SF6 Decomposition Research Articles

Adsorption Properties of Pt/N-doped Graphene for SF6 Decomposition Species

Adsorption Properties of Pt/N-doped Graphene for SF6 Decomposition Species

Gas-sensing properties of Pb, Pd modified C3N4 for SF6 decomposition products detection: A DFT study

The detection of SF6 decomposition products plays an important role in the diagnosis and evaluation of the discharge faults of SF6 insulation equipment. The effects of Pb/Pd modification on the gas-sensing properties of C3N4 material to H2S, SO2, SOF2, and SO2F2 were studied. The adsorption capacity of pristine C3N4 to SF6 is very weak or even does not react. Pb/Pd significantly improves the conductivity and gas sensitivity of C3N4. The adsorption performance of Pb-C3N4 and Pd-C3N4 on SF6 decomposition products is significantly improved, and the reaction rate is fast. The conductivity of the adsorption system changes obviously after the adsorption of four gases. The types and concentrations of SF6 decomposition products can be identified according to the varying degrees of electrical conductivity. The band gaps of Pd-C3N4 adsorption systems after H2S, SO2, SOF2, and SO2F2 adsorption are 0.019 eV, 0.024 eV, 0.023 eV, and 0.007 eV, respectively. This study provides an effective method for online diagnosis and evaluation of discharge faults of SF6 insulation equipment.

Adsorption behaviors, electronic and gas-sensing properties of C3N4 monolayers and heterojunctions for SF6 decomposition products

We investigated systematically adsorption behaviors, electronic and gas-sensing properties of SF6 decomposed gases, i.e., H2S, SO2, HF, SOF2 and SO2F2, on the C3N4 monolayers and heterojunctions via first-principles methods. The pure C3N4 monolayer was predicted to be reusable gas sensors for H2S detection with high sensitivity at room temperature in a dry environment. We further found two stable configurations of the C3N4/graphene heterojunctions, (simply as R-C3N4/graphene and T-C3N4/graphene). Their stabilities were confirmed by lattice mismatch, binding energy and MD simulations, and both of them can be distinguished via their different optical properties. Finally, we found that the T-C3N4/graphene heterojunction has little sensitivity to SF6 decomposed species, which indicates that the T-C3N4/graphene heterojunction is unaccommodated for SF6 decomposed gas sensor, however, the R-C3N4/graphene heterojunction could be viewed as a promising gas sensor towards H2S, SOF2, and SO2F2, whether the humidity exists or not.

Comparison of Gas-sensitive properties of Au, Ag and Cu Metal-doped GaNNT for SF6 decomposition gases

SF6 gas will produce various decomposition products When the partial discharge fault occurs in SF6 gas-insulated equipment, resulting in significantly reduced insulation performance of the insulated equipment. Early latent insulation faults in gas-insulated equipment can be diagnosed by monitoring the concentration of SF6 typical decomposition products (H2S, SO2, SO2F2 and SOF2) inside the insulated equipment. Gallium nitride nanotubes (GaNNT) have shown promising applications as gas-sensitive materials for sensors, and the gas-sensitive properties of the materials can be better improved by doped-metal. Therefore, the Density functional theory (DFT) calculation approach is proposed to compare with the gas-sensitive response characteristics of Au, Ag and Cu metal-doped GaNNT (M−GaNNT) to SF6 typical decomposition gases in the paper. The adsorption mechanism is analyzed by band structure, density of states, frontier molecular orbital theory and differential charge density, and the results are in high consistency. The metal-doped GaNNT introduces a large number of impurity bands which makes the probability of electrons crossing the forbidden band to reach the conduction band larger, and thus the gas-sensitive characteristics are improved. The adsorption of gases by M−GaNNT causes the resistivity of the system to vary, and sensing response (SR) and response time (RT) of M−GaNNT adsorbs gases are also analyzed. The results show that the ability of metal-doped GaNNT is Ag-GaNNT>Cu-GaNNT>Au-GaNNT, and the average values of SR are 516.9, 29.3 and 8.7, respectively. Ag-GaNNT has higher selectivity for SO2F2 gas. In summary, it shows that Ag-GaNNT is a potential gas-sensitive material that can be a new material for the online monitoring of fault gas content in gas-insulated equipment.

Trace photoacoustic SO2 gas sensor in SF6 utilizing a 266 nm UV laser and an acousto-optic power stabilizer.

