The effect of power supply frequency on the initiation and growth of water trees

The effect of power supply frequency on water trees has not been well understood: there are considerable discrepancies above frequencies as low as ten times normal power frequencies. Furthermore nearly all the work so far has concentrated on growth rates and not inception times and on single trees grown from field-enhancing water needles and not from planar interfaces such as those found in cables. This paper reports on water tree inception and growth under planar interface conditions at frequencies from 50 Hz to 2170 kHz. A de-convolution method is illustrated which enables the estimation of the inception and growth characteristics of individual trees within the large number which grow from a planar interface-this will enable probability of failure calculations to be made. The work indicates at least some of the factors which make more simple measurements confused when frequency acceleration is used