Analysis of water treeing in solid insulated cables

The physical and internal structure of water trees grown in power cables are. studied and analysed. The new deviced mechanism for studying water trees shows that microvoids under water tree consists of air and water voids. The tree starts from an air void. The age of the cable depends on the time required for the pressure to build up inside the air void in order to overcome the mechanical strength of solid insulating material. At this instant water tree inception starts. This age depends also on the tip radius of protrusion defect which has the effect to decrease this age abruptly as it becomes small. The voltage required for this stage is the switching overvoltages. The time required after water inception is small because it propagates under normal op-erating voltage of cables. Also with this new water tree mechanism the large water bouquets and very small crack connecting it has been accepted.