Arc-quenching Medium Research Articles

SF6 Gas Humidity Prediction Model Based on Deep Learning

SF6 gas is widely used in Gas Insulated Switchgear(GIS) as an insulating and arc extinguishing medium in electric power industry. However, SF6 gas humidity has a significant impact on the performance and reliability of GIS equipment. The accurate prediction of humidity level is one of the keys to ensure the long-term stable operation of GIS equipment. Traditional humidity prediction methods are often limited by model complexity and data processing ability, which is difficult to meet the actual demand. In this paper, deep learning, as a powerful data-driven approach, shows great potential in gas humidity prediction. An efficient SF6 gas humidity prediction model for GIS equipment is constructed based on deep learning algorithm. The deep learning model can learn complex feature representations from a large number of historical data, and then accurately predict SF6 gas humidity.

Study on Breakdown Characteristics and Attenuation Characteristics of Air Mixed Gas

Abstract Nowadays, the global demand for environmental protection and energy saving is getting higher and higher. In the past, SF6 gas was regarded as an environmentally unfriendly gas in the circuit breaker with SF6 gas as the insulating medium. In order to save energy and reduce emissions, this paper uses clean and environmentally friendly air as the arc extinguishing medium. The gas mixture studied contains N2, O2 and CO2. Through two approximate values of Boltzmann equation, we obtain the electron energy distribution function of air mixed gas under different electric field reduction conditions. By studying the changes of ionization and adsorption coefficients of particles under various collision conditions, we obtained the conversion breakdown field strength (E/N) Cr of air mixture. An arc attenuation model is built to characterize the arc attenuation characteristics using the prior transport characteristics as input. The arc attenuation process is broken down into three steps: heat recovery, pre-ignition, and arcing. All of these phases are determined by the changes in axial temperature and arc conductance over time. Analysis is done on the air and nitrogen thermal recovery and pre-dielectric recovery phases. This study explores the use of clean dielectrics to ensure optimum performance of primary equipment in the power system, based on current circumstances.

Comparison of machine learning algorithms based on machine learning for the prediction of thermal plasma physical parameters of C4F7N and CO2 environmentally friendly gas mixtures

With the goal of “carbon peak and carbon neutrality,” the need for environmentally friendly gases to replace SF6, a high greenhouse effect gas, is urgent. C4F7N, as an environmentally friendly gas with the greatest potential to replace SF6 as an arc extinguishing medium in circuit breakers, can be mixed with CO2 to greatly improve the shortcomings of its high liquefaction temperature, and the calculation of the physical parameters of the mixed gas plasma is a prerequisite for the computational simulation of the arc process in the opening of circuit breakers. Because solving the physical parameters is expensive, based on the system of differential equations, this paper adopts several machine learning algorithms by mining the relationship between the data using the known physical parameter data to predict the results of the physical parameters to be solved under certain conditions, which greatly reduces the cost of computation. The machine learning algorithms used in this paper are K-nearest-neighbor regression, decision tree, random forest, support vector machine, and gradient boosting regression, of which for the support vector machine, hyperparameters find it difficult to determine the problem of optimization using the gray wolf algorithm. The prediction results of several algorithms show that they are more accurate and that the problem can be solved better by using the method of machine learning. Finally, the comparison results show that the support vector machine exhibits better performance in most cases and that the gray wolf algorithm can make the results of the support vector machine more accurate.

