Study on Storage Activity of Cross-Linkable Polyethylene Material Used for High-Voltage Cables

Cross-linked polyethylene (XLPE) is widely used as insulation material in high-voltage cables. Impurities, moisture, microvoids, extrusion technology, and other factors all have an effect on insulation properties. However, the primary of this article focus is the self-decomposition characteristic of the cross-linking agent in the cross-linkable polyethylene during the storage process. In general, cross-linkable polyethylene used for 220-kV power cables must be manufactured to cable within one year. However, no studies have been conducted on the performance and stability of cross-linkable polyethylene and its usability during the long-term storage process. As a result, an accelerated storage experiment is carried out in this article to simulate the long-term storage of the cross-linkable polyethylene at room temperature. The electrical and mechanical properties of XLPE samples made from the cross-linkable polyethylene with different equivalent storage times are then measured. The storage activity refers to the activity of dicumyl peroxide (DCP) acting on the properties of the cross-linkable polyethylene after long-term storage because the DCP will be decomposing slowly over time. The result shows that, as storage time increases, the storage activity of the cross-linkable polyethylene decreases due to the gradual decomposition of cross-linking agents in granules. When the XLPE is made from cross-linkable polyethylene stored for an extended period, the cross-linking degrees decrease, and mechanical properties deteriorate significantly. Long-term storage, on the other hand, aids in the improvement of crystal structures and, to some extent, increases ac breakdown strength. The final XLPE properties still meet the Chinese National Standard after one-year storage of the cross-linkable polyethylene. After two years, the thermal extension property, i.e., the elongation under load, is close to the requirements of the Chinese National Standard. However, after five years, the thermal elongation property has degraded to the point where it is no longer acceptable.