Simulation of electrical trees in XLPE cable insulation and electric field analysis

Abstract

To understand the non-breakdown phenomenon during the accelerating electrical tree ageing in cross-linked polyethylene (XLPE) cable insulation, the non-breakdown mechanism of electrical tree is investigated in this study. The needle electrodes were inserted into the cable insulation samples to accelerate electrical tree ageing. The electrical trees which were not broken down had a larger expansion range and branch density. Referring to the actual cable slice for the internal structure of the sample, the electrical tree model with different number of tree channels was built. The correspondence between electric distortion and the number of tree channels was discussed. According to the calculation of the electric field distribution by the finite element method, the results showed that the electric field strength at the tip of electrical tree was reduced when the number of channels was increased. Compared with the single electrical tree channel, when the insulation was completely carbonised in the electrical tree region the electric field strength at the tip of electrical tree was reduced by 20.8%. The electric field shielding which was formed by the tips of electric trees could reduce the electric field strength at the tip of the tree and it could result in the formation of the non-breakdown electric tree.

Keywords

• XLPE insulation
• finite element analysis
• electric fields
• trees (electrical)
• power cable insulation
• ageing
• electric breakdown
• ekectric field shielding
• finite element method
• electrical distortion
• needle electrodes
• electrical tree region
• single electrical tree channel
• electric field strength
• electric field distribution
• tree channels
• electrical tree model
• cross-linked polyethylene cable insulation
• accelerating electrical tree ageing
• nonbreakdown electric tree