Effect of charge transport on electrical degradation in polypropylene/organic molecular semiconductor composites for HVDC cable insulation

Polypropylene is considered to be the material of choice for environmentally friendly high voltage direct current cable insulation. The high power transmission of electrical energy exposes insulating materials to high temperatures and electric fields, resulting in the degradation of material properties. This paper reports that organic molecular semiconductors with strong electron affinity can effectively modulate electrical properties of polypropylene. The charge injection and transport process are analyzed by considering a combination of relations describing various conduction models in dielectrics, including the Richardson-Schottky (RS) emission and the hopping conduction. Based on the performed experiments, a modified Wiesmann-Zeller (WZ) model is proposed to simulate the electrical treeing process of polypropylene. The electrical treeing results are well verified with the simulation results, which offer a valuable tool for further analysis of the effect of intrinsic barrier height, hopping distance, and activation energy on the electrical degradation in the material. This work provides an insightful analysis of multiple charge transport mechanisms affecting the electrical degradation of the polymer, which is crucially essential for the rational design of high-performance insulation materials.