Transformer Oil Testing Using Comb Structured Capacitive Sensor

Different insulation degradation chemicals are produced when the transformer’s insulation system ages. These insulation degradation by-products are discovered in the oil as dissolved impurities. Estimating the concentration of these by-products in the oil allows one to evaluate the condition of an oil-immersed transformer. The two crucial degradation compounds that may be utilised to assess the age of insulation systems or the health state of the transformer are 2-FAL (2-furfuraldehyde) and moisture. Capacitive sensor-based measurement of these degradation compounds, owing to the high dielectric constant, in comparison to that of the pure oil, can detect incipient faults. Early detection of insulation conditions allows preventive maintenance. In this paper, a comb-type capacitive sensor is proposed for 2-FAL and moisture detection. A simulation based study is performed in COMSOL Multiphysics to analyse the feasibility and characteristics of three variants of the proposed sensor. The variants analysed are: first, without an additional sensing layer; second, with Aluminium oxide (Al
2
O
3
) as the sensing layer; and third, with Zinc oxide (ZnO) as the sensing layer. Among these, ZnO based sensor shows the highest sensitivity for both 2-FAL (0.0523 pF/ppm) and moisture (0.0322 pF/ppm) measurement. The proposed sensor is simple, low cost and effective method of on-site monitoring of transformer insulation health.