Why residual life estimation and maintenance strategies for electrical insulation systems have to rely upon condition monitoring

There is no doubt that the electrical and thermal stress conditions in modern electrical networks are becoming much more challenging than in the past. The presence of voltage transients and power electronics, especially in grids involving renewables, is stressing insulation systems in a not-conventional and often not-predictable way. This paper is looking at the potential effect on insulation aging of repetitive voltage transients, in the presence or absence of partial discharges, raising the point that such transients can cause significant aging acceleration, thus reduce life considerably with respect to the design life. This is why condition monitoring becomes a must: the health of an insulation system has to be evaluated dynamically as a function of time, in order to approach in the most convenient way the matter of maintenance and asset reliability. A general approach to aging under non-sinusoidal waveforms is presented here, referring to both phenomenological and probabilistic algorithms, and examples are reported for speed-controlled rotating machines and train transmission lines. It is emphasized that the aging processes in a transformer will require a more complex modeling approach.