Numerical Analysis of a Continuous Vulcanization Line to Enhance CH4 Reduction in XLPE-Insulated Cables

Herein, we apply a computational diffusion model based on Fick’s law to study the manner in which a cable production line and its operating conditions can be enhanced to effectively reduce the CH4 concentration in cables insulated with cross-linked polyethylene (XLPE). Thus, we quantitatively analyze the effect of the conductor temperature, curing tube temperature distribution, transition zone length, and online relaxation on CH4 generation and transport during the production of 132 kV cables with an insulation thickness of 16.3 mm. Results show that the conductor temperature, which is initially controlled by a preheater, and the curing tube temperature distribution considerably affect the CH4 concentration in the cable because of their direct impact on the insulation temperature. The simulation results show 2.7% less CH4 remaining in the cable when the preheater is set at 160 C compared with that when no preheater is used. To study the curing tube temperature distribution, we consider three distribution patterns across the curing tube: constant temperature and linear incremental and decremental temperature. The amount of CH4 remaining in the cable when the temperature was linearly increased from 300 to 400 C was 1.6% and 3.7% lower than in the cases with a constant temperature at 350 C and a linear temperature decrease from 400 to 300 C, respectively. In addition, simulations demonstrate that the amount of CH4 removal from the cable can be increased up to 9.7% by applying an elongated and insulated transition zone, which extends the residence time for CH4 removal and decelerates the decrease in cable temperature. Finally, simulations show that the addition of the online relaxation section can reduce the CH4 concentration in the cable because the high cable temperature in this section facilitates CH4 removal up to 2.2%, and this effect becomes greater at low production speeds.