Gas-insulated Electrical Equipment Research Articles

Online Detection of Hydrogen Fluoride under Corona Discharge in Gas-Insulated Switchgear Based on Photoacoustic Spectroscopy.

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.

External-Cavity Quantum Cascade Laser-Based Gas Sensor for Sulfur Hexafluoride Detection

The external-cavity quantum cascade laser (ECQCL) is an ideal mid-infrared (MIR) spectral light source for determining large molecular-absorption spectral features with broad transition bands. For this paper, a gas sensor system was developed using a broadband tunable ECQCL and a direct absorption spectroscopy detection scheme with a short path absorption cell of 29.6 cm. For spectral signal detection, a cheap and miniaturized quartz crystal tuning fork- (QCTF) based light detector was used for laser signal detection. The characteristics of the QCTF detector were theoretically simulated and experimentally observed. To demonstrate this sensing technique, sulfur hexafluoride (SF6) was selected as the analyte, which can be used as an effective indicator to identify fault-types of gas-insulated electrical equipment. Preliminary results indicated that a good agreement was obtained between experimentally observed data and reference spectra according to the NIST database and previous publications, and the gas sensor system showed a good linear response to SF6 gas concentration. Finally, Allan–Werle deviation analysis indicated that detection limits of 1.89 ppm for SF6 were obtained with a 1 s integration time, which can be further improved to ~0.38 ppm by averaging up to 131 s.

Synthesis of sphere-like WO3 and their application to SO2 sensing

The detection of SO2, one of the main SF6 decomposition gases, can be applied to diagnose faults in gas-insulated electrical equipment. In this study, spherical WO3 nanoparticles were prepared by a simple hydrothermal method. Their physical phase, microstructure and ability to sense SO2 gas were investigated by various techniques. The experimental results show that the spherical gas sensors of WO3 have excellent performance for SO2 gas detection in terms of selectivity, response time and operating temperature, and can be used for effective detection of the major decomposition products of SF6.

POFBG-Based Humidity Detection Method for Insulating Gas in Electrical Equipment

The accumulation of moisture content undoubtedly threatens the safe operation of gas-insulated electrical equipment. On-line humidity monitoring of SF6 is an important way to check the insulation status of live equipment. This paper presents a direct optical measurement method based on a Polymethyl Methacrylate Fiber Bragg Grating (POFBG) sensor for the humidity detection requirement of SF6 gas with a very small water content. The experiments results show that this method is feasible with the sensitivity and resolution of the POFBG sensor studied being 14.3pm/%RH and 0.1%RH in the range of 8.4~30.4%RH. Additionally, the temperature variation can affect the relative humidity change of GIS and other sealed containers. Therefore, a reduction method of relative humidity centered on the initial baseline conditions under the condition of constant water content is also proposed. It can eliminate the error in relative humidity measurement caused by temperature variation.

Investigation on insulation properties of HFO‐1336mzz(E) and N 2 /CO 2 mixtures as SF 6 substitutes in gas‐insulated electrical applications

The emissions of SF6 have been restricted owing to 3400 years of atmospheric lifetime and high global warming potential (GWP) as an insulating gas in gas-insulated electrical equipment. In this study, HFO-1336mzz(E) and N2/CO2 mixtures are proposed as SF6 substitutes for their short atmospheric lifetime, low GWP and superior insulation performance. The GWP of HFO-1336mzz(E) is only 18 and its atmospheric lifetime is days to weeks. The breakdown voltage of 15% HFO-1336mzz(E) and N2/CO2 mixtures is nearly equal to that of pure SF6 under alternating current. The self-recovery ability of HFO-1336mzz(E) and CO2 mixtures is superior to that of HFO-1336mzz(E) and N2 mixtures. The decomposition characteristic of HFO-1336mzz(E) shows that a tiny amount of its gas might initiate a carbonisation reaction to form carbon after multiple breakdown tests, which is verified by observations using energy dispersive X-rays spectroscopy and scanning electron microscope. The acute toxicity test of HFO-1336mzz(E) indicates that the gas is non-toxic. The results show that HFO-1336mzz(E) and N2/CO2 mixtures are potential substitutes for SF6 in electrical applications.

Morphological Characteristics of Molybdenum Disulfide and Current Application on Detecting SF6 Decomposing Products

MoS2 has been considered a potential novel material in various fields due to thelarge specific surface area, high carrier mobility and tunable electronic properties. However, with the increasing demand for substrate properties, different strategies have been made to achieve its high performances, usually by adopting the method of controling microstructure. SF6 gas-insulated electrical equipment has gained considerable attention in electric system with the advantages of small volume, high security, strong breaking performance and fracture tolerance high-pressure. Nevertheless, in the process of equipment operation, the SF6 gas will occur inevitably decomposition due to partial discharge, resulting in the deterioration of insulation performance of the equipment. Therefore, detecting SF6 decomposition products is of positive significance for the safe and stable operation of power system. In this mini-review, we start from the synthesis of various MoS2 morphological structures. Then, the beneficial characteristics of the unique synthesized nanostructures at present are analyzed. Besides, we focus on the gas-sensing mechanisms and applications of the MoS2 based sensors for detecting SF6 decomposition products. Finally, the future development in this field is proposed.

