When the insulation defect occurs in the gas-insulated combined electrical appliance

the SF

6

gas may decompose to generate the decomposition products inside the device. It will cause the degradation of insulation and arc extinguishing performance. The detection of SF

6

decomposition products is of great significance to detect and evaluate the internal insulation of the equipment. SO

2

is one of the main products in the decomposition products of SF

6

and the accurate detection of SO

2

is helpful to evaluate the internal insulation of the equipment. An experimental platform for SO

2

detection is built by the mid-infrared tunable laser spectroscopy in this paper. The linear relationship between the SO

2

concentration and the average value of the second harmonic peak is obtained by detecting the SO

2

gas with different concentrations

and the experiment of error analysis is further carried out. The response speed and recovery time of the device are analyzed. The experimental results show that the SO

2

concentration has a good linear relationship with the average value of the second harmonic peak value. The goodness of fit is 0.987. The fitting curve is verified by the different concentrations of SO

2

gas

and the maximum error is 4.86%. The response speed and recovery time of the device are 202.2 s and 49.4 s. The fit of the SO

2

concentration to the average of the second harmonic peak is 0.981 under CO interference. The results of the research provide technical reference and support for the effective detection of trace SO

2

.