Discharges, space charge, and the shape of electrical trees

The movement of residual positive charges along the walls of tree tubules and into the surrounding polymer is a critical determining factor in the shape (bush or branch) of electrical trees. Positive charge that has a higher mobility along tubule walls promotes single discharges propagating to the tree tip. Lower mobility positive wall charge tends to more, but perhaps smaller, discharges. The former may favour branch tree growth, the latter bush trees. Spread out positive wall charge may occur when there are a number of discharges per half cycle. The resulting damage may favour bifurcation (transverse extension).