Characteristics of periodic grounded DC tree in high voltage DC cable nano-composite insulation under different temperatures

A new high voltage DC cable insulation material, based on cross-linked polyethylene(XLPE) and containing 0. 5wt% nano-MgO, was developed independently. In order to investigate the characteristics of grounded DC tree and its influencing factors in this material under different temperatures. Periodic grounded DC tree experiments were conducted on this material and a commercial grade high voltage DC cable insulation material at 20~80℃ under different polarities and different voltage amplitudes. The results show that electron is easier to be injected than hole, and has larger mean free path in material, so the negative tree is easier to generate, and grows more dispersedly. The addition of nano-MgO increases the trap density in material, and weakens charge injection, so the nano-MgO/XLPE insulation material shows a better resistance to electrical tree. The increase of temperature enhances the charge injection and detrapping, and improves the electron mean free path and charge distribution uniformity, making the electrical tree easier to generate and propagate, and denser in shape. Thus it can be seen that the change of voltage polarity and temperature, and the addition of nano-MgO all have effect on the initiation and growth of periodic grounded DC tree. © 2016 Chin. Soc. for Elec. Eng.