Monitoring SF6 Gas Leakage Based on a Customized Binocular System

Sulfur hexafluoride (SF6) gas is extensively utilized as an insulating and arc-quenching medium in the circuit breakers and isolating switches of electrical equipment. It effectively isolates the circuits from the atmosphere and promptly extinguishes arcs. Therefore, the issue of SF6 gas leakage poses a significant threat to the related application fields, and the detection of SF6 gas leakage becomes extremely important. Infrared imaging detection offers advantages including non-contact, high precision, and visualization. However, most existing infrared detection systems are equipped with only one filter to detect SF6 gas. The images captured contain background noise and system noise, making these systems vulnerable to interference from such noises. To address these issues, we propose a method for monitoring SF6 gas leakage based on a customized binocular imaging (CBI) system. The CBI system has two filters, greatly reducing the interference of system noise and background noise. The first filter features the absorption resonant peak of SF6 gas. The second filter is used to record background noise and system noise. One aspect to note is that, in order to avoid the interference of other gases, the central wavelength of this second filter should keep away from the absorption resonant peaks of those gases. Accordingly, the central wavelengths of our customized filters were determined as 10,630 nm and 8370 nm, respectively. Then, two cameras of the same type were separately assembled with a customized filter, and the CBI prototype was accomplished. Finally, we utilized the difference method using two infrared images captured by the CBI system, to monitor the SF6 gas leakage. The results demonstrate that our developed system achieves a high accuracy of over 99.8% in detecting SF6 gas. Furthermore, the CBI system supports a plug-and-play customization to detect various gases for different scenarios.

Rapid Recovery Technology of SF6/N2 Mixed Insulation Gas in Electrical Equipment

SF6 mixed gas is widely used as an insulation and arc extinguishing medium in electrical equipment in cold regions of northern China. Due to its low liquefaction temperature, existing gas recovery technologies are unable to achieve efficient and rapid recovery of SF6/N2 mixed insulation gases. In response to this challenge, a two-stage membrane separation and recovery technology has been proposed, which can efficiently and quickly separate SF6 and N2 from the mixed gas. The volume fraction (V/V) of obtained product SF6 gas reaches 90%, and the use of compression and refrigeration units can achieve rapid filling of 50 m3/h mixed gas. At the same time, the enrichment and recovery of trace SF6 gas in the exhaust gas are achieved. After enrichment, the volume fraction (V/V) of SF6 gas reaches 92%, and the volume fraction (V/V) of SF6 gas in the emptied mixed gas is 600 μL/L, far below the national standard value, solving the problems in actual production.

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.

Eco-friendly gas insulating medium for next-generation SF6-free equipment

Gas-insulated equipment (GIE) that utilizes the most potent greenhouse gas sulfur hexafluoride (SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> ) as insulation and arc-quenching medium has been widely used in the power industry. Seeking eco-friendly insulating gas with advanced performance for next-generation SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> -free GIE is significant for the “net-zero” goal and sustainable development. In this paper, the utilization, emission, and reduction policies of SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> around the world were summarized first. Then, we systematically reviewed the latest progress in comprehensive performance evaluation of eco-friendly insulating gas in terms of molecular design, dielectric insulation, arc-quenching, stability and decomposition, materials compatibility, biosafety, etc. Further, the representative applications of eco-friendly insulating gas in medium-voltage, high-voltage GIE as well as relevant maintenance-related technologies were highlighted. Accordingly, the existing challenges and future perspectives were proposed, presenting a roadmap to hopefully steer the development of eco-friendly insulating gas and GIE.

Transport Coefficients of H2–Cu/Al2O3 Plasma Mixtures Considering Solid and Liquid Status

Obtaining the plasma transport coefficients of the mixed system of arc-extinguishing medium and erosion product is the precondition of numerical simulation of erosion–diffusion in an arc chamber. In this article, the minimum Gibbs free energy method was used to calculate the composition of the H2–Cu/Al2O3 system, including solid and liquid copper (aluminum oxide), because copper and aluminum oxide are commonly used as electrode and ceramic materials in hydrogen dc contactors, respectively. The transport coefficients of H2–Cu/Al2O3 system and the phase transition of erosion products provide the basis for the subsequent simulation of erosion–diffusion of electrode and arc chamber in the H2 plasma. Results revealed that: 1) in the low-temperature range, copper (aluminum oxide) mainly exists in the form of a solid or a liquid state, resulting in the transport coefficients of the H2–Cu/Al2O3 system consistent with that of the H2 system; 2) as temperature increases, the copper (aluminum oxide) undergoes gasification (sublimation–decomposition) reaction that exists in a gaseous state and begins to affect the transport properties of the H2–Cu/Al2O3 system; in particular, the proportion of copper (aluminum oxide) has the most significant effect on viscosity; and 3) as the temperature continues to rise, atoms and molecules in the H2–Cu/Al2O3 system are completely ionized and the proportion of copper (aluminum oxide) has little effect on the transport properties (except electrical conductivity) of the H2–Cu/Al2O3 system. Finally, the transport coefficients of H2–Cu/Al2O3 plasma mixtures are reliable enough, in engineering application aspect, to be applied for simulation of erosion–diffusion in hydrogen dc contactors.

