Influence of oxygen on AC treeing at high temperature

The influence of oxygen on AC tree initiation in LDPE (low-density polyethylene) in the temperature range of 25-100°C is studied experimentally, using both a semiconducting polyethylene electrode and a steel needle electrode. It is shown that degassing treatment at 25°C suppresses tree initiation when the voltage is applied at 25 or 50°C, but not when voltage is applied at 75 or 100°C. The tree initiation rates at 75 or 100°C decrease with the temperature of the degassing treatment. This result may be explained by the fact that the degassing treatment at elevated temperature removes oxygen molecules better than at room temperature. The shape of the tree changes from bush type to branch type as the temperature of voltage application is increased. The degraded region is formed in the sample with the semiconducting electrode as well as in the sample with the steel electrode