Gas-insulated Lines Research Articles

Atmospheric pressure plasma jet deposition of TiO2 layer on alumina/epoxy to improve electrical properties

Abstract In gas-insulated lines, basin-insulators can accumulate charge under non-uniform electric fields, distorting the field distribution and potentially causing surface flashover, which threatens the stability of power systems. In this study, Atmospheric Pressure Plasma Jet (APPJ) technology was used to deposit TiO2 on the surface of alumina/epoxy (Al2O3/EP) composites. The impact of deposition of TiO2 layer on the surface morphology and chemical composition of Al2O3/EP was studied using testing methods such as Scanning Electron Microscope, X-ray photoelectron spectroscopy, Fourier Transform Infrared Spectrometer, and Energy Dispersive Spectrometer. It was found that APPJ creates a dense, rough Ti-O layer on the Al2O3/EP surface, which bonds tightly with the substrate. The efficacy of APPJ was found to depend on processing time, with optimal results observed at 3 min, DC and AC flashover voltages increased by 29.6% and 15.7%, respectively. TiO2 layer enhances the conductivity of the resin and shallows trap levels. Through the synergistic effects of various factors, surface charges are efficiently dissipated and evenly distributed. This study not only reveals the physicochemical process of TiO2 deposition via APPJ but also integrates surface characteristics with electrical performance. The findings offer a new strategy to enhance surface flashover voltage and ensure equipment safety.

Stationary thermal field in the direct current gas-insulated line

Stationary thermal field in the direct current gas-insulated line

Comparison of simulations of the gas conduction in HVDC GIL by application of nonlinear conductivity model and ion-drift-diffusion model

PurposeGas insulated systems, such as gas insulated lines (GIL), use insulating gas, mostly sulfur hexalfluoride (SF6), to enable a higher dielectric strength compared to e.g. air. However, under high voltage direct current conditions, charge accumulation and electric field stress may occur, which may lead to partial discharge or system failure. Therefore, numerical simulations are used to design the system and determine the electric field and charge distribution. Although the gas conduction shows a more complex current–voltage characteristic compared to solid insulation, the electric conductivity of the SF6 gas is set as constant in most works. The purpose of this study is to investigate different approaches to address the conduction in the gas properly for numerical simulations.Design/methodology/approachIn this work, two approaches are investigated to address the conduction in the insulating gas and are compared to each other. One method is an ion-drift-diffusion model, where the conduction in the gas is described by the ion motion in the SF6 gas. However, this method is computationally expensive. Alternatively, a less complex approach is an electro-thermal model with the application of an electric conductivity model for the SF6 gas. Measurements show that the electric conductivity in the SF6 gas has a nonlinear dependency on temperature, electric field and gas pressure. From these measurements, an electric conductivity model was developed. Both methods are compared by simulation results, where different parameters and conditions are considered, to investigate the potential of the electric conductivity model as a computationally less expensive alternative.FindingsThe simulation results of both simulation approaches show similar results, proving the electric conductivity for the SF6 gas as a valid alternative. Using the electro-thermal model approach with the application of the electric conductivity model enables a solution time up to six times faster compared to the ion-drift-diffusion model. The application of the model allows to examine the influence of different parameters such as temperature and gas pressure on the electric field distribution in the GIL, whereas the ion-drift-diffusion model enables to investigate the distribution of homo- and heteropolar charges in the insulation gas.Originality/valueThis work presents numerical simulation models for high voltage direct current GIL, where the conduction in the SF6 gas is described more precisely compared to a definition of a constant electric conductivity value for the insulation gas. The electric conductivity model for the SF6 gas allows for consideration of the current–voltage characteristics of the gas, is computationally less expensive compared to an ion-drift diffusion model and needs considerably less solution time.

