A New Insight into Discharge Ablation Mechanism of Buffer Layer in High Voltage Power Cable

In recent years, discharge ablation failures of buffer layer in crosslinked polyethylene (XLPE) cable are becoming the main threat for the reliability and the safety of the electrical grid system. However, the discharge ablation process mechanism is controversial. In this paper, the discharge ablation mechanism of buffer layer in high voltage power cable was systematically studied from both the thermal and electrochemical perspectives. The results showed that the discharge ablation product of the buffer layer was mainly made up of NaHCO3, Na2CO3 and trace Al2O3 and Al(OH)3. The main ingredients of the water blocking powder, sodium polyacrylate (PAANa), did not degrade at normal operating temperatures. However, with the help of water, electrochemical decomposition of PAANa molecule occurred under the action of electric field with a relatively low intensity, and some parts of -COONa or -COO- could cleaved from the PAANa backbone, forming CO2 and NaHCO3. The existence of the high-resistance NaHCO3 could bring out the high heat in the local regions of the buffer layer, resulting in the discharge ablation of the buffer layer of XLPE cables. To prevent discharge ablation failures, the buffer layer must be kept as dry as possible.