AFM-IR provides detailed sub-micron chemical maps of the local damage inflicted by partial discharges.

High voltage outdoor composite insulators used on transmission lines can be subject to degradation due to electrical discharge activity at the core-sheath interface. A methodology is described to explore the effect of de-bonding or loss of adhesion between the sheath and core in composite insulators. The use of planar geometry materials allows interfacial pressure to be varied and facilitates physical and optical imaging of the tracking as it grows and chemical analysis of the samples after aging. The associated electrode geometry allowed the tracking to develop in a constant field, unaffected by the earth electrode. Low pressure between the materials accelerated the growth the tracks. A correlation between partial discharge magnitude and track development is identified. Electrical tree growth was also observed penetrating the epoxy resin, initiated from the interfacial tracks.

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To enable the continued development of power transmission cabling, an understanding of the processes which result in their failures is essential. In order to do so, powerful analysis techniques are required. However, those which consider chemical degradation are lagging behind those for visible degradation. This paper presents the Atomic Force Microscopy-Infrared Spectroscopy (AFM-IR) chemical analysis technique, which can provide surface chemical analysis with resolution of ~50 nm across the infrared spectrum. Two cases are considered: interfacial tracking between epoxy and silicone rubber, and the degraded region formed in front of a needle tip in the electrical tree initiation process. The results obtained using AFM-IR are compared to the outcomes from other techniques. It is found that AFM-IR offers a unique and powerful insight into visible and non-visible degradation of solid dielectrics.

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