Contact Defect Detection of Gas-Insulated Line Via Thermal–Vibration Feature Fusion and Deep Neural Network Technique

Contact Defect Detection of Gas-Insulated Line Via Thermal–Vibration Feature Fusion and Deep Neural Network Technique

Research on detection technology of sulfur hexafluoride decomposition products of GIL based on carbon nanotubes

Sulfur hexafluoride (SF6) gas is a stable gas that is widely used in gas insulated lines (GILs) in power systems. However, in GIL, SF6 gas is in the environment of high temperature, high pressure and high voltage for a long time, SF6 gas will decompose into toxic gas, damage electrical equipment, and pose a huge threat to human body and ecological environment. In addition, SF6 gas is a greenhouse gas that is strictly forbidden to leak. Once leaked, it will cause great harm to the environment. Therefore, it is necessary to recover and purify the SF6 gas in the power system GIL. In this paper, a molecular model of carbon nanotubes is constructed, and the density functional theory is used to analyze the changes of charge distribution, density of states and molecular orbitals after adsorption of SF6 decomposition products by carbon nanotubes, and determine the gas-sensing response of carbon nanotubes to gas molecules characteristic.

Fault diagnosis of free-conducting particles within GIL based on vibration signals

Accurate quantitative diagnosis of free-conducting particle faults plays an important role in improving the reliability of the gas insulated line (GIL) system. However, the existing fault diagnosis methods cannot accurately identify the free-conducting particle faults with different quantities and sizes. Motivated by this, this paper proposes a novel fault diagnosis method based on vibration signals, which integrates variational mode decomposition (VMD), self-adapting whale optimization algorithm-multiscale permutation entropy (SAWOA-MPE), and deep forest (DF). First, the raw vibration signals of free-conducting particle faults are decomposed via VMD, and the decomposed signals are reconstructed based on the correlation degree. Afterwards, SAWOA is employed to optimize the critical parameters of MPE, and the optimized MPE is further utilized to extract the fault features of the reconstructed signals. Finally, the extracted feature vectors are trained and tested to construct a valid DF classification model that identifies the free-conducting particle faults. The experimental results indicate that the identification accuracy of the proposed method can reach 99.5%. Moreover, comparative tests based on various feature vector extraction methods and classification models further validate the superiority of the proposed method.

Evolution of Elements on Electrode Surfaces in Gas-Insulated Systems under Electrical Heating

Accidents always occur in gas-insulated switchgears (GIS) and gas-insulated lines (GIL) since filmed joint electrodes are produced when internal gases react with the electrode’s surface when there is a discharge or when internal electricals overheat. To solve the problem, this paper analyzed the evolution of elements on the contact electrode. The reaction of the SF6 and electrode’s surface under breakdown currents and overheating conditions was obtained, and the discharge time and discharge current effects upon the transfer of the element were proposed. It was found that the mobility of the F element on the electrode’s surface typically increases after electrical heating. The number of interruptions and short-circuit currents are important factors affecting the transfer of the F element to the electrode. The flashover current is the essential factor that accelerates the transfer of the F element to insulating materials. Frequent switching is a main factor that accelerates the transfer of the F element to the contact. It was also found that Al has little correlations with the breaking process, and metal fluorides become the main components on the electrode’s surface under discharge heating. The research provides a theoretical basis and data support for GIS/GIL surface optimization treatments and the improvement of fault detection methods.

Tech-Economic Assessment of Power Transmission Options for Large-Scale Offshore Wind Farms in China

China is taking initiative in energy transition to cope with the long-term controversy of its enormous energy consumption, aiming to use less carbon. Wind power, especially offshore wind energy, has become a prevailing alternative due to its low carbon emissions, renewability, competitiveness, and operation security. The layout of a transmission channel is a key consideration in marine project implementation. This paper investigates the technical characteristics, application status, and viable advantages of a conventional AC transmission, voltage source converter-based high-voltage direct current (VSC-HVDC) transmission, gas-insulated line (GIL) transmission, and hybrid HVDC transmission. A component-resolved evaluation model was proposed to estimate the costs to be incurred of four electrical transmission options for offshore wind power along the coast of Eastern China, with technical feasibility and economical considerations. Cost comparisons and component sensitivity analyses were developed with different transmission distances and capacities. Results suggest HVAC transmission and VSC-HVDC are the preferable solutions for present offshore wind farm development in Eastern China, and the economic potential of the hybrid HVDC makes it feasible for future deployment. Some conclusions can be applied in disparate regions across the globe.

