The Characteristics of Winding Temperature for the Natural Ester Filled Transformer up to and Including 500 kVA

Because of environmental friendly and higher fire point, Natural ester fluids are widely used for transformer cooling materials. Natural ester has higher viscosity than that mineral oil. Top oil temperature and hottest temperature will be warmer when using natural ester fluid in transformers designed for conventional transformer oil. Although natural ester has less influence on deterioration of cellulose paper than mineral oil, an increased hottest temperature might have an effect on the aging of insulating paper in coil winding. When comparing natural ester with mineral oil at the same designed transformers up to 500 kVA. The deviation of hottest temperature between the two is increased with load. For preventing additional aging of insulation paper, design changes are required when substituting natural ester for conventional transformer oil.