Cellulosic Particles Accumulation and Conductivity Characteristics of Natural Ester Used in Power Transformer

Transformer plays an important role in providing a reliable and efficient electricity supply and is one of the most critical equipment in electric power transmission and distribution systems. The majority of high voltage transformers are filled with liquids that work as an electrical insulation as well as a heat transfer medium. Natural esters are used today for the insulation of high voltage transformers. The paper made comparative experimental analysis of the cellulosic particles accumulation and conductivity characteristics of natural ester and mineral oil under AC and DC electric field. The effect of the electric field on bridging in natural ester and mineral oil has been compared. When the voltage is applied on the oil with cellulosic particles, the particles began to move within the whole electric field. Cellulosic particles bridge was created between electrodes under DC. The conductivity current through the natural ester with particles is smaller. The bridge is thick and strongly bonded under DC electric field. While under AC, the rate of particles accumulation in mineral oil and natural ester are all slower than that under DC electric field. However, there is thin cellulose particles bridge in natural ester after applying AC voltage 120min, this is different from the phenomenon observed in mineral oil. It is better to consider this phenomenon for operation transformer using natural ester.