Cause Analysis and Improvement of Bulging in Medium-Voltage Cross-Linked Polyethylene Insulated Cables

Bulging phenomenon in medium-voltage cross-linked polyethylene insulated cables was investigated, focusing on its impact on operational safety and service life. A systematic analysis was conducted from multiple aspects, including insulation material formulation, degassing process, copper tape tension control, optimized wrapping tape structure, and cable sealing process. It was found that bulging was primarily caused by the accumulation of internal gases due to factors such as excessive or unevenly dispersed crosslinking agent, insufficient degassing, overly tight shielding layer wrapping, and improper sealing design. Gel rate tests and thermogravimetric experiments were carried out. Results was verified that increasing degassing temperature to 80 °C and extending degassing time to 48 h significantly could improve degassing effectiveness. After process improvements were implemented, no bulging was observed in cables exposed to outdoor conditions for over six months, confirming that the proposed measures could effectively enhance cable reliability.