Contribution to the overall and local characterization of the condition of electric ageing of HV insulation in large rotation machines

The authors presents two novel approaches to the assessment of the electrical condition of the HV (high-voltage) insulation in large rotating machines. The first considers the overall condition on the basis of the conduction index, which makes use of the ionic contribution to the electrical conductivity of the HV insulation. The second is concerned with the local aspect defined in terms of a parameter V _BF, which is associated with the concentration of rapid ions at mica/resin or microvoid/resin interfaces. Both are based on an analysis of the physical mechanisms responsible for the slow electrical polarization of the HV insulation and the processes leading up to dielectric breakdown