Comparative Study of Lighting Impulse Properties for Mineral Oil and Ester Liquids

It is well known that insulating liquids have been widely used in transformers, and mineral oils are usually and traditionally utilized in electrical equipment. Inrecent years, environmental-friendly ester liquids (which can partly replace mineral oil) have been drwan more and more attention, and also gradually applied in more and more power industry. This paper dealed with a comparative breakdown study of various insulating liquids, including mineral oil, natural ester, synthetic ester (pentaerythritol ester) and glycerol trioleate. Each insulating liquids was tested under a standard lighting impulse voltage of positive and negative 1.2/50μs. This study was concentrated around the electrode gaps with 1-50mm of the point-plane electrode arrangement. The breakdown voltage and breakdown time were simultaneously recorded. The Weibull distribution functions were used to analyze the experimental data and estimate the breakdown voltage with risk of 63.2% probability. The results showed that, for negative voltage, in the larger gaps, ester oils always had a significant lower breakdown voltage than mineral oil, while the breakdown voltages of various ester liquids were approximate, for positive voltage, the breakdown voltages of various ester liquids were quite different.