Unveiling Thermal Degradation and Fire Behavior of 110 kV Ultra-High-Voltage Flame-Retardant Cable Sheath After Thermal Aging

To evaluate the fire safety of 110 kV ultra-high-voltage flame-retardant polyvinyl chloride (PVC) cables in the service process, the effects of thermal aging on the pyrolysis and combustion behavior of the cable sheaths were studied using thermogravimetric (TG), limiting oxygen index (LOI), UL-94 vertical burning, cone calorimeter, open flame, and muffle furnace tests. The results showed that thermal aging causes a slight decrease in the LOI value of the cable sheath (28.3% vs. 28.5%), but it also passed the UL-94 V-0 test. The butane torch test showed that the cable sheath was more easily ignited after aging; however, a better char layer was formed in the later stage of burning, which led to a longer failure time. Interestingly, the aging treatment prolonged the ignition time of the cable sheaths and reduced the peak heat release rate (pHRR) and total heat release (THR) by 17.5% and 24.4%, respectively, in the cone calorimeter test, indicating that aging resulted in a reduction in the fire hazard of the cable sheaths. Moreover, aging mechanisms were proposed based on the composition and structural evolution of the cable sheaths. In summary, this work comprehensively evaluated the fire hazard of 110 kV ultra-high-voltage cables and provided theoretical support for the formulation improvement, durability enhancement, and fire protection design of cable sheath materials.