Water Tree Growth Characteristics in XLPE Power Cable Insulation

In order to understand the growth characteristics of water tree, by combining the morphological changes of water tree in XLPE cables with COMSOL model simulation, we studied the growth characteristics and development rules of water tree in different periods. Water-needle electrode method was used to obtain cable samples of different ageing stages, and a microscope was used to observe the microscopic morphology. Based on changes in morphology and growth rate of water tree, the development of the ventilated water tree was divided into three stages: initial stage, stagnation stage, and follow-up stage. IR and SEM physicochemical analyses were used to illustrate the difference between the stagnation and initial stages. Moreover, we constructed a COMSOL simulation model of three stages, and analyzed and explained the growth of water trees through the simulation results. The results shows that water tree growth appears to exist simutaneously-straight growth along the direction of the electric field lines and intra-regional growth. During the three stages, the branches of water trees are few and develop rapidly in the initial stage; in the stagnation stage, for the electric field change in the water tree region and the water droplets becomes larger, the growth rate of water trees slows down along the electric field lines and the density of the water tree becomes larger, gradually forming a fan-shaped area; the water tree forms a new branch again due to the electric field distortion points in the follow-up stage. The stagnation stage and follow-up stage will alternate until the cable insulation is fully bridged. © 2019, High Voltage Engineering Editorial Department of CEPRI. All right reserved.