## 5 Conclusions  
This paper mainly studies how to detect partial discharge caused by insulation defects in high-voltage air switchgear online through characteristic gases. Three defect simulation models are constructed, and the effectiveness of the simulation models was verified using the output characteristic curves of the constructed physical defect models. After simulating the relationship between partial discharge and characteristic gas volume fraction, the inverse relationship between the change of characteristic gas volume fraction and the development of partial discharge was established. The conclusions obtained from this process are as follows:  
(1) By comparing the volt-ampere characteristic curves and numerical models of partial discharge caused by insulation defects in the air switchgear on the experimental platform, it is proved that the numerical model established in this paper can describe the physical process of partial discharge in the air switchgear under atmospheric pressure;  
(2) This paper establishes the correlation between the volume fraction of the characteristic gases and the partial discharge quantity. Through the volume fraction curve and the partial discharge quantity curve, it shows that CO, NO\({}_{2}\), and O\({}_{3}\) as characteristic gases have uniqueness, which can be used as the monitoring index for the study of the partial discharge quantity of insulation defects of the air switchgear cabinet. (3) When partial discharge occurs in the air switchgear cabinet, according to the change of volume fractions of the three characteristic gases in the air components, combined with the time domain regression equation, the main type of defects in which the discharge occurs can be determined. Then, the partial discharge amount can be calculated by using the partial discharge amount inversion regression equation to calculate the partial discharge amount of the insulation defects in the air switchgear cabinet at present. This paper provides guidance for online detection of partial discharge in high-voltage air switchgear through characteristic gases. Considering the computational complexity and feasibility, this paper adopts one-dimensional fluid mechanics to systematically analyze and study the physical process of particles at the moment of discharge in the simulation model. However, in actual working conditions, the environment where insulation defects are located is complex. Therefore, setting more variables and chemical reaction processes can obtain more accurate data results and reduce the error between simulation results and actual situations. This paper lays the foundation for the systematic study of the decomposition phenomenon under the action of discharge faults in air switchgear, and the subsequent work should focus on:  
(1) The influence of air humidity, the distance between the needle plates of solid metal protrusions, and the use of different materials for each defect model on the decomposition components of air partial discharges, so as to improve the diagnostic methods of air decomposition components for the types of local discharges. (2) Improve the decomposition components of insulator air gap discharge, metal particle discharge and metal protrusion discharge under the solid switchgear. (3) Study the use of characteristic gases generated by insulation defect discharge to invert and calculate the partial discharge caused by defects under complex working conditions with multiple insulation defects present simultaneously. Conceptualization and writing--original draft, Y.T. ; formal analysis and formal analysis and writing--review and editing, H.N. and S.W. ; software, G.Z. ; investigation, Y.T. ; resources and writing--review and editing, H.N. ; All authors have read and agreed to the published version of the manuscript.