Gas Insulated Research Articles

The Characteristics of CF₃I Dielectric Barrier Discharge

The high global warming potential (GWP) of sulfur hexafluoride (SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ) pushed the researcher to find an alternative environmentally friendly gas for high voltage applications. Trifluoroiodomethane (CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I) has attracted a great deal of attention as new insulation gases. This article has investigated the use of CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I in dielectric barrier discharge (DBD) based on a 1-D model. Three symmetric waveforms named sinusoidal, triangular, and the clipped waveform was used as a feeding voltage with a frequency of 5 kHz and amplitude of 5 kV. The obtained results revealed that the discharge current consists of many sequential current pulses at each half of the applied voltage and the number of these pulses depends on the waveform of the applied voltage. The discharge current pulses are identical during the positive and negative halves of the applied voltage which refer to the CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> I providing a stable DBD discharge regardless of the polarity of the applied voltage. The first discharge current peak moment, for each waveform and during each half of the cycle, has been selected as the characteristic parameter to investigate the discharge characteristics. At the moment of the first current peak, for all tested waveforms, the results showed that the spatial distribution of the electric field across the gap takes a shape of the letter V referring to the minimum point of the electrical field inside the discharge gap dividing the gap to electronegative and electropositive parts.

Effects of High Magnetic Field on Partial Discharge and Flashover Behavior of Epoxy Resin

High-field magnets use epoxy resin as the insulation for superconducting coil terminals. Surface flashover on the interface between the gas and solid insulation will cause insulation failure. In this paper, effects of high magnetic field on surface partial discharge and surface flashover of the epoxy resin are investigated. Experimental results show that high magnetic field causes the decrease of relative permittivity and further changes the electric field distribution along the surface of epoxy resin. Surface partial discharge behavior is directed by both the decrease of surface electric field at the interface and the decrease of breakdown voltage of air gap in high magnetic field. Lorentz force begins to play a role during the extension of electron avalanche by changing the migration of charge carriers and weakening the equivalent effect of the normal electric field near the triple junction. Opposite trends are observed with the increase of magnetic flux density when the direction of Lorentz force is parallel or perpendicular to the surface of epoxy resin.

Trend of Sulfur Hexafluoride (SF6) Gas Mixtures and Other Alternatives as Insulation Gas: an Overview

Research works are actively ongoing to seek a solution for reducing the usage of sulfur hexafluoride (SF6) as a gas insulator in high-voltage equipment since it was listed as one of the greenhouse gases under the Kyoto Protocol. However, manufacturers still in favor of using SF6 due to its excellent insulation and arc-quenching properties. One way to reduce SF6 usage is to mix it with other gases or replace it with alternative gas mixtures. The research status of SF6 gas mixtures and other potential substitutes is summarized in this paper. Electrical insulation properties, physical and chemical mechanisms, and environmental considerations, along with the scope and limitations of such mixtures were analyzed. The development prospects of SF6 gas mixtures were forecasted based on their best mixture ratio. Hybrid insulation gases consisting of three compounds (two electronegative gases with one buffer gas) have shown to be an ideal compromise in terms of cost, distinguished low environmental impact, and high dielectric strength. Trifluoroiodomethane (CF3I) offers great advantages among other dielectric gases, since it exerts minimal greenhouse effects, and has a considerable liquefaction temperature and higher dielectric strength. Therefore, the application of CF3I for reducing the usage of SF6 in gas mixtures was highlighted. The fundamental knowledge on the breakdown strength of the gas mixtures and their behavior under different electric fields need to be analyzed before any recommendations can be made.

Instability of a viscous liquid sheet under the influence of a tangential electric field

The linear stability analysis has been analyzed for an electrified liquid sheet confined between two symmetric dielectric movable ambient gas. The present study aims to estimate the planer jet systems response when applying a tangential electric field. The dispersion relations for varicose and sinuous modes have been formulated. The electrical Euler number and some flow parameters have been tested for their influence on the electrified liquid sheet instability. In other words, the effects of electric field on the dominant wave number, and instability range (cutoff wave number) are discussed. The results clarify that the tangential electric field has a stabilizing effect for sinuous mode over the whole range of gas velocity ratio. On the other hand, for varicose mode, the electric field slightly improves the system stability to a certain limit, but it has a great role in stability for higher values of gas velocity ratio.

