Effect of Mechanical Stress on Electrical Tree Degradation Characteristics of Polypropylene Cable Insulation at Low Temperature

Polypropylene（PP） insulation represents the primary development direction for thermoplastic high voltage（HV） cable insulation materials. HV cables are subjected to mechanical stress during production, installation, and operation, while PP exhibits poor toughness at low temperatures. Therefore, it is essential to study the effects of mechanical stress on PP-based insulation materials under low-temperature conditions. The effect of mechanical stress at low temperatures on electrical tree degradation characteristics of PP/POE blended insulation is investigated. The results indicate that volume conductivity significantly increases with the tensile ratio at low temperatures, with lower temperatures causing more obvious conductivity increases. Additionally, mechanical stretching leads to a reduction in AC breakdown strength, with the deterioration of breakdown characteristics being particularly notable at lower temperatures. As the tensile ratio increases and the temperature decreases, the microstructure of the material is damaged more seriously, resulting in intensified electrical tree growth and partial discharge characteristics. The electrical tree in the sample with a 15% tensile ratio at-40 ℃ exhibits the most significant deterioration, with its morphology transitioning from a branch-like structure to a bush-branch-like structure. In conclusion, the insulation properties of PP/POE blended insulation in their glassy state at low temperatures are more vulnerable to mechanical stress.