Characteristic Gas Production Law of Dodecylbenzene Insulating Oil under Thermal Fault

Dodecylbenzene (DDB) insulating oil is widely used in high-voltage submarine oil-filled cables, but there is a lack of research on the gas production law of DDB oil under fault which can be used for fault diagnosis of equipment filled with DDB oil. Herein, we built thermal fault simulation system to study the law of seven gases (H2, CH4, C2H6, C2H4, C2H2, CO, CO
2
) produced by DDB oil with paper and without paper at 100°C~350°C. Existing dissolved gas-in-oil analysis (DGA) methods (three-ratio method and Duval triangle) were selected to analyze the gas dissolved in DDB oil to verify their applicability to DDB oil. Results show that at low temperatures, DDB oil mainly produces H2 and CH4, as the temperature increases, the main characteristic gases change into C2H4 and C2H6. For oil-paper, the final trend of gases with temperature is similar to that of pure oil. Moreover, insulating paper in DDB oil begins to produce large amounts of CO and CO
2
at 150°C~250°C. Three-ratio method and Duval triangle can detect the thermal fault through the gas dissolved in DDB oil, but the temperature of thermal fault cannot be determined accurately.