Electro-convection in natural ester based transformer fluid

The electro-convection phenomenon is among the pre-breakdown phenomena influencing the dielectric strength of insulating fluids. In transformer mineral oils, electro-convection can lead to catastrophic failure of transformers. With the current trend to replace mineral oils with natural ester fluids, it is important to characterize this phenomenon in vegetable fluids. This paper deals with the influence of different parameters on the electro-convection phenomenon in natural ester fluid; mineral oil is also considered for comparison. The investigations concern especially the dependence of the electro-convection threshold voltage of the electric field distribution, electrodes spacing distance, electrode material, water content in oil and temperature. The electro-convection threshold voltage in natural ester fluid is also compared to that in mineral oil. It is shown that the electro-convection threshold voltage is the lowest with electrodes made of copper and the highest for those made of aluminum; it is in between for electrodes made of brass. Also, the electro-convection threshold voltage is smaller in natural ester fluid than in mineral oil; the influence of water content is weaker in natural ester fluid.