A sulfur dioxide (SO2) gas sensor based on the photoacoustic spectroscopy technology in a sulfur hexafluoride (SF6) gas matrix was demonstrated for SF6 decomposition components monitoring in the power system. A passive Q-switching laser diode (LD) pumped all-solid-state 266 nm deep-ultraviolet laser was exploited as the laser excitation source. The photoacoustic signal amplitude is linear related to the incident optical power, whereas, a random laser power jitter is inevitable since the immature laser manufacturing technology in UV spectral region. A compact laser power stabilization system was developed for better sensor performance by adopting a photodetector, a custom-made internal closed-loop feedback controller and a Bragg acousto-optic modulator (AOM). The out-power stability of 0.04% was achieved even though the original power stability was 0.41% for ∼ 2 hours. A differential two-resonator photoacoustic cell (PAC) was designed for weak photoacoustic signal detection. The special physical constants of SF6 buffer gas induced a high-Q factor of 85. A detection limit of 140 ppbv was obtained after the optimization, which corresponds to a normalized noise equivalent absorption coefficient of 3.2 × 10-9 cm-1WHz-1/2.

Long-term corona behaviour and performance enhancing mechanism of SiC/epoxy nanocomposite in SF6 gas environment

Surface coating technology is an effective way to solve the interface insulation problem of DC GIS/GIL basin insulators, but the performance of the coating will change greatly, and the insulation strength will be completely lost, after long-term use in the extreme conditions of corona erosion. In this research, the multi-needle-plate electrode platform was constructed to explore the long-term use performance of SiC-doped nanocomposite exposed to corona discharge in SF6 gas. Samples with a high SiC content have advantages in maintaining physical and chemical properties such as elemental composition, erosion depth, surface roughness and mass loss. The nanocomposite doped with 6 wt.% SiC has prominent surface insulation strength after long term exposure to corona, and the others are close to losing, or have completely lost, their insulating properties. Furthermore, the degradation mechanism of physicochemical properties of composite exposed to corona discharge was investigated with the proposed ReaxFF MD model of energetic particles from SF6 decomposition bombarding the epoxy surface. The reaction process of SF particles and F particles with the cross-linked epoxy resin, and the SiC nanoparticles providing shelter to the surrounding polymer and mitigating their suffering direct bombardment, have been established. The damage propagation depth, mass loss and surface roughness change of nanocomposite material bombarded by SF6 decomposition products is reproduced in this simulation. Finally, the deterioration mechanism of insulation properties for the SiC-doped composite was elucidated with DFT analysis. The band gap of the molecule containing S drops directly from the initial 7.785 eV to 1.875 eV, which causes the deterioration of surface electric properties.

SF6 decomposition behaviour under partial discharge of typical insulation defects in gas‐solid insulated valve‐side bushing of converter transformer

AbstractIn this paper we investigated SF6 decomposition behaviour of typical insulation defects in gas‐solid insulated converter transformer valve‐side bushing under partial discharge (PD). Additionally, we compared the results with that of gas insulated switchgear (GIS). The results indicated that SF6 decomposition behaviour varies with the insulation defects type. For metal protrusion defects, the proportion ranking of CO2 and SO2 can be related to whether the needle tip is wrapped with epoxy resin‐impregnated paper (ERIP). The proportion of carbon‐containing products is much higher under contamination defect than under other defects. Moreover, the proportion of carbon‐containing components is higher under flashover condition than under PD condition and is accompanied by the appearance of H2S and CS2. However, the yield of SO2F2 is always low. Compared to negative DC voltages, positive DC voltages have a higher proportion of carbon‐containing components, mainly in the form of more CO2 and less SOF2. Compared to the PD decomposition behaviour of typical insulation defects in GIS, when PD involves ERIP, the proportion of carbon‐containing products, especially CO2, is significant higher, while the proportion of sulphur containing products, especially SO2F2, is lower.

Highly Sensitive SF6 Decomposition Byproducts Sensing Platform Based on CuO/ZnO Heterojunction Nanofibers