SF 6 decomposition and insulation condition monitoring of GIE: A review

The statistics of the Conference International des Grands Reseaux Electriques (CIGRE) indicate that the operational reliability of SF6 gas-insulated equipment (GIE) is very high; however, the failure rate of the GIE in operation is much higher than that of the IEC standard, and the fault occurs frequently in the GIE at a high voltage level. The reason is due to the complex and strong on-site electromagnetic interference environment and fully enclosed structure of GIE. The key method and technology for effective on-line monitoring and fault diagnosis of GIE are still lacking. Given the partial strong electromagnetic energy and high temperature induced by early latent insulation faults in the equipment, SF6 gas insulation presents different degrees of decomposition. The decomposition products mainly include SO2F2, SOF2, SO2, HF, and H2S. The decomposition characteristics of SF6 are closely related to the property of insulation faults. At present, this area is attracting attention from the power industry and research institutes. This study summarises the current research on SF6 decomposition component analysis (DCA). The content mainly includes the latest progress of SF6 decomposition characteristics and mechanism under fault conditions, and fault diagnosis methods based on decomposition components.

Influence of Temperature on Surface Discharge Characteristics of PEEK under Positive Repetitive Square Voltage

PEEK (Polyetheretherketone) and N2 are used as the frame material and insulation gas in the packaging of high voltage power electronic devices, respectively. Considering the IGBT device in normal operation, the chip will produce a large amount of Joule heat, which will increase the temperature of the insulation material in sub-modules. However, there has been no investigations on the influence of temperature on the surface discharge characteristics and mechanisms under positive repetitive square voltage (PRSV). In this paper, surface discharge current pulses and optical photos of surface streamer propagation of PEEK in N2 at different temperatures are collected under PRSV. The effects of different temperatures on discharge current pulse, charge quantities of discharge and time delay of discharge are analyzed in detail. Besides, the surface trap parameters at different polarization temperatures are measured by TSDC. The effects of temperature on the effective ionization rate, surface trap depth and densities are revealed. A reasonable model is used to explain the role of surface traps in the streamer propagation along the surface of PEEK. Besides, the time delay theory is introduced to quantitatively analyze the effect of temperature on the time delay of forward discharge (FD) and backward discharge (BD). The influence mechanism of temperature on specific pulse parameters of discharge current, time delay of discharge and charge quantities of discharge are all analyzed on the basis of the trapping and detrapping of surface electrons and ions at different temperatures.

Nonlinear Materials Applied in HVDC Gas Insulated Equipment: From Fundamentals to Applications

The electric field distortion along the gas-solid interface on insulators in GIS or GIL greatly threatens their long-term insulation performance. In recent years, with the developments of field grading materials, their application on GIS/GIL insulators has been considered as an effective approach to suppressing the field distortion and enhancing the insulation property. Many reviews about field grading materials had been published. However, these articles rarely focus on the nonlinear materials and their unique characteristics when used in gas insulated equipment. Compared with traditional applications, such as cable accessories, generator coils, and motor stator bars, nonlinear materials in GIS/GILs are mainly used for grading the surface electric field and avoiding unwanted charge accumulations. Hence, there are two characteristics of the material that need to be paid special attention to-the surface insulation performances and the charge release functions-which are not so critical in previous applications. In this paper, first, types and principles of several commonly used nonlinear grading materials are summarized briefly. Then, the existing application cases of nonlinear materials in gas insulation equipment are sequentially introduced from the optimization ideas, material selection, manufacturing process, and using effects. Finally, the problems encountered in the application of field grading materials in practice are discussed. Suggestions for the follow-up studies are given in order to guide the application of nonlinear materials in GIS/GIL insulators.

Breakdown Characteristics of Cone-type ε-FGM Spacer for Gas Insulated Switchgears

Breakdown Characteristics of Cone-type ε-FGM Spacer for Gas Insulated Switchgears

New Method of Leak Rate Measurement in SF6 Free Medium Voltage Switchgear Using Helium and Ambient Air

Abstract The current medium voltage Gas Insulated Switchgears (GIS) predominantly use Sulphur Hexafluoride (SF6) as insulation medium. The leakage tests performed on GIS use either SF6 or Helium medium to ensure gas tightness. However, SF6 has been strictly regulated for the last years due to the high global warming potential effect on the planet. As a response, new technologies are emerging using air as insulation medium. The present work establishes a basic comparison of the leakage rate in a medium voltage GIS using two different leak detection methods: Helium leak detector and Residual Gas Analyser (RGA). Both methods use Helium and additionally RGA using air as tracer gas.