Etching and annealing treatment to improve the plasma-deposited SiOx film adhesion force

In this paper, an atmospheric pressure plasma jet driven by an AC power supply was applied for SiOx film deposition on a metal surface. To improve the adhesion strength between the film and substrate, the processes of plasma etching and annealing were applied. The deposited SiOx film properties, including film thickness, surface morphology, chemical composition and electrical properties, were studied systematically. In addition, the deposited film was used for the metal particle lift-off voltage in a gas-insulated line (GIL) system. Our results showed that the adhesion strength between the film and substrate was 5 times higher in the films subjected to plasma etching and annealing treatment than that in the untreated group. The high oxygen content attained in the SiOx film after the etching and annealing processes was responsible for the adhesion force improvement. The composition changes in the film also increased the relative constant value, which was in good agreement with the metal particle lift-off voltage results. After thermal annealing, the sample showed a 119% improvement in the lift-off voltage compared to that of the bare electrode.

Evaluation of Sustainable SF 6 Alternative Gas Mixtures Used in Electric Power Equipment

Sulfur hexafluoride, SF6, has been the preferred dielectric medium in electrical power applications for decades. However, due to its extremely long atmospheric lifetime and very high global warming potential the industry is designing SF6-free technologies for many applications, including switchgear, circuit breakers and gas-insulated lines or bus bars. Alternative gas mixtures incorporating a fluoronitrile or a fluoroketone have low climate impact and are being successfully used in gas-insulated equipment currently operating on the grid in Europe. This paper reviews the toxicological studies conducted on these gases and the parameters required to perform a risk assessment for their use in electric power applications. The toxicological studies demonstrate that the alternative gases are low in acute inhalation toxicity which is the primary mode of potential exposure to an insulating gas. The occupational exposure limits established for these SF6-alternatives are well above the typical concentrations of insulating gas found near electric power equipment. In the event of accidental release of insulating gas, the alternative gas mixtures present potential exposure risks similar to those exhibited with SF6-filled equipment. Thus, these alternative gases and their mixtures provide a wide margin of safety required for these applications.

Recent Development of Two Alternative Gases to SF6 for High Voltage Electrical Power Applications

For many years, SF6 has been the preferred dielectric medium in electrical power applications, particularly in high voltage gas-insulated equipment. However, with the recognition that SF6 has an extremely long atmospheric lifetime and very high global warming potential, governments have pursued emission reductions from gas-filled equipment. The electrical power industry has responded to this environmental challenge applying SF6-free technologies to an expanding range of applications which have traditionally used SF6, including gas-insulated switchgear, gas-insulated circuit breakers and gas-insulated lines or bus bars. Some of these SF6-free solutions include gas mixtures containing fluorinated compounds that have low climate impact, among them, a fluoronitrile and a fluoroketone developed as 3M™ Novec™ 4710 Insulating Gas and 3M™ Novec™ 5110 Insulating Gas, respectively. Both fluoronitrile and fluoroketone mixtures are successfully used in gas-insulated equipment currently operating on the grid where they reduce greenhouse gas emissions by more than 99% versus SF6. This paper reviews these leading components of alternative-gas mixtures with updates on the performance, safety and environmental profiles in electrical power applications.

Study on the Propagation Characteristics of Partial Discharge Electromagnetic Waves in Gas Insulated Line

Defects in the gas insulated line can cause partial discharge, and the electromagnetic wave is generated. The finite difference time domain method is used to research the propagation of electromagnetic wave in gas insulated line structures. The electric field strength of time-domain waveform is selected as characteristic factor for analysis. By changing the gas insulated line model, the attenuation of electromagnetic wave through double insulator, L-type corner, T-type corner, straight tube and different GIL sizes is studied. In the straight tube structure, the amplitude attenuation of electromagnetic wave is linear and the attenuation band is between 1 GHz and 1.7 GHz. In the insulator, basin insulator has more serious influence on signal isolation than disc insulator. After passing through the insulator, the signal attenuation is obvious in the frequency band above 1 GHz. The amplitude of electromagnetic wave decreases more seriously through the corner structure, and the attenuation is at the whole frequency band. In different sizes of gas insulated line, the larger diameters of shell and conductor, the larger electromagnetic wave will be, and the faster attenuation will be; the length of gas insulated line cavity has little effect on electromagnetic wave. The theoretical research is expected to help to arrange the position of ultra-high frequency sensor reasonably.