Study of the dielectric breakdown strength of CO2–O2 mixtures by considering ion kinetics in a spatial–temporal growth avalanche model

The gas mixture CO2–O2 has been considered as an insulation and arc-quenching medium in gas-insulated switchgears. In this paper, the dielectric breakdown properties of CO2–O2 mixtures at different O2 concentrations and gas pressures were studied theoretically by considering ion kinetics in a spatial–temporal growth avalanche model. A kinetic scheme that includes all the main reactions likely to occur in CO2–O2 mixtures is presented. An improved method to calculate the dielectric strength of the gas mixture is developed, based on an avalanche model that considers both spatial growth and temporal processes. Next, the reaction rates of ionization, attachment, detachment and ion conversion, the effective ionization Townsend coefficient αeff/N, and reduced critical electric field strength (E/N)cr in CO2–O2 mixtures at different mixing ratios and gas pressures are analyzed in detail. Finally, a pulsed Townsend experiment is performed to verify the validity and accuracy of the calculation method. Based on this, one detachment reaction rate is modified to yield more accurate results. Better consistency between the results and the experimental values supports the validity of the kinetic system, reaction rates, and the improved calculation method.

Arc decomposition behavior of C 4 F 7 N/Air gas mixture and biosafety evaluation of its by‐products

At present, reports on the arc interruption and decomposition behaviour of a C4F7N/air gas mixture especially the biosafety of its by-products are limited. Herein, a 57% C4F7N/43% air gas mixture was employed as an arc-quenching medium to conduct 200 breaking tests on a load switch (630 A/24 kV). The arc interruption and decomposition behaviour of the gas mixture were evaluated, and the biosafety of the decomposition products was assessed based on an acute inhalation toxicity test. It was found that the average arcing time of the 200 breakings was about 10.1 ms and that breakings were basically completed at the zero-crossing of the second or third current half-cycle. The gas mixture after breaking decomposed dramatically (the C4F7N content decreased by 75.6%), generating a large number of gaseous by-products (CO, CF4, C2F6, C3F8, CF3CN, C4F8, CO2, C4F10N2, C3F6, C2N2, etc.) as well as solid by-products (carbon particles). The lethal concentration (LC50) of 50% (LC50, 4 h) of C4F7N/air after 200 breakings was 31 ppm (male mice) and 34 ppm (female mice), respectively, and the toxicity was classified as Grade 1. In general, C4F7N has an arc interruption capability, albeit weaker than that of SF6 under the same conditions. After breaking, the C4F7N gas mixture has a relatively high acute inhalation toxicity, and relevant safety protection measures for research or operation personnel are strictly needed.