Foreign Body Detection and Analysis in Gas Insulated Switchgear Based on Vibration Signal

Maintenance tools are often left inside the equipment in the process of installation and maintenance of Gas Insulated Switchgear (GIS). Vibration detection can make up for the shortcomings of foreign body detection in traditional GIS to a certain extent. In this paper, the vibration signal during the operation of the circuit breaker is collected and analyzed based on the 330kV GIS test platform. Through the method of Ensemble Empirical Mode Decomposition (EEMD), by comparing with the multiple measurement results between the two cases of whether there is a foreign body in the equipment or not, it is found that there is a great difference in the characteristics of the two kinds of vibration signals. The presence of most foreign objects can be detected by the above methods.

Improved DC surface insulation performance of epoxy resin by gradient plasma fluorination

In order to improve the flashover voltage of the disc insulator in gas insulated transmission line under DC voltage, this paper considers reducing the electric field intensity on the surface by adjusting the surface conductivity distribution. Based on the joint simulation of improved particle swarm optimization algorithm and finite element, the surface conductivity gradient partition optimization model is constructed to obtain the optimal surface conductivity distribution sequence. The relationship between conductivity and treatment time is obtained by plasma fluorination, and the gradient distribution of the surface conductivity of the sample is realized by adding different ring polytetrafluoroethylene baffles. Microscopic tests are used to characterize the differences between different regions of the sample surface. The two-dimensional (2D) electric potential distribution, 2D charge density distribution, electric field intensity distribution and flashover voltage on the sample surface under pre-charging conditions are studied and compared with the simulation results. The results show that the maximum field strength of the sample with gradient treatment can be reduced by 71% and the flashover voltage can be increased by 45%. The research in this paper provides a good reference and theoretical support for the surface modification of disc insulators, such as the surface parameters with gradient distribution.

Effect of annealing temperature on optical, dielectric and NH3 gas sensing properties of ZnxFe3−xO4 (x = 0 and 0.5) nanoparticles synthesized by sol-gel auto-combustion method

The effect of annealing temperature and Zn doping on structural, magnetic, optical, dielectric, and gas sensing properties of iron oxide nanoparticles have been investigated. For this purpose, ZnxFe3−xO4 (x = 0 and 0.5) nanoparticles have been synthesized using sol-gel auto-combustion method. The samples are annealed at 200, 400, and 500 °C temperatures for 6 h. With the increase in annealing temperature, for x = 0, the transition from Fe3O4 (magnetite, cubic) to α-Fe2O3 (hematite, rhombohedral) phase is confirmed from the XRD analysis. With Zn doping, independent of annealing temperatures, for ZnxFe3−xO4 nanoparticles, the cubic spinel structure is evidently observed. The lattice constant of iron oxide nanoparticles increases with Zn2+ doping. With increase in annealing temperature and with Zn doping in iron oxide nanoparticles, the particle size decreases from 63.89 nm to 29.25 nm. With the increase in annealing temperature and doping with Zn in iron oxide, the reduction in the band gap is observed. Dielectric properties of synthesized ZnxFe3−xO4 (x = 0 and 0.5) nanoparticles have been investigated as a function of frequency. At room temperature, the sensitivity (%) as a function of flow rate have been investigated and observed that ZnxFe3−xO4 (x = 0 and 0.5) nanoparticles annealed at 500 °C achieved the highest sensitivity towards NH3 gas. For Zn doped iron oxide nanoparticles, the enhanced sensitivity is attributed to smaller particle size and increased specific surface area as compared to that of host nanoparticles.

Evaluation of structural, dielectric and LPG gas sensing behavior of porous Ce3+- Sm3+ doped Cobalt nickel ferrite

The Co0.5Ni0.5CexSmyFe2-x-yO4 (CNCSF) XRD pattern revealed the purity of the samples without any secondary phase. The crystallite size CNCSF are in nano range. Further, the calculated lattice parameter of CNCSF are found to increasing with the RE content. From SEM micrographs surface morphology and the microstructure of the CNCSF was studied. The porous nature of the samples is revealed by SEM, which will aid in increasing their sensing response. Energy dispersive X-ray spectroscopy (EDS) patterns have confirmed the stoichiometric presence of Co2+ Ni2+, Ce3+, Sm3+ and Fe3+, those are used to prepare the CNCSF. The dielectric behaviour is similar to that of conventional spinel ferrite structures, in that the dielectric constant is highest at low frequencies and decreases at higher frequencies due to electron hopping, resulting in dielectric dispersion. Only one semicircle is seen in each Cole-Cole plot, which has uncovered that the contribution to conductivity is predominantly from the grain boundaries. At room temperature, the gas sensing responses of CNCSF thin films were investigated. For liquified petroleum gas (LPG), the gas sensing characteristics of the prepared thin films were investigated. At room temperature, the x = 0.03 thin films showed excellent sensitivity to liquified petroleum gas. The sensing response and recovery time of all of the thin films that had been prepared were reported. The sensing response of x = 0.03 thin films was highly stable over a period of 60 days on exposure to LPG (1000 PPMv), according to the stability analysis. The sample thin film with x = 0.03 can be utilized in gas sensor technology, particularly for the detection of LPG at room temperature, due to its increased sensitivity, quick response and recovery times, and stability.

