Using SF6 Decomposed Component Analysis for the Diagnosis of Partial Discharge Severity Initiated by Free Metal Particle Defect

Theoretical Study on Adsorption Behavior of SF6 Decomposition Components on Mg-MOF-74

SF₆ gas is an arc extinguishing medium that is widely used in gas insulated switchgear (GIS). When insulation failure occurs in GIS, it leads to the decomposition of SF₆ in partial discharge (PD) and other environments. The detection of the main decomposition components of SF₆ is an effective method to diagnose the type and degree of discharge fault. In this paper, Mg-MOF-74 is proposed as a gas sensing nanomaterial for detecting the main decomposition components of SF₆. The adsorption of SF₆, CF₄, CS₂, H₂S, SO₂, SO₂F₂ and SOF₂ on Mg-MOF-74 was calculated by Gaussian16 simulation software based on density functional theory. The analysis includes parameters of the adsorption process such as binding energy, charge transfer, and adsorption distance, as well as the change in bond length, bond angle, density of states, and frontier orbital of the gas molecules. The results show that Mg-MOF-74 has different degrees of adsorption for seven gases, and chemical adsorption will lead to changes in the conductivity of the system; therefore, it can be used as a gas sensing material for the preparation of SF6 decomposition component gas sensors.

Determination of Dielectric Losses in a Power Transformer

The article presents a method of determining dielectric losses that occur in insulating materials in a power transformer. These losses depend mainly on the electric field stress, pulsation, dielectric loss coefficient, and electrical permittivity of insulating materials. These losses were determined by integrating an expression describing unit losses. The determined dielectric losses were compared with the total losses of the transformer. It turned out that dielectric losses are a fraction of a percent of the total losses. The influence of the electrical permittivity of the insulating liquid and paper insulation on the value of dielectric losses was investigated. This influence was ambiguous, which is characteristic of stratified systems made of materials with different permittivity. An analysis of the influence of the dielectric loss coefficient tan(delta) on the value of dielectric losses in the transformer was carried out. The impact of this coefficient on the amount of dielectric losses turned out to be directly proportional.

Optical H2S and SO2 sensor based on chemical conversion and partition differential optical absorption spectroscopy

An optical sensor based on chemical conversion and partition differential optical absorption spectroscopy is developed to detect hydrogen sulfide (H₂S) and sulfur dioxide (SO₂) gas in sulfur hexafluoride (SF₆) decomposition products. Given that the absorption cross sections of SO₂ and H₂S overlap in 170-230 nm band, the differential lines of H₂S are very few, meanwhile the corresponding absorption cross sections are small in comparison to that of SO₂, thus H₂S can be detected by reacting with oxygen to convert to SO₂ in the presence of UV light. Through the concentration variation of SO₂ before and after chemical reaction, the concentration of H₂S can be obtained. Meanwhile the partition differential optical absorption spectroscopy method deduced from Beer-Lambert's law is introduced to weaken the influence of electronic noise on the measuring result, especially in low concentration. The SO₂ detection limit of 12 ppb per meter can be achieved. The optical sensor can measure the concentrations of H₂S and SO₂, so it is suitable for the fault diagnosis of gas insulated switchgear (GIS).

A DFT Study on the Adsorption of H₂S and SO₂ on Ni Doped MoS₂ Monolayer

In this paper, a Ni-doped MoS₂ monolayer (Ni-MoS₂) has been proposed as a novel gas adsorbent to be used in SF₆-insulated equipment. Based on the first-principles calculation, the adsorption properties of Ni-MoS₂ to SO₂ and H₂S molecules, the main decomposition components of SF₆ under a partial discharge (PD) condition have been studied. The adsorption energy, charge transfer, and structural parameters have been analyzed to find the most stable gas-adsorbed Ni-MoS₂. Furthermore, the density of states (DOS), projected density of states (PDOS), and electron density difference were employed to explore the interaction mechanism between SO₂, H₂S, and the Ni-MoS₂ surface. It is found that the H₂S molecule and SO₂ molecule interact with the Ni-MoS₂ surface by strong adsorption energy. Therefore, we conclude that the interaction between these two kinds of gases and the Ni-MoS₂ monolayer belongs to chemisorption, and the Ni-MoS₂ monolayer might be a promising gas adsorbent for the fault recovery of SF₆-insulated equipment. Additionally, we have to point out that all of the conclusions only considered the final adsorption energy, the barrier in the transition state has not been analyzed in this paper.

Electrochemical and Infrared Absorption Spectroscopy Detection of SF₆ Decomposition Products

Sulfur hexafluoride (SF₆) gas-insulated electrical equipment is widely used in high-voltage (HV) and extra-high-voltage (EHV) power systems. Partial discharge (PD) and local heating can occur in the electrical equipment because of insulation faults, which results in SF₆ decomposition and ultimately generates several types of decomposition products. These SF₆ decomposition products can be qualitatively and quantitatively detected with relevant detection methods, and such detection contributes to diagnosing the internal faults and evaluating the security risks of the equipment. At present, multiple detection methods exist for analyzing the SF₆ decomposition products, and electrochemical sensing (ES) and infrared (IR) spectroscopy are well suited for application in online detection. In this study, the combination of ES with IR spectroscopy is used to detect SF₆ gas decomposition. First, the characteristics of these two detection methods are studied, and the data analysis matrix is established. Then, a qualitative and quantitative analysis ES-IR model is established by adopting a two-step approach. A SF₆ decomposition detector is designed and manufactured by combining an electrochemical sensor and IR spectroscopy technology. The detector is used to detect SF₆ gas decomposition and is verified to reliably and accurately detect the gas components and concentrations.