AC Current Interruption Characteristics of Liquid Nitrogen

There is an increasing tendency to integrate several High-temperature superconducting equipment into a network. Along with it is the increasing demand for cryogenic power switches that could work in the liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) to reduce temperature transfer areas. However, none of the current AC arc extinguishing mediums could work reliably in the LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . As the insulation and cooling medium of the HTS equipment, LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> can be a potential arc extinguishing medium due to its strong cooling effect. However, the AC interruption performance of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is unknown up to now. The objective of this paper is to obtain the AC interruption performance of the LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . A free-burning type and a magnetic blowout type LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> switch are tested, respectively. Current ranging from 1 kA to 6.3 kA is conducted. Heat loss of the arcing process is also calculated. Experimental results show that a 2700 A AC is successfully interrupted by the free burning type switch at a 10 mm gap. The increase of the contact gap leads to slight growth in current interruption ability. Meanwhile, the magnetic blowout type can interrupt an AC higher than 6300 A. Based on the high interrupting properties of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , a potential application in novel environmentally friendly switchgear is proposed. The LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> switch in the switchgear can switch the closed-loop current that could be typically more than 50% of the continuous current. Meanwhile, the heat loss generated during the arcing process will not add an extra burden to the cooling system of the switchgear.

Effect of Arc Chute on DC Current Interruption by Liquid Nitrogen in HTS Electrical System of Distributed Propulsion Aircraft

The distributed propulsion aircraft with HTS electrical system is a novel concept for future airliners, which can reduce by more than 70% fuel burn and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> emissions. The circuit breakers ensure the security of this novel aircraft by isolating electrical faults timely. Solid-state circuit breakers (SSCBs) are preferred due to their fast response and high performance in the cryogenic circumstance. However, the high conduction loss of SSCBs impedes their further application. A mechanical switch using liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) as an arc extinguishing medium shows excellent DC current interruption performance. The LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> switch is characterized with extremely low contact resistance, and the proper use may reduce the conduction loss of power switches significantly. Nevertheless, the effect of metal type arc chutes on the arcing process in the LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is still not clear. Thus the objective of this paper is to understand the effect of metal type arc chutes on the current interruption performance of LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Silicon iron arc chutes are employed. Neodymium (NdFeB) magnets are used to stretch the arc into the arc chutes. The maximum interrupting current is 1 kV/ 2 kA when only magnets are applied. Further applying the arc chutes leads to a significant drop in the arc voltage and interruption performance. Since the high relative permeability of silicon iron weakens the magnetic field acting on the arc, metal type arc chutes are not recommended. 1 kV / 10 kA fault current is successfully cleared by the combination of resistance type superconducting fault current limiter (R-SFCL) and LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> switch with magnets, during which the R-SFCL responds to the fault within 420 μs, compensating the long clear time of the LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> switch.

Room temperature monitoring of SF6 decomposition byproduct SO2F2 based on TiO2/NiSO4 composite nanofibers

Sulfuryl fluoride (SO2F2) is one of the ideal decomposition components of sulfur hexafluoride (SF6), which is widely used as an insulating and arc extinguishing medium in gas-insulated switchgear. To detect the decomposition component of SF6 at room temperature, the use of SO2F2 is still a challenge. In this work, we have successfully fabricated TiO2 nanofibers and nickel sulfate (NiSO4 NPs) via simple electrospun and hydrothermal methods, followed by calcination process to improve the sensing performance. Metal oxide semiconductor materials (MOSs) are widely used in gas sensing applications due to their superior performance and fast recovery speed. Although the performance of our TiO2/NiSO4 composite nanofiber sensor decreases at higher temperatures, it shows an excellent response to target gasses at room temperature. Ni-decoration on the outer surface of the nanofibers could maximize the sensing response of 100 ppm SO2F2 by up to 189% at room temperature, showing that the TiO2/NiSO4 composite nanofibers are 2.5 times superior to the pure TiO2 nanofiber sensors. Thus, the approach for this novel composite nanofiber-based material is promising for the fabrication of superior gas sensors for decomposition of SF6.

