A Novel Three-Element Mixed Insulation Oil and Its Application in 10kV Distribution Transformer

Taking into account the advantageous and disadvantageous properties of mineral oil and natural esters, a novel three-element mixed insulation oil has been developed by our team. The main parameters of the novel three-element mixed insulation oil (76 v.% mineral oil + 19 v.% soybean oil + 5 v.% PFAE oil + 0.2 wt% T511+0.2 wt% L06) meet the IEC standard (60296:2012) for mineral oil. The novel three-element mixed insulation oil has a similar kinematic viscosity as mineral oil. The oxidation stability properties of the novel three-element mixed insulation oil are superior to those of mineral oil. Its specific heat capacity and thermal conductivity values are higher than those of mineral oil between 30 °C and 100 °C. The saturated water content of the novel three-element mixed insulation oil is approximately 3-4 times larger than that of mineral oil above 45 °C. The mixed insulation oil has a higher AC breakdown voltage than mineral oil under the same absolute water content. In this research, without changing the insulation structure of the transformer, an old mineral oil distribution transformer (SBH15-M-400/10-0.4) serviced for 8 years was filled by the novel three element mixed insulation oil. In addition, a new distribution transformer (S11-M-400/10-0.4) was also filled by the novel three element mixed insulation oil. All the parameters of the both distribution transformer above meet the requirement of the standard. Compared with the same distribution transformer filled by mew mineral oil, the distribution transformer filled by the novel three-element mixed insulation oil has good insulation resistance, DC resistance, dielectric loss, no-load and load loss, etc. The good performance of the novel three-element mixed insulation oil could ensure the safe operation of the old and new 10kV distribution transformer.