| Reduced-oil transformer equipment tends to operate in a relatively enclosed, oxygen-deficient environment, in which an arc discharge can cause insulating oil to undergo thermal cracking under high temperature and high energy, generating combustible gas mixtures with explosion risk. To evaluate the gas generation and explosion risk under oxygen-deficient conditions, a sealed arc-discharge experimental setup was designed. Fourier-transform infrared (FTIR) spectroscopy was employed to investigate the gas generation rate, gas composition and theoretical explosion limits (LEL/UEL) under different arc energies, oil temperatures and ageing degrees. The results show that when the oil temperature increases from 45 °C to 90 °C, the gas generation rate rises by approximately one order of magnitude, with a maximum value of 23.53 mL/s. As the arc energy increases from 6 J to 13.8 J, the lower explosion limit decreases from about 3.3% to about 2.8%, while the upper explosion limit increases from about 16% to about 32%, indicating a significant expansion of the flammable concentration range. Oil aged for 144 h exhibits the highest gas generation rate and explosion sensitivity, which slightly decrease after 288 h. In addition, an improved three-ratio diagnostic scheme independent of hydrogen measurement is proposed using the acetylene volume fraction and the ratios C?H?/C?H? and C?H?/C?H?, enabling discrimination of arc energy levels and oil ageing degrees under oxygen-deficient conditions. The results can provide a useful reference for arc fault identification and fire and explosion prevention design of reduced-oil transformers and high-voltage bushings. |
