Abstract
Cross-linked polyethylene (XLPE) cables are widely used for AC transmission. However, for DC tranmlssion, they are still under feasibility study due to severe concern about space charge. In the bulk of XLPE insulated cables, there remain chemicals such as acetophenone. We have examined the influence of acetophenone on the space charge evolution in PE. The samples tested are additive-free LDPE and LLDPE sheets. Two types of specimens were examined. The first one is a two-layered specimen consisting of a non-treated sheet and an acetophenone-soaked sheet. The second one is a LDPE or LLDPE sheet, onto which a few drops of acetophenone were spilt so that the sample surface was coated with acetophenone. The important conclusions obtained are as follows:(1) Positive charges are easy to migrate from the acetophenone-existing region to the non-existing region in the case of LDPE, while negative charges are difficult. (2) Both positive and negadve charges are rather immobile in LLDPE, and they tend to accumulate at the interface between the acetophenone-existing and non-existing regions. (3)The values of mobility and conductivity calculated from the space charge profile agree with the assumption that ionic carriers are responsible for the conduction in the acetophenone-existing region.
