Fault gases dissolved in vegetable insulating oil under electrical faults

Natural ester fluids are biodegradable and fire-resistant liquid dielectrics which have been used in power transformers in recent years. This paper presents the results of an experiment to simulate typical thermal faults in power transformers. The temperatures of thermal faults ranges from 90 °C to 800 °C. Dissolved gases in natural ester fluids under the thermal faults were investigated. The experiment results show that the characteristic gases dissolved in natural ester fluids differ from those in mineral insulating oils under the thermal faults. The criteria of the three-ratio method in the IEC standard for the traditional dissolved gas analysis (DGA) are not suitable for fault diagnosis of transformers filled with natural ester fluid.