抄録
Oxygen gas absorbed in polymer has significant influence on treeing phenomena. The AC treeing resistance of low density polyethylene (PE) is drastically improved in oxygen free condition at room temperature or below. XLPE power transmission cable is generally operated at higher temperature. This paper describes the effect of oxygen on AC electrical tree initiation in PE at high temperature (25-100°C).
The degassing treatment of sample carried out at room temperature increases the tree initiation AC voltage Vt at room temperature. However it does not increase the Vt at high temperature. Oxygen molecules strongly attaching to PE matrix, which are not removed by degassing at room temperature, may be gradually released during voltage application at high temperature and cause chain oxidation resulting in tree initiation.
On the other hand, the degassing made at high temperature increases the Vt at high temperature. This result may be well explained by that the high temperature degassing removes better strongly absorbed oxygen molecules than the room temperature degassing does.
The shape of tree changes with temperature. Bush type tree is dominant at room temperature, while branch type tree at high temperature regardless of vacuum-treatment.
The deteriorated region was found around semiconducting electrode tip by the microscopic observation. This region resembles that formed in the sample with steel needle. So, both deteriorated regions may be formed by the same mechanism.
