In the treeing experiment it is suggested that similar
initiation mechanisms exist among all of the trees, which
agrees with the findings of other researchers [12]. The
initiation process of electrical tree is attributed to electron
injection and extraction at the needle electrode due to high
electric field. Part of the insulation in front of needle will be
deteriorated by this process. This is followed by the intense
partial discharge and photo-ionization due to charge
recombination in the channel of the tree. The continuous
micro-breakdown at the tree tips and the electron avalanche
mechanisms are also factors for insulation degradation.
At 10 kV, all samples must take special attention during
tests because of break down, which may occur at any
time. The surface flash over was also expected.
Therefore, short time plan was followed to prevent this
situation.