Numerical study of polymer-ablation arc with polyacrylic acid + H2O mixture

As described in this paper, we proposed the adoption of polyacrylic acid (PAA) with H2O, which becomes PAA + H2O mixture gel, as an ablation medium for arc quenching in a low-voltage DC circuit breaker. It is well known that H2O is a highly arc-quenching medium, but it has been difficult to use H2O in liquid phase directly as an arc-quenching medium. The arc performance of PAA + H2O mixture gel was studied using numerical and experimental approaches. Numerical thermofluid simulation was conducted to obtain the arc temperature and gas flow distribution at different H2O mixing ratios in PAA + H2O gel. To consider ablation of PAA + H2O gel, a method of alternately arranging PAA and H2O in the ablation wall was also proposed. Calculation results demonstrate that increasing the H2O mixing ratio in PAA + H2O mixture gel makes the arc narrower in the temperature and electrical conductivity distributions. The experimentally obtained results also indicate that arcs confined in PAA + H2O mixture gel with higher H2O mixture become narrower than those in PAA or other materials. Moreover, arcs confined by PAA + H2O mixture gel with higher H2O mixing ratio enhance the arc resistance rapidly. The results suggest that PAA + H2O mixture gel can have higher arc-quenching performance than pure polymers.

Types of overvoltages in 10-35 kV distribution networks and modern methods and means of their limitation

The basis for the transmission of electrical energy from sources to receivers are overhead power lines 10-35 kV. In these networks, an isolated transmission line or transmission line, grounded through resistors or using arc-quenching reactors, is used. The Republic of Mari El uses networks with isolated transmission line, the total length of which is more than 7000 km. When operating distribution networks, their insulation is affected by a number of internal factors such as long-term operating voltage and voltage fluctuations, short-term overvoltages associated with arc closures, wire breaks, and insulation overlaps. These networks are located on an open area, so they are exposed to lightning overvoltages, temperature, wind loads (mechanical forces), precipitation (snow, humidity). Overvoltages occurring in electrical systems are one of the main factors that significantly affect the reliability of power supply. Despite the short-term effects, overvoltages are characterized by a high multiplicity with respect to the long-term operating voltage, the impact on all electrically connected elements of the system, regardless of the place of occurrence. Overvoltage is the main cause of defects and accelerated aging of structural components. Currently, 90 % of 10-35 kV overhead lines are made on the basis of the use of reinforced concrete structures of supports that require grounding devices, depending on the value of the soil resistivity. Highspeed vacuum circuit breakers are used as switching devices in modern distribution networks of 10-35 kV. The specific properties of vacuum as an arc-quenching medium contribute to the transients in their switching, which require scientific understanding.

Research on Influence Factors and Acceleration Methods of Current Commutation

The vacuum interrupter is widely used due to the advantages of no arc-extinguishing medium and high insulation strength. However, the arc voltage generated by the commonly used CuCr contacts is low. In hybrid DC circuit breakers (DCCB), hybrid automatic transfer switches (ATS), medium voltage compound switches and other fields, it is difficult to rely on vacuum arc to complete natural commutation, which restricts the development of hybrid switches. In order to understand the current commutation process deeply, the influence of internal and external factors on the current commutation is analyzed by experiments. The coupling mathematical model of arc-commutated branch is established. The criterion for the success of current commutation is summarized. The parameters of the arc model are reconstructed through repeated breaking experiments to explore the influence of internal factors on the arc characteristics. Based on this, the influence law of arc current, contacts gap and transverse magnetic field (TMF) is analyzed. An acceleration method of current commutation is proposed. A prototype for accelerating experiments with an electromagnetic repulsion mechanism and TMF is developed. The commutated branch equivalent to practical applications is built. The experimental results show that the commutation time is effectively shortened and meets the requirements of practical applications through the acceleration method, which provides new thought for the development of hybrid switches.