Theoretical Analysis of the Decomposition Pathways and Species of Environmentally Friendly Insulation Gas C6F12O Based on the DFT and TST

C6F12O (1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)pentan-3-one) is one of the most potential alternative insulation medium to SF6 due to its excellent electrical strength and environmental effect. Although several works on the insulation and decomposition properties of C6F12O have been carried out in recent years, the detailed decomposition pathways and mechanism of C6F12O haven’t been revealed up to now. A comprehensive analysis of the decomposition mechanism of C6F12O is performed through high-level quantum chemistry calculations with DFT and TST in this paper. The results show that more than ten decomposition products are formed. C4F10(a), C5F12(b), and CO can be used for evaluating slight failures. C3F8, C2F6, C2F4, C3F6, C4F10(b), C5F12(a), C6F14(a) and C6F14(b) etc. can be taken as typical products when a general failure is caused in the equipment. CF4 can be used as a basis for determining whether a serious failure has occurred in the gas-insulated electrical equipment. According to the analysis, primary decomposition products such as C4F10(a) and C5F12(b) have relatively high dielectric strength. Besides, the concentration of decomposition products of C6F12O is low to have a major impact on the overall electrical performance at normal conditions. However, the insulation properties of C6F12O gas mixtures after the prolonged operation or multiple arc extinctions deserve further investigation. In the view of human safety and environmental effect, several toxic products such as C2F4, CO, and C3F6 should be effectively managed and handled with care. This paper could provide a theoretical basis for related engineering applications.

The detection and quantification of heptafluoroisobutyronitrile(C4F7N) and its decomposition products by infrared spectroscopy and chemometrics.

As an excellent alternative gas for sulfur hexafluoride(SF6), heptafluoroisobutyronitrile(C4F7N) has received widespread attention. C4F7N gas mixture has the potential to be applied to gas-insulated electrical equipment due to its good insulation properties. Quick and easy quantification of the gas mixture and its decomposition products has great significance. In this paper, the infrared spectroscopy is used to detect the three decomposition products of hexafluoropropene(C3F6), carbon monoxide(CO), and carbonyl fluoride(COF2). Combining chemometrics, a partial least squares(PLS) analysis model of C4F7N and its decomposition products is established. Quantitative analysis of CO, C3F6 and C4F7N is achieved by infrared spectroscopy and chemometrics. The research provides new ideas for the decomposition products detection and future online monitoring of alternative gas-insulated equipment.

The adsorption properties of environmentally friendly insulation gas C4F7N on Zn (0 0 0 1) and ZnO (1 0 [formula omitted] 0) surfaces: A first-principles study

Recently, C4F7N has been considered as one of the most promising candidates to replace SF6 due to its excellent insulation performance and environmental-friendly property. Metal zinc is widely used as a coating material in gas-insulated electrical equipment. However, its compatibility with C4F7N has never been explored before. In this paper, the adsorption properties of C4F7N on Zn(0 0 0 1) and ZnO(1 0 1¯ 0) surfaces were theoretically studied by a first-principles calculation. Adsorption energy, total charge transfer, density of states, and electron density difference were calculated to evaluate the compatibility of C4F7N with Zn and ZnO. The results demonstrated that the interaction between C4F7N and ZnO(1 0 1¯ 0) is stronger than that of Zn(0 0 0 1). The dissociation pathway of C4F7N after adsorption on the ZnO(1 0 1¯ 0) surface was also determined, which shows that ZnO(1 0 1¯ 0) has a catalytic effect on the decomposition process of C4F7N. Compared with Al(1 1 1) and Cu(1 1 1), the dissociation of C4F7N on ZnO(1 0 1¯ 0) has a higher energy barrier, indicating that the reaction is more difficult to occur. As a result, Zn and ZnO have certain compatibility with C4F7N, which was also verified by experiments. Therefore, we infer that Zn shows potentials to be used as anti-corrosion coating in C4F7N gas-insulated electrical equipment.

Decomposition characteristics of C4F7N/CO2 mixture under AC discharge breakdown

Recently, the C4F7N/CO2 mixture has been highly considered as a promising SF6 alternative due to its low greenhouse effect and excellent electrical performance. Apart from its dielectric strength and arc-quenching capability, the decomposition characteristics of C4F7N/CO2 also play an important role in its future applications in gas-insulated electrical equipment. Therefore, decomposition experiments of the C4F7N/CO2 mixture were carried out under multiple AC discharge breakdowns by using a needle-to-plate electrode configuration. The compositions of the gas mixture before and after breakdowns were detected by using a gas chromatography-mass spectrometer. The results show that a trace amount of C3HF7 exists in the C4F7N product; the decomposition of the C4F7N/CO2 mixture mainly produces CO, CF4, CO2, C2F4, C2F6, C3F8, CF3CN, C3F6, C4F6, C4F10, C2F5CN, C2N2, HCN, C2F3CN, and HF. As the number of breakdowns increases, the content of most decomposition products increases significantly, while the content of C3HF7 decreases. The possible formation pathways of the decomposition products were determined, and the corresponding reaction enthalpies were calculated by quantum chemistry calculation. Relevant results not only reveal the decomposition characteristics of C4F7N/CO2 under AC breakdowns but also help us to better understand the corresponding physicochemical mechanisms, which will provide a good reference for stable operation and safe maintenance in applications.

