and the morphology on the trap characteristics. The increase of conductivity activation energy measured at lower field strength corresponds to the increase of deep trap energy

so the charge injection is significantly inhibited. The introduction of charge traps also decreases the conductivity with the increase of particle content. The DC breakdown field strength can be increased by the morphology and the trap characteristics. Therefore

adding 0.5% nano-TiO

2

into crosslinked polyethylene material for HVDC cable can further improve the DC dielectric properties

and the coupling agent modification will make the improvement more significant.