Although the increase in frequency improves the transmission efficiency of high-frequency transformer, a higher probability of insulation failure is caused by high-frequency partial discharges. Through a high-frequency experimental platform, emission spectrum tests on two types of insulation faults were carried out under high-frequency square wave voltages. Subsequently, the influence of frequency and voltage amplitude on the light intensity and the number of photons of emission spectrum caused by air corona were studied. Finally, the variation of the spectrum of the partial discharge occurring at the interface of gas-solid insulation with frequency was analyzed. The results show that, the characteristic spectrum of air corona is composed of the near-ultraviolet spectrum, which is caused by the energy level transition of N2 molecules, and the number of photons of air corona is positively correlated with voltage amplitude and frequency. Partial discharges at the gas-solid insulation interface have band spectrums in the visible light region and the near-infrared light region except for the near-ultraviolet spectrum due to the energy level transitions of outer layer electronics and the vibrations of C-H chemical bonds of PET molecules. This paper preliminarily verified the feasibility of applying the emission spectrum diagnostic method to two typical partial faults under high-frequency square wave voltages.

Gas–oil separation by membrane stands for a promising technique in dissolved gas analysis (DGA). Since the accuracy of DGA relies on the results of gas–oil separation to a great extent, it is necessary to study the influence factor of membrane for better performance. Although plentiful studies have been conducted aiming at membrane modification to obtain better separation performance, it cannot be ignored that the conditions of oil also affect the performance of membrane much. In this work, a photoacoustic spectroscopy-based sensor for DGA, which employed membrane for gas–oil separation, was established first. By detecting the photoacoustic signal, the performance of membrane could be evaluated. Furthermore, the influences of feed velocity and pressure have on the performance of membrane were analyzed. Both simulation and experiment were employed in this work to evaluate the influences by collecting the equilibrium time of membrane under different conditions. As a result, the simulation and experiment agreed with each other well. Moreover, it was reasonable to draw the conclusion that the equilibrium time was evidently reduced with the raise of feed velocity but remained with a minimum change when pressure changed. The conclusion may serve as a reference for the application of membrane in optical sensor and DGA.

Sulfur dioxide (SO₂) is a key indicator for fault diagnosis in sulfur hexafluoride (SF₆) gas-insulated equipment. In this work, an in situ photoacoustic detection system using an ultraviolet (UV) LED light as the excitation source was established to detect SO₂ in high-pressure SF₆ buffer gas. The selection of the SO₂ absorption band is discussed in detail in the UV spectral regions. Based on the result of the spectrum selection, a UV LED with a nominal wavelength of 285 nm and a bandwidth of 13 nm was selected. A photoacoustic cell, as well as a high-pressure sealed gas vessel containing it, were designed to match the output optical beam and to generate a PA signal in the high-pressure SF6 buffer gas. The performance of the proposed system was assessed in terms of linearity and detection limit. An SO₂ detection limit (1σ) of 0.17 ppm was achieved. Additionally, a correction method was supplied to solve PA signal derivation induced by pressure fluctuation. The method can reduce the derivation from about 5% to 1% in the confirmation experiment.

Internal discharge and overheating faults in sulfur hexafluoride (SF₆) gas-insulated electrical equipment will generate a series of characteristic gas products. Hydrogen fluoride (HF) is one of the main decomposition gases under discharge failure. Because of its extremely corrosive nature, it can react with other materials in gas-insulated switchgear (GIS), resulting in a short existence time, so it needs to be detected online. Resonant gas photoacoustic spectroscopy has the advantage of high sensitivity, fast response, and no sample gas consumption, and can be used for the online detection of flowing gas. In this paper, a simulated GIS corona discharge experimental platform was built, and the HF generated in the discharge was detected online by gas photoacoustic spectroscopy. The absorption peak of HF molecule near 1312.59 nm was selected as the absorption spectral line, and a resonant photoacoustic cell was designed. To improve the detection sensitivity of HF, wavelength modulation and second-harmonic detection technology were used. The online monitoring of HF in the simulated GIS corona discharge fault was successfully realized. The experimental results show that the sensitivity of the designed photoacoustic spectroscopy detection system for HF is 0.445 μV/(μL/L), and the limit of detection (LOD) is 0.611 μL/L.

Accurate quantitative detection for trace gas has long been the center of failure diagnosis for gas-insulated equipment. An absorption spectroscopy-based detection system was developed for trace SF₆ decomposition SO₂ detection in this paper. In order to reduce interference from other decomposition, ultraviolet spectrum of SO₂ was selected for detection. Firstly, an excimer lamp was developed in this paper as the excitation of the absorption spectroscopy compared with regular light sources with electrodes, such as electrodeless lamps that are more suitable for long-term monitoring. Then, based on the developed excimer lamp, a detection system for trace SO₂ was established. Next, a proper absorption peak was selected by calculating spectral derivative for further analysis. Experimental results indicated that good linearity existed between the absorbance and concentration of SO₂ at the chosen absorption peak. Moreover, the detection limit of the proposed detection system could reach the level of 10⁻⁷. The results of this paper could serve as a guide for the application of excimer lamp in online monitoring for SF₆-insulated equipment.