Effect of Humidity on the Detection of Dissolved Gases in Transformer Oil for Tin Oxide Based Gas Sensor

Dissolved gas analysis (DGA) is an efficient method to diagnose faults of oil-immersed power transformer in the early stages. Tin oxide $(\mathrm {S}\mathrm {n}\mathrm {O}_{2})$ has been extensively studied as a gas sensing material since it is well known to be effective in sensitively detecting various gases. However, the sensitivity of gas sensor will be deteriorated seriously when the humidity of working detecting environment changes, which makes response curve fluctuate and drifts distinctively. As humidity has a huge impact on the detection accuracy, it becomes one of the most important considerations in the practical use of sensors. In this paper, three gas sensors based on $\mathrm {S}\mathrm {n}\mathrm {O}_{2}, \mathrm {P}\mathrm {d}/\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ and $\mathrm {Z}\mathrm {n}/\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ sensing materials were synthesized by hydrothermal method and characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS). Meanwhile, the performance of the gas-sensing under different environmental humidity was tested. The results show that metal doped gas sensors are better sensitivity and stability than that of the pure $\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ gas sensor. Moreover, with the increase of humidity the detection sensitivity of $\mathrm {P}\mathrm {d}/\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ and $\mathrm {Z}\mathrm {n}/\mathrm {S}\mathrm {n}\mathrm {O}_{2}$ sensors emerge a phenomenon of increasing first and decreasing then. Ultimately, based on the sensing properties of pure, Pd and Zn-doped gas sensors, the possible sensing mechanism for them in humid atmosphere was investigated, which will make contribution to the application of $\mathrm {S}\mathrm {n}\mathrm {O}_{2}$-based gas sensors in the online monitoring of dissolved gases in transformer oil.