Image for illustrative purposes

Eskom has completed a multi-phase technical investigation into the use of methanol and ethanol as supplementary indicators for monitoring transformer insulation degradation. The findings were presented at CIGRE Southern Africa 2025 by Hlengiwe Nzima.

Large power transformers rely on kraft paper insulation, whose remaining life is closely linked to the degree of polymerisation (DP). As insulation ages under thermal stress or fault conditions, it produces degradation by-products such as carbon monoxide, carbon dioxide, furans, and alcohols. International research has suggested that methanol may indicate early-stage cellulose degradation, while ethanol may be associated with higher-temperature ageing or localised hotspots.

Eskom evaluated whether alcohol analysis using headspace gas chromatography with flame ionisation detection (HS-GC-FID), conducted in line with ASTM D8086-20, could provide diagnostically useful information alongside established techniques such as dissolved gas analysis (DGA) and furan (2-FAL) testing. Laboratory results confirmed that the method could reliably detect both alcohols at low parts-per-billion concentrations.

The study analysed approximately 250 in-service transformer oil samples. Early phases highlighted the sensitivity of alcohol measurements to sampling and storage conditions. Later phases, focusing on syringe-sampled oils from sealed transformers, showed detectable alcohol levels even in units with “excellent” estimated DP values. However, no consistent linear relationship was established between alcohol concentrations and transformer age, DP, or total dissolved combustible gas.

The study concluded that methanol and ethanol analysis should be used as supplementary diagnostic indicators, with further long-term monitoring recommended to assess their contribution to asset health assessment.

Source: energize.co.za