Partial Discharge yang Merusak Isolasi SF6 pada Gas Insulated Switchgear (GIS) Tiga Fasa Pengaruh Keberadaan Partikel Asing

This paper analyzes the effect of the presence of foreign particles on an equilateral arrangement of 3 phase gas insulated switchgear (GIS) insulation equipment. Gas Insulated Switchgear (GIS) that uses SF6 insulation, partial discharge will occur as the insulation ages and there are several other factors that affect the insulation. Partial Discharge needs to be detected to avoid failures that cause damage to equipment in theGIS. In this calculation, the electric field characteristics will be analyzed in 3-phase equilateral GIS by varying the location of the particles in the GIS tank. Particles are modeled to have a length of 5 mm and a thickness of 0.5 mm located in a 3 phase GIS equilateral arrangement with a tank diameter of 150 mm and a conductor diameter of 25 mm. The electric field calculations are reviewed at several points in the 3-phase equilateral GIS tank. The simulation and calculation of the electric field were calculated with FEM method software. The results of the calculations show that thereare differences in the characteristics of the electric field between normal GIS and GIS where foreign particles are present. The difference in these characteristics can be seen in the magnitude of the electric field, and the ratio of eccentricity from some point of view.

Automatic Optimization of Gas Insulated Components Based on the Streamer Inception Criterion

Gas insulated transmission lines (GILs) are used in electrical systems mainly for power transmission and High Voltage substation interconnection. In this paper, we focus on the development of complex numerical tools for the optimization of gas insulated HVDC components by the estimation of realistic electric field distribution and the voltage holding of the designed geometry. In particular, the paper aims at describing the correct modelling approach suitable to study high voltage components in DC, considering the nonlinear behaviour characterizing the electrical conductivity of solid and gas insulators. The simulated field distribution is then adopted to estimate the voltage holding of the dielectric gas, with a convenient engineering technique, based on the streamer criterion. These two tools are integrated in an automatic optimization package developed in COMSOL® and MATLAB®, with the purpose of adjusting the critical geometry features, suffering from excessive electrical stress and possibly giving rise to electrical breakdown, in order to guide the designer towards a robust solution.

First-Principles Calculations for Adsorption of HF, COF2, and CS2 on Pt-Doped Single-Walled Carbon Nanotubes.

HF, CS2, and COF2 are three important decomposition components of the SF6 gas insulation medium. In this paper, the gas sensitivity of Pt doped on (8, 0) single-walled carbon nanotube (SWCNT) to HF, CS2, and COF2 is investigated based on density functional theory. The binding energy, charge transfer, density of states, and frontier molecular orbital theory are discussed. It is found that all processes of HF, CS2, and COF2 adsorbed on Pt-SWCNT are exothermic. Pt-SWCNT donated 0.182 electrons to CS2 molecules during the interaction process but acts as an electron acceptor during adsorption of HF and COF2 on it. After comprehensive consideration of binding energy and charge transfer, the response of Pt- SWCNT to CS2 may be the best, and those to HF and COF2 are almost the same. In addition, after the adsorption of the three kinds of gases on Pt-SWCNT, the order of the conductivity of the Pt-SWCNT material is CS2 > COF2 ≈ HF via frontier molecular orbital theory analysis. The Pt-SWCNT material is probably more suitable as a gas sensor for the detection of CS2 in the application of gas-insulated equipment.