Hydrogen sulfide (H2S) and sulfur dioxide (SO2) are two typical decomposition byproducts of sulfur hexafluoride (SF6), commonly used as an insulating medium in electrical equipment; for instance, in gas circuit breakers and gas insulated switchgears. In our work, fiber-like p-CuO/n-ZnO heterojunction gas sensing materials were successfully prepared via the electrospinning method to detect the SF6 decomposition byproducts, H2S and SO2 gases. The sensing results demonstrated that p-CuO/n-ZnO nanofiber sensors have good sensing performance with respect to H2S and SO2. It is noteworthy that this fiber-like p-CuO/n-ZnO heterojunction sensor exhibits higher and faster response–recovery time to H2S and SO2. The enhanced sensor performances can probably be attributed to the sulfuration–desulfuration reaction between H2S and the sensing materials. Moreover, the gas sensor exhibited a high response to the low exposure of H2S and SO2 gas (below 5 ppm). Towards the end of the paper, the gas sensing mechanism of the prepared p-CuO/n-ZnO heterojunction sensors to SO2 and H2S is discussed carefully. Calculations based on first principles were carried out for Cu/ZnO to construct adsorption models for the adsorption of SO2 and H2S gas molecules. Information on adsorption energy, density of states, energy gap values and charge density were calculated and compared to explain the gas-sensitive mechanism of ZnO on SO2 and H2S gases.

Multi-mechanism collaboration enhanced photoacoustic analyzer for trace H2S detection

To realize the real-time highly sensitive detection of SF6 decomposition product H2S, a multi-mechanism collaboration enhancement photoacoustic spectroscopy analyzer (MCEPA) based on acoustic resonance enhancement, cantilever enhancement and excitation light enhancement is proposed. An SF6 background gas-induced photoacoustic cell (PAC) was used for acoustic resonance (AR) enhancement of the photoacoustic signals. A fiber-optic acoustic sensor based on a silicon cantilever is optimized and fabricated. The narrow-band acoustic signal enhancement based on cantilever mechanical resonance (MR) is realized in the optimal working frequency band of the PAC. A fiber-coupled DFB cascaded an Erbium-doped fiber amplifier (EDFA) realized the light power enhancement (LPE) of the photoacoustic signals excitation source. Experimental results show that the MR of the fiber-optic silicon cantilever acoustic sensor (FSCAS) is matched with the AR of the PAC and combined with the LPE, which realizes the multi-mechanism collaboration enhancement of weak photoacoustic signals. The Allan-Werle deviation evaluation showed that the minimum detection limit of H2S in the SF6 background is 10.96 ppb when the average time is 200 s. Benefiting from the all-optimization of photoacoustic excitation and detection, the MCEPA has near-field high-sensitivity gas detection capability immune to electromagnetic interference.

Adsorption of SF6 decomposition gases on Ag2O(1,2)-WSe2 monolayers: A DFT study

The internal faults of gas-insulated switchgear (GIS) will be detected through analyzing the decomposition products of its insulating gas. We present a new gas sensing material based on the Ag2O doped WSe2. The adsorption properties of Ag2O(1,2)-WSe2 monolayer upon four SF6 decomposed gas (H2S, SO2, SOF2, SO2F2) were investigated by the density functional theory (DFT). Different adsorption structures were built to analyze the adsorption energy, band structures, density of states. For further analysis, differential charge density, molecular orbital theory and recovery time are also investigated. Results indicate that Ag2O(1,2)–WSe2 has the potential to be a promising material to detect these gases in GIS.

High-sensitivity Detection Technology of SF6 Decomposition Product H2S Based on Multi-pass Photoacoustic Cell

High-sensitivity Detection Technology of SF6 Decomposition Product H2S Based on Multi-pass Photoacoustic Cell

Construction of LaF3 QD-modified SnS2 nanorod composites for ultrasensitive detection of H2S

In this paper, LaF3 QD modified SnS2 nanorods were used to create an ultrasensitive sensor for detecting the SF6 decomposition product H2S.

The adsorption and decomposition of SF6 over defective and hydroxylated MgO surfaces: A DFT study

Plasma degradation is one of the most effective methods for the abatement of greenhouse gas sulfur hexafluoride (SF6). To evaluate the potential of MgO as a catalyst in plasma degradation, we investigate the catalytic properties of MgO on SF6 adsorption and activation by density functional theory (DFT) where the O-defective and hydroxylated surfaces are considered as two typical plasma-generated surfaces. Our results show that perfect MgO (001) and (111) surfaces cannot interact with SF6 and only physical adsorption happens. In case of O-defective MgO surfaces, the O vacancy is the most stable adsorption site. SF6 undergoes a decomposition to SF5 and F over the O-defective MgO (001) surface and undergoes an elongation of the bottom S-F bond over the O-defective (111) surface. Besides, SF6 shows a physically adsorption at the stepsite of the MgO (001) surface, accompanied by small changes in its bond angle and length. Furthermore, SF6 is found to be physically and chemically adsorbed over 0.5 and 1.0 ML (monolayer) H-covered O-terminated MgO (111) surfaces, respectively. The SF6 molecule undergoes a self-decomposition on the 1.0 ML hydroxylated surface via a surface bonding process. This study shows that defective and hydroxylated MgO surfaces have the surface capacities for SF6 activation, which shows that MgO has potential as packing material in SF6 waste treatment in packed-bed plasmas.

