Applicability of Methanol as a Solid Insulation Ageing Indicator in Retrofilled Transformers

One of the most convenient methods to estimate the condition of the transformer solid insulation is to measure the byproducts in the oil which generate from the solid insulation degradation. Furanic compounds and carbon oxides have been the commonly measured by-products. However, alcohol based by-products such as methanol and ethanol have been emerged as new ageing indicators. The measurement of alcohol based byproducts may be used as a complementary measurement to gain more confidence in the condition assessment of the solid insulation. In this paper applicability of methanol as a solid insulation ageing indicator for retrofilled transformers have been investigated. Retrofilling is simulated using natural ester and synthetic ester liquids in a lab environment. An accelerated ageing experiment is performed at three different temperatures and methanol is measured. 2-furfural (2-FAL) is also measured as a reference for comparison purpose. The results indicate an increase in methanol and 2-FAL contents with increase in temperature. Also, methanol appears very volatile as decrease in methanol contentis observed when the solid insulation degrades more (DP <400) or in insulation system with higher moisture content. Therefore, further investigation of the effect of moisture and solid insulation ageing on the methanol content needs to be done to appropriately use the methanol as a solid insulation ageing indicator.