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.

Crosslinked polyethylene (XLPE) has a successful history as a cable insulation material. Nevertheless, in recent years, as environmental awareness has grown, concerns about the ease with which it can be recycled have emerged. Although technologies have been developed for XLPE recycling, this report concentrates instead on the development of a thermoplastic alternative. Specifically, a 20 : 80 blend of high density and low density polyethylene (HDPE : LDPE) was selected and subjected to a non-isothermal crystallization procedure. It was found that, provided the cooling rate falls between 0.5 and 10 K min -1 , the blend exhibits superior breakdown strengths and high temperature mechanical stiffness compared to XLPE. A trial cable was then extruded from this blend using such a cooling rate. The breakdown behavior of the morphologically-designed cable was finally compared with that of LDPE and XLPE reference systems.

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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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