Estimating the true growth rate of water trees from a series of samples taken at different ageing times

A theoretical basis has been developed for a method of estimating the mean growth rate of different sized trees in sampled populations grown in standard test geometries. This method has been proved to be practical and to give consistent results which are providing information on water tree growth laws. Evidence has been found of two stages of growth, separated by a transition length, with overall growth following a stretched exponential law.