交联聚乙烯电缆绝缘材料长时挤出焦烧特性近似模拟实验研究

Manufacturing large lengths of high-voltage submarine cables requires cross-linked polyethylene (XLPE) insulation to be extruded continuously over long periods of time. However, problems such as premature cross-linking and scorching can occur during this process. Furthermore, effective simulation methods for scorching are lacking, as is research into the changes in the structure and properties of XLPE insulation materials during the scorching process. For this reason, this paper proposes simulating the scorching phenomenon during the long-term extrusion of XLPE insulation materials using a screw extruder with multiple extrusion cycles. The effect of scorching on XLPE insulation structure and properties is investigated by comparing the chemical structure, crosslinking degree, oxidation induction period, thermal properties, crystallisation behaviour, mechanical properties, and dielectric properties of two XLPE insulations after different numbers of extrusion cycles. The mechanical properties of crosslinked insulation materials were found to deteriorate significantly at high temperatures after scorching. The dielectric constant increased and the DC breakdown strength decreased by around 10%, while the AC breakdown strength remained relatively stable. Crosslinking exothermic curves of different extruded batches of insulation materials were tested by DSC. Combined with the results of the OIT test, it was found that, after cyclic extrusion at 132℃, the content of the crosslinking agent and antioxidant in the insulation materials decreased significantly, but the gel content increased only slightly, stabilizing at around 2%. The reduction in the cross-linking agent means that the crosslinking network of the XLPE specimen remains relatively sparse, even after complete cross-linking at high temperatures, resulting in deterioration of its mechanical properties at high temperatures. Infrared spectroscopy shows that, with an increase in the number of extrusions, the carbonyl content of the A and B insulation materials increased. An increase in polar groups, such as carbonyl, and impurities will decrease the dielectric properties of the insulation materials and cause them to appear yellow. This paper compares the structural changes and performance differences of insulation materials in different extrusion batches and draws the following conclusions: (1) The cyclic extrusion method of the screw extruder can simulate the scorching phenomenon of XLPE insulation material and distinguish the scorching resistance performance of different grades of insulation material. The scorching process is dominated by the formation of weak local cross-linking. After continuous extrusion of the insulation material, the gel content of the scorching product fluctuates around 2%, which is close to the gel content of the scorching product in factory production. (2) Scorching of cable insulation materials leads to an uneven cross-linked network structure in XLPE insulation, an increase in weak connection areas and defects, and changes in crystalline structure. Under prolonged high-temperature conditions, XLPE insulation materials consume cross-linking agents and antioxidants at different rates. XLPE insulation materials with slower antioxidant consumption rates exhibit superior scorching resistance performance. (3) As scorching severity increases, XLPE insulation material gradually turns yellow, accompanied by an increase in carbonyl content. After high-temperature crosslinking, the cross-linked network becomes sparser, resulting in a significant decline in the high-temperature mechanical properties and DC breakdown resistance of XLPE insulation. However, AC breakdown resistance has not decreased.