12. XLPE-Based Products Available in the Market and Their Applications

Today, power cables use primarily solid extruded insulation compounds of polyethylene in its cross-linked form. Thermoplastic polyethylene was first used, but quickly evolved into longer lasting cross-linked materials. In North America, high molecular weight polyethylene (HMWPE) was also used with poor results. For medium voltage cables, either cross-linked polyethylene (XLPE), ethylene propylene rubber (EPR), or polypropylene (PP) are used as insulation for medium voltage cables. For high and extra high voltage cables, mainly XLPE is used. This chapter will describe the differences that exist in commercially produced polyethylene, specifically high-pressure, low-density polyethylene (LDPE), since this is most commonly used in power cable applications as the base resin. Understanding the differences between the two production methods that are used to produce LDPE, that is the autoclave and the tubular reactor, may clarify the influence of material properties on cable performance, especially cleanliness. This polymer, LDPE, is then further processed to produce XLPE. On the other hand, EPR is produced in a different way and afterwards compounded as cable insulation. At the beginning of this century, PP was introduced as an insulation compound for medium voltage cables and has recently seen equal market share with XLPE in several countries. With PP, the final formulation is produced during the cable production process. Further investigations are currently underway using other polymers such as POE or PB-1 for medium voltage applications. PP is currently used up to 150 kV for AC cables and has passed Type and PQ testing for 600 kV DC cables. This chapter presents the differences between cable compounds and examines the specific features of individual XLPE compounds that are currently available on the market. In addition, details will be presented on the application of different polymers that are currently used for the semi-conductive layers as part of the cable insulation system.