Thermo-electrical ageing of paper insulated MVAC cables: experience from laboratory experiments

This paper investigates the thermo-electrical ageing of paper-insulated lead-covered (PILC) medium voltage AC (MVAC) cables, focusing on the impregnating compound. The study aims to understand the ageing mechanism and the accompanying impact on cable reliability. Laboratory experiments were conducted using field-aged PILC cable samples, with artificial ageing applied to some samples under controlled temperature and electrical field conditions. The results show that the impregnating compound of a field-aged PILC cable (without waxing behaviour) exhibits typical viscoelastic behaviour, transitioning from a solid-like to a liquid-like state with increasing temperature. Artificially aged samples of this compound demonstrated similar rheological properties, but transitioned to a liquid-like state at lower temperatures compared to non-artificially aged samples. However, the field-aged compound of another PILC cable exhibited waxing behaviour, which could not be replicated in the laboratory, suggesting additional influencing factors. The study suggests the investigation of the chemical mechanisms underlying the waxing of the compound.