Experimental Test of Superconductor Fault-Current Switchgear Using Liquid Nitrogen as the Insulation and Arc-Quenching Medium

With an impressive dielectric constant of 1.43 at 77.3 K, liquid nitrogen (LN2) has the potential to be used as a promising insulation medium for next-generation power switchgear protection systems. It can potentially replace the conventionally used SF6 gas. We have the privilege of having firsthand knowledge of the arc conditions in LN 2 . This paper deals with the experimental approach of first limiting the fault current using an SFCL, and then, interrupting it using the LN 2 switch and a controlled magnetic field. This is a series of totally R&D based tests to show that the limited fault currents can be interrupted using LN 2 as an arc quenching medium. The experiments were conducted on 50 Hz, 500 VAC. Nine-meter superconducting tapes were used to limit the prospective current of 15.7 kA into 800 Amps. The 800 Amps were tested to be interrupted using the LN 2 switch. The electrode gaps were taken to be 35 mm for all the cases. Pure copper and aluminum alloy (Al6061) made electrodes were employed. NdFeB (N35 type) magnets were used to control the shape, size, and direction of the arc plasma. Total circuit voltages, arc voltages, SFCL voltages, arc currents, and arcing times were measured. The optical observations were done using a high-speed camera. Some very important and preliminary results were achieved. All the interruption tests were successful. The results show that the prospective currents were limited by the SFCL within 1 ms and the LN 2 switch extinguished arcs in 2.1 ms.

Partial discharge detection and diagnosis in gas insulated switchgear: State of the art

Power utilities are struggling to reduce power failure incidents in substations and their components to operate more reliably and economically [1]. Many power failures are produced directly or indirectly because of the insulation system of utility components [2], [3]. The selection of the insulation should ensure power plant operational continuity along with completely resolving or significantly limiting the actual power system's failures [4]. Gas insulated substations (GIS) have the best insulation performance which ensures achieving minimum failure incidents, although at high installation cost. The most common insulating gas used in GIS is Sulfur hexafluoride (SF 6 ) gas, which is widely used as an effective electrical insulation as well as an arc-quenching medium [5]. Basic GIS and gas insulated transmission lines (GITL or GIL) consist of a conductor supported by solid insulators inside an enclosure filled with SF 6 gas or its mixture [6].

Failure analysis of arc ablated tungsten-copper electrical contacts

Tungsten-copper (WCu) contact materials are the core components of high-voltage electrical switches. However, significant arc ablation effect at high voltage and high current often leads to connection interruption and mechanical loss, which seriously affects the safe operation of appliances. In this paper, the failure mechanisms of tungsten-copper contact materials caused by significant arc ablation in the sulfur hexafluoride (SF6) atmosphere were investigated. Results showed that the arc ablation of contact materials is mainly caused by the evaporation and splashing of copper component which has a low melting point, followed by the ablation and spallation of the tungsten (W) skeleton structure. All of these have roughened the surface of contact materials and then further accelerated the volatilization of copper (Cu) component and the reactions between the contact materials and arc extinguishing medium of SF6. Finally, the contact materials lost their functions of arc extinguishing and current switching. Simulated experimental work has also been performed and it verified the above observed failure mechanisms of contact materials. Due to the instantaneously high temperature and high voltage generated during the arcing, both the Cu and W phases in the WCu alloy have suffered significant evaporation and mass losses.

Influence of trace H 2 O and O 2 on SF 6 decomposition products under arcing conditions in electric power equipment

SF6 has been widely used as an insulating and arc extinguishing medium in electric power equipments. Detection of gas decomposition products is an important means for condition monitoring and fault diagnosis. Trace H2O and O2 have a significant influence on the species and concentrations of SF6 decomposition products. It is important to explore the influence mechanism of trace H2O and O2 on SF6 decomposition products under arcing conditions. A series of SF6 decomposition tests were carried out on a 40.5kV SF6 circuit breaker, and a gas chromatograph and an electrochemical sensor were used to measure decomposed components. First, the H2O content remained constant, and the O2 content and arcing energy changed in the tests. It has been found that the decomposition products of SF6 are SOF2, SO2, CO, CO2, CF4, C2F6 and C3F8. Then, the O2 content remained constant, and the H2O content changed. The decomposition products are mainly SOF2, SO2, CO and CO2. Concentrations of all these decomposition products increase first and then tend to be stable slowly over time, but change differently with the increase of H2O and O2 contents, because H2O and O2 play different roles in the formation process of each decomposition characteristic components.