Investigation of electrical tree propagation from water tree by utilizing partial discharge and optical observation

In order to clarify the mechanism of electrical tree propagation from a water tree within polyethylene, we have carried out simultaneous observation of partial discharge (PD) characteristics, electrical-tree propagation and associated phenomena. The electrical tree inception voltage increases with the area of water tree degradation. An electrical tree is initiated from a water needle tip. When the electrical tree connects with water needle, PDs become large abruptly. There are two types of electrical-tree growth, in one of which only small PDs occur only at the electrical-tree tips. After removing the applied voltage, water fills the electrical-tree channels, and water trees propagate from the electrical-tree tips when the voltage is applied again.