The effect of conductivity distribution in tree channel on PD behavior in electrical tree

Under the conditions of long electrode distance or low applied voltage, a tree from the needle tip can not directly reach the plane electrode, and it begins to grow fast again when the partial discharge (PD) extincts. Prior to the PD extinction, the φ-q-n pattern of PD changes from wing-like (or triangle-like) pattern to turtle-like pattern. In a tree-like tree, obvious increases of the PD number and the total PD charge can be observed before the PD extinction. But in a bush-like tree, the PD is likely to extinct gradually. Assuming the effective conductivity near the needle tip is lower than that at the tree tips or in tree channels, computer simulation results on the PD sequences in a single channel may explain these phenomena