Space charge suppression in environment-friendly PP nanocomposites by employing freeze-dried MgO with foam nanostructure for high-voltage power cable insulation

摘要

Space charge accumulation along insulation thickness is still regarded as a critical issue during the operation of high-voltage direct current transmission cables, which will result in the distortion of the partial electric field, seriously causing the degradation or aging of the main insulation. Polypropylene (PP) environment-friendly thermoplastic cables without cross-linking have shown great potential, which tend to gradually substitute the traditional unrecyclable extruded cross-linked polyethylene cables. Here, the styrene-ethylene-butylene-styrene block copolymer is selected to optimize the mechanical properties of PP. An extremely small amount of MgO with a foam nanostructure synthesized through a designed freeze-drying process is introduced to suppress the accumulation of space charge and further improve the electrical properties of PP insulation. With a very low concentration of foamed MgO (0.2 phr), it is found that the injection and accumulation of space charge could be largely suppressed under 60kV/mm and the DC conductivity of PP composites remains as low as similar to 1.6x10(-15) S/m. Besides, the DC breakdown strength of the composites is up to 315kV/mm. Therefore, the PP-matrix composites can be considered as potential high-performance insulating materials in the non-cross-linking environment-friendly thermoplastic high-voltage power cable.