Controlling Factors of Degassing in Crosslinked Polyethylene Insulated Cables

Abstract

Here, we analyze the degassing process of a byproduct (methane) formed during the peroxide-induced crosslinking of polyethylene. A diffusion model based on Fick’s law is used to obtain the controlling factors of degassing in a crosslinked polyethylene (XLPE) insulated power cable (132 kV with 18 mm of insulation). We quantitatively analyze different scenarios of the diffusion of methane through the XLPE insulation and two semiconductor layers under various in situ degassing conditions. The analyzed degassing conditions include heat transfer and its effect on the diffusion properties, the different transport and boundary conditions due to the free spaces within the cable conductor, and the nonuniform distribution of methane concentrations within the insulation layers. Our simulation results clearly demonstrate that the free spaces between the copper strands in the cable conductor significantly affect the degassing efficiency. However, the temperature-diffusion coupling has a relatively minor effect on the overall degassing efficiency due to the rapid temperature increase of the polymer layers during the initial stages of degassing. Moreover, we find that the nonuniform distribution of methane in the initial stages also plays an important role in degassing in the cable, but this effect varies significantly during the degassing process.

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

“…Cross-linked polyethylene (XLPE) is one of the most popular insulation materials for producing power cables due to the exceptional electrical properties, production efficiency, and resistance to chemicals, moisture, and temperature [ 1 , 2 , 3 , 4 , 5 ]. To manufacture and apply XLPE for cable insulation, dicumyl peroxide (DCP) is commonly used as a cross-linking initiator of polyethylene (PE) due to its relatively fast decomposition rate at typical cable manufacturing temperatures, especially in the curing tube [ 4 , 6 ]. However, the production of XLPE also causes obvious issues regarding the creation of its byproduct such as methane (CH ), acetophenone (AP), and cumyl alcohol (CA) (See Figure 1 ).…”

“…To properly remove such byproducts from the cables, a thermal treatment process, namely byproduct degassing, becomes increasingly important. The byproduct transport phenomenon during the degassing was analyzed experimentally [ 12 , 13 , 14 , 15 , 16 , 17 ] and numerically [ 1 , 4 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Among the studies, Youn et al [ 4 ] found that the initial concentration distribution plays a crucial role in determining the degassing efficiency, and the distribution is majorly based on the cable production phase called the continuous vulcanization (CV) process.…”

Numerical Study of CH4 Generation and Transport in XLPE-Insulated Cables in Continuous Vulcanization

“…In the cable industry, this cross-linking reaction typically uses peroxide as a reaction initiator. Dicumyl peroxide (DCP) is one of the preferred initiators due to its relatively fast decomposition rate at normal cable processing temperatures [3]. Figure 1 illustrates the PE cross-linking reaction scheme using DCP as an initiator.…”

“…In the degassing process, the cable is placed in a degassing chamber and the chamber temperature is typically controlled to around 70°C to facilitate byproduct removal from the power cable. This process is expensive and time consuming, and is considered to be a critical bottleneck for cable production, especially for HV and EHV power cables, which generally have thicker insulation [3].…”

“…Several studies have been performed, either experimentally [7][8][9][10][11][12] or numerically [1,3,[12][13][14][15][16][17]] to better understand byproduct transport and removal during the degassing process. The initial distribution of a byproduct in a cable, which depends on byproduct generation and transport during cable production, has been shown to affect the degassing process [3]. Several studies have simulated cable production conditions [18][19][20][21]; however, these studies have focused only on simulating the temperature and cross-linking completion during cable degassing.…”