A novel method of measuring length and location of single channel carbonized trees in oil-impregnated pressboard

Partial discharges are considered to be an important role in the deterioration process of the oil-impregnated pressboard insulation system. It was found that the PDs are favor to produce carbonized tree inside the pressboard. High voltage experiments were carried out to find the formation rule of the carbonized trees. A strip of pressboard instead of a piece of pressboard was used to bear high voltage, in order to limit the branch number of the tree. A serial of copper strips were arrange between the pressboard and the earth electrode to couple the electric field signal. From the AC frequency signal on the copper strips, the length of the carbonized trace can be calculated. From the transient voltage increase on the copper strips, the spatial charge remained by the partial discharge can be calculated. High voltage experiments were carried out to produce carbonized trace on the strips, signals were record online. Then, the strips were torn to layers to observe the trees. From the experiment results, the trace lengths can be obtained from the AC voltage on the copper strips, and the spatial charge quantity can be obtained from the transient signals. Thus, the amplitude and location of partial discharge can be research through the copper strips.