Effect of viscosity and water content on the breakdown strength of vegetable oils

The effect of viscosity on AC breakdown strength was studied using aged sunflower oil. After ageing, the oil was darkened and the viscosity and water content increased. Whilst the electrical conductivity increased with ageing as anticipated, the AC breakdown strength showed an unexpected increase. In addition the effect of water on breakdown strength was probed using carefully treated olive oil. Whilst extended periods of drying did not change the electrical properties, adding water increased the electrical conductivity and reduced the breakdown strength. This indicates that increased viscosity is the cause of the observed unexpected increases in AC breakdown strength.