Treeing modeling and the effect of rejuvenation fluid in aged XLPE power cables based on the finite element method

This article examines vented-type water tree and electrical tree in an XLPE-insulated cable, as well as the effect of rejuvenation fluid on the medium-voltage 20 kV XLPE cable insulation. Initially, laboratory specimens are placed under a scanning electron microscope and imaged to determine the dimensions and characteristics of water treeing and electrical treeing. Then, these specimens are immersed in the rejuvenation fluid, and their dielectric properties are evaluated over a 1-month period. The obtained results are analyzed using COMSOL Multiphysics software, and the outputs are discussed and examined. The initiation of vented-type water tree and its growth from a water filled cavity near an impurity was studied by building electric field simulation model and finite element analysis. The moisture in environment is gathered at the impurities or defects of cable insulation and the water filled cavities are formed under the action of alternating Maxwell stress. Although the field around the water tree is relatively low, if the cable is subjected to high stress (such as lightning strikes), the field at the ends of the cavities can intensify even further. In such cases, it can lead to the formation of electrical tree that can cause the XLPE breakdown. Therefore, stopping the growth of water trees and controlling them can be crucial for improving the electrical performance of water tree aged cables. One way to control water trees is by injecting a rejuvenation fluid into the cable (rejuvenation technique). The main components of the rejuvenating fluid include siloxanes and catalysts that react with water molecules and form oligomers, filling the water tree areas. This chemical reaction decomposes water molecules, leading to improved insulation performance. The objective of this article is to study the initiation of water tree and investigate the intensified electric field around vented-type water tree and how it can lead to electrical tree, as well as the role of the rejuvenation material in improving cable performance.