Insight into the new role of titanium isopropoxide catalyst on rejuvenation for water tree aged cables

In this paper, a new role of titanium isopropoxide (TIPT) catalyst is revealed on rejuvenation of water tree aged cables, and TiO₂ inorganic particles are found in the water tree voids after injecting a rejuvenation fluid. Through analyzing the products of TIPT hydrolysis, the nano-scale TiO₂ particles are observed. This proves that the hydrolysis reaction of TIPT can generate the TiO₂ particles. Furthermore, a water tree accelerated aging system with a needle electrode is used to obtain water tree in cross-linked polyethylene (XLPE) cable samples. The water tree aged samples are injected with a fluid including a siloxane and TIPT for rejuvenation, and the breakdown voltage of the injected samples is significantly higher than that of the water tree aged samples. By use of a scanning electron microscope (SEM) and energy disperse spectroscopy (EDS), some agglomerated TiO₂ particles are found in the water tree areas of the injected samples. Also, the TiO₂ particles are observed inside the breakdown channels of the injected samples. This indicates the TIPT can react with water in water tree and form the TiO₂ gel to fill water tree voids. Because of the filling effect of inorganic TiO₂ particles, the breakdown strength of the rejuvenated cables can be improved, which possibly suppresses the damage generated by the partial discharge inside the water tree.