High voltage dielectric frequency response measurements on polyethylene samples during water tree ageing

摘要

1. During water tree deterioration, the real and imaginary part of the permittivity increase in the studied frequency range 1 mHz-100Hz.rn2. This is accompanied by increased non-linear behaviour of real and imaginary part of the permittivity.rn3. The non-linearities are independent of frequency in the measured frequency range.rnA proposed origin for the non-linear behaviour is the Maxwell force acting on the water treed regions. This agrees well with the measured odd harmonics of the dielectric response. After removal of applied voltage (50 Hz) the losses decrease rapidly, probably due to out diffusion of water from the water treed regions. One should have this effect in mind in the interpretation of various dielectric response measurements on water treed insulation.