Stochastic procedures for the investigation of tree growth in insulating materials for H.V. applications

The results of partial discharge measurements performed during treeing tests made on specimens of insulating materials by the point-plane electrode system are processed by statistical operators. It is shown that the partial discharge height distribution well fits the two-parameter Weibull function at any time of tree growth, before starting of the breakdown leader. Moreover, the Weibull parameters are correlated with the tree-growth features, thus providing a statistical tool for partial discharge pattern recognition. Other statistical operators, already proposed in literature, are considered, that is, skewness, kurtosis, cross correlation. They are applied, in particular, to charge vs phase distributions, and show behavior characteristic of the examined phenomenon