CLOSE-RANGE PHOTOGRAMMETRY METHOD FOR SF6 GAS INSULATED LINE (GIL) DEFORMATION MONITORING

Abstract. Close-Range Photogrammetry (CRP) technology advanced rapidly along with the development of camera sensors. CRP has many advantages over other methods in terms of technical data acquisition, product quality, and cost. Because of these advantages, the CRP method can be used in various applications. In this study, the CRP method is used to monitor the deformation of the SF6 Gas Insulated Line (GIL) object between two substations of the Indonesian National Electricity Service in Kuningan Barat, South Jakarta. Planning was carried out with a simulation using 3D field data obtained from reconnaissance process. During the survey, photo data was collected using a smartphone and processed to form a 3D model. The simulation produced a configuration of control points, check points, and camera stations that have the best Strength of Figure (SoF) values. In the planning process, camera pre-calibration is carried out to get the best camera orientation parameter values from several experiments. The planning results are used in the next stage, namely field data acquisition and data processing. The data acquisition process was carried out for two sessions. This is done to see the changes in coordinates that occur between these sessions. Data processing was carried out by following the classical photogrammetric stages. The results obtained from this study are the average accuracy produced by Close-Range Photogrammetry method for measuring deformation which is below a tolerance of 3 mm. With this method, deformation measurements can be carried out quickly, accurately, and at a relatively lower cost than other observation methods.

Conductor Surface Roughness-dependent Gas Conduction Process for HVDC GIL—Part II: Experiment

In this paper, an electric field ranging from 0.44-5.24 kV/mm was applied to a gas-insulated line (GIL) model filled with SF6 at different values of gas pressure and relative humidity (RH). Dark current was measured using high voltage conductors with different surface roughness (Sz). The results show that the dark current reflects a multi-factor-dependent ionization process, which has a strong correlation with electric field strength, RH, and electrode surface roughness. At 45% RH, an Sz value of 14.152 μm, and an electric field less than 2.2 kV/mm, the gas pressure was found to have a significant inhibitory effect on dark current. However, at an electric field greater than 2.5 kV/mm, the increase of RH has a significant positive correlation on dark current. From the results, it is verified that the values of conductor surface roughness requirements for AC GIL are too high to be used for DC GIL. We emphasize that the ionization leading to high dark current is due to local protrusions at different environmental conditions. For the DC GIL, the surface roughness of conductors should be minimized to achieve satisfactory performance.

Investigation of Free-Moving Particles under AC Electric Field in Different Insulating Gas Mixtures

Free-moving conductive particles may affect the dielectric reliability of gas-insulated systems, e.g., gas-insulated lines (GIL) or gas-insulated switchgear (GIS). This paper reports on investigations on the behavior of free-moving particles under AC electric field, using different insulating gas mixtures. Multiple particles were positioned inside a GIL test setup with each particle placed within the same distance to a particle trap. To ensure reproducible and realistic particle geometry, cuboid particles were used. In this paper, a width correction factor was empirically determined for a well-known formula from the literature, which is used to calculate the lifting field strength for cuboid particles. While increasing the applied voltage, the movement of the particles was observed with a camera and further evaluated using ultra-high frequency (UHF) partial discharge (PD) measurements. The UHF phase-resolved partial discharge (PRPD) patterns of steel and aluminum particles in SF6, as well as in different alternative insulating gas mixtures, are compared and discussed. To determine the effectiveness of particle traps for different gas mixtures, further parameters are evaluated, such as the duration of each particle's movement and the number of particles reaching the inner conductor.

