Power frequency breakdown characteristics of new 3-element mixed insulation oil and oil-impregnated pressboard

Abstract

Mixed insulation oil has attracted widespread attention in recent years due to its excellent performance. In our previous works, we proposed a novel 3-element mixed insulation oil with superior physical and electrical properties. To promote the application of the mixed insulation oil to transformers, we studied the AC breakdown characteristics of the 3-element mixed insulation oil and the mixed insulation oil-impregnated pressboards and then performed a comparison to Karamay 25# mineral oil. Oil or oil-impregnated pressboard samples with different moisture contents were obtained by moisture absorption or by controlling the drying time. The breakdown tests were carried out at different temperatures in an oil bath. The results showed that the AC breakdown characteristics of the 3-element mixed insulation oil are better than those of mineral oil and that the mixed insulation oil can maintain breakdown strength over a range of moisture contents. The breakdown mechanism of insulation oil is discussed according to the experiment results. Moreover, the breakdown characteristics of the pressboard impregnated with the 3-element mixed insulation oil are also better than those of the pressboard impregnated with mineral oil. These advantages of mixed oil promote application of the 3-element mixed insulation oil to power transformers.