The importance of morphology on electrical strength of LDPE/XLPE insulations

An attempt was made to change the morphology of LDPE/XLPE (low-density polyethylene/cross-linked polyethylene) by several methods, and the impulse breakdown strength IBDS of the samples was investigated. It was found that the thermal procedure which effectively changed the morphology of polypropylene did not alter the morphology of LDPE/XLPE significantly; consequently, IBDS was not influenced in this way. Monoaxial and biaxial mechanical stretches of XLPE resulted in a certain alteration of the morphologies of these samples. IBDS was enhanced during these stretches. Removal of the lower-molecular portion from the LDPE matrix produced an increase in density and enhanced IBDS for the resultant LDPE. This suggests that this removal would give a compactly arranged amorphous region for LDPE, and that the amorphous part in LDPE may play the predominant role in electrical breakdown phenomena