Redesign Gas Insulated Switchgear to Semi Air Insulated Switchgear 500 kV side and 150 kV side in EHVS Kembangan

The main role of 500 kV extra high voltage Gas Insulated Substation in transmission system is serves connection between the electrical generation and transmission system. To improve equipment performance and the quality and reliability of electricity distribution need time to maintain gas insulated line compartment but preparation to maintenance requires a long time, limited maintenance duration and long implementation of gas evacuation. This paper is object to redesign Gas Insulated Switchgear (GIS) to Semi Air Insulated Switchgear (AIS) on 500 kV side and 150 kV side with new design of Gas Insulated Line compartment in order to accelerate maintenance and gas evacuation job. with surveys, observations, analyses and Root Cause Problem Solving (RCPS), it can be seen the initiation of improvement to accelerate the maintenance of IBT and accelerate the repair of anomalies in the gas insulated line. After redesign Gas Insulated Switchgear to Semi Air Insulated Switchgear, this results show maintenance IBT after redesign is 25 hours faster and duration anomaly on GIL after redesign 24 hours faster.

Research on Steady‐State Thermal Behavior of SF6/N2 and CF3I/N2 Mixtures in High Voltage Gas‐Insulated Lines (GIL)

Gas‐insulated lines (GIL) are widely used due to their many advantages in power plants and substations. The security and reliability of GIL is achieved by continues testing and monitoring. The main fault in the GIL compartments is overheating, which is rarely to occur, nonetheless, it cannot be ignored. In the present study, GIL steady‐state thermal behavior was investigated. For this reason, a multiphysics finite element model (FEM) was built to analyze the magneto‐hydro‐thermal characteristics of the GIL insulation gas. The simulation coupling includes the electromagnetic field, flow field and thermal heat transfer field. SF6/N2 and CF3I/N2 mixtures were studied and the influence of different gas properties on the magnetic flux density, heat distribution and flow velocity had been investigated. The results were compared to an experimental setup to validate the model calculations. Temperature rise tests have been conducted on the GIL inner and outer shell. The measurements were in good agreement with the simulation results. Finally, the presented work is also to serve as a good reference in future design and optimization of GIL structure. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

The Influence of Longitudinal Force on the Internal Force Distribution and Deformation Coordination Mechanism for Segment Lining

A series of local prototype tests are conducted on the Sutong GIL (Gas-Insulated Line) and Shiziyang Tunnel. These tests investigate the redistribution law of segment deformation and the bending moment during construction. The results reveal that the transfer ability of deformation and the bending moment improve with an increase in the longitudinal force. Stage characteristics are observed for the effect of the longitudinal force on the opening of the circumferential joints. Segments are fully contacted for the circumferential joints when the joint opening is not observed. The frictions between the segments are the key factors for the bending moment and segment deformation control. The opening of the circumferential joint with an increase in the joint opening then becomes the primary control factor. The transfer ability becomes stable when the load continues increasing after mortise and tenon contact. Better transfer ability occurs with a general segment with four pairs of mortises and tenons. This was presented as a smaller value of an increasing rate and the stable magnitude of the joint opening. From the perspective of practical engineering, mortises and tenons can be added to the vault to increase the load and deformation transfer ability of the general segment after the loss of the longitudinal force.

Determination of the Operating Temperature of the Gas-Insulated Transmission Line

Gas-insulated lines (GILs) have been increasingly used as high-current busducts for high-power transmission. Temperature is one of the most important factors affecting the performance and ampacity of GILs. In this paper, an analytical method was proposed to determine the temperature of a three-phase high-current busduct in the form of a single pole GIL. First, power losses in the phase conductors and enclosures were determined analytically with the skin, and proximity effects were taken into account. The determined power losses were used as heat sources in thermal analysis. Considering the natural convection and radiation heat transfer effects, the heat balance equations on the surface of the phase conductors and the screens were established, respectively. Subsequently, the temperature of the phase conductors and the enclosures were determined. The validation of the proposed method was carried out using the finite element method and laboratory measurements.

Current State and Prospects of Development of Gas-Insulated Power-Transmission Lines and Busbars at 110–1100 kV

Issues related to the development and technical operation of gas-insulated lines are considered. A comparison of the technical parameters of lines with different types of insulation is performed. The throughput of and losses in power-transmission lines of different types are identified; the specific electric capacity and technical losses in the gas-insulated lines are determined, and their safety and environmental friendliness are evaluated. The assessment of gas-insulated line construction variants and dependence of their real dimensions on the nominal voltage is carried out. Options for using different gases in gas-insulated lines are considered. The comparison of the intensity of magnetic fields of overhead, cable, and gas-insulated power lines showing the efficiency of the gas-insulated line application is performed.