Polycyclic Compounds Affecting Electrical Tree Growth in Polypropylene Under Ambient Temperature

Polypropylene (PP) has great potential to be used as recyclable high-voltage direct current (HVDC) cable insulation material. Electrical tree is the key factor that leads to cable insulation failure and limits the increase of HVDC transmission voltage level. In this study, three different polycyclic compounds, namely 4,4'-bis(dimethylamino)phenylazo, 2-hydroxy-2-phenylacetophenone and 4-phenylbenzophenone, are added into PP matrix with the addition content of 0.1 wt%. The electrical treeing experiments are conducted under impulse superimposed DC voltage at 30, 70 and 90 °C. Then the polycyclic compound with the best effect on inhibiting electrical tree is selected, and its filling ratio is further changed from 0.1 wt% to 0.3 wt% to get the optimal inhibition effect. It is found that the addition of 2-hydroxy-2-phenylacetophenone can inhibit the electrical tree degradation. However, the addition of 4-phenylbenzophenone and 4,4'-bis(dimethylamino)benzene will increase the electrical tree length and accumulated damage. As the content of 2-hydroxy-2-phenylacetophenone increases, the electrical tree length and accumulated damage decrease firstly, and then increase. The effect of polycyclic compounds on the electrical tree degradation is affected by the relative polarity of impulse superimposed DC voltage and temperature. The experimental results reveal that adding 0.1 wt% 2-hydroxy-2-phenylacetophenone polycyclic compound to PP can effectively inhibit the electrical tree degradation, which has great potential for application in recycle HVDC cables.