Effect of Cumylalcohol in XLPE on Space Charge Formation and Electric Breakdown under DC High Electric Field

For an insulation layer of a DC power transmission cable, space charge properties of various insulating materials have been investigated using pulsed electro acoustic (PEA) method. Especially, cross-linked polyethylene (XLPE), which has an improved heating resistance by forming a bridge between molecular chains of low density polyethylene (LDPE), is expected to be applied to the insulating layer of the cable. So, the insulating performance of XLPE under high DC stress is important. In the bulk of XLPE layer for power cables, there remain some chemical residues of crosslinking by-product such as acetophenone, alpha-methylstyrene, and cumylalcohol. Such residues are thought to affect the breakdown strength and space charge behavior in the insulating layer under dc high electric field. Therefore, we have examined the effect of each remaining chemical by-product in LDPE under dc high electric field. In this report, to investigate the effect of cumylalcohol, one of cross-linking by-product, on space charge formation and electric breakdown characteristics in XLPE, we tried to observe the space charge accumulation in XLPE with cumylalcohol under very high dc stress. As the results, it is found a curious and quite interesting space charge formation. In the material, an apparent backward flow of a negative packet-like charge against the electric field is observed. The performance of the packet-like charge is like a "Pororoca" in Amazon River. Furthermore, the relatively low dc breakdown strength was observed in the material. It seems to be a certain relationship between the "Pororoca" and the lower breakdown strength. In this report, the curious phenomena is mainly introduced.