## 1 Introduction  
In the process of power generation, transmission, distribution, and energy conversion in the power system, high-voltage air switchgear is used for opening, closing, controlling, and protecting electrical equipment, with a working voltage level mainly between 10-35 kV. However, throughout the manufacturing, transportation, and operational maintenance phases of the switchgear, scratches and metal fragments may accumulate within the cabinet due to improper handling. Due to different coefficients of expansion and aging of materials inside the switchgear, air gaps may occur in the components. The above defects will deteriorate the original insulation conditions of the air switchgear, change the electric field distribution, and lead to partial discharge, which will cause serious safety accidents [1, 2]. When partial discharge occurs, various signals can be detected in the surrounding area, such as electrical, ultrasonic, and electromagnetic signals [3; 4; 5; 6]. For these signals generated by partial discharge, they can be obtained through pulse current method, ultrasonic detection method, and UHF detection method [7; 8; 9; 10; 11; 12; 13; 14]. The analysis methods for detecting signals mainly include spectrogram method, wavelet transform method, compressed sensing method, and phase-diagram-based analysis method [15; 16]. These methods are indirect measurements, and their accuracy is easily affected by external interference. Furthermore, the classification of sources that cause partial discharge still needs further improvement. The gas inside the air switchgear is composed of 78% N\({}_{2}\), 21% O\({}_{2}\), and 1% other gases. When the electric field strength inside the air switchgear reaches the critical electric field strength, charged particles acquire sufficient kinetic energy in the electric field, collide with other neutral particles, and ionize. When these particles collide, some new gas is produced. Detecting these newly generated gases can determine whether partial discharge has occurred. By analyzing the volume fraction and rate of change of the detected characteristic gases, the discharge situation of partial discharge can be evaluated. The gas composition analysis method is used to detect characteristic gases, and its working environment has little impact on the detection results. The commonly used methods for detecting gas composition are dedicated sensor method and ultraviolet and gas chromatography method [17; 18]. In recent years, the study of characteristic gases generated by partial discharge in switchgear has attracted considerable attention. The decomposition components of switchgear partial discharge characteristics are studied [19]. Materials Studio was used to simulate and calculate all possible components generated during the air discharge process. The generation process of each component gas is analyzed, and it explains the reasons why characteristic gases cause insulation defects in air switchgear. A characteristic gas concentration detection system based on the characteristic gases generated by partial discharge is designed, and the distribution of derived gases is determined using the FLUENT fluid dynamics research platform, providing a theoretical basis for the optimized layout of the characteristic gas detection system [20]. The simulation model of defect construction during atmospheric pressure gas discharge processes has been studied [21; 22]. The volt-ampere characteristic curves of insulation defects at both ends during partial discharge were measured and compared with the volt-ampere characteristics output by the simulation model, thus verifying the accuracy of the constructed simulation model. The characteristic gas method is to detect one or more characteristic gases, which is a chemical detection method, so it will not be affected by the same kind of interference signal in the surrounding environment. When the power equipment partially discharges, air, as an insulating medium, will decompose composite and other chemical reactions, resulting in new gases.