Detection of decomposition products of SF6/air gas mixture by electron attachment mass spectrometry

Sulphur hexafluoride (SF6) is widely used in gas insulation, and its decomposition products can be used to diagnose potential insulation failures. Quick and accurate detection of decomposition products can help to understand equipment-operating conditions in time. In this study, the decomposition products of SF6/air gas mixtures under different pulsed discharge voltages were studied. It was found that the main products were SOF2, SO2F2, SO2, CF4 and SOF4, and the yields of SOF2, SO2F2, SO2 and SOF4 increased with the number of discharge pulse. The productive rate of SOF2, SO2 and SOF4 were positively correlated with the discharge voltage, and when the discharge voltage increased from 5 to 15 kV, their yields after 50,000 discharges increased by 49%, 120% and 1100%, respectively. The productive rate of SOF2 and SO2 were positively correlated with the proportion of air in the gas mixtures while that of SOF4 was opposite. When the proportion of air increases from 0% to 90%, their yields after 50,000 discharges became 270%, 3169% and 10% of the originals, respectively. In addition, the productive rate of SO2F2 was not affected by discharge voltage and the proportion of air in the gas mixtures. SO2F2, SOF2, SOF4 and SO2 can be used as the basis for judging the discharge failures and the discharge degree of power equipment.

1 MV Rectifier With SF6-Gas Insulation and Cooling for ITER Neutral Beam Injector System

This article presents the development results of a five-stage dc-1 MV rectifier for an international thermonuclear experimental reactor neutral beam injector system. Each rectifier outputs -200 kV, and the total five rectifiers are connected in a series. The feasibility of both gas insulation and gas cooling for semiconductor devices was validated to achieve dc-1 MV output and 1-h continuous operation. We devised a novel structure of cylindrical dense alignment of the heatsinks with stud-type diodes, which enables both the mitigation of electric-field concentration on the heatsinks and the improvement of heat dissipation from diodes. The difference in the temperature rise for three different directions of the heatsink in an SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas atmosphere was also clarified. The heat flow was analyzed to quantify the cooling effect of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas, taking into account the gas circulation by the external cooling system. Rectification operation and temperature rise were tested with an actual-scale rectifier including a step-up transformer. Additionally, dc-1.2 MV withstand voltage was tested for a fifth-stage actual-scale rectifier. The test results demonstrated the validity of the proposed design.

Optical charged sensing detection technology for H2S, SO2, CS2 and CF4 gas of sulfur hexafluoride decomposition products

In view of the current situation that it is difficult to prevent and control in advance the generation of trace H2S, SO2, CS2 and CF4 gases by SF6 gas insulation equipment under fault conditions, there is no effective monitoring method and detection device. This paper studies the gas detection technology based on the UV spectrum and non dispersive infrared analysis, deeply studies the spectral characteristics of low Concentration H2S, SO2, CS2 and CF4 gas with the SF6 as background gas, and simulates the spectral absorption capacity. According to the absorption spectrum line and its variation with temperature and pressure, the concentration inversion algorithm is fitted to improve the effective detection ability of the instrument. Using optical fiber sensing technology, an optical path structure suitable for on-line detection of high-voltage equipment is designed. Using the characteristics that the optical signal is free from electromagnetic interference, the transmission of optical signal by optical fiber is studied, and finally the on-line analysis of the trace H2S, SO2, CS2 and CF4 gas components in the high-voltage equipment is realized. The high-voltage switch model is constructed through three-dimensional modeling, and its fault tolerance and anti-interference ability are analyzed. The stray light and space light are analyzed by simulation software, and the effects caused by vibration and deformation are simulated. The on-line optical fiber sensing detection method of H2S, SO2, CS2 and CF4 gas in high-voltage GIS equipment is proposed. The optical noise suppression technology suitable for the field is studied, the optical path system is designed to withstand the gas pressure of high-pressure equipment, and the influence of field vibration and temperature change of high-pressure equipment on the optical path structure is solved. The on-line gas detection experiment was carried out, and the automatic calibration simulation device of the optical path system was calibrated to ensure the accuracy and stability of H2S, SO2, CS2 and CF4 gas detected by the optical path system.

Design and Characterization of a Magnetic Loop Antenna for Partial Discharge Measurements in Gas Insulated Substations

A recent investigation explored a new measuring concept used in partial discharges (PD) measurements in gas insulated substations (GIS), consisting of a magnetic loop antenna. The sensor’s frequency response was characterized up to some tens of MHz. This paper proposes an improved version of the sensor with an extended bandwidth (BW) one order of magnitude higher: a resonance, attributed to a common mode current in the mounting hole, is identified and eliminated employing ferrite beads in the feeder cables. Moreover, this publication proposes an electric circuit model that fully covers the transverse electromagnetic mode (TEM) frequency range in GIS. The electric model is compared against experimental measurements using a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</i> GHz bandwidth testbench, giving accurate results. Two contributions are achieved in this research: an improved magnetic loop antenna with extended bandwidth and an accurate electric circuit model. This publication paves the way for further research on time resolution and signal postprocessing techniques for magnetic loop antennas in GIS.