Experimental and theoretical analysis on decomposition and by-product formation process of (CF3)2CFCN mixture

Although sulfur hexafluoride (SF6) is widely used in gas-insulated electrical equipment due to the excellent electrical insulation and arc-interruption behaviors, its strong greenhouse effect with high glow warming potential (GWP) has been driving the research on environmentally friendly gases for SF6 alternatives. Recently, the heptafluoro-isobutyrontrile (CF3)2CFCN (3M NovecTM 4710) is reported to have the potential to replace SF6. The decomposition characteristic of gas insulating medium is one of the basic conditions to measure whether it has the feasibility of replacing SF6. However, the decomposition characteristic of (CF3)2CFCN and the formation mechanism of by-products are still unclear. In this paper, a series of AC corona discharge experiments were performed, and the gas by-products of (CF3)2CFCN mixed with CO2, N2 and air were qualitatively analyzed by gas chromatography mass spectrometry (GC/MS) method, respectively. Then, the decomposition mechanism of (CF3)2CFCN molecule and the formation mechanism of gas by-products were studied via density functional theory (DFT) method. The results show that the major gas by-products are CO, CO2, C2O3F6, CF4, C2F6, C3F6, C3F8, C2F4, (CF3)3CF, CF3CN, C2F5CN and CNCN, in addition to trace amounts of F3CC≡CCF3 and CF3CF=CFCF3. Among the three initial dissociation pathways of (CF3)2CFCN molecule, a C-CF3 bond fission pathway that produces CF3CFCN and CF3 radicals is identified as the thermodynamically favorable channel. The bond energy of C–CF3 bond calculated at M06-2X/def2-QZVP//M06-2X/6-311G(d,p) level is 94.7 kcal/mol.

Study on the properties of compounds formed by the reaction of SF6 gas with metal electrode

Plenty of solid products will be produced when the arc discharge fault occurs in SF6 gas-insulated electrical equipment, which will extremely threaten the internal insulation properties of the equipment. Therefore, it is necessary to carry out research on the solid products formed by the reaction of SF6 with metal electrode under electric arc, aiming to study their effect on the operation of the equipment. First of all, the formation characteristics of the solid products with different metal electrodes and different pressures are studied. Then, the composition of the solid products is determined. Besides, the quantitative relationship between the mass of the solid products and the discharge energy is analyzed as well.

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.

DC corona discharge from floating particle in low pressure SF/sub 6/

The final objective of this research project is clarification of the particle-triggered corona mechanism in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas-insulated electrical equipment as well as development of high precision diagnostic method of foreign metallic particle in GIS insulated by SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas using the electrical signal due to corona discharge. The following research steps are conducting to achieve our goal: 1) clarification of particle-triggered corona phenomena in air which is well-understood corona mechanism, 2) clarification of particle-triggered corona phenomena under dc and ac applied voltage in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas at low pressure in which a stable corona occurred, and 3) clarification of the pressure effect on the particle-triggered corona mechanism. This study is the second step of our research series research, which focuses on characteristics and the mechanism of particle-triggered corona discharge in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas on the basis of measurements of corona current pulses at a pressure range of 30 kPa to 50 kPa under dc applied voltage. The identification of positive and negative corona pulses in SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6 </sub> gas from the waveform, amplitude and repetition rate of corona current pulses is difficult; thus, current and light pulses of coronas from the both tips of particle were measured simultaneously to discriminate the polarity of corona current pulses. Experiments showed that near the corona onset voltage, positive corona accompanied pulse current but negative corona tended to be glow-like corona. As the applied voltage was increased, negative corona changed into streamer type accompanying strong current pulse. Positive corona pulses maintained a small amplitude with an instantaneously high repetition rate, even if the field enhancement on the positive tip of particle occurred due to the positive-ion inflow to the particle produced by negative corona. On the basis of current pulse measurements, the mechanism of particle-triggered corona was discussed. Moreover, corona activity and breakdown voltage were investigated by changing the particle position. This study confirmed that the active corona development and fall in breakdown voltage were due to the effect of intermittent short-circuit arc in the minor gap between particle and electrode when the particle was in the vicinity of the electrode

Sulfur hexafluoride and the electric power industry

The use of gas-insulated electrical equipment has a demonstrated value for society. The problems relating to SF/sub 6/ are not without solution and can lead to new opportunities. To this end, besides the current efforts to curtail the releases of SF/sub 6/ into the environment, a comprehensive and focused program is needed to develop alternative gaseous insulators and alternative high-voltage technologies.