There is much interest in the development of replacement materials for crosslinked polyethylene (XLPE) that are both recyclable (i.e. thermoplastic) and capable of high temperature operation. Thermally, polypropylene is the ideal choice, although its stiffness and low electrical breakdown strength make for a challenging materials design problem. We report here on the compositional optimization of a propylene homopolymer/propylene-ethylene copolymer blend in terms of its dynamic mechanical properties and thin film electrical breakdown strength. The extrusion of a trial minicable using the optimized blend is also discussed, which is shown to exhibit a significantly improved electrical performance, as gauged by its DC breakdown strength, than an XLPE-insulated reference.
Two polyethylene and two polypropylene blends crystallized under non-isothermal conditions were compared to a crosslinked polyethylene (XLPE) reference material. Selected blends contained a gelation agent, which forms a network structure within the material. Compared to XLPE, the blends offered higher melting points, reduced electrical conductivity, increased electrical breakdown strength, improved space charge performance and enhanced thermo-mechanical stability. Additional improvements in space charge behavior were also noted in systems containing the DBS gelation agent. The ability to provide recyclable insulation materials capable of operating at much higher temperatures than XLPE, combined with enhanced dielectric properties, may prove advantageous to cable manufacturers, particularly in renewable energy applications.
Abstract-Crosslinked polyethylene (XLPE) has been the cable insulation material of choice in many different transmission and distribution applications for many years and, while this material has many desirable characteristics, its thermomechanical properties have consequences for both continuous and emergency cable ratings which, in turn, have implications for system operational flexibility. In this paper, we describe the principles and two embodiments through which new thermoplastic insulation systems can be actively designed with improved electrical and thermo-mechanical properties for use in cable applications. First, a blend system based upon high density (HDPE) and low density polyethylene (LDPE) is considered, before comparable principles are applied to combinations of polypropylene grades. In both cases, a suitable formulation is first developed through laboratory testing of film and plaque specimens, before a mini-cable is produced and tested.
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