Abstract: When electrical or thermal faults occur inside the transformer, the organic polymers in the insulating oil will undergo cracking, leading to the production of C2H2, C2H4, CO2, and other gases. However, high concentrations of CO2 will interfere with the photoacoustic (PA) spectroscopy detection of C2H2 gas. This article first explores the reason for the interference of CO2 on the detection of C2H2 gas by analyzing the infrared absorption spectra of CO2 and C2H2. On this basis, a distributed feedback (DFB) laser combined with a small non-resonant PA cell is used to build a C2H2 detection system based on PA spectroscopy, and high reliability of C2H2 gas detection is achieved by optimizing the laser modulation parameters. The experimental results show that the system can significantly suppress the interference of CO2 gas on C2H2 gas detection. At a sampling integration time of 30 s, the calculated minimum detection limit of the system is about 64 × 10−9, and the normalized noise equivalent absorption coefficient is 1.5 × 10−9 cm-1·W·Hz−1/2.

Key words: spectral analysis, interference characteristics, comparative experiment, dissolved acetylene in oil