GIS Fault Prediction Approach Based on IPSO-LSSVM Algorithm

With the improvement of industrialization, the importance of equipment failure prediction is increasing day by day. Accurate failure prediction of gas-insulated switchgear (GIS) in advance can reduce the economic loss caused by the failure of the power system to operate normally. Therefore, a GIS fault prediction approach based on Improved Particle Swarm Optimization Algorithm (IPSO)-least squares support vector machine (LSSVM) is proposed in this paper. Firstly, the future gas conditions of the GIS to determine the characteristic data of SF6 decomposition gas are analyzed; Secondly, a GIS fault prediction model based on LSSVM is established, and the IPSO algorithm is used to normalize the parameters LSSVM. The parameters of c and radial basis kernel function σ2 are optimized, which can meet the needs of later search accuracy while ensuring the global search capability in the early stage. Finally, the effectiveness of the proposed method is verified by the fault data of gas-insulated switch. Simulation results shows that, compared with the prediction methods based on IGA-LSSVM and PSO-LSSVM, the prediction accuracy rate of the proposed method reached 92.1%, which has the smallest prediction absolute error, higher accuracy and stronger prediction ability.

Carbon Monoxide Detection Based on the Carbon Nanotube-Coated Fiber Gas Sensor

Accurate detection of the internal decomposition components of SF6 electrical equipment plays an important role in the evaluation of equipment status. However, gas samples are usually taken out for detection at present, which makes it difficult to understand the real situation inside the equipment. In this paper, a carbon nanotube-coated fiber gas sensor is proposed, which has the potential to be applied as a built-in gas sensor. The fiber loop ring-down (FLRD) gas detection system based on the carbon nanotube-coated fiber gas sensor was built, and the detectable decomposition components among the four typical SF6 decomposition components of SO2, SO2F2 and SOF2 and CO were analyzed. The results showed that the fiber gas sensor was most sensitive to CO. Based on density functional theory, it was found that single-walled carbon nanotubes had the best adsorption effect on CO molecules under the same conditions, with the adsorption energy reaching −0.150 Ha. The detection performance of the system for CO was studied, and the results showed that there was a good linear relationship between CO concentration and ring-down time: R2 was 0.984, the maximum inversion error of 0~200 ppm CO was 1.916 ppm, and the relative error was 4.10%. The sensitivity of the system was 0.183 ns/ppm, and the detection limit of the system was 19.951 ppm. The system had good stability, with the standard deviation of single-point repeatability being 0.00356, and the standard deviation of the long period of the experiment being 0.00606. The research results provide a new idea for the detection of SF6 decomposition components, and lay the foundation for the component detection method of built-in fiber sensor of SF6 electrical equipment.

Detection of SF6 gas decomposition component H2S based on fiber-optic photoacoustic sensing

A high-sensitivity fiber-optic Fabry-Perot (F-P) photoacoustic gas detection system with properties of anti-electromagnetic interference and intrinsically safe was presented for quantitative analysis of SF6 decomposition component H2S. Erbium-doped fiber amplification was combined with acoustic resonance amplification to enhance the photoacoustic signal. A fiber-optic cantilever acoustic sensor (FOCAS) was used to sense weak photoacoustic signals. To enhance the sensitivity and stability of photoacoustic signals detection, the effect of SF6 gas on the responses of FOCAS and photoacoustic cell (PAC) was investigated. When SF6 is the background gas, the resonance frequency of the PAC will be greatly reduced and the sensitivity of the FOCAS will be improved. With the excitation light power of 1 W and an averaging time was 200 s, the minimum detection limit (MDL) of H2S gas in the SF6 background reached 14 ppb, and the normalized noise equivalence absorption (NNEA) was calculated to be 3.14 × 10−9 cm−1·W·Hz−1/2. The combination of excitation enhancement and detection enhancement of the photoacoustic signal solves the problem that the traditional sensor is difficult to improve the detection sensitivity due to the low absorption coefficient of H2S gas in the near-infrared region.

Study on the Detection Characteristics and Response Mechanism of SnS2-Based Sensors for SO2 and SOF2

Based on the wide application of sulfur hexafluoride (SF6) gas in the power industry, the analysis and detection of its decomposition components have become important technical means for state detection and fault evaluation of gas-insulated equipment. The gas-sensitive characteristics and adsorption mechanism of the SnS2 sensor for SO2 and SOF2 gases were investigated using SO2 and SOF2, the main SF6 decomposition components, as the target detection gases. SnS2 gas-sensitive materials and components were prepared, and the temperature response, concentration response, response recovery and stability of the SnS2 sensor for the two SF6 decomposition components were tested based on the gas-sensitive test platform. The results demonstrate that the sensor had the best working performance at 200 °C, with obvious response and ideal recovery for both target gases and good stability in a certain time. Based on the first principle, the SnS2 surface structure model and the target gas adsorption model were established, and the adsorption mechanism was analyzed in terms of frontier molecular orbital theory to verify the correctness of the gas-sensitive test results. The gas-sensitive test analysis and simulation calculation can provide data basis and theoretical support for the study of SF6 decomposition components detected by gas sensors.

Ru doped aluminum nitride monolayer for detecting and scavenging SF6 decomposition components

The SF6 decomposition components detection and elimination are crucial for preventing paralysis of the gas-insulated switchgear (GIS). In this work, Ru doped AlN monolayers with two doping strategies (Ru adatom and Ru substitution) are firstly investigated for selectively sensing and scavenging SF6 decomposition gases (SO2, SOF2, and SO2F2) based on first-principle theory. The most stable structures of Ru adatom and Ru substitution strategies are studied and named Ru-AlN-A and Ru-AlN-S, respectively. The adsorption calculation results show that Ru-AlN-A and Ru-AlN-S possess diacritical adsorption behaviors for SF6 decomposition species. Under the operating temperature, Ru-AlN-A monolayer can serve as the gas sensor or scavenger for selective detecting or removing SO2, SOF2, and SO2F2, whereas Ru-AlN-S monolayer can act as the gas scavenger or one-time gas sensor for SO2 and SOF2 due to the strong adsorption energies. Especially, the adsorption of SO2F2 by Ru-AlN-A makes SO2F2 decompose, while for SOF2, this phenomenon happens when adsorbed by Ru-AlN-S, which is insensitive to SO2F2. The above analysis suggests that Ru-AlN-A and Ru-AlN-S can be explored as novel gas sensors and sweepers for detecting and eliminating the SF6 decomposition species.

A DFT Based Approach to Sense the SF6 Decomposed Gases Using Ni-doped WS2 Monolayer

In this paper, we investigated Ni-doped WS2 (Ni@WS2) to detect the H2S, SO2, SOF2, and SO2F2 gases, which are also decomposition gases of SF6 (sulphur hexafluoride). Hence, Electron Difference density, adsorption length and energy, band structure (B.S.), charge transfer, and density of states (DOS) are detailed and studied in depth. The adsorption energy of SF6 decomposition gases i.e. H2S, SO2, SOF2, SO2F2 on Ni@WS2 are found to be −1.3, −1.46, −1.64, and −1.8 eV, respectively, which is superior as compared to other materials. It has been observed through the band structure analysis that after adsorption of SF6 decomposed gas on Ni modified WS2 bandgap reduces, and as a result, conductivity also changes. The dip in bandgap after adsorption of H2S, SO2, SOF2, and SO2F2 on Ni decorated WS2 can be arranged as Ni@WS2@SO2F2> Ni@WS2@SOF2> Ni@WS2@H2S > Ni@WS2@SO2. In brief, these investigations are very efficacious for detecting H2S, SO2, SOF2, and SO2F2 gases, by Ni-doped WS2 monolayer.

WS₂ Nanostructure-Based Gas Sensor for SF₆ Decomposition Products: Experimental and First-Principles Study

Pompon-like WS2 nanostructure-based gas sensor was fabricated, and the sensing performance with micromechanism to SF6 decompositions was discussed. At optimal working temperature, the sensor experiences resistance increasing for all four SF6 decompositions (SO2, SOF2, SO2F2, and H2S). At low concentration (0–50 ppm), the sensor shows high linearity (R2 > 0.99), and the rank of the sensitivity is: H2S>SO2>SO2F2>SOF2. Furthermore, the first-principles results indicate that the different sensitivity is derived from the chemical interactions and electron transfer between the adsorbed molecule and the edge structures of WS2. This work gives experimental and theoretical support of transition metal dichalcogenide (TMDC)-based gas sensor to detect SF6 decompositions and provides insights to design high-performance TMDC-based gas